Ignition Control Modual

[Mitsumark]

Fellas-I'm troubleshooting a weak spark issue on my 91 Z..Car started running terrible a few weeks ago..Turns out while checking spark output,every single cylinder starts out with a fat Blue spark when cold.Also runs great when cold..Once warmed up,every cylinder outputs a weak orange spark and the car misses,backfires,and the smell of raw fuel comes from the exhaust..The car has 75k on it and all the coils were replaced in 2010 with GM units..They also only have about 3k on them..My thinking is that it is highly unlikely that every coil is failing at the same time..Does this sound like a bad ICM?..The car is highly modified and running an updated Heibeck chip but all sensors are in place.It also ran fine before this started..

[GOLDCYLON]

The DIS module under the plenum is a possibility as is the ECM. Are you sure you dont have any bent Pins in the harness and plug that mates the DIS under the plenum before you screw it in? What year ZR-1 do you have?

[Mitsumark]

The car is a 91..I did replace the PCV valves,related hoses,and a new MAP sensor...The problems started shortly after.. Is it possible I disturbed one of the DIS harnesses?..Am I able to try to screw in the harness tighter without pulling the plenum? I did check that all 4 plugs on the main PCM are seated properly.I also removed the cover underneath the check the pins on the Heibeck memcal.. They looked fine.. No other harnesses were ever removed by me and the problem just started out of nowhere..

[GOLDCYLON]

The car is a 91..I did replace the PCV valves,related hoses,and a new MAP sensor...The problems started shortly after.. Is it possible I disturbed one of the DIS harnesses?..Am I able to try to screw in the harness tighter without pulling the plenum? I did check that all 4 plugs on the main PCM are seated properly.I also removed the cover underneath the check the pins on the Heibeck memcal.. They looked fine.. No other harnesses were ever removed by me and the problem just started out of nowhere..


Did your problem start after a plenum pull ?

if thats the case then the answer to your question is No you will have to pull the plenum. I would check to see if you bent a couple of pins while reinstalling it last time

if you are stating all these issues occur a long while AFTER you pulled the plemum then indeed you may have a DIS issue and they are not being reproduced.

Are you getting any codes? Is the SES light coming on.

[Mitsumark]

No..I haven't pulled the plenum..The plenum hasn't been removed since early 2012..I did however replace parts as stated above in the area behind the plenum.I did so trying to fix my running issues..However it didnt help and thats when I noticed the weak spark.NO CHECK ENGiNE LIGHT no matter how bad it runs..You said the ICM are not being produced anymore..Can I troubleshoot my current one? Also,how can I find out if my problem is the PCM or the ICM?..As you know,it's not like owning an LT1 where I can go to a local yard and pick em up and swap them out easily.Sorry for the questions.. I ordered a FSM but it won't be here until next week..

[GOLDCYLON]

No..I haven't pulled the plenum..The plenum hasn't been removed since early 2012..I did however replace parts as stated above in the area behind the plenum.I did so trying to fix my running issues..However it didnt help and thats when I noticed the weak spark.NO CHECK ENGiNE LIGHT no matter how bad it runs..You said the ICM are not being produced anymore..Can I troubleshoot my current one? Also,how can I find out if my problem is the PCM or the ICM?..As you know,it's not like owning an LT1 where I can go to a local yard and pick em up and swap them out easily.Sorry for the questions.. I ordered a FSM but it won't be here until next week..


Well you will need to start by using the FSM and a scanner to determine if codes are being thrown without being set. Also the FSM lists the troubleshooting procedures to troubleshoot the ignition system in the electrical suppliment. Turn your key to run without starting it and verify that the SES light is indeed still there and does light in the DIC before starting the car.

So we can rule out a bent pin since these symptoms did not happen after a recent plenum pull. I doubt you harmed a harness while working behind the plenum on the the MAP sensor unless the wiring is exceedingly roached out.

On a 91 three things come into play. The ECM, the DIS and lastly the Quad drivers and of course the wiring. Your right these are not LT1 parts for you to find in a bone yard you in somecases have to swap parts after going through all the diganostics in the FSM which also can be frustrating when the FSM simply states "replace module". There are no more DIS modules in the system and they only rarely come avaialble if somebody is parting a vehicle and then parting the engine.

The ECM can be rebuilt but there is no known replacement for the DIS (Distributer Ignition System) Module under the plenum.

[Mitsumark]

SES light does come on with key in the acc position.. Excuse my ignorance,but what are quad drivers?.If they are related to the injectors,the injectors were replaced last year with FIC stainless units..I just found MSD coils in stock at Advanced Auto..I don't think that's my problem but I'm gonna start there.

[GOLDCYLON]

SES light does come on with key in the acc position.. Excuse my ignorance,but what are quad drivers?.If they are related to the injectors,the injectors were replaced last year with FIC stainless units..I just found MSD coils in stock at Advanced Auto..I don't think that's my problem but I'm gonna start there.


OK so the SES light works and is functional. Quad drivers feed the DIS telling the secondaries to fire. If you replaced the coils a few years ago with GM units your problem is prob not the coils