I have been following this thread from the beginning since I to had an ignition module fail. I was fortunate that a replacement fixed mine right out of the box.

The part of this thread that I personaly keep getting stuck on is the fact that the old module will fire up the car and the replacement won't. I feel that this area and the reasons why this happens should be explored.

Is there a way to verify that the connection to the new module is sound, maybe with the use of jumper wires to rule out a bad pigtail harness.

I have another thought which might be out in left field, with the new module in place try to check for spark at plugs. I was offered a great tip on the forum of using a timing light with an inductive pickup to verify spark.

Or the use of that scope which is totally over my head. I think once that this area is ruled out, then the exploration of the rest of distubutor should be looked at. I don't think its an ECM issue since the car fires up with the old module.

I hope that this issues gets resolved quickly and I totally understand your frustriation about the car!!! I would just hang in their a little longer these folks here on the forum are the best in solving problems

 

Nope they don't have it and I was talking with their most senior person there (16 yrs exp). Every stinking connector except ICM connector. This is unbelievable no where can this thing be found: Ecklers, GM, MAD, I even got the PDF catalog for Car-Pak in Troy, MI and they list every connector on this vehicle but the ICM connector.

What gives????

 

Here's the theory:

The capacitor in the tach filter is breaking down when a certain voltaqe is applied to it.
The old module doesn't have enough current capability to drive the primary of the coil to cause the voltage to meet the breakdown voltage of that tach filter capacitor, but the new module does.
This is an extremely easy check -- disconnect the tach filter.

Since the old system works intermittently, it is hard to pin down the problem -- just like the scope signals, it is working most of the time. But, with the new module, it doesn't work at all -- so, this is the best place to trouble shoot the problem. The new module is consistent -- it doesn't work. This is where I would be spending my time, finding out why the new module doesn't function.



On the subject of different modules by year, I can tell you this:
On my '92, I've had the original '92 coil and module, a '96 coil and '96 module, and now a Delteq setup. And, my ECM signal was able to drive them all without any problems.
But, I never mixed the combinations. I still find it hard to believe the '96 and '92 modules are the same.


Tom Piper

 

OMG I found one at Bill Heard, so I'm off to get one. They don't have the tach filter but I can drive over to Ecklers and get one of those.

So off I go.....

 

Tom you are such a wealth of knowledge its just unbelievable. Too bad I am not closer to Tallahassee.

I'll be gone a couple hours as it takes about an hr to get to Titusville. And I have to get there before 1pm Ecklers is only open a few hrs on the weekend. I'll be back....

 

If you are looking for connectors around the ignition system on an LT1/LT4, try Pete at Delteq (http://www.delteq.com/), if anyone can get them, he can. He has worked with manufacturers (not GM or other supply houses) of those connectors more than anyone. I recently bought the ignition module connector from him. Knowing they are hard to find, I even bought a spare.
But, since you are not a Delteq customer, I can't promise you results.

Tom Piper

 

Just out of curiosity what is your battery voltage?Is it possible it is low?Tom's thoughts are what I am thinking too. Older elctronic devices can operate differently.A transistor will develop different peak voltages with age although usually they will lower over time.It is possible for a trigger voltage to change amplitude and become weak.

I mentioned cleaning your plug contacts with cleaner.A dirty or corroded contact acts like a resistor and can cause a voltage drop or no voltage at all.Not only that a slightly bad contact will generate heat further increasing the degredation.When you had the modules at NAPA do you know what kind of test they did to determine they were good?Did they inject an input signal and measure the output?I was thinking for some reason your input is not generating enough to trigger your output.It would have been nice to have side by side scope shots of both modules to look at the input amplitude.

Another point might be the actual connection on the ECM plug itself. You will not be able to go inside the ECM to measure continuity between the ECM and the connector.Although this is a long shot at best because the ECM conector is no where near where it can get polluted with anything that can cause corrosion.

