I'm STUMPED...Crazy RICH XTerra P0172 (Part 2)
ฝัง
- เผยแพร่เมื่อ 28 ส.ค. 2024
- It's been 2 months, and the 2004 Nissan XTerra is STILL running RICH even with a brand-new OEM MAF sensor installed!! Hmmm.....
Owner said that fuel economy has improved, but it's still setting a P0172 - Too RICH code and can't pass the NYS Emissions test. Dang.
What other variables did I MISS in Part 1?
Might have to resort to some "unorthodox" NPR methods to get this crazy Nissan running right again...
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Enjoy!
Ivan - ยานยนต์และพาหนะ
I worked at a Nissan dealer during that era. There were a lot of driveability issues that involved not only changing the mass airflow sensor, but also doing a software update on the pcm. It might be worth checking that the pcm is correct for the truck with the latest software calibration. We would get a lot of vehicles that had new oem maf sensors installed but would still have fuel trim problems if the pcm wasn't recalibrated to match the updated sensor.
Dude. You gotta be on the right track there.
I know on an altima about the same year we had the same problem. There was a t.s.b. on it for a reflash.😊😊
@@brucebrown4183eflash pcm yep
I miss Radio Shack
I miss the mindset of the nation during the times radio shack flourished
Me too!
Yep.. very handy place..
We had Maplins electronic shops in the UK, same story.😢
I went on a shopping spree for small electronic components before they closed maybe 15 years ago 😅
Ooooooohhhh, a part 3 😮
I recall in other videos, where there's been volts where there shouldn't be, there's some green crusties knocking about.
One common problem area with those VG33e engines after many years of use is poor contact at the ground connections, which can cause the condition you've observed. The two main circuit grounds are connected at the top of the intake manifold closest to cylinder bank one.
grounds connected to intake manifolds always cause problems.I usually move them if possible.
But wouldn’t a bad ground lower voltage the ecu sees and hence under report on the maf vs over report like we see here?
If this vehicle uses a laminar flow screen upstream of the MAF make sure it's there. If it's missing it will read just wrong enough to mess with you and offsetting the MAF with a divider network will only work at the speed it was set with. Same way with partially blocking the MAF port. So make sure there are no missing seemingly meaningless parts in the tunnel.
Been there, done that...with a 06 Toyota Camry..my own vehicle. It had been to the dealer 4 times with the same issue and despite replacing the very expensive front oxygen sensor, it would run rich and the check engine light would come on again.
Took me multiple weeks to finally sort it. I replaced the MAF sensor as it wasn't the correct one. (Yes, it was OEM but not the exact same part number). Didn't make any difference. The long and short term fuel ranges would peck out after a while again. On my Toyota it takes 3 cycles of the same condition before it sets the Check Engine light. So the Dealer simply replaced parts, then disconnected the battery for the long term fuel trims to start from zero and it would take multiple runs before the light would turn back on.
The problem was simple slight pin corrosion in the MAF female plug. Simple electrical cleaner spray and multiple plug/unplug would improve the fuel trims. After doing this 3 times, they finally came well into the lower single digits at idle/engine warm/closed loop and aircondition OFF.
It's been more then 4 months now and the problem hasn't returned, plus fuel efficiency improved by a mile.
I purchased the car 2nd hand and the owner of course washed the engine to make it look good.
Electrical components and water/cleaning solvents to not belong in the engine bay, unless extreme care is taken.
The MAF sensor is actually a "Current device" measuring currents my uA. It's represented via voltage using ohms law. At such extreme low currents measured, the slightest increase on resistance at connectors or wiring, has a detrimental effect of the fuel trims.
What you have effectively done is you added the resistors in parallel and increased the current flow, therefore dropped the voltage slightly, creating the same effect as resolving the high resistance issue.
My thoughts: I think like you do that the PCM needs a lower voltage, but I'm thinking that the reason the PCM is reading it wrong is that there is a missing ground in the PCM. It floats some of the internal voltages that it reads. Check all the grounds at the PCM. Also maybe install another ground strap to the engine.
