I've got to say.. This guy knows his stuff. I had multiple problems with both my blazers. This guys videos are whats up. Thanks for taking time to put this info out to the public. A garage would have charged me thousands by now to do this stuff. Your the man, keep it up!
thanks for the very precise diagnosis, I used it for checking voltage drop and had very little for my pump. I had low fuel pressure and it appeared that the check valve on the pumpp was bad. Not the case, when I had the pump removed I saw that the rubber hose from the pump outlet to the metal supply line was loose. Bought a couple of new hose clamps and a foot of hose and solved the problem. Thanks again
Finally! Problem detected and solved. Perfect execution of problem solving skills. Steps are common sense, but must be shown in order to teach inexperienced or experienced shade tree diy'ers the art of "KISS" (keep it simple stupid). I'm truly impressed; been on YT since day one (IT guy) and this is my first comment ever. I know this video is older, but owning two blazers and an S10 truck I've been thru just about every one of these videos since before 911. Mostly cursing and being frustrated. And then this morning eureka! Well done sir. Well done. I will subscribe.
I been looking for someone that could explain things to me in a way I can understand, I’m glad I stumble upon ur video I work for Lexus and I’m moving up the ladder to become the diagnostician and every day I get more and more diagnostic so far not one comeback it don’t matter how long it take me I want to be sure of my diagnostic, and watching your Rich and lean condition video the other day it like opened my mind on that subject and sure enough I went in plugged in my scanner and started to see the numbers change and able to make more sense of the info in the data pids now
that’s excellent to hear. You should definitely check out my website at www.schrodingersboxqm.com. It takes this stuff to whole new level and you will really master the diagnostic foundational skills.
Hello Matt. You truly are a positive force in the world! Out of shear curiosity I've been perusing your videos over the last few days and you have quite expanded my diagnostic capabilities. Finding someone who applies the scientific method towards a service industry which so desperately craves it. It's quite a breathe of fresh air! Anyhow, for future reference the resistance in the wire you connect to your voltmeter does not matter because the voltmeter is connected in parallel with the fuel pump wire. Voltmeters by nature of design have incredibly high internal resistance (usually 10+ M Ohms). Therefore you won't be perturbing the initial circuit much by measuring it so you will get an accurate reading regardless of the resistance of the wire. Thank you for your contributions.
Thanks bro. Yea since this video I have learned about the insignificance of resistance in the lead wire. I am learning as well. Love your screen name btw. It would be an appropriate name for this channel!
@12vgs- Yes you are absolutely correct, and in fact I Would have preferred to do exactly that. However the connector for doing voltage drop inside the tank was extremely hard to reach and I figured ruling out every other possibility is as good as identifying the actual issue and in this example it happened to be easier. If I had a friggin lift instead of jackstands it would have been so much easier lol!!!!
Very good, thorough job! I just bought a 1996 Chevrolet S10 that is having a P0303 code, along with a P0106 and P0107. I am not about to just go buy a MAP sensor until I test the one that is now on the vehicle. Thanks for all your videos! Dan
An excellent series of videos especially about fuel trims. I must comment on burnt out wiring. Had the burnt out cable been outside the pump you should not just repair it you also need to know why it is burnt out. In this case almost certainly the fuel pump motor coils shorting. Since the fuse did not blow your friend should also check he is using the correct fuse.
voltage drop on last test will be probably even higher with pump pumping fuel. then it will be under load and taking more amps from the batery. Very helpful videos on you channel Thanks
Thank you Matt for these wonderful sets of videos. At minute 5:45 where it showed 12.7 volts for the positive voltage drop before you cranked the engine. The question is, why was it showing any voltage drop at all between the positive battery terminal and right up to the pump. Shouldn't it be zero or very few millivolts? The actual load or the source of resistance was the pump itself and we were measuring the voltage drop at rest before cranking the engine.