Don't know if anything I am saying here will help other than to understand some of the variables that might apply
Good Luck

 

Well that was a long trip to the coast and back. But I got the GM pigtail connector from BH, then over to Ecklers for a Tach filter. Napa for some miscellanous stuff. Now to start and finish this.

I think I will install the new harness, the new tach filter, the new coil and coil module and see what happens. I want to wait on the ECM for a couple of reason. If I don't need it immediately to solve this problem I want to talk to Chris about it, its a reman and the case looks horrible plus I noticed something doesn't sound secure inside, something rattles if you shake it slightly. An ECM is going to shake with the vehicle and that doesn't seem right like it is.

Oh BTW, anyone reading this and needing to replace their ECM, Eckler's has them for 99.00 plus core charge/refundable.

Keep your fingers crossed LOL.

 

fingers crossed.

Reading this thread has been a real eye opener.

I agree, the pigtail is a real possibilty... when a harness gives up, it gets really wierd.

Good luck!!!!

 

Question, the new tach filter: first how come I can't find anything in the service manuals about it? And it has a pink/black and white wire that comes out of the gray connector half of that which plugs into the coil. It appears to me that the pink/black and white would go directly to the ignition coil module connector to splice into those two pink/black and white. That would not be an issue except the new one has those two wires except the half to be close to 6' long (longer than my arms width and that's about 5.5) on the pink/black end it has a male pin connector and the white wire at the end has a spade connector plus another white wire that comes out of that spade about a foot long with a male pin connector.

The gray connector to the coil module is only like 8 inches.

I can take picture?

 

Pictures removed, this was confusing things.

 

According to this site: http://www.partsamerica.com/Default.aspx
here are the Delco part numbers for these ignition control modules:

'92 = Delco D1971A
'94 = Delco D1986A
'96 LT1/LT4 = Delco D579

Tom Piper

 

This link is for an F=body LT1 wiring but it might work I will keep looking
http://shbox.com/1/95_ign_system_schematic.jpg

 

Thanks I have that in my Helms Service Manual. Is the tach filter called something else?

 

Ah I found a schematics for it, page 8A-20-4 Multiport Fuel Injection: V8 Vin P Distributor Ignition System and Malfunction Indicator Lamp.

Correction the connectors are labeled next to the module. Sorry to much in a hurry I guess. Spent a little more time studying the schematic helps.

LOL people reading this must be having a chuckle. Ah the life and times... well back to work.

 

Well the way things are going did you really expect it to be?

Did you find the little black part on your car? That is the filter it has 3 wires one white goes to coil the other goes into the firewall. When you figure out which goes where you can cut the 3 wires on the filter mark one coil(spliced to pink) the other dash(long white one) and splice just the filter in.I hope you are using Sta-Con connectors to do this.

All this filter does using a capacitor(and resistor) to filter out the coil static and sends the excess to ground. If it shorts to ground that is when the troubles start.Sorta like the capacitor we used to install on a staticy radio in the old days.

 

Gee...

According to the book, "Corvette Fuel Injection and Electronic Engine Controls," by Charles Probst, the Tach Filter has 1 wire in, 2 out.

Now... looking at that pigtail, it appears as though they want you to disassemble the connector and replace with their wires. If you don't have a weatherpack tool, you can make a quick extractor from some small tubing available at your local hobby shop.

Check out the scanned page from the book.



A copy of this book is available from Robert Bentley Publishers. It's about $35.00.

 

Just like I got done typing one white goes to the IP the other to coil the black to ground.I really believe it does not matter which white wire goes where but to be safe trace the on from the coil and keep them the same.A Filter just taps into a line to draw off signals to ground at whatever Freq it is designed to do.

If you try to route the wires you are going to have your hands full if it was me I would splice it.

 

unless it's an electrolytic capacitor, but then, I would expect arrows pointing the correct direction.

 

Does not matter the Cap will not be in series it will just tap to ground.But as I said for consistancy keep the wires the same.