Chevy Mystery Misfire...After Engine SWAP?
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- เผยแพร่เมื่อ 28 ส.ค. 2024
- After the frustrating Ford F150 EcoBoost no-start, the next diag sounds more straight-forward:
1999 Chevy small block that runs "rough", showing a Cylinder 6 misfire at hot idle.
The engine is brand-new, and so are a lot of the parts under the hood.
The owner loves his truck, and wants it to run PERFECT, so let's see if we can pinpoint the root cause of the misfire.
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Enjoy!
Ivan
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I had the same symptoms years ago on an old Ford V6 after a service including tappet adjustment and new spark plugs. Fearing I'd over adjusted the valve clearance I rechecked and they were spot on. Turned out one of the new Champion spark plugs, when hot was giving a great enough resistance to effect the spark. Swapped the Champion plugs for a set of NGK and had no further issues.
That's because your system was probably designed for non resisted plugs keep in mind this has to do with RF interference typically you want resisted plugs so you don't get noise in your radio or cause interference with other components
Yeah champion spark plugs are just crap.
@@SHSPVR Doubt it unless his ignition system was already very weak. Probably a faulty plug. I’ve run resistor and nonresistor on both carb and efi on the same engine and no difference to functionality with a properly functioning ignition system. Also ran resistor and non resistor wires. My research and experience says that it’s an old wives tale that resistor plugs and wires actually cause any kind of performance degredation. But of course they do help with electrical noise when running efi.
@@ryan_layne Resistor and Non Resistor plug wires are diff story like example with may 07 Ninja 250R it req CR8HSA "R=Resistor" and Coil Wire are Non Resistor being it has Multistrand Copper core wire My used bike that got a few year was basket case that I rebuild of winter someone had install C8HSA plug being it causing too much electrical noise it didn't run right and it was even causing my motorcycle dashcam that I installed to flake out with RF interference so much I had to apply two layers of RF shielding just to keep the cameras from flaking out with pink screen. I generally what run is MSD suppression core wires with high output coil and reg plug E3 plug on Chevy 5.7l (350).
@@SHSPVR Yup as i said and agreed resistor plugs and wires are important with modern car electronics. My custom setup is a bit less prone to that interference so it didn’t make much of a difference, but i did see less noise in various places on the oscilloscope which was cool. Anyways my original statement was directed at resistor plugs and wires not having a negative effect on a properly functioning carby system. 😋
One great thing about you Ivan is your honesty. You could have said nothing about the post repair issues with the Ford & the Chevy and we would never had known the diagnosis was incorrect, well at least seemingly incorrect with the Chevy. For all we know the second gasket may have been damaged during the install. It will be interesting to see what you find, especially as you did not repair the Chevy (nor the Ford for that matter). Keep the video's coming!
I have owned diesel vehicles for well over 20 years now, so am out of touch with petrol vehicles, though I have seen people spray brake cleaner to see if there is a vacuum leak. Would this have worked around the gasket or was it not accessible to spray?
Valve sticking in guide. Was common back in the day. Always the inner cylinders.
i was thinking the intake manifold surface could be damaged, that stuff has to be carefully checked.
@@86753091974 That's a potentially good call. Would running carbon cleaner through the intake help that out possibly?
@@TheFrenchPug no. Needs machine work.
@@86753091974 ughh. No bueno.
If you have a can of carb clean or brake clean, you can spray around where the suspected leak is with the engine running and if there is a leak the engine will let you know. I have used this trick and it works.
Works better with starter fluid
Great trick to know. I’ve seen Ivan do this in a video so I’m sure he knows already - still a good tip for all of us viewers.
Soapy water is good too... Bit safer on a warm engine too
@@davyarthurs Not sure if soapy water works on vacuum. It needs to be flammable fuel-- and when you spray it next to the leak with the engine running, it will suck it in and cause the truck to idle higher-- and there's you leak.
@@calholli news to me...
I look forward to the follow up, I've got a 2000 Tahoe 5.7 with similar issue, runs rough with a hard intermittent P0300 and P0303 while accelerating to highway speed. Compression is good, has new distributor, injectors, upper and lower intake gaskets and smoke tested for leaks. I've changed just about every sensor MAF, MAP, ECT, AIT, CKP, Knock from a spare Yukon I have. I'm at my wits end, may throw a new timing chain and valve adjustment at it and if that don't fix it I'll have to finally accept that I'll never be able to fix it. Maybe my CAT's are plugged such a nightmare and I'm not a parts thrower but here I am.