Hi Matt, good video. The only thing that I would have done different was your procedure in checking voltage drop to the fuel pump. Measure the voltage at the source, then measure the voltage at the pump with it turned on of course. Subtract the two readings and there's your voltage drop. This would save a lot of time instead of running a wire from the battery which is adding more drop to the circuit. Then if the difference is too high, you could do the follow-up as you've shown.
Man, how I love you... No, really though. You have no idea how awesome your videos are! And even though I don't (yet) do the more advanced things you're showing in some of your vids, it's so informative and inspiring! Love watching them, and learn so much, especially about understanding the electrical stuff... Let's face it, automotive electrics is a brain-twister sometimes, and it amazes me every time how clearly and logically you see/approach it all. Keep it up, you are a true inspiration! Greetings from Norway :) Oh, and btw, I feel your pain when it comes to cold garage floors, haha! Only, we also have the risk of polar bears mauling us when we least expect it, so at least you have that going in your favor! A volt/ohm meter and a shotgun, that's like standard equipment for a day in the garage ;) Have a great weekend, sir!
Thanks man. This is a really old video... since I've improved my skills (and I show them to you in future videos) I spend a lot less time on the garage floor than before lol. I normally do diagnostics through relay ports now.
Yeah, I'm well aware, I've watched most of your videos several times. Just random that I chose this old one to comment on, didn't really think that through before I commented lol. Surprised you even saw the comment, but thanks for the reply :)
I just wanted to point out that you do not need to be too concerned about the gauge of the wire as well as additional voltage drop across the wire from the battery to the meter when doing the voltage drop test. The wire is not supplying current to the pump, only to the the volt meter. Most modern voltmeters have an input impedance of 1 Meg or greater. At 1 Meg Ohms and with at 12 Volts, you have 0.000012 Amps running through the test wire into the meter. If the test wire has a resistance of 50 Ohms (which is a ridiculously high value for argument sake) the voltage drop introduced would only be 0.0006 Volts. So you can see it is negligible. I think someone already stated this but you can just measure the voltage at the battery, then the voltage at the pump by back probing both leads in the connector. Subtract the pump voltage from the battery voltage you get the full voltage drop to the pump from both wires. If you find the drop is excessive, then you can do the individual lead voltage drop as you described to determine which one is at fault. Resistance checks can also be made but either way you go, I would start with the ground wire. It’s probably most likely to have a faulty connection. Thanks for some great videos. I'm having intermittent misfires while accelerating on a Vortec V6 which lead me to your video on replacing the spider fuel injectors. The videos will help me determine the problem.
Vitiay, Provided your Civic has normal fuel pressure under load, I might suspect a faulty MAP sensor (I am pretty confident your car doesn't have a MAF or I'd definitely suspect that). It is also possible (but quite unlikely) injector problem could explain the low fuel delivery and thus lean condition. Heck, could be throttle is opening wider than TPS detects. Honestly there are too many variables to just guess- again you must think in terms of "what would cause less fuel than is really needed"
Bill Nye the science guy for mechanics...YOUR AWESOME MAN... Very informative and helpful info.Ive been listing to you videos for about 4hrs now. Starting watching dianosed on a distributor but love all your other videos..When i pulled my distributor of my 97 chevey chyenne v6 vortec 4.3 it is all rusted. this is the 2nd one that does this..Any ideas on why im gettin moisture in tho top of the distributr inside the cap...the cap looks perfect no cracks or nothing
esco361 There is a gasket that goes between the distributer and the intake manifold deck- my bet is you are missing that (you can also just use sealant). Otherwise you might have water/coolant in the oil. But I am betting the absence of the gasket explains it.
So, Matt if you had measured the voltage at the back probe, you could have found the voltage drop inside the pump? Actually you can review the tape and see what was the number that you got when probing for the correct wire. You should be able to see the extra .3V drop in the grey wire as reduced battery voltage at the probe by that amount
Awesome video, Matt. In my situation this is the same exact scenario with the lean condition under load ( Honda Civic1998 ). I went through everything that you mentioned. But I still can't figure out the problem ( . I just won't give up. Can it be a glitching sensor or an electrical problem only when the car is moving ?
