Misfire Mystery

Charles2021

Newbie
Joined
Feb 26, 2021
Messages
4
Points
1
Make
Chevrolet
Model
Monte Carlo ls
Year
1995
Miles
170,000
Engine
3.1 V6
Got up a couple of months ago to go to work and when my car started it had a miss in the engine. I thought that it might be a spark plug or plug wire. I changed them out with new ones and still had the same problem. I then started looking at the fuel injectors, changed them out as well as the upper intake. Same result. I then replaced both crank sensors ,cam sensor and knock sensor. Still the same problem. I then replaced the harmonic balancer, alternator and battery. I took it to two garages that had good reviews and the first on said that the was no pulse on the #3 fuel injector. I told the mechanic that they had been replaced and he said the pcm was bad. I replaced that with a new one. Same problem. The second mechanic basically got me for 118.00 just to tell me what I already had found out on my own. Now I am extremely frustrated. I broke down and bought me a good scan tool but it is not able to tell me anything because I check engine light is not on so its not throwing any codes. It does show that Quad Driver 1 is bad, until you start the car then it reads good. 2 and three are good and the Quad 4 Driver is bad whether the car is running or not. can some body tell what is on the Quad 4 Driver circuit? The car is running horrible. I it possible that it is running in limp mode? I have a 1995 Monte Carlo ls with the 3.1 v6.
 

billr

wrench
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Mar 12, 2007
Messages
7,109
Points
63
It is "running horribly" and there are no codes, not even in history??? What are the compression readings; compression testing was done some time during all this parts-swapping (hopefully before any parts-swapping!), correct? How about fuel pressure, has that been checked?

I don't know what Quad 4 drives on that particular engine, but it won't be an injector. Injector drivers are much more robust than the quad driver ICs.

Between the PCM and injectors is wiring/connectors that must all be OK, has any of that wiring been checked out?

Have you checked now for an injector #3 drive pulse at the connector on the (new) PCM?
 

nickb2

Wrench. Diagnostic Tech.
Joined
Nov 22, 2008
Messages
11,954
Points
63
Location
St-Hyacinthe, Quebec, Canada
As usual, just seconding at this point, but the ignition module on these jobs used to cook quick when heat sink got corroded and such.

The IG module is found underneath the coil packs.

Think of this a modern day CPU cooling in a fast home pc like mine.

Proper heat dissipation is essential in these old 2 wire jobs

Anykind of dielectric goo will suffice.

So buy a new ig module, obviously, only AFTER you have heeded bill r advice. Comp, fuel, air.

Very common issue back then. Dime a dozen if you will.

Goo goes on much like when mating a cooler to a cpu.

 

Mobile Dan

wrench
Joined
Mar 1, 2002
Messages
3,763
Points
48
Location
Kentucky

 

Charles2021

Newbie
Joined
Feb 26, 2021
Messages
4
Points
1
It is "running horribly" and there are no codes, not even in history??? What are the compression readings; compression testing was done some time during all this parts-swapping (hopefully before any parts-swapping!), correct? How about fuel pressure, has that been checked?

I don't know what Quad 4 drives on that particular engine, but it won't be an injector. Injector drivers are much more robust than the quad driver ICs.

Between the PCM and injectors is wiring/connectors that must all be OK, has any of that wiring been checked out?

Have you checked now for an injector #3 drive pulse at the connector on the (new) PCM?
 

Charles2021

Newbie
Joined
Feb 26, 2021
Messages
4
Points
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Thanks for getting back to me. I have also done a compression check and it was fine. The fuel pump and fuel filter have also been replaced. There is no pulse to the #3 injector.The ICM I had checked at AutoZone. They tested it four times. It passed every time. I also took a spare injector harness and tied it in to the existing harness so I could check the voltage without having to keep taking off the upper intake. Does anyone know what the voltage should be going to the injectors when the car is running? I also checked the primary and secondary resistance on each coil pack. They read in the range stated in the book.
 

billr

wrench
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Where are you checking voltage/current for the #3 injector pulse? If you are doing that at the injector, then there is more checking you need to do. You have to go to the connector on the PCM.

How are you checking? You must have the injector (or some other load) connected to the harness. One wire should always have battery voltage (~12VDC) relative to ground when the engine is running. The other wire should pulse between 12VDC and near-zero VDC (again, relative to ground). It is probably easiest to see that pulsing using an AC voltage scale, and use a "range lock" on the meter so the reading isn't flitting around as much. The AC reading will probably be fairly low, like <1VAC at idle.
 

Mobile Dan

wrench
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Mar 1, 2002
Messages
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Location
Kentucky
1614650512243.pngI use this tool to test injector wires. With engine running (or cranking), one of the two injector wires should show steady light when tool clip is on battery negative post. The other wire (with engine running or cranking) should show a flashing or pulsing light when the tool clip is on the battery positive post. If the tool is connected to BOTH injector wires (simulating an injector) you should get a flashing or pulsing light. Google "noid light".
 

grcauto

Hero Member
Joined
May 29, 2014
Messages
784
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I doubt your scan tool is setup for your transitional model. It should code? I have diagrams and service lit if you need it. Most quad 4 faults are tranny related.
 
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