I've had a similar misfire. It's a 454 Chevy. I'd do some acceleration and the idle was rough after that. It turned out to be an exhaust valve that was not rotating and not seating correctly. A valve job corrected the problem.
Everybody loves a good mystery and this one is promising :-) Really curious to see how this evolves - I really enjoy following your thought process!
1, I know you blocked off the crank case to test but could you fit a pressure pulse sensor in place of the pcv, referenced off no.6 injector. Use one of the cylinder over lays then look for a pull on 6 intake stroke to test if it is still something to do with the intake pulling from the crankcase? It will still build pressure in the crankcase from the other 5 cylinders.
Could still be finger error, mating surfaces not right etc. Would also account for the darkened plug burning oil.
2, on the fuel side. Could you perform an injector balance test, using you pulser and fuel pressure?
Can't wait to see the result on this one!
I really appreciate you bringing the content and especially showing when you don't nail it first time. You'd be bored out of your mind if it was carbon tracking on a spark plug!
Your a good man, I admire your ethic. I had a 3500, 7.4 litre once with a slight misfire and changed plugs wires and cap.
Misfire still there... turned out that the new Napa corrected distributor cap was cross firing inside itself.
Two things that I would check just for poops and giggles: spark plug and fuel injector. The resistance on the plug could be changing due to heat or the winding in the injector could be breaking down causing it to stutter.
Swap the both with known good and see if the miss moves.
Don't think you can swap injectors on the spider system?
On the old spider systems, you couldn't swap the injectors. The later ones had 2 wires going to each injector for control. I know they had that on the 96 V6 minivans.
Yep replace those junk copper plugs with iridium an bet that would fix it
@@codyarizona4925 ..copper plugs cannot handle high voltage arcing in modern cars which have a hotter spark ....irridium way to go although $20/plug
@@nickmalone3143 Actually those Autolight iridium plugs @ $9 I've used in dozens of vehicles foreign &domestic with zero issues. GM's really seem to like them.
As always, love the content. I recall on these vortecs that sometimes the plastic intake would form hairline cracks where the gasket seats. Ran ok cold, but would open up hot, causing lean codes and PO300s if bad enough. Overtightening can do this on an old piece of plastic. Try some propane or carb cleaner while running, at the mating surfaces. Note that since this is an older OBD2 in a 1 ton, the computer may not even be programed flag misfires at idle, though it still counts them. I've seen that all the way up through 04 on some Express vans!
At the end of the video I was shocked that the new gaskets didn't solve the problem, the lean misfire seems only that it could be caused by an intake leak somewhere allowing too much air in. But, if those intakes are prone to their own leaks, that makes a ton of sense! I'm assuming the intake was swapped over...and so very old.
Bummer that you did not find the problem... However, I appreciate that you posted the video anyway, to show us that even the best can be frustrated by an unusual problem. I'm sure you will find the source, but will take more time... Good luck!
Hi, spray carb cleaner around 6 intake and see if miss goes away. Many thanks.
that is the easy
i usually watch o2 sensor when i am spraying carb cleaner good idea
YES! My first idea.
Starter Fluid also works
@@thehemiolds455 sma ?
The thing is the gaskets are the most obvious, but not the only possible source of a heat related air leak. There could be a crack in the runner that allows some air in, and it would be worse when hot (expansion).
I think you may have missed a chance on the injectors as well, It would have been a good experiment to move the injector away from that hole and see if the miss follows the injector or not. It may flow very well in your testing, but it may not flow quite as well when warm. That would doubly explain the lack of power as well, as the engine could be essentially running on 7 instead of 8.
Great comment! I will do some detailed experiments when I get the truck to my shop 😁👍
Ive done the upgrades with new spider injection could be difficult swapping the injector to another hole because of the fuel tubes on the injectors. Also when the injector clips into the lower intake it clips in, possibility you could hurt the injector getting it out of the hole.
@@PineHollowAutoDiagnostics Hello Ivan, Was there ever a part 2 video for this truck? I am interested to see as I have a similar issue, rough idle but I have change the intake gasket with a Felpro,new plugs and wires, leak down test on the fuel injectors, Maf sensor, map sensor and nothing has worked but it runs fine while driving.