So I cleaned my MAF and IAT and everything reversed. Now my B2 LTFT increases at idle. For a minute that condition switched to B1 but now it's back to B2. I bought a fuel pressure gauge and at 41 degrees outside with a cold engine my fuel pressure at KOEO was 30 psi (should be 35-45) and was holding pressure. With cold engine running it was at 30 psi and when I shut it off it held pressure for 20 min until I released it.
An alternative method of measuring voltage drop is to measure point voltages relative to local ground (a clean quality local body ground is necessary). This avoids stringing a wire to the battery. Voltage drops are calculated by subtracting point voltage at pump power lead from battery source voltage (for positive power lead), and voltage on ground wire lead at the pump w/ a backprobe relative to local body ground (this will directly measure voltage drop in pump ground wire).
Hi Matt, Another good video diagnosis, but I wasn't sure about the voltage drop explanation until I thought about it in terms of a garden hose, that is, if a garden hose is restricted or kinked then the flow of water through it will be affected. After i thought about it like that, then i was able to picture the reasoning behind a voltage drop test. If the voltage is being restricted then the load will also be restricted or minimized. would that be a fair comparison?
Fair comparison. :) If I wire is bad it'll have more resistance or less flow. Look up Ohm's law. Ohm's law named it after himself and at work I even ran into one of his relatives who was aware she was related.
Another easier test would be to put a known load such as a light bulb appropriate resistance to provide 10 amps or so back probed into the connector to replace the fuel pump as a load thereby verifying the integrity of your wire feed to the pump from the front of the car. This will prove the actual power and ground wires are able to supply amperage as well as supply voltage.
Schrodinger i didn't understand this drop test that you say about the voltage drop in positive side i understand that drop test of the circuits in positive side should be around .2 i'm not sure but can you explain me why to much voltage drop great video by the way
Rafael, I am not sure I understand your question but let me try anyway. The voltage drop test is a test for resistance in the wire- in other words if the wiring is very old and not in good condition it will have a high resistance. This resistance will cause a drop in voltage because it cannot carry electricity very well. If I had found a high voltage drop in any of the wiring outside the fuel tank, then it is possible the fuel pump is fine- it just does not get enough electricity to pump fast enough to build fuel pressure. But since I found all the wiring outside of the tank is good because there was a low voltage drop, this means the problem MUST be inside the fuel tank. At the end of the video, I show that actually, the wiring inside the fuel tank was bad because it had a high voltage drop. The fuel pump was probably fine, but since I had to remove the tank- it makes sense to replace the pump rather than repair the bad wiring. I hope this answers your question.
Jumper cables are perfect for this, because the heavy gauge wire has very low resistance and will result in a negligible voltage drop through the cable, itself.
Great video, but you incorrectly determined the voltage drop of the long wire to the battery for the voltage drop test. The meter you are using as a voltage meter has a high impedance, about one megohm or so, compared to the resistance of 20 feet of copper wire, the voltage drop across the wire will be neglible. So, you can ignore the 20 foot wire voltage drop. Thanks, -Arlen
@arlen raasch Hmmm you bring up a good point, I agree with you- that makes sense and in retrospect seeing the minimal voltage drop on the negative confirms your statement. Now I wish I had done the voltage drop test at the very end of the video with and without that same extension wire see if there would have been a difference at all much less my calculated difference. Great input! Well, even if the calculation was not necessary, it did set a higher stringency for the voltage drop test to pass and thus even further confirmed the wiring ouside of the tank was indeed fine. Great comment and thank you.