I was thinking that too
@T.J. Kong 300mV was SIGNAL wire KOEO. Ground was a nice 57mV 🙂
I had to diagnose a 4wd issue on a 2002 Tahoe that kept drying the transfer case module whenever it was in 4wd and the power windows or blower were being used and it turned out to be a missing ground from the engine to the firewall. The transfer case module became a path to ground for the windows and blower circuits which ultimately fried the module and I only figured that out after frying a new module but was able to repair the blown mosfets and it's been working great for two years now. That ground strap that was missing is only accessible when the engine is removed so if it's not installed before it's put back in it's not likely to be installed and that's what happened to this Tahoe. That's my favorite example of bad or missing grounds.
I agree, what is the voltage at the computer measured at its ground and signal wire? I don't agree with a band aid fix as a permanent solution.
I ran into a similar issue with a Jeep that had an engine replaced. When the new motor was installed they accidentally connected the ground wire for the E.C.M. to a bolt that was isolated from the body with a rubber mount (I think it was the bracket for the air cleaner) and that lack of ground was messing with everything. The weird part is that it was still getting a limited ground from somewhere but not enough to allow the sensors to read correctly. I seem to remember that it was throwing the map sensor and intake air temperatures off as well. The temp sensor is what clued me in because it said the intake air was like 285 degrees or something on a cold start. Lol
This is an interesting problem. My uneducated guess is that there is a voltage or ground issue. If I am not mistaken, if the MAF sensor is disconnected, there should be 5V between the signal wire and the ground wire on the harness. If it is higher than 5V, then when the sensor is reconnected, then the resulting signal voltage would also be higher. In addition, the occasional spike in air flow reported by the computer that you saw would seem to indicate an intermittent wiring problem or problem with the ECU. Looking forward to part 3.
I'm wondering if there's a dry joint starting in the calibration resistance inside the ecm and applying a " pull down" load at the maf is compensating for this?
Damn I love this TH-cam Channel. The learning aspect and gathering evidence alone is incredible. Thanks Ivan!
WatchWesWork had a very similar problem with a Ford van. He eventually discovered leaking condensors in the ECU. He swapped those and the engine ran supersmooth again.
I struggled to figure out the high negative fuel trims on my 2000 Camry with 350K miles. It turned out that valve seat recession caused diminished exhaust valve clearance, and correcting that took the negative fuel trim from about -20 to near zero. Gas mileage improved significantly. The car does not have a MAF sensor so I have info on that.
I'm a DIYer and have always fixed my own cars, nowhere near a pro mechanic, however, I do have an electronic background so the concept of a discreet component or integrated circuit losing tolerance over time is something I've experienced. Anyway, looking forward to part III also!
I would be wanting to inspect/reseat the connector at the ECM. It does seem that what your voltmeter is seeing at the MAF and what the ECM is seeing is not the same
Maybe its time to break out the pico and see how much noise is on the signal or check the computer ground(s).
Ivan writing in the Title "I'm Stumped" has to be considered click bait🤣 Thanks for another great video!
cool case study i just had a gm that was doing the same thing over reporting the air new mass air no help i took the air filter box off to see if i could see anything and there was a plastic diffuser laying on top of the air filter it clicked right back into place problem solved no parts required 😀
I just saw a video where there was also a plastic sleeve or wrap on the bottom of the square airfilter blocking air flow. How it got there the mechanic had no idea.
This is quite the enlightening series as I have a friend with a nearly identical truck and the same problem. I have yet to find a reliable solution to it. So I am looking forward to part 3.
Wow. So, this is not an isolated issue. You would think Nissan might have something on this. But maybe not for the age of the vehicle.
As far as i know its fairly isolated. I own 7 Xterras and none has this issue nor are mainy reporting it on ClubXterra often
I'd like to check to make sure the PCV system isn't restricted, since that's essentially a calibrated vacuum leak for the engine. Also, even though no EVAP codes are setting, I'd like to verify that the purge valve isn't stuck open. The stuck purge valve may be the more likely culprit, since the engine would be able to suck raw fuel vapors from the tank and severely reduce the fuel economy, which was a customer complaint.
cccp engineering at its finest. I remember a guy that worked on IBM machines way back when in the former Soviet Union and figured out all the bugs and how to maintain and fix them because they didn't have access to IBM support. Coming to the US he was able to put that skillset in use by coming up with solutions most IBM field techs would not even think of as it was typically and rip and replace for simple stuff..nice job figuring a solution that didn't cost an arm and a leg
Watching a TST Seminars video right now and G Trulia mentioned on how Nissan’s P0101 can be fixed by reprogramming…resistor is cheaper…LOL !!