Those first waveforms look like high secondary resistance on cyl 6. With the updated injection it's possible the injector is not seated properly, or on the wrong cylinder.
I was thinking the same thing with an injector not being seated properly. I'm not familiar with GM's spider injection system, but if an injector was installed in the wrong cylinder wouldn't that leave two cylinders with reversed injectors and misfires?
@@averyalexander2303
Thinking fuel injector also. Sealing or "low quality" and electrical failure when hot.
If it was an "ls" type engine, would also chase hot coils, but does not apply here.
Only my 2 cents.
PS: Gotta love Ivan's tool kit. Pressure transducer test! NICE! I would have tried a relative, but this issue is intermittent, as view on scope,....aka most likely electrical.
Hey Ivan…. I found that the propane at the intake flange test works as good for these engines as the old small block Chevys.
We had the same thing happen with a Chevy engine swap. Intermittent misfire on #5. Couldn't figure it out. Seemed like a vacuum leak but didn't respond to spraying around the manifold. Finally pulled the manifold. The mechanic had left a piece of rag in the intake.
How did this not get sucked in and destroy the engine ?
@@nickmalone3143 It looked like it was pinched between the manifold and gasket. Just a small piece, but it was enough to mess with the flow in that port. It would throw a code on long de-acceleration too.
One of the risks of diagnosing on the road quickly. Kudos to you Ivan for posting your mistakes as well as your many successes. I'm really curious if it is a cracked manifold. If so, your diag was really close to being correct. And you never know when someone else is doing the work if they are making the same mistake again.
Great one Ivan. That sec waveform on scope looked like excessive secondary resistance on cyl 6 dist cap. Ig wire also on perceived vac leak on 6 runner. A propane wand may smooth out engine as propane gets sucked in. Thanks for video
Yes, Ivan, I do enjoy your trip so far.
Honestly, I would check the distributor cap first. They have a tendency to be junk. Looking at how rich the plug looked, I would say it's showing "false lean" condition in that cylinder.
It could be a cracked intake too.. You could weld it shut, if you can find it. But those hairline cracks are harder to spot. There are kits that you can buy that have a powder and dye that makes the cracks much more visible. (HAO) Visible Dye Penetrant Crack Testing Kit)
My first assumption is the owner changed the gaskets and then said it was still running bad so he could get out of paying your diagnostic fee, but then again I am a cynical and untrusting SOB! Hope you get the truck sorted, and more importantly, let's hope the price of gas stops increasing otherwise none of us will be able to afford to drive our V8's. My Sequoia is no longer my daily driver, I cannot afford to use it for my work commute.
Due to gas prices I've parked my 2012 Chevy PU. It has the V-6. It gets worse gas mileage than the V-8. Now driving Toyota Matrix.
Good point. I won't be a bit surprised if he never brings it back and we don't get a follow up video because it's fixed.
@@ourtexasfamilyvideos62 I'm commuting with a beater with a heater 97 Celica, even though it has over 230,000 miles it runs good, and more importantly I get double the gas mileage of my Sequoia.
Welcome to joe bidens america ...gas to be at $10/gal this summer as diesel shortage will curb gas deliveries ...gas and food will be affected.. stock up !
People typically are not that dishonest and he didn't say that he's refunding the diag fee.
I really thought you were going to get to checking for a vacuum leak with propane, carb. or brake cleaner. and look at short term fuel trim to see if it changed when spraying the intake. I was surprised when you didn't. It's a quick and easy way to find vacuum leaks. Another quick check would be with spraying a fine stream of water around the intake and listening for changes in RPM. Also these composite intake are susceptible to cracking and warping. The first test I mentioned would likely find these problems as well. God luck sir. Looking forward to the follow up video. Love your work and honesty. I been watching for years and have learned quite a bit from you. Thank you.
i have a 92 turbo nissan and made a boost leak smoke tester thats simply a soldering iron in a jar wrapped in a sock with mineral oil and a inlet/outlet ports on the jar to add compressed air in one port and other goes to a vacuum port on the manifold and found these simple diy boost leak testers are the best for finding vacuum leaks.there are hundreds of diy boost leak down tester ideas on youtube,some as simple as blowing into a vacuum line or using a vape pen.
