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'92 Grand Prix Fuel injection Problem


joeneedshelp's Avatar
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04-03-04, 07:54 PM   #1  
'92 Grand Prix Fuel injection Problem

'92 Pontiac GrandPrix. 3.1 mutli-port fuel injection, auto transmission. Won't start. Can start by squirting starting fluid into intake, but won't stay running unless I keep squirting. Checked fuel pressure at fuel bar shrader valve and it is good (about 45 lbs.) I have been told that it is probably an electronic device that tells the fuel injectors to fire. Don't know where this device is in order to test or replace it. Diagnostic check shows no errors. I am sure it has ignition - starts with starting fluid. I am sure it has fuel pressure - tested at 45 lbs and can hear fuel pump.

Any idea where the injector timing control device is or what it looks like? Other ideas?

Thanks in advance for any help.

 
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04-03-04, 08:27 PM   #2  
Correct me if I am wrong but doesnt the crank sensor also control injector pulse on those engines?

 
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04-03-04, 09:10 PM   #3  
Yep. The cranksensor can be checked with a digital storage oscilloscope (DSO) tapped into the appropriate signal wire.

Best to let a professional do this unless you have some experience in this area.

You could also just change the sensor, but "shotgunning" parts can get expensive and frustrating.

HTH

Matt

 
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04-04-04, 01:11 AM   #4  
mike from nj
i'm pretty sure if it had a bad crank sensor, it would never run on the spray. you would have no spark also.


simple thing to check, is for 12 volts at any injector connector(which is fed by a fuse). next is for the pulsing ground which is supplied by the computer, that is your "injector timing control device"


let us know what you find

 
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04-04-04, 10:15 AM   #5  
Sounds easy enough to try. Unfortunately, it is my college daughter's car which is 70 miles away, so will take a few days. I really appreciate the advice.

Now, if I find no voltage at any of the injectors or find no intermittent ground, where do I go from there? I have always been willing to risk swapping out some good parts, when they are not horribly expensive (~$200 or less) when I am reasonably confident the part is the problem. Sometimes I waste money - most times I save by doing it myself.

When you say "intermittent ground" I assume that means ground when that particular injector is supposed to fire? So, with a 12volt test light or ohm meter I would see it go to ground as I crank the engine?

All fuses seem to look good.

If there is no intermittent ground, is my only choice to replace the computer?

Thanks to everyone for their advice.

Joe

 
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04-06-04, 02:55 AM   #6  
mike from nj
i'm not real knowledgable on GM's, but on the few i've worked on, the injectors are supplied by a fuse labeled "fuel inj" , that should be direct feed to the injectors. if it's blown, there is obviously a short somewhere and it needs to be fixed.

i use a test light clipped on the battery positive terminal, with the probe stuck (carefully) into the injector connector, and yes, the light should light everytime the injector would fire. that's when the pcm would supply the ground to actuate it. if there was no grounding, then i would suspect the pcm, but i would first confirm that the pcm is receiving a crank reference signal. that is it's only way of knowing that the engine is basically rotating. how you would do that without a scan tool is a good question. if it has a dashboard tachometer, and if it works might be one way. you might also be able to hook a voltmeter up to the pcm connector and read the pulses from the crank sensor, but i don't know exactly how to do that, or which wires they would be. the ignition coil module receives it's own crank reference signal(to make spark), and that doesn't necessarily mean it's reaching the pcm.


if you shop around, good stores (like maybe a napa) should have a remanufactured pcm for not much more than $120-130. (it was the last i checked though).



hopefully someone else will chime in.

 
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04-06-04, 04:29 AM   #7  
Sticking a regular test light into the PCM side of that connector can be a little risky to the Quad drivers unless it is a computer safe (diode type) light. It's much safer to just buy a noid light to plug into it. They should be under $10. That will answer both questions as it is cranked. If it doesn't flash you can check for power with a regular test light but I wouldn't use it on the ground side. You won't need to if you know you have power and no flash. The crank sensor supplies the reference signal for both the spark and the PCM so since you have spark, power loss at the injector is very possible. The fuse could be labeled "fuel inj" or "ECM". Check to be sure the "check engine" light is lighting when key is turned on.

 
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04-08-04, 04:25 PM   #8  
Fuel Injection problem

Ok, now I am really baffled. I had the car hauled home. I ordered a NOID light. In the meantime I find I have constant 12 volts (12 volt test light lit) on both terminals of the wiring connector removed from one of the injectors. This is with the key on. I thought one should be constant 12 volts and the other side an intermittent (as the engine cranks) ground. Am I missing something here?