MY GUESS IS YOU NEED THE LATEST FLASH UPDATE FOR THAT PCM-ECU AND YOU SHOULD BE ALL GOOD AND WELL . THANKS FOR THE VIDEO AND YOUR TIME 🙏👍
This is getting interesting! I have an idea but not a big fan of shoe leather, so I will wait for the finale. Great stuff!! 👍👍🇺🇸
Leak before o2 sensor causing closed loop to run richer. Usually a pinhole in front of the catalyst that pulls ambient air in the exhaust falsely leaning out the system causing the ecu to then add more fuel (usually 10-11%)
Common on SH7075-sh7078 processors like this Hitachi ecu.
350z In 2004 do the same thing.
I tune the ecus and can resolve any issue like this in the lambda target tables
Also, better datalogger setup like a 10.00 Elm327 works wonders with a laptop. Far Faster than that scrap Bluetooth drew technologies scanner.
I subscribed good sir. Do you do anything with Jeeps?
I'm trying to understand the relationship of O2 sensor and Fuel trim. Extra air brought into the system before O2 would make the O2 sensor believe more fuel would need to be added, wouldn't it? If so, wouldn't that fuel trims be positive not negative as they are here? The O2 sensors seem to be telling the computer "there is too much fuel in the exhaust" and the computer is triggering the injectors to push out less fuel (negative fuel trims). I defer to your experience though.
@@IsItTrueThat You are quite correct, air leaks in the exhaust near the O2 sensor tend to cause positive fuel trims to go with the rich running.
Very interesting! Seems the MAF sensor is not properly calibrated on the engine computer. I was going to suggest to test with a 10k potentiometer, but you had a resistance box :-) Good call to externally "calibrate" the output with a parallel resistor! And when all seemed under control, you announce a Part 3! Getting wild :-)
Why was the value glitching upwards? Seems like a clue! It also happened with the previous MAF (it is visible in part 1). Perhaps there is corrosion somewhere in the harness, causing voltage to bleed from a battery positive circuit into the sense circuit. Then when you wiggled it, it made better contact with the short? You probably would have seen it if it was in that connector, so it seems like the source of the glitch must be further down but nearby? I would unplug the computer and the MAF and check resistance on that wire to battery positive. I bet it is not infinity.
You're a sharp one, Jessica. You are talking about a capacitive short, as well as a resistive one. These are the kind of things that stump a lot of mechanics out there, as these are some of the most diabolical of problems that can change with the humidity. Glad you brought it up.
@@vilefly While I have no doubt such a short would have capacitance, I'm not sure how that would come into play? It would probably not be more than a handful of pF (????), we're essentially at DC here, and I would expect the line impedance to be somewhere on the order of tens of k ohms (if it were directly into an MCU ADC it would be on the order of hundreds of k ohms). With an impedance of 10k and 1000pF of capacitance, the RC time constant is 23 microseconds, completely immaterial. Or are you talking about capacitively coupled interference signals from the alternator or something? Still that would be too low frequency to matter.
@@jessicav2031 Capacitively coupled interference from nearby ac or pulsed dc signal circuits. I have experienced this with water that is trapped up into the harness that has cracks or tears in the insulation. It may not apply directly to this situation, since it is a dc signal. It is something to be on guard against, nonetheless, since we have an active ignition system in play. Noise on the o2 sensor signal line is quite possible. DC bias vs ground is also possible with dissimilar metals and some not-so-pure water.
Great question! Just silly OBDII data is my guess... Otherwise engine would have sputtered or stumbled or set a code... But it ran smooth as glass 🙂
Oh nooooo a part 3 hopefully it is here very very soon as I'm ready for the rest of it
That little "glitch" at 7:03 might be a clue, perhaps it is occasionally getting voltage spikes on the signal feed, but data refresh rate on OBD2 with 7 pids is too slow to catch it?
I think it was just a silly scanner glitch 😆
@@PineHollowAutoDiagnostics Maybe, but I noticed it happened more than just that one time you were outside of the truck! Looking forward to part 3 :)
PCM may normally have it's own pull down resistor for that circuit but it isn't working so you doing it externally is taking care of it. PCM's often have a few ground wires, perhaps the one this circuit uses for pull down has a weak ground so cannot properly pull down the input.
