I've been chasing an ignition misfire problem with my 96LT4. I've noticed that most Coil and ignition control modules are listed as 91 or 92 to 95 and the 96 is always listed as a diffrent part. Ecklers has ignition modules for 92-93, 94-95 and another for 96. They all look exactally the same! Do any of you elecrtonic whizz guys know what is the difference between them, like amp rating ramp up time or RPM limit? I noticed that the coil on mine looks like the one listed for a 95 instead of looking like the 96 coil I saw on line. Am I burning up modules because it has the wrong coil on it? (P0300 random misfires keeps popping up) Everything is new except for the coil and possibally the wrong module from NAPA.

 

Good question. The only thing unique to the 96 that comes to mind is The Crank Position Sensor. Added for misfire detection in OBD II.

 

it could just be a harness connector difference, but even that would make it NOT interchangeable.

Per my parts cd for LT1's (and the acdelco.com website):

the coil for 93 is AC-Delco D535,
for 94-95 is AC-Delco D573,
but for 96, it is AC-Delco D577.

It's anyone's guess what the differences really are...

 

Yep different plug

 

So a 96 has harness plugs that will only plug into 96 coil?

 

Yesterday I took my original and replacement ignition modules to Advanced Auto to have them tested. The new one didn't run the car but about 2 weeks before I popped a P0300 code again, so I wanted to test them both again. Well, after fumbling around for 5 minutes or so with all kinds of harnesses, the guy finally hooks up the module with some aligator clips to the tester. (there must have been twenty harnesses in the tester drawer that had plugs on them, but mine takes aligator clips?) Old module fails, New module fails too so the guy puts a new one off the shelf on the tester and it fails too!!! How the hell am I ever supposed to figure out what is wrong with this car if I can't even depend on the component test results? Do I just replace the coil anyway even though IT tested OK? Everything else has been replaced already and I'm back to a failure of random misfires again!

 

Take it somewhere that has competent folks.

 

Due to the fact that the LT4 had a higher red-line, GM made the '96 ignition system (both the one for the LT1 and the LT4) a little bit hotter than the previous years.
The '96 coil is supposed to have less primary resistance and inductive reactance to reach coil saturation sooner.

Many after-market coil makers have hotter coils, but many of them will not last as long because they overheat.

The '96 ignition module is designed to accomodate the higher primary current.
You should always use a '96 ignition module with the '96 coil.



Tom Piper

 

Thanks Tom, that makes more sense than anything else I've heard yet. I still have to find somebody that can really test these two items so I can stop chasing ghosts and find the real problem, what ever it may be. The module may very well be the wrong one. I told the guy at NAPA what I needed and he gave me one, but wheather it is a true LT4 or a crossreferenced module, I can't say. I tested the coil myself and it throws a fat blue spark, but that doesn't mean it will work under load and speed on the car. I need a real world tester. I just have to find one around here that doesn't have that deer in the headlights look about them!

 

Klondike do that thing of putting washers behind the ICM when you put it back as that works much better than the silicone fix GM uses.
A tip from shoebox.com.

 

Thats correct.

 

Hadn't heard this before. What's the reasoning here?

 

I guess the washer thing keeps an airgap between the module bracket and the head so it keeps heat from transfering from the hot head into the module. I think I'll try both the gap and the thermal paste when I go back together. I just can't find ANYBODY that can test these stinkin' modules!

 

A couple things. I'm hearing the same airgap thing from other sources. This isn't a simple issue. The module is not a simple low wattage item that gets heated up by the head surface. Most ignition modules do not have large built in heatsinks or fins, and rely on nearby large mass items to draw off the heat. Most GM modules are built to run while fastened to heat sinks up to 250*F. The cylinder head should be well below that level. Without the cylinder heat sink, the module will continue to rise in temperature until one of two things happen. The module will reach an equalibrium temperature where the heat is taken away at the same rate as it is generated, or it will continue to rise in temperature until it fails. I would put some serious thought into any modification (such as increasing the thermal path length via extra washers) unless I was certain there was going to be a 100% chance that there will always be sufficient airflow to pull away (wattage) heat from a flat baseplate (a very hard thing to do) on the bottom of the module. The engineers who measure the engine compartment environment and determine the mounting location for items like these are not idiots.
It's your module (and your money), and the decision is entirely yours.

ps: Testing the module is not that big of a deal, but it just takes a few extra items to test it under load (with an actual high current coil) and also a means to control the temperature of the part so that it can more easily simulate the actual environment that it operates in. (Modules very rarely find themselves running down the road in an environment that is found in an air conditioned parts store.)

 

 

The head isn't going to get any hotter than about 220*, so I dont think that would be enough to toast the electronics in the module. I always use the thermal paste on any power handling electronic device. I don't think the car gets nearly as hot as some power supplys. I think if anything was transfering heat it would be that module to the head, not the other way around.

 

It's easy to test these things...probe the four pins on the connector. One is PWR, one is GND, one is the signal coming from the PCM, and the last is the signal going to the coil. I think that's the white one, but check your FSM to be sure.

Stick a digital multimeter (DMM) on the wire that goes to the coil. Set it to VAC (even though this is a DC system) and crank. You should see an AC voltage, when I do it it appears to be around 1.4V AC. The duty cycle of the DC pulse looks like an AC voltage, probably due to the multmeter's resolution capability.

Don't waste your time going to the auto parts store, this is an easy one. Plus, I recommend getting very familiar with your C4 ignition system, as you'll be fixing it as long as you own your car. Understand how it works, don't just go through someone else's troubleshooting list. You'll thank me

I have two spare coils, two ignition modules, two PCM's, and about 8 optisparks...