John Dodge A DVOM (Digital Volt Ohm Meter) when used in a mode to measure a voltage (AC or DC) has an input impedance. You are correct that most commonly used DVOMs have a high input impedance, so much so that for most people they can ignore that just applying the meter to a circuit modifies the voltage slightly. However in high output impedance circuits, it still can matter. The DVOM's high input impedance can lead to some confusion when doing some common tests as well. For instance if a starter motor is not working, disconnecting the battery lead from the starter and measuring from this lead to ground with a DVOM may well show +12V, but when actually connected to the starter the same lead reads close to 0V. Why? There may be a poor battery terminal connection or a high resistance in the positive lead to the starter. Hope this helps.
Where do you find the specs for the parts in a car that you are diagnosing? ie, what's the right fuel pressure at various parts, the right cylinder pressure, the expected voltage drop, etc?
So when you’re doing a voltage drop you connect to your negative terminal of the battery and on the other DVOM lead you back probe it to the negative wire from the connector and viceversa?
Positive is same. You always measure voltage drop on a single polarity. Unless you are using kerchoffs law then you can subtract from source voltage. I find the latter to be way easier. I like simple.
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Very good at diagnosing,trouble shooting I wish more mechanics were as thorough as you!excellent at what you do!
I've got to say.. This guy knows his stuff. I had multiple problems with both my blazers. This guys videos are whats up. Thanks for taking time to put this info out to the public. A garage would have charged me thousands by now to do this stuff. Your the man, keep it up!
thanks for the very precise diagnosis, I used it for checking voltage drop and had very little for my pump. I had low fuel pressure and it appeared that the check valve on the pumpp was bad. Not the case, when I had the pump removed I saw that the rubber hose from the pump outlet to the metal supply line was loose. Bought a couple of new hose clamps and a foot of hose and solved the problem. Thanks again
Man, great job on the explanation. Most helpful video I've seen on the lean/rich topic.
Finally! Problem detected and solved. Perfect execution of problem solving skills. Steps are common sense, but must be shown in order to teach inexperienced or experienced shade tree diy'ers the art of "KISS" (keep it simple stupid). I'm truly impressed; been on YT since day one (IT guy) and this is my first comment ever. I know this video is older, but owning two blazers and an S10 truck I've been thru just about every one of these videos since before 911. Mostly cursing and being frustrated. And then this morning eureka! Well done sir. Well done. I will subscribe.
I been looking for someone that could explain things to me in a way I can understand, I’m glad I stumble upon ur video I work for Lexus and I’m moving up the ladder to become the diagnostician and every day I get more and more diagnostic so far not one comeback it don’t matter how long it take me I want to be sure of my diagnostic, and watching your Rich and lean condition video the other day it like opened my mind on that subject and sure enough I went in plugged in my scanner and started to see the numbers change and able to make more sense of the info in the data pids now
that’s excellent to hear. You should definitely check out my website at www.schrodingersboxqm.com.
It takes this stuff to whole new level and you will really master the diagnostic foundational skills.
@@SchrodingersBox I sure will I went back on your channel to your first videos i want to watch them all.
Hello Matt. You truly are a positive force in the world! Out of shear curiosity I've been perusing your videos over the last few days and you have quite expanded my diagnostic capabilities. Finding someone who applies the scientific method towards a service industry which so desperately craves it. It's quite a breathe of fresh air!
Anyhow, for future reference the resistance in the wire you connect to your voltmeter does not matter because the voltmeter is connected in parallel with the fuel pump wire. Voltmeters by nature of design have incredibly high internal resistance (usually 10+ M Ohms). Therefore you won't be perturbing the initial circuit much by measuring it so you will get an accurate reading regardless of the resistance of the wire.
Thank you for your contributions.
Thanks bro. Yea since this video I have learned about the insignificance of resistance in the lead wire. I am learning as well.
Love your screen name btw. It would be an appropriate name for this channel!
Nice series Matt..thanks teaching attention to detail👍
Love the way you only except a diagnosis to the exact problem. To many parts changers out there.
@12vgs- Yes you are absolutely correct, and in fact I Would have preferred to do exactly that. However the connector for doing voltage drop inside the tank was extremely hard to reach and I figured ruling out every other possibility is as good as identifying the actual issue and in this example it happened to be easier. If I had a friggin lift instead of jackstands it would have been so much easier lol!!!!