I’m thinking faulty/clogged egr. The higher than specified air flow thru the maf at idle is because it’s not getting air from the egr.
At idle EGR is closed 🙂
If EGR is off (as it should be at idle) the MAF should be measuring the airflow into the engine accurately. When EGR is enabled it drops the measured airflow, which is how the ECM can check that EGR is functioning correctly.
Looking forward to part 3 for sure! I have been chasing rich long term fuel trims in my 18 year old Chevrolet Malibu V6, but not quite negative enough to set a code. Went through the same thought process as here and replaced the MAF with OEM. Also checked most of the other systems mentioned by commenters here. Hoping this case study will provide insight.
I had the same issue with Kia . the MAF sensor read 4gps and should be 2gps i found out the timing is wrong . because the MAF sensor report what it seen
Very interesting case study . best of luck
I was considering a cam timing issue but the engine seems to run very smoothly. Absolutely worth checking though.
@@ferrumignis well ur right but it was just one teeth off . thanks for the comment
Another vote for timing. How did anyone end up coming to that conclusion? 🤔
@@TheFrenchPug i had the same issue and found out the timing is off after fix the MAF read just 2gps no 4 gps
Had a very simular issue on my car when I bought it. The sensor would say it went way rich but in reality it did go lean. Swapped out the sensor fixed it for a while but issue came back. Then I remapped the engine not to use the maf sensor and it ran fine until eventually the ecu died. Replaced the ecu and still don't have the sensor connected or the boost sensor. I run my Volvo at full send all the time. My right foot is basically the sensor. If it doesn't feel right don't force it. But if she wants to pull let her rip :)
Does the ECU use any other inputs besides the MAF to calculate that flow rate in g/sec? Like maybe an intake air or ambient temp sensor?
In order to calculate the actual mass flow, the ECU would need to know the speed of the air past the sensor (which is what the hotfilm/hotwire probe in the MAF is measuring), as well as the air temperature (air temperature and density are inversely related), and the cross sectional area of the intake duct where the MAF is located (would be a constant in the ECU firmware, model dependent). So an improper ECU input for intake air temp and/or improper firmware from a junkyard or "tuned" ECU might cause what you are seeing here. As would a shift in the gain of whatever amplifier/ADC processes the MAF signal inside the ECU (caused by component degradation or improper firmware values)
Adding the bodge resistor might make it run sort of OK, but isn't really addressing the root cause of the issue.
amen
A MAF (Mass Air Flow) sensor calculates air _mass_ , not volume, so it already corrects for air density. Air temperature is still needed to correct ignition timing etc.
You need a known good to compare to. Id be leary of putting resistors in the signal line because then if you're compensating for something else causing a rich issue, you could cause transmission pressure related damage.
hadnt thought of that but your right, Ive been learning abt transmissions lately and amazed at how many inputs they get.. MAP. MAF, TPS, 02 SENSORS, ECT. I will never drive far with a check engine light on again,.
Radio shack vintage packs 👍
Grounds are my go to item to look at when vehicle has a crazy problem and components are verified as good. I have found bad engine and bad computer grounds in too many vehicles causing inexplanable problems.
I may have missed it, but did you check the voltage received at the computer relative to computer ground? I'm wondering if there's something wonky in the received data...
Dammm, a part 3…not good for you but great for us. Looking forward to your final diagnosis and fix.
So - If a hot-wire MAF is reporting high, the air flow across it must be a bit high. Has anybody removed the air cleaner box to check if the tube is partially occluded? This would force more of the air across the MAF sensing element and artificially raise the perceived airflow - same as using a MAF tube with a smaller cross-section (has anyone changed the MAF tube off the airbox by chance)?
We call this one, "the leaf-maf conundrum".
Aaahhh part 3! Who needs fiction when we have these cliffhangers! Thanks!
A problem with adding the resistor is that if the internal circuit rights it self then you will have a lean condition/ low maf reading. ECM autopsy may be required
Disconnecting something and calling it a fix - meh - okay. But introducing unwarranted loads on electronics is a no-no. Especially with some old ass carbon film resistors. Check powers and grounds.
Just when I was thinking that was such a good idea for a fix too.. Though looking fwd to part 3 now then :)... Love ya vids and diagnosis skills btw... xoxo
I've been through this. I know it doesn't work. As soon as you rev outside of the cell the fix was made with all hell breaks loose again.