I would have swapped plugs 4 and 6 to see if the misfire followed the plugs.
Then it will be more of a rich miss fire and the wave form will show more induction due to a more homogeneous mixture.
I was wondering how the vacuum leak explained the low power complaint, although the new engine might have a different cam or CR. The injector balance test is usually at full open and might not be valid at idle loads. Scoping voltage and current to the injector might reveal something. Also, there appears to be a vacuum port near the no.6 runner. that could be the source of the leak.
Dont get discouraged Ivan, you have it in you, you are the best!!!
💪😅
Ivan. When you get the truck. I had a similar truck with a 350. A customer came to me regarding a misfire under load. Customer also asked if I could replace the spider assembly too. I obliged and took on the job. Replaced spider assembly. Still a misfire. ??
Customer had purchased cheap cap and rotor. Wires and plugs to save$$.
Took about 1 hour to find a very small burn mark underneath the distributor cap.
Bought a brand new AC Delco cap n rotor. Replaced the suspected bad plug. Truck immediately ran smooth and no codes.
I found that the very cheap cap and rotor are made cheap cheap. They short out internally.
bad plugs or wires quickly kill those stupid flat spider caps and the cheap aftermarket ones are junk right from the start.
I've had those with new style injectors (under plenum) in wrong cylinder. The cyl # is marked on the spider assembly.
Hey, it can be tough out there! Your use of diagnostic equipment is spot-on - it amazes me you can maintain a thought train while switching things around and speaking intelligently about the process. I'm not familiar with the "spider", but since it seems to have more than the single throttle-body injector, I wonder if the #6 injector may have an issue. Now, on a really old-school carburated 5.7 like mine, one of the vacuum lines (HVAC) ties into the manifold on a runner to one cylinder. I had a completely dead cylinder at idle, and checked compression expecting to find that cylinder having a burnt exhaust valve. I was elated to find compression was fine and it was simply a vacuum line off on that runner! Good luck - and I can't wait to see your result!
Why do you wonder if he has an injector 6 problem when at the beginning of the video he mentioned he did a fuel injector flow test and it was fine? That right there is your hint its not an injector
@@mikesabin8568 I'm not familiar with the test or whether it's accurate at extremely low flows for idle situations - but the truth is that I missed his comment about doing it.
Heard him say that,, but I'm curious how he did an injector test, the spider injector system is hidden underneath the intake.
@@_RiseAgainst scanners can do it. Bi direction control. Or you can access the wires at the ecm and do it from there
@@mikesabin8568 Interesting. It was my understanding some of these vortec "multi port fuel injection" systems didn't actually control the poppets separately.
Makes you wonder about the spark plug ? Maybe a set of imposter brand marked plugs put in ?
Cheap chinese stuff ...would like to know where reman is from
This is where Paul Danner comes. You need to do the water test on the intake manifold. Start with a cold engine. Add water to a soda bottle. And put the cap on the bottle. Punch a few small holes in the cap. Then you just squeeze and spray the whole thing. Until you here a change in rpm.
Always a problem to come in and clean up after the issue, nice diagnostics!!
You got this. Great work Ivan.
You can help diagnose intake manifold gasket leak with a little bit of spray on the top of the manifold and also tiny bit in the crank case
Oh man! Strike 2.. geez. We all get those days or weeks. Lol I know I've been there and it feels discouraging but what does help is when you finally figure it all out. It's just so satisfying, even more than a regular diag. I know you have so much perseverance and will succeed in the end. Looking forward to seeing Staten Island, as I don't see myself going back anytime soon. Saw Corey about 2 wks ago near me. Always fun to hang out with him. 😅🤣
Hi Cuba! This cursed truck was just East of Philly 😄
But u do charge customers for your so called strikes.
@@elcomandante9299 he took the time out to drive there, that's 1. Gas money. 2. Time for doing the testing, both using scan data but also the scope, which the tools cost money. 3. Put time into the vehicle to pull parts off to do some of the tests.
He should've done that for free?? You hire a plumber or electrician... it's $100 plus minimum charge JUST TO COME OUT. Mobile diag is no different. Unlike most plumbers or electricians, Ivan isn't charging anything additional to put more time into it. He's guaranteeing his work. This is a tough field, being mobile & having time or tool constraints.
