So I seem to have aquired an ignition module problem. Intermittant no start (power comes on but no click from starter) let it cool for a 1/2 hour - starts fine. seems to get more frequent over trime. first time it wouldn't start after hot laps on the track - replaced module (according to NAPA the old one tested bad) - fired right up. Next time - overheated the car - (stuck thermostat - during HDPE) no start - replaced module - started right up.

Now with radiator replaced it runs under 200 no matter what I do - and typically stays about 170 degrees - but now I'm having intermittant no start. Should I replace the module again? It seems to cure the problem - but why does it keep going bad?

Carl Johansson

 

The same happened on my CFI Ford. Would die and not start when hot, clearly no spark. Followed the factory diagnosis to the ign module. New ign modules fixed this everytime, but would eventually start acting up again. After the third module, I replaced the ignition coil and it has worked ever since. The coil was opening when hot, but it tested out fine when cold.

I'm guessing a brand spanking new module helps mask the effects of a failing coil somehow.

 

If you have a no cranking problem then it starts after 15 min. i would check into the VATS system first.

 

Thats what it diagnoses out to - but I pulled the fuse behind the center console to get rid of the VATs crap - unfortunately - I lost my horn - fortunately - I still have a middle finger!

Carl still wondering" Johansson

 

I might be the starter solenoid... Next time it won't start, give it a few smacks with a long stick or screwdriver...

I had a bad starter on my old Camaro that had the same problem...

 

You said you replaced the control module, have you swapped out the coil at the same time?

You didn't say what year and I didn't see anything in your profile.

You can also look at the tach filter as well.

Next item on the list is your ECM. I just had to replace all these items and yes it was a heat soak issue. Cold it was fine except rough idle, but as soon as it got to temp it would studder and die. Wouldn't start until it cooled down 30-40 degress. During the replacement of the ECM, while moving the PROM over to the new unit, I detected the familiar scent of burned silicone. One good whiff from the old unit and it was obvious where the problem was. Swapped the ECM and things are good again.

Oh forgot to ask, you are applying the heat grease on the metal back that accompanies the module correct?

 

Critical must be used and the right stuff too.It should have come with it.

 

I agree about the ignition module grease. Ignition modules frequently fail for three reasons: heat, vibration or voltage overload.

Excessive heat can damage sensitive electronic chips. GM ignition modules and Ford TFI modules, in particular, rely on a layer of thermal grease under the module to help carry heat away from the electronics.

If you or someone else replaced the module and forgot to apply the grease, the module may have failed due to overheating.

The leads that connect the module to the wiring are also vulnerable to breakage, often as a result of vibration.

Finally, a module can be destroyed if the high secondary voltage in the distributor somehow finds a path to the module.

In some applications, modules can be checked by using a high impedance (10 megohms) digital ohmmeter to measure resistance between various terminals.

If any of the measurements are out of spec, the module is defective and needs to be replaced. But on most applications, a process of elimination is used to isolate a bad module. Or, a "known good module" is substituted for the old one to see if it cures the problem.

If the engine starts, the old module must have been bad. If it still doesn't start, then it's something else. The problem with this technique is that the new module may be damaged if there's a short in the wiring that caused the old module to fail.

Be sure you apply the grease that comes with the module to the back of it because it is designed to dissipate the heat generated by the module.

If the grease did not come with the module, then Heat Sink or Thermal Transfer Grease may be purchased in small tubes (about a quarter ounce) at Radio Shack outlets nationwide for approximately $2.

If you need a larger quantity it can be found at professional electronic stock houses, look in the Yellow Pages under Electronic Parts and Components.

As others have advised, DO NOT USE silicone grease on your ignition module.

 

These kinds of problems can drive you nuts too. I had a situation where replacing the coil and ignition coil module, the engine would not start, put the old module in and it would fire instantly. Come to find out the Tach filter was causing the new module not to work. Once I spliced in a new Tach filter, it fired instantly with the new module and coil.

 

Thanks for the replies guys
86coupe with a ZZ4 and a tremek tko500 - sorry about that!

- I do use the grease as supplied. I don't think it's a starter solenoid issue - because it Fixes itself - but maybe - the heat messes it up - but why only sometimes?

I did not swap out the coil - maybe that ought to be my first step.

It's frustrating because the car starts 95% of the time - so if I change out something - and it fires up - did I solve the problem?

Where would I find this Tach filter?

Thanks for the ideas - right now I gotta get my old Ford 8n running - then it's back to the Vette!

Carl Johansson

 

I don't know if it is on an 86' but it's a black module that comes off the wires going to the coil connector. It's about 1 inch long. Here's a picture:



Oh, the two wires with the crimps already on is not normal. Those wires are like 6' long and go all the way back to the tach and the ETBCM. Yours may be different. I just spliced them, I wasn't going to tear all the harnesses up and route them back through the system. The grey connector is half of the connector for the coil.

 

Nevermind, my coil problem would make the car die while running, yours is only a no start.

Is the car turning over when you try to restart it? If not, its definitely the solenoid. I've seen some that work on a bench and not on a car. The solenoid is just a energized coil that drives a plunger. The starter motor is also wired in series with the solenoid, so if the windings in the starter open, or the solenoid coil opens, neither will get power.

 

Try to find 93jetjockeys post it was a real mind twister.If I remeber right he had some weird tach readings too that sort of pointed to it.Does your tach do anything strange?

 

Well - it (the tach) routinely Revs through 5400 - and sometimes gets to 5700 - is that what you mean by strange?

Carl "gotta start shifting earlier" Johansson

 

Nope thats normal.His was spiking and jumping at times.The engine wasn't.