Thanks for these videos. I now have the long list of questions to ask my mechanic as he starts the diagnostic process on my lean codes...
I bet you end up with a really short list of answers ;-)
That's a very instructive example, with a bad internal wire externally showing no drop leading to and from the pump.
Very good, thorough job! I just bought a 1996 Chevrolet S10 that is having a P0303 code, along with a P0106 and P0107. I am not about to just go buy a MAP sensor until I test the one that is now on the vehicle. Thanks for all your videos! Dan
An excellent series of videos especially about fuel trims. I must comment on burnt out wiring. Had the burnt out cable been outside the pump you should not just repair it you also need to know why it is burnt out. In this case almost certainly the fuel pump motor coils shorting. Since the fuse did not blow your friend should also check he is using the correct fuse.
voltage drop on last test will be probably even higher with pump pumping fuel. then it will be under load and taking more amps from the batery.
Very helpful videos on you channel
Thanks
Ah good point- I probably should have tried that using a nonflammable liquid. never thought of that
Thank you Matt for these wonderful sets of videos. At minute 5:45 where it showed 12.7 volts for the positive voltage drop before you cranked the engine. The question is, why was it showing any voltage drop at all between the positive battery terminal and right up to the pump. Shouldn't it be zero or very few millivolts? The actual load or the source of resistance was the pump itself and we were measuring the voltage drop at rest before cranking the engine.
If I remember in this video I measured the voltage drop across the positive and negative for fuel pump and activating pump.
I like the diagnosis, very well explained on all your videos
Outstanding.
I'm going to work my way through all your videos.
Thanks.
Great videos. I was a drivability tech 20 years ago. I could used these videos back then.
Hi Matt, good video. The only thing that I would have done different was your procedure in checking voltage drop to the fuel pump. Measure the voltage at the source, then measure the voltage at the pump with it turned on of course. Subtract the two readings and there's your voltage drop. This would save a lot of time instead of running a wire from the battery which is adding more drop to the circuit. Then if the difference is too high, you could do the follow-up as you've shown.
Man, how I love you... No, really though. You have no idea how awesome your videos are! And even though I don't (yet) do the more advanced things you're showing in some of your vids, it's so informative and inspiring! Love watching them, and learn so much, especially about understanding the electrical stuff... Let's face it, automotive electrics is a brain-twister sometimes, and it amazes me every time how clearly and logically you see/approach it all. Keep it up, you are a true inspiration! Greetings from Norway :)
Oh, and btw, I feel your pain when it comes to cold garage floors, haha! Only, we also have the risk of polar bears mauling us when we least expect it, so at least you have that going in your favor! A volt/ohm meter and a shotgun, that's like standard equipment for a day in the garage ;) Have a great weekend, sir!
Thanks man. This is a really old video... since I've improved my skills (and I show them to you in future videos) I spend a lot less time on the garage floor than before lol. I normally do diagnostics through relay ports now.
Yeah, I'm well aware, I've watched most of your videos several times. Just random that I chose this old one to comment on, didn't really think that through before I commented lol. Surprised you even saw the comment, but thanks for the reply :)
I just wanted to point out that you do not need to be too concerned about the gauge of the wire as well as additional voltage drop across the wire from the battery to the meter when doing the voltage drop test. The wire is not supplying current to the pump, only to the the volt meter. Most modern voltmeters have an input impedance of 1 Meg or greater. At 1 Meg Ohms and with at 12 Volts, you have 0.000012 Amps running through the test wire into the meter. If the test wire has a resistance of 50 Ohms (which is a ridiculously high value for argument sake) the voltage drop introduced would only be 0.0006 Volts. So you can see it is negligible.