I'd love to see you work for free.
@@PineHollowAutoDiagnostics @Pine Hollow Auto Diagnostics geez. Probably only a few mns from me. I'm on the E part of Philly, bordering Bucks County. Could've stopped on through. 😁 Next time. Lol.
Smooth like butter 🧈. Another great video
The closer you get to Staten Island the stranger things get! Thanks Ivan.
Good diagnosis! Hard to fix since it's spider injector encased in the intake. That will be hard to test injectors. But I'm interested in how you test that. Similar case study with the other 5.7 v8 with bad gaskets. I remember this one. I want to know what you find out when the truck in your shop
I haven't watched the entire video yet, but I did come across a similar problem on a late '90s S-10 Blazer with a 4.3. The valve guide on the #6 exhaust valve didn't have enough clearance. When hot, the exhaust valve would hang partially open, causing a misfire. The fix was to pull the head and hone or ream the valve guides. I'm fairly certain there was a TSB on this problem, but I don't remember if the bulletin applied to the truck you're working on.
How would you go about finding that? High rpm compression test?
@@kipamore I'd love to tell you that my genius level diagnostic skills nailed the problem in 15 minutes, but that isn't what happened.
The truck initially presented with a misfire and a leaking fuel pressure regulator, which was common on those engines. We replaced the CSFI unit with the updated part, road tested and returned it to the customer. He comes back a week later saying that the truck runs rough sometimes. It took me a week of lunch time road tests to even confirm his complaint. I then spent way too much time replacing questionable (but not visibly *bad*)ignition parts, warrantying the CSFI unit, etc. Eventually a post in the iATN drivability forums led me to suspect the exhaust valve guide. I got the engine as hot as possible, which caused the misfire on #6 cyl. With the engine still hot , I quickly pulled the plug (not recommended...I still have the burn scars from that job) and did a leakdown test. The exhaust valve was leaking. I pulled the valve cover and found the valve hanging open. I then scheduled the repair with the customer.
TL;DR--I spent a long time chasing my tail until a fellow tech pointed me in the right direction.
The pressure transducer test would have picked that variable up.
@@alantrimble2881 I'm going to tuck this tale away in a corner of my brain. I suspect it will come in handy at some point. Thanks.
Spraying some carb or break cleaner along the affected cylinder should smooth out the miss.
Maybe spraying starting fluid near the intake to see if there were any intake leaks.
This was my thought as well except using propane gas from a small tank/torch, not lite obviously.
I work on Analytical Labs and bad Karma always comes in sets of 3. You got one more heading your way at some point.
If I recall correctly those plastic intakes are prone to warping.
Thats my guess too
Be sure to check vortec intake surface with a straight edge to see it is warp in the middle one other possibility is there to hair line cracks in intake manifold runner or the plenum also check map sensor seal and brake vacuum port seal, personally I think it's a spider injector is self because #6 plug look a bit richer than #4
Check intake with a straight edge? That's so early 50s
@@elcomandante9299 you are aware that the vortex heads and intake manifold only has 4 bolts pre-side only cover the water passage unlike the earlier Chevy 350 which has six bolts per side keeping the center of the intake manifold from warping.
@@elcomandante9299 .. but then you would have mess with a carbuerator
That #6 plug looks like it's a bit rich. Possibly a problem with that particular injector. (?) We do know that just because its new doesn't mean it's good. Would the fuel trims tell us anything ? Please excuse my DIYer ignorance.
He said at the beginning of the video he did an injector flow test and it was fine
@@mikesabin8568 Ah, not that I think it is injector related, because I do not, but he did say is happens after load.... meaning HOT. A flow test usually isn't done HOT. (usually)
@@HouseCallAutoRepair why not do the flow test when its hot? Thats when he experiences the problem. Performing tests when the car exhibits the problem sounds like a great idea to me and thats what ivan did, correct?
Careful on your next one Ivan, bad things seem to come in three's - Great video. I'm looking forward to the next one
Ivan I do not see you are using pulse sensor on exhaust or intake , or abosulte sensor, I would have done RC. intake and exhaust pulse sensor to try to nail down the misfire on that cylinder . Great testing methods and of course it is difficult to find the method to prove some faults . Great job thanks for sharing.