 
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04-08-04, 04:53 PM   #9  
You are correct. One side should be open circuit and the other B+ with the plug off. You need to find the source of that power. Start by unplugging things until the light goes out. Start with the other injectors, the the power source for the injectors, then the PCM main plug and find out which direction it's coming from. It could be another injecter if they fire in gangs, but that engine being sequential might not, although I don't think it goes sequential until it sees a cam signal. I could be wrong about that.

 
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04-08-04, 06:07 PM   #10  
most early model 3.1 liter engines the injectors was wired together even all 6 on some years, I doubt you will want to remove the upper intake to find out that if you do disconnect all injectors you would only have power at one terminal but you still need to check for injector pulse.

 
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04-09-04, 03:47 AM   #11  
Originally posted by bejay
most early model 3.1 liter engines the injectors was wired together even all 6 on some years, I doubt you will want to remove the upper intake to find out that if you do disconnect all injectors you would only have power at one terminal but you still need to check for injector pulse.
He can't check for pulse until he finds the source of the power on the trigger side. I believe they fire on all 6 only until seeing a cam signal and then go sequential. It's going to damage the PCM if it hasn't already.

 
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04-09-04, 09:48 AM   #12  
actually its not sequential and doesn't even have a cam sensor until later years, and probably just has 1 or 2 injector drivers firing all 6 injectors or 3 at a time simutanously the power he is seeing on the trigger side is after it has went through the other injectors the ones that are still connected as you only have access to 2 injectors without removing the upper intake, when an injector is still connected it will show power on both terminals and is not a problem he should be looking for.
if it was a newer model car say a 95 and had sequential injection timing and the computer had 6 individual drivers one for each injector then i would agree it shouldnt have power on both terminals with just one injector disconnected.

 
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04-09-04, 10:46 AM   #13  
bejay's response

So, Bejay (or others that would like to respond), if I understand your response, it is perfectly normal for me to see power on both sides of a disconnected injector plug, right? I have the intake partially removed, that is, I can raise it high enough to reach some of the covered injectors and have no problem completely removing the intake, if need be. The particular injector I tested is the one on the back corner of the passenger siden of the car, if that helps. I do not understand why both terminals are hot, but I guess you are telling me that is normal. I have a noid light ordered and will arrive tomorrow. Not sure where to go from here. If I test and find juice at all injectors, I am eliminating the "positive" side of the equation, right? That is, the problem lies in whatever causes the intermittent ground to cause the injectors to fire? Does this leave to ECM? Are the ECM and PCM the same thing?

Thanks again for everyone's help. The daughter is home for Easter weekend and I hope to send her back to college with her own car instead of mine!

 
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04-09-04, 12:05 PM   #14  
since you have the intake partially removed anyway and can access the injectors if you disconnect all 6 you will find that you will only have one power source at one terminal the injectors dont have much resistance usually around 13 ohms and you should probably ohm every one of them while you have access to them compare the readings with alll 6 and replace any injector with obviously lower resistance readings as this can cause failure of the ecm drivers.
you probably dont have injector pulse as im sure you will find out when you get a noid light but it may be difficult to find out why without a scan tool, manual that cover engine performance and emmisions that will have a no start flow chart for your vehicle to help guide you to the faulty component, you may want to visit your library or subscribe to all data for the flow charts you will need but even then the flow chart may ask you to use a scan tool which is an expensive piece of equipment that is not feasible to buy for fixing one car and you may consider taking it to a shop for diagnossis.
you will need to check all your fuses both underhood and inside the vehicle easily done with a test light because if you have no power to the ecm you will not have inj pulse, possible bad components would be ecm, ignition module or even tps sensor, you could eliminate the tps by just unplugging it and re checking for injector pulse. but determining which of the other 2 components may be bad could be difficult without all the proper testing equipment.

 
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04-12-04, 02:54 PM   #15  
Success!

Got it running! One lousy injector caused the whole problem. Seems that when the ECM senses virtually no resistance on one injector it stops sending a signal to all. NOID lights and testing the resistance of each injector isolated the problem.

Thanks to all who posted. It kept me in the hunt. This is a great forum!

Joe

 
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04-12-04, 03:02 PM   #16  
Good job man!
Now, just for my benefit, do you read power on both sides of the injector plug with the key on? I'm guessing you won't.

 
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04-12-04, 06:05 PM   #17  
I am assuming you are talking about after I replaced the injector. Sorry to say, I did not bother to check.

Thanks again.

 
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