Odd that it is only reporting a p0172, did like the resistor hack. Looking forward to part 3. I would have changed that MAF for OE (part1) as well.
Few suggestion Ivan, maybe worth disconnectiong to MAF and forcing it to go on to limp home mode see how the fuel trims like that, or see what the injector dwell time is, thats where the buck stops, if thats normal maybe the injectors are dribbling, and lastly fuel pressure is that too high, i assume you have checked the air filter lol, also i assume the thermostat is ok and engine is at correct temperature, not too cool......good luck, enternaing stuff...Fred in England..
Unfortunately Nissan doesn't have a good back up strategy without the MAF...
I was into Nissan's during the early 90's to 2000's, I remember a lot of problems with the capacitors(puking) in the ECUs caused all kind of weird problems.
My uncle had an 04 Frontier with same problem. It had 4 cyl though. It had extended Nissan warranty and it was repaired by them. They reflashed PCM and it corrected the rich condition. Then it set catalyst efficiency code. They had to reflash again. Truck had less than 45K. Ended up being a problematic truck.
The input to the computer would probably have a load resistor as standard but if faulty it could cause an issue. Definitely worth checking out the voltage at the computer input.
You guys love piercing those lines. Do you go back and seal those exposed wires? A little exposure goes a long way when it comes to green crusties.
Could try feeding test voltage directly into computer to test g/s on MAF.... maybe bad cable/connector. I also like another posters tip on checking ground contact for PCM.
Oops. Can’t wait to part three
Part3 Oh no!! what can it be? You will crack it Ivan we know. Many thanks from UK.
Bernie's V.E. test has served me well when I need a sanity check on a MAF reading. Speaking of the Master, perhaps the XTerra has a magnetized crankshaft?? ;-)
who is bernie?
in my next life i might have found that problem 69 l1 master car and truck never seen anything like that.
@@randy1ization: @AutomotiveTestSolutions
My Money is on a solder joint or capacitance issue inside the ECM. Ivan, Great case Study!
If the PCM is working properly then it would have to be a calibration file error. One check on the PCM would be to check the +5VREF output. If this is okay, then I think we can assume that the A/D front end is working correctly. So, the error would have to be in the 2D MAF look up file. If there is a calibration update needed there should be a TSB or a recall notice which includes the MAF 2D table transfer function. Many times the check is to see the current loaded version of the PCM Frimware/Calibration and if a newer one is available, to then reprogram the PCM.
Gotta be a shotty ground somewhere.. not on the maf obviously but betting is on the o2 or ecm side..
Those MAF spikes while the decade box was hooked up seemed strange and unexpected.
I am wondering if the engine controller isn't getting proper grounds or something. Very strange.
Couldn't a bad ground at the PCM cause similar issues if it can't carry enough current? Also noticed the intake air temp was 73-85F before the resistor was installed (and you were wearing a hat and coat so I assume it was cooler than that) and 53-65F afterwards. Interested for part 3.
As soon as I saw you’d fixed the truck with that decade box, I could sense a Russian repair coming 😂. However, will await part 3…….
I would like to see Eric and Keith’s take on this.
I'm thinking EVAP...... disconnect to see if it's geting to much fumes from canister filter from gastank. Be happy to see the final of this car.
Great job Ivan, Of course this is better than a new computer. Thank you
Do a voltage drop test on the sensor ground. Engine running, all electrical loads on snap throttle on a scope or min/max on the meter. Should be under 200mv.
I wonder if the engine was ever replaced? Maybe it has additional displacement and it's real air the sensor is counting.
Check that injectors are correct part number. Engine coulda been changed at some point and they are flex fuel injectors or something
Ok now that I'm watching the video before commenting is there a ground issue which would elevate the voltage?
@@eddiereichel9354 The MAF ground was in the 50mV range.
Fuel injectors couldn't cause the MAF to read too high.
Ok. Here we go.
1) Check for electrolysis in the cooling system by measuring voltage (with one lead in the coolant) from coolant to ground. Should be less than .5 volts. More than that, change coolant. Galvanic action can create stray voltage across the ground plane of the ecm and other devices. This throws everything off.....just a little. Most overlooked test. Old coolant.