I'm not a mechanic but was wondering why #6 plug looked rich when #6 was diagnosed as lean? I also noticed that #5 cylinder occasionally looked lean (at 7:59)
I was thinking the same about the plugs. Maybe the plug is arcing internally?
@Jasher M. OK, so it's not lean, it's just being "reported" as lean. Got it.
Valve sticking in guide. Was common back in the day. Always the inner cylinders.
Had this one time. Junk yard engine. Took upper intake plenum off and found that the number 2 injector was plugged into number 6 hole and number six injector plugged into number 2 hole . Put them where they were supposed to be and reassemble plenum and ran engine. No more miss.
My reading of the spark was an outside the cylinder ignition high resistance. Those caps are infamous for leaking in the top of the cap. OEM only is trustworthy. The 6 plug looked kind of dark, blackish, indicating unburned fuel. A lean plug should have been lighter than the normal.
Interesting! I wonder if the spark plug itself is acting up when it gets hot. I just experienced that with a lawn mower. Ran good when cold, but started running rough after a few minutes then dies out and wouldn't restart until cool. Heat can do interesting things to failing electrical components.
Your still awesome Ivan 👍👍👍
Intake gasket leaks are always confirmed with some brake clean or WD40 squirted around the joint - if the miss goes away or you see the liquid being drawn in, Bingo. Also check for a tight valve clearance on cyl 6 intake,
This has really turned into the road trip from hades. I'm really intrigued to find out if there is an electronic or electrical gremlin with cylinder 6. Hope you have better results from Staten Island.
Back in the day, any intake manifold leak we'd spray carb cleaner around the area and listen for the idle to change. That was the 80's though. LOL
Nothing against using a scope and related fancy gadgets during driveability diagnostics but I like to start with cheap(hopefully free lol) and/or easy. Try swapping spark plugs/plug wires/fuel injectors (if easily accessible) between cylinders. Try carb cleaner around the intake gasket sealing surfaces.
No one likes to be wrong but it's even worse to be wrong after the customer watches you "hook up the computer" to their vehicle.
6:30 when you were stepping through the #6 shots, while the shoulder was a little higher most of the time, about 1 in 8 was completely messed up, and that's about how often it was missing when running at idle.
My truck is doing the same thing..same truck,basically with one exception..it has a 7.4,454..I'll be watching this one closely!..I can't find anyone to work on it😳..I wish I were closer to you Ivan!..I'm in Covington Tn 👍
When I worked at at a Chevy dealership I remember a jasper reman engine doing the same thing the one rocker arm was adjusted incorrectly took me forever to figure it out.
I never realized how often your customers watch right over your shoulder. Aahhgghhj!! That creeps me out and messes with my concentration. Don’t know how you do it, Ivan. You have the patience.
Pressure transducer test on manifold vacuum may show some data. Waiting for the conclusion.
I was thinking injectors, but I've been watching your videos for a long time and wouldn't have argued with your call, it could still be the manifold gasket or even the manifold
Love the road trip. I watched entire video with "LG-IMS..." error sharing screen with PHAD 😆. Of course, see if some vacuum device has a port on runner 6. Also, if truck has EGR, is there an EGR runner in manifold that might have a crack effecting runner 6. If lower intake is wet bottom, I've used exhaust analyzer and choke cleaner to prove or disprove intake leaks. Looking forward to next installment.
Looks like an upslope on the #6 spark line. Tends to be something going on in the cylinder. Increasing resistance through the burn.
I had a Ford Taurus that did exact same thing. It was the injector. When it got hot, the windings separated and it failed and car ran lean. Once it cooled or was not stressed it worked just fine. I replaced the injector and it was fine.
That looks to be a nice truck. Clean, manual trans :)
Check it out. Ivan's got a Mini-Me on his shoulder around min 14. Had to relook 3 times.
I can see a definite difference in the scavenging event on the cyl 6 waveform. Not sure if it was camera angle, but it looked like the compression peak was leaning a bit. I haven't gotten used to these yet, but I'm thinking exhaust restriction from a lazy valve or partially blocked exhaust port.
Did someone put a gasket in backwards?
Prior to scopes and OBD etc, we used to play a unlit gas torch near the inlet, if the misfire went, it was a proof of a leak😁
swapped the plugs I like that one the best.