I think someone already stated this but you can just measure the voltage at the battery, then the voltage at the pump by back probing both leads in the connector. Subtract the pump voltage from the battery voltage you get the full voltage drop to the pump from both wires. If you find the drop is excessive, then you can do the individual lead voltage drop as you described to determine which one is at fault. Resistance checks can also be made but either way you go, I would start with the ground wire. It’s probably most likely to have a faulty connection.
Thanks for some great videos. I'm having intermittent misfires while accelerating on a Vortec V6 which lead me to your video on replacing the spider fuel injectors. The videos will help me determine the problem.
Yes you are very correct- at the time I did this video I was not as familiar with the concept as I am now.
Fenomenal work.
Vitiay, Provided your Civic has normal fuel pressure under load, I might suspect a faulty MAP sensor (I am pretty confident your car doesn't have a MAF or I'd definitely suspect that). It is also possible (but quite unlikely) injector problem could explain the low fuel delivery and thus lean condition. Heck, could be throttle is opening wider than TPS detects. Honestly there are too many variables to just guess- again you must think in terms of "what would cause less fuel than is really needed"
Bill Nye the science guy for mechanics...YOUR AWESOME MAN... Very informative and helpful info.Ive been listing to you videos for about 4hrs now. Starting watching dianosed on a distributor but love all your other videos..When i pulled my distributor of my 97 chevey chyenne v6 vortec 4.3 it is all rusted. this is the 2nd one that does this..Any ideas on why im gettin moisture in tho top of the distributr inside the cap...the cap looks perfect no cracks or nothing
esco361 There is a gasket that goes between the distributer and the intake manifold deck- my bet is you are missing that (you can also just use sealant). Otherwise you might have water/coolant in the oil. But I am betting the absence of the gasket explains it.
thank you very much for the info and your time!!
So, Matt if you had measured the voltage at the back probe, you could have found the voltage drop inside the pump? Actually you can review the tape and see what was the number that you got when probing for the correct wire. You should be able to see the extra .3V drop in the grey wire as reduced battery voltage at the probe by that amount
Awesome video, Matt. In my situation this is the same exact scenario with the lean condition under load ( Honda Civic1998 ). I went through everything that you mentioned. But I still can't figure out the problem ( . I just won't give up. Can it be a glitching sensor or an electrical problem only when the car is moving ?
So I cleaned my MAF and IAT and everything reversed. Now my B2 LTFT increases at idle. For a minute that condition switched to B1 but now it's back to B2. I bought a fuel pressure gauge and at 41 degrees outside with a cold engine my fuel pressure at KOEO was 30 psi (should be 35-45) and was holding pressure. With cold engine running it was at 30 psi and when I shut it off it held pressure for 20 min until I released it.
An alternative method of measuring voltage drop is to measure point voltages relative to local ground (a clean quality local body ground is necessary). This avoids stringing a wire to the battery. Voltage drops are calculated by subtracting point voltage at pump power lead from battery source voltage (for positive power lead), and voltage on ground wire lead at the pump w/ a backprobe relative to local body ground (this will directly measure voltage drop in pump ground wire).
+Texas Pipeliner Always best to connect to BAT to ensure - circuit is complete.
thanks for your efforts...
Hi Matt,
Another good video diagnosis, but I wasn't sure about the voltage drop explanation until I thought about it in terms of a garden hose, that is, if a garden hose is restricted or kinked then the flow of water through it will be affected. After i thought about it like that, then i was able to picture the reasoning behind a voltage drop test. If the voltage is being restricted then the load will also be restricted or minimized. would that be a fair comparison?
Fair comparison. :) If I wire is bad it'll have more resistance or less flow. Look up Ohm's law. Ohm's law named it after himself and at work I even ran into one of his relatives who was aware she was related.
Another easier test would be to put a known load such as a light bulb appropriate resistance to provide 10 amps or so back probed into the connector to replace the fuel pump as a load thereby verifying the integrity of your wire feed to the pump from the front of the car. This will prove the actual power and ground wires are able to supply amperage as well as supply voltage.