2) Check any and all data items related to inferred flex fuel percentage (or anything similar). If this is a flex fuel vehicle, and someone added only some E85, then this can cause an adaptation error is a system that doesn't use a fuel composition sensor. Do a hard reset or flex fuel adaptation reset with the scan tool......just like ford. (They sleep together at night)
3) What is the Baro or Map sensor reading? What is your elevation? Does it jive? Are deliveries made in mountainous terrain?
4) What is the purge valve doing? Is the gas tank at a low pressure as a result? (doubt this is it)
5) is the oil still loaded with hydrocarbons? Block off the PCV hoses and find out.
6) What is the fuel composed of? Take a sample, and do an alcohol % test.
7) What is the fuel pressure? Is a regulator diaphragm secretly adding fuel?
Forgot one. 8) Make sure someone has not crossed the o2 sensors on you.
Electrolysis in the coolant system... I learned about that phenomenon the hard way on my 89 Mazda MPV when the radiator would literally corrode through and start leaking every 2 years! On the 4th replacement I noticed one of the metal mounting tabs was tweaked and touching the body of the radiator. Bent it back and no more radiator failures in 15 years!
E85 would cause lean running and positive fuel trims. Also wouldn't cause a high air mass value to be reported.
@@ferrumignis Going from E85 to E10 gas will run negative trims, since it is inferred composition instead of measured composition. Doesn't always adapt very well.
@@vilefly Would a 2004 Xterra be flex fuel?
@@ferrumignis I'd have to look it up, which I'm too lazy to do since he declared it fixed in part 3. I honestly hope it isn't flex fuel, for his sake.
It's gotta be inside the PCM, nice try and it might have been the best fix
How's that alternator, Ivan? Also suspiciously eyeballing that green(?) paint pen mark on top of the airbox, and having flashbacks to a 22 Corolla I had a while ago that got an OEM sensor, but an aftermarket airbox causing a rich condition...
Also check all the intake for air to make sure there's no hidden nest
That would restrict air intake, lowering the MAF reading not increasing it.
make do and mend that will chase the fault out like setting fire to the field to chase a snake out extreme but works
I can remember on the Nissan RB25DE computer out of the Nissan R33 Skyline GTS the ECU Only needed to see a 1 volt reference but the signal was ignored at idle speed & the air to fuel mixture was controlled by the oxygen sensor & it was an OBD1 ECU.
I think that in your case that you have either leaking fuel injectors,a bad fuel pressure regulator or a bad ECU !
Man, you brought up radio shack, lol i miss those days lol. I bought 300 dollars, worth of parts lmao! I'm not sure putting current sense resistors like 3k ohms. Is the right logical choice. I didn't see any clips of the ecm being original or aftermarket. Or having worked on to check for any failing drivers. But on that test drive, it may show perfect, but something happened.
I used to be a District Manager at Radio Shack. But this was towards the end of their run. What I thought I came on for was to help sell electronics and their components. Nope. All I did was push cellphone sales every day all day long. Saw the writing on the wall and left within a year. Used to be a very cool company and store. A Radio Shack was an area on old ships where the dedicated communications equipment lived.
2 things maybe. Mousey chewed some wires and extra voltage is on the signal wire, or bad calibration on the ECM
Some days you just have to hate working on cars, I had a Toyota recently that the customer had installed aftermarket fuel injectors that where providing too much fuel no matter what the mass air flow or o2 sensors where telling them causing a rich condition. This is a very interesting case, if your resistance readings at your mass air sensor are correct something is changing that reading before or at your pcm, green crusty at pcm connector maybe? You would think not as you had to increase the resistance in the circuit to get to a correct reading.
He decreased the value. He did put 3k in paralel, making the total resistance lower 1/Rt = 1/Rmaf + 1/3000
@@mauricevandoeselaar ahh ok I thought he had it in series, that would make more sense that a poor connection of a poor ground at the pcm might be causing the false reading from the maf sensor, thanks.
I understand why you put the resistors there, I understand the cost savings for the customer if the ECU is "straying" due to a component iss, maybe dry joint or whatever. I just query whether it is a legitimate fix. If the MAF fails totally, will it mask the failure or will it not matter as the 3K resistor will be what the ECU sees (well the voltage due to the 3K resistor). I saw the comment at the end re a Part 3, so I am guessing my concerns are warranted.