I did not notice you inspecting valve timing precisely on the in cylinder waveform?? All the nice exhaust pocket says is the rings or valves are not leaking. Good luck Ivan.
GM 5.7L V8's used to have a problem with the valve guides causing the valves to be to tight in the guides after a long or hard or loaded pull especially going uphill. Some machine shop work fixed the problem.
Another thing was valve springs. Weak valve springs did the same thing. Once the engine cooled, all was well.
You'll find the problem Ivan! On to part 2.
I was thinking bad valve spring also
This possibility crossed my mind... But how to test for this while it's acting up? 🤔
@Pine Hollow Auto Diagnostics
There was a TSB from GM about this problem years ago, I don't remember if or how testing is done during the failure. IATN "might" have information about that or maybe Keith might be helpful.
Also check #PIP3081: SES Light and P0300 When Towing , Cruising Uphill or on Hard Acceleration - kw 4.3 5.0 5.7 accelerate cruise cylinderhead DTC L30 L31 L35 LF6 LU3 P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 - (Jul 23, 2004)
I'm attempting to paste the TSB.
Subject: SES Light and P0300 when Towing, Cruising Uphill or on Hard Acceleration.
The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.
Condition/Concern:
The vehicle may exhibit a SES Light due to a P0300 and misfire. If the misfire is related to the information below, it will typically happen while cruising uphill, pulling a trailer or on hard acceleration and then stop misfiring shortly after returning to an idle. Typically, cylinders 3,4,5 or 6 will be the ones to experience this.
Recommendation/Instructions:
If the P0300 SI diagnostics did not isolate a concern, the following may help:
Remove the valve cover, valve springs and valve seals on the effected cylinder or cylinders. A small wire tie or rubber bands can be placed in the valve stem keeper groove to prevent the valve from falling into the cylinder. Rotate the valve while moving it up and down in the guide to see if it binds. If a binding valve is found, remove both cylinder heads and use either of the following methods to increase the stem to guide clearance:
Send the head out to a machine shop and advise them to increase the valve stem to guide clearance to 0.002 inch per guide.
Hone the guide with a 9 mm hone, such as Snap On BCG249, until a clearance of 0.002 inch is obtained. This will usually take about 4 strokes of the hone.
Reassemble the cylinder heads using new valve seals.
Models:
(96 - 02 Chevrolet Astro) and (96 - 02 GMC Safari) and (96 - 00 Old Body Style Chevrolet Suburban) and (96 - 00 Old Body Style Chevrolet Tahoe) and (96 - 02 Chevrolet Express) and (96 - 00 GMC Yukon) and (96 - 00 Chevrolet Old Body Style C/K Truck) and (96 - 00 GMC Old Body Style C/K Truck) and (96 -02 GMC Savana) and (96 - 99 P32 Cab and Chassis) and (96 - 02 Chevrolet S-10) and (99 - 02 Chevrolet Silverado with 4.3L V-6 Engines (96 - 02 GMC Sonoma) and (96 - 02 GMC Sierra with 4.3L V-6 Engines).
Ah man thats a bummer. Super interested to see what the issue is.
Darn it! On the older carbureted SBC with EGR valves the intake gasket would fail on the #6 cylinder because the extra heat from the EGR valve would burn the gasket. Not all of them but a lot of them. I definitely would have made the same call.
Spray starter fluid in the suspect area at cylinder 6 and see if he engine smooths out briefly
Check the distributor cap,,, that vintage chevy are notorious for cracking and burnthru, allowing spark misfire. when they first start, they usually act up when hot. problem will continue to get worse as burnthru advances.
Could have just taken some brake clean or propane near the suspect intake runner to see if it smoothed out to determine if the intake gasket was faulty.