Schrodinger i didn't understand this drop test that you say about the voltage drop in positive side i understand that drop test of the circuits in positive side should be around .2 i'm not sure but can you explain me why to much voltage drop great video by the way
Rafael, I am not sure I understand your question but let me try anyway. The voltage drop test is a test for resistance in the wire- in other words if the wiring is very old and not in good condition it will have a high resistance. This resistance will cause a drop in voltage because it cannot carry electricity very well. If I had found a high voltage drop in any of the wiring outside the fuel tank, then it is possible the fuel pump is fine- it just does not get enough electricity to pump fast enough to build fuel pressure. But since I found all the wiring outside of the tank is good because there was a low voltage drop, this means the problem MUST be inside the fuel tank. At the end of the video, I show that actually, the wiring inside the fuel tank was bad because it had a high voltage drop. The fuel pump was probably fine, but since I had to remove the tank- it makes sense to replace the pump rather than repair the bad wiring. I hope this answers your question.
Great video you are suppose to test the fuel pump amp draw just in case it was a block filter.
Use jumper cables as the ground return wire for the voltage drop test. Daisy chain them if one is too short.
Jumper cables are perfect for this, because the heavy gauge wire has very low resistance and will result in a negligible voltage drop through the cable, itself.
confused: the pump conductors would have conductor length requardless. Not accounting for?
Great video!
100% correct
In doing Volt Drop on AC circuits, would you follow the same procedure as DC, by checking NEG to NEG, HOT to HOT, and etc?
GOOD JOB
Great video, but you incorrectly determined the voltage drop of the long wire to the battery for the voltage drop test.
The meter you are using as a voltage meter has a high impedance, about one megohm or so, compared to the resistance of 20 feet of copper wire, the voltage drop across the wire will be neglible.
So, you can ignore the 20 foot wire voltage drop.
Thanks,
-Arlen
@arlen raasch Hmmm you bring up a good point, I agree with you- that makes sense and in retrospect seeing the minimal voltage drop on the negative confirms your statement. Now I wish I had done the voltage drop test at the very end of the video with and without that same extension wire see if there would have been a difference at all much less my calculated difference. Great input! Well, even if the calculation was not necessary, it did set a higher stringency for the voltage drop test to pass and thus even further confirmed the wiring ouside of the tank was indeed fine. Great comment and thank you.
John Dodge A DVOM (Digital Volt Ohm Meter) when used in a mode to measure a voltage (AC or DC) has an input impedance. You are correct that most commonly used DVOMs have a high input impedance, so much so that for most people they can ignore that just applying the meter to a circuit modifies the voltage slightly. However in high output impedance circuits, it still can matter. The DVOM's high input impedance can lead to some confusion when doing some common tests as well. For instance if a starter motor is not working, disconnecting the battery lead from the starter and measuring from this lead to ground with a DVOM may well show +12V, but when actually connected to the starter the same lead reads close to 0V. Why? There may be a poor battery terminal connection or a high resistance in the positive lead to the starter. Hope this helps.
I'd have mimicked what the pump sees. For battery ground, I'd have just used the nearest metal frame point.
Where do you find the specs for the parts in a car that you are diagnosing?
ie, what's the right fuel pressure at various parts, the right cylinder pressure, the expected voltage drop, etc?
Tristan Wibberley Google
So when you’re doing a voltage drop you connect to your negative terminal of the battery and on the other DVOM lead you back probe it to the negative wire from the connector and viceversa?
only if measuring voltage drop on a ground, yes
@@SchrodingersBox and on a positive? Or would that be signal return?
Positive is same. You always measure voltage drop on a single polarity. Unless you are using kerchoffs law then you can subtract from source voltage. I find the latter to be way easier. I like simple.
Back then it was carbuerators and basic tbi.
Can you perform Voltage Drop on AC circuits?
+jake ounce Most definitely
What if pump runs ? last you put 12 to it , but what if it ran ?
+Headshothorror4488 I don't understand, how could it run? If it ran I made a mistake earlier.
wow, that pump just sounds bad