The tolerance bands on that MAF sensor seemed awfully large. Maybe there was some kind of re-learn procedure for it?
I've had an issue like this before on a Chevy Sonic. It seemed to be comparing the MAF and and MAP sensor. I can't remember what I did to fix the issue but you had to unplug both to see if the engine was rich due to the sensors or not.
a large part of the vehicals that iv;e had driability issuse with has been caused by grnds. or to say voltage drops.
I mean electrically, the 'correction' the resistor is doing at idle is fine, but at higher RPMs, the fixed resistance value doesn't 'maintain' a proportional 'correction', by my figuring, at higher RPM, thus higher signal output voltage (meaning lower resistance in the MAF sensor side) it will correct/subtract more voltage proportionally than it would at idle (this is a simple voltage divider, say, random values, MAF at idle 10k, ECU side sense resistor to ground 3k, plus 3k 'fix' resistor, so now 1.5k (signal voltage factory 3.3V, 'fixed' 1.85V =44% reduction!, but at high RPM MAF will be at say 3k, ECU still at 1.5k instead of the factory 3k, resulting in a much higher signal voltage reduction at high RPMs! now: factory voltage 7.1V, 'fixed' 4.7V=33% reduction) Now this looks like it 'works' after the short test drive, but the electrical logic is a bit flawed with this fix but now after running my sample numbers, it actually looks pretty decent really, and kind of negates my critique! I wonder if putting a shottkey diode in series with the signal wire, which would drop 0.3V under all conditions, the fix would be better or worse...
I think he put the resistor in paralel I think, but other than that you are right. The response factor is changed together with the better offset. A simple diode would be the better solution. Or finding the real issue (bad ground signal wire ?)
@@mauricevandoeselaar yep, or course the resistor is in parallel with the ECU sense resistor connected to ground. by series i meant the usage case of a diode...
I see, yes that would be the better solution
On test drive fuel trims stayed in single digits for all rpm and load ranges so it actually worked great!
@@PineHollowAutoDiagnostics Yep I agree, just think it was a tad bit of luck the resistor happens to behave electrically that fits this situation so well...
defiantly could be that the pcm calibration is from a different setup and interrupts the same voltage as more gps.
like if it were calibrated for a engine with a bigger intake tube would make the pcm interrupt less change as more gps
have the same concern here in las vegas it was a bad ground
This channel is so good. 🇺🇸🇺🇸🇺🇸
It's the aftermarket radio! 😂
That crazy thought crossed my mind too. 😂😂
Lord knows I've been blamed for unrelated problems from a stereo install months after the install
@@soundman6241 😂😂. I feel you. I guess aftermarket add-ons are just the low hanging fruit.
Ivan, Another great informational video. Your skills always amaze me. The fact you're willing to go outside the box to repair is so cool, and it worked, which is to me a success.....Pete
Super interesting since I've been working to track down a rich condition on my 1994 Olds 3800. (So disappointed I didn't know you were making a road trip not far from me!)
One thing I was wondering is where the target MAF value of 3 g/s came from? Is that a rule of thumb (3 liter engine = 3g/s at idle)? One thing I checked on my car was the MAF readings. Its a 3.8 liter engine and the factory shop manual says MAF should vary around 4.9 g/s at idle (which it does).
I won't go into detail since my car is beside the point here, but I believe I've narrowed the problem to (2) injectors which have low ohm readings and when either of these are disconnected the fuel trims are fine.
But certainly your diagnosis of the Nissan and the hundreds of comments regarding it are much appreciated as they may be pieces of the puzzle in case the injectors aren't my problem.
I've learned SO MUCH watching this channel, in fact I'd probably just be throwing parts at my Olds if not for your example of methodical and logical process of elimination!
Looking forward to Part 3!
Flow test your injectors!
@@PineHollowAutoDiagnostics I did! However, the results were inconclusive, numbers varied but all were within 2 PSI (8 to 10 psi) of each other which I understand to be in the acceptable range. Strange thing is, injector with the lowest ohms reading had the lowest pressure drop, which of course would cause lean, not rich.
Hopefully Its not a mechanical problem with cylinders 3 and 5 (the ones with low ohms and which when O2 sensor disconnected fuel trims were practically normal). Guess it could be a really bad spray pattern causing incomplete combustion.