Many years ago I bought a brand new Mr goodwrench 350 engine, when it got hot it had a hard time cranking over like something was binding. I installed the engine myself, I told friends of mine who were mechanics and owned a shop, in fact they loaned me the hoist and engine stand and any tools I ever wanted, they even brought them to my house, they only were a few blocks from my house, they recommended I bring it to the local Chevy dealer in town and explain the problem, the engine had the factory warranty and I only had it about a month, I went to the dealer and explained what happened, they immediately wrote up an order, I left the car which was a 1979 Malibu classic sport coupe, the next day was a Saturday, they closed early so in the evening I went to see if my car was still sitting outside but to my amazement it was I side and the engine was out already. They determined th st the number 5 piston was binding, they installed another brand new engine and it was fine after that, if this engine is still under warranty I'd tell him to go talk to the dealer. That's the beauty of buying a factory trans or engine because the manufactured is responsible after the fact and they perform the work under warranty. My friends woukd always use gm or whatever engines and transmissions for that reason.
o-ring gaskets on the spider injector at the injector port.. if the injector is not fully seated or the O-rigs fail it will leak only at temp when the manifold is heated and expanded.. Had the same issue w/ 2.3 v6 in a s10
Very interesting
My guess is the intake is expanding with heat or something like that and allowing excessive air into number 6 or just junk gaskets being used aftermarket cheap
If you have a vacuum leak your iac counts will be close to 0 gm's typically run between 9 and 19 dirty throttle body will go high usually around 39 . Remove valve cover loosen intake valve and exhaust valve 3/4 of a tern on number 6. Valves are tight
Having a bad run on diags , it can play with your mind and confidence s##t tends to happen in groups . I've heard of toyota diesel engines having cracks in the head that only open up when very hot then reseal perfectly once cooled down . Looking forward to seeing what the problem is.
Man, does it ever happen in groups!!! You got that right. I call them my bad weeks. It’s funny that you can actually feel it happening.
Aftermarket distributor caps are a known problem on these engines, still to this day. I think a simple spark tester at the end of the plug wire for #6 would have shown spark to be dropping, the plug is evidence. If you look at the cap, you can see how the electrical pathways cross all over each other. The ignition waveform can look lean because the spark is jumping to a different cylinder. Lots of experience with these, I won't even replace one unless the customer is okay with the AC Delco price, burned too many times.
Back in the day, a guy could block off the pcv ports and check for vacuum in the crankcase to warrant pulling the intake for a vacuum leak, would that still be a valid test?
You could still be right. If the intake manifold is out of flat, the same symptoms could occur even with the best gaskets.
Classic test would be to spray some ether (or your favourite flavour of aerosol spray) around the gaskets to test if they're letting anything past.
I was surprised you busted out the pressure transducer before doing something so simple.
Spray some starter fluid around the intake. If theres a leak it will suck it in and you will see it on the scope
I was waiting to see if you were going to use brake clean or water to check for the vaccum leak.
We all make mistakes. I'm very curious to want the problem is. At this point I'm guessing a bad(new ) spider injector. It's the only thing else that could cause a lean condition that I could think of
Great video
Carb cleaner works great for checking vaccum leaks.
Ahhh....that sucks Ivan. It will be better to have it in your shop so you can possibly stumble onto the answer since your not pressed for time. I don't know why but those #6 cylinders against the firewall always seem to be a problem. A lot more heat back there I guess. You'll figure it out if you get it in there. Gotta be something simple but unseeable.
Greeting from Ireland love the videos !!
The #6 plug looked more like it was not burning all the fuel completely?
2:35. I haven't seen windows XP in a while. Especially that wifi icon. 😂
like others say intake leak could be comming from anywhere , alota variables also maybe the intake isnt on quite the same plane as new engine , or maybe is bad plug ??? look forward to the findings on this one too
i have 13 silverado i had same issue coast to a stop and run rough smell to much fuel i replace maf sensor 4 times finally got gm one and boom fixed
I would be sure that engine has a new set of valve springs as they have problems with valves hanging when real hot because of weak valve springs
Dont they put cheap valve springs in those rebuilds ?
Cool cases and cool road trip.
13:56 - Dude, there is someone right behind you!
Amanda?
That was the owner of the truck 😂
Yeah I saw that too
@@PineHollowAutoDiagnostics I believe you! ;-) ;-) ;-) :-D
@@PineHollowAutoDiagnostics You Don`t Pay, You Get Taken Away ! haha
ive always have been a huge fan of thermal intake manifold gaskets as well as throttle body ..... they are 1000 times better
#6 comp spike was leaning left. Why? Many years ago had a parts store 2.8 carb'd reman in a S-10 Blazer. No power. Finally tracked it down to poorly ground camshaft. THAT was a tough one with no scope. Had to use a degree wheel & indicator to check valve timing.