Hello, I'm new here but a regular on NastyZ. I have been searching and researching all day but can not come up with a solution.

I have a 1991 5.7 Z28 that I bought brand new back in 1990. It only has about 130,00 miles on it and has been running fine. The other day I was out for a pleasure drive and the car died about a mile from home. The starter turns over and I am getting fuel out of the Schrader valve on the fuel rail. I did some troubleshooting and have decided it must be ignition related as there is no spark to the plugs, or coming out of the coil. I have now swapped out the ignition coil, the ICM and the pickup coil to no avail. I checked fuses, swapped relays. I have verified that I am getting power to the red wire at the ignition coil, but from there my diagnostic skills have failed me. I verified that there are 12.6v when checking the "distributor "button" inside of the cap.

Can anyone help explain the workings of how the ICM and the pickup coil interface with the ignition coil ?

I do have an aftermarket chip in it which bypasses the VATS, but I believe when VATS is tripped, it won't even turn over the starter so I don't think VATS is the issue.

Are there other fuses, relays or circuits that I should be checking ?


Any help would be greatly appreciated.



Thanks in Advance !

Joe

 

VATs won't cause the engine to stall. Once it passes and the engine is running it is out of the picture.

Check the 2-wire pigtail that goes between the coil and ICM (PNK and a WHT wire). On the coil end the wire likes to break inside of the insulation. There is no strain relief where the wire exits the connector.

As for the pickup coil, ICM, and ignition coil. The pickup coil sends an A/C signal to the ICM. The rotating star magnet and pickup coil are basically an alternator/generator.

The ICM buffers this A/C signal and sends a reference pulse to the ECM. The ECM uses it to know when to fire the injectors. Then once the engine is running to calculate the proper EST signal for the spark plugs.

During cranking or with the EST/BYPASS connector open, the ICM handles spark timing.

The ICM provides a ground to the ignition coil in order to dwell/charge it. This is the C- terminal on the ICM with the white wire that goes to the coil.

To fire the coil/spark the plug, the ICM releases, or opens, that ground.

RBob.

 

Thanks RBob for taking time to reply. I appreciate it. I checked the ignition coil to ICM pigtail you mentioned using an ohm meter and it is getting continuity from both ends of both wires, I will try again and jiggle the wires as I'm testing to see if it looses anything.

I was reading in another thread about the rotator star magnet, so maybe I will pull everything apart again and take a look at that.

If any other ideas come to mine, please chime in.


Thanks !

Joe

 

Hello, if anyone is reading this, I am still at a loss. Everything seems to check out, but still no start. Can anyone chime in if something like a faulty Oil Pressure Sensor would lock out the ignition system ? I believe there is a oil pressure sender that is tied to the fuel pump,, but I don't know if anything interrupts the spark. Would the Oil Pressure, Temp Sensor, Knock Sensor or Throttle Position Sensor prevent the spark ? Any thoughts on if it could be a potential issue with the ECM ? I had to replace the ECM many many years ago as the car would intermittently stall, but on that issue it would always restart.

Driving myself nuts on this...., any thoughts or leads would be greatly appreciated.


Thanks !

Joe

 

I don't think it would be any of those things. Maybe the ECM but I doubt it. I recommend picking up the factory service manual, it has step by step diagnostics for each component of your ignition system. While unlikely, it is also possible that one of your new parts is faulty. Were they AC Delco / GM Genuine parts?

 

Hi





RBob.

 

Many thanks to you RBob and Komet, and RBob, thanks and I really appreciate the efforts to upload the docs.

I will give these things a try.


Thanks again !

Joe

 

I also have a Z28 with TPI engine from -91. It has been running fine untll today, when I just as you lost the spark on all cylinders. We might have the same problem, how are you getting on?

 

Hey Ricky, I am still in the diagnostic stage, but I did find out I believe the pickup coil in the distributor may be bad. I was going to just replace it, but you have to pull the whole distributor to remove it and I went ahead and bough a new distributor that comes complete with a new pickup, new Ignition Control Module, new cap and new rotor. I figured this would be the way to go rather than piecing together my 20 year old unit. The distributor should be here this week, hopefully I'll get a chance to mess with it this weekend and will post back up next week.

If you make any findings on your car in the meantime, please post up what you did.



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Hope a new distributor solves everything for you. Mine looks to be in a really good shape, so I hope it can be fixed.
I was out looking at the engine today. This is what I found out.
I have +12v to the ignition coil.
When testing with a light on the cables from distributor to coil, I just had a steady light while cranking, no blinking.
Opened the distributor and measure the pickup coil to 800 OHMs
Ignition coil primary side 0,5 OHMs
Ignition coil secondary side 7,65 KOHMs
Could it be a bad ignition module?

 

I've gotten bad ignition control modules from the parts store before, right out of the box. I recommend buying another and throwing it on.

Make sure your ICM and Coil are the same brand. Having them mismatched can cause one or the other to not play nice (been there, done that).

 

Many Thanks to all of you for your input and help, especially RBob. thanks for the diagrams. I checked the pickup coil under the distributor and got 0 ohms. I thought I had replaced that before, but according to the intenet, you have to pull the distributor, remove the drive gear and pull the shaft, of which I know I have never done, so I guess the pickup coil was the original.

Anyway, I researched around a bit and looked at replacement AC Delco distributors which were rebuilt, and I looked at Summit/Jegs and read up on the Mallory, MSD and Pertronix, but after reading some of the review, I opted for the Davis Unified Ignition brand. This came complete with distributor, pickup, ignition control module as well as a cap and rotor for $199 at summit. It was delivered today and I pulled the old one, dropped in the new one and it fired right up.

I'm good to go again.

Thanks again to all of you'all.


Smokin'Joe
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When you pull the shaft from the old distributor, varnish buildup can make it difficult to remove. Use a carb gum cutter such as 2+2 to tackle this issue.

RBob.

 

I just installed a new ignition control module, car started right up.
Thanks for helping out here, I was really lost when the car first died. Think I'm always going to keep a spare module in the car from now on.