Car runs great (except for full throttle isn't as powerful as normal) when O2 sensor is disconnected. Did try old O2 sensor from an identical car I used to have, no change.
New injectors should arrive today - at least I'll have something to put back in so ports aren't open any longer than necessary. Any additional ideas would be most welcome - thanks!
To close the loop, for Ivan and anyone else interested. Installed injectors today, car runs MUCH better, I'd say 95% of perfect so there is still work to be done.
Fuel trims led me to injectors but only "proof" I had was disconnecting them one at a time and watching fuel trims. Apparently they failed in some way that didn't show up on the flow test. Yet fuel trims are still low, which threw me until I learned this is normal for this engine when EVAP valve is open.
Sometimes ya gotta go through the process of elimination. Everything is a possibility until you rule it out!
Thanks for the inspiration and endless stream of knowledge, Ivan!
@@billb6899 It was the injector flow pattern. If it dribbles unevenly, the huge droplets of fuel burn incompletely, causing a rich condition in the exhaust. Most prevalent at idle speeds. Causes mild rough idle.
Step 2: make sure the egr valve is not leaking exhaust gasses into the engine. This creates a rough idle, spastic o2 waveform, and tricks the o2 rich, since it only detects 0xygen, not co2 or hydrocarbon emissions.
Step 3: check your PCV o-ring if it has a plastic manifold. Could be sucking oil.
its a resurected buick err i mean nissan(datsun?) big thing is here is to make absolutely sure your data is correct. remember roger rabbit is waiting at every corner, even in a round room. the resister hack is only a confirmation something is off. try another scanner check powers and grounds. check for ac ripple in the dc. check that the readings are the same at the pc. we have faith you'll figure it out or you'll call kieth lol
I would investigate the throttle body
Check all of the grounds from battery to PCM to engine etc.
Time for new caps in the ecm.
Ivan...destroying wire harnesses one pin prick at a time...
Common mistakes when diagnosing the P0172 code
A technician may not inspect the coolant temperature sensor and cooling system. When the engine is cold, more fuel is added to help warm it up to a desirable temperature. If the coolant temperature sensor is not sending the proper signal there is a possibility that the engine ECU may assume that it is always running cold.
im placing my bet now...... i say as you have many times before..... the green crusty's!!!!!
Ivan, did you check the throttle plate to see if its dirty? May need a throttle body cleaning? Might be propped open just a tad with crud.
Rich codes can be puzzling. From leaking injectors to vvti control issues and computer updating to a host of other problems and also consistent fuel pressure. The bucket list is endless. The maf is not happy as elevated results on grams/second is an indication of trouble. Basic earths and powers on pcm and other earths might give a clue ? Definitely a very tricky head scratcher and from the comments, the supply outdoes the demand.
Stick at it you will slay the dragon we all have confidence in your ablities to resolve the hard ones.Cheers.
Dear Mr. Ivan, in my perspective maybe sometimes a slightly stretched timing chain might cause a very tiny vacuum change which might in turn cause a very sensitive MAF to miscalculate. Also, maybe the automaker knows that after a certain hundred thousand miles that the vacuum will slightly decrease, thus the manufacturer policy designs or calibrate the MAF in a very precice way to act in a certain way if a vacuum is drop by whatever tiny amount relevent to a certain high mileage. Just an opinion. Take Care.
Good evening Ivan... Have a great weekend...
First thing i would do at this point is put a wide band o2 in the pipe and actually monitor the situation maybe the computer is full crazy
Programmed to get you in the dealership. It's not impossible to hide that in the programming. Whatever you do, avoid a CVT . Id keep the oldie. At least you don't have to fix a distributor on that model right?
I wonder what the PCM input impedance for that sensor line was? There could be an resistor inside PCM pulling down the signal line and increase current in the line, on order to reduce harmful interference. That or the AD converter might have failed? I guess there was no voltage information for MAF line in data? I can not figure anything else than bit faulty AD (volts to digital number) conversion inside PCM. One way to check that is to compare the input impedance of the line between a known good PCM and this one.
If there is an difference, then you at least know that PCM:s are different thus one of those is faulty. If you get the same impedance, it does not mean that PCM is good, the fault is not visible to the input line. To me PCM is missing an 3,3 kOhm pull down resistor, from the end of line inside PCM. Solder joint again?