HELP - Engine fires and dies - DTC 41
 

I have a 92 LT1 from a Vette that fires up for about 3 seconds then sputters out and dies. If I keep pumping the gas really fast after it fires, I can get it to run. But it backfires and runs like junk.

I'm getting a DTC 41 - ignition control circuit open. I have GM service manual and followed the flow chart. All voltages test good and it the chart says it's a bad ignition module. I've replaced the module twice, same problem.

I know I have spark because it runs on ether. I have good fuel pressure at the rail - 53psi, then 45psi when it starts.

It has a Painless wiring harness and VATS is disables on the PROM.

I appreciate any help or suggestions.

Denny

IF and this is a big IF, 92 Vetts used the same DTC's then, your getting the typical response by the PCM when it throws a "41" !!!!!!

It disables the injectors !!!!! Surprised you didn't find it in the manual.

Your goal is going to be to find which PCM connector and pin has the wire that goes to the ICM and ohm it out. I also suggest you put another "jumper" wire in it temporarily along side the wire that is already there.

Speedy,
I ohm'd out the wire that goes from the ICM to the ECM. It's good.

It goes to pin A12 on the ECM to terminal B on the ICM and is called CKT 423. I also ran a jumper wire as you suggested. Same problem.

I know that the injectors are being disabled because the code 41. What's stumping me is - Why is the code 41 being set?

The service manual says 'Code 41 will set if voltage on CKT 423 exceeds 4.6 volts during cranking.' It doesn't. It's around 2-3 volts.

Always measure the continuity with at least one end disconnected. Associated circuitry that a wire is connected to can give you a false continuity reading.

Try "tightening" the pins on both connections.

Double check the ground to the ICM, probably the black wire.

Your use of the term circuit 423 has me curious since that's what it is called in a 94 F body manual. Do you have the actual 92 Y body manual?

Remember that internally to the PCM there are 2 functions to many of the control lines. Control obviously and the other is monitoring. It is possible that the montoring portion of the PCM is damaged but the functioning portion will still work. It might be time to try someones PCM to see what happens.

I do have the 92 Y body service manual.

The ECM has already been replaced - along with the Opti, ICM, coil, and the entire wiring harness.

I will work on that circuit 423 wire some more. I'll also double check the ground to the ICM.

Does it make sense that I'm getting a code 41 and still getting good spark? The engine runs great on starting fluid.

41 only says it disables the injectors. Doesn't say anything about the spark.

Since you ran the extra jumper, have you reset the code to see if it reappears?

Remember a loose connection (intermittent loss of continuity) can cause the code. Have you "tightened" the connector pins at each end of the harness?

I wonder what a voltage divider would do if the line were forced to stay at 3 volts? Would be very easy to make to a voltage divider with 2 resistors. Maybe you could try that if everything else fails.

Yes, I've cleared the codes several times. It will come back after only a couple seconds of cranking the engine.

I did 'tighten' the ICM connector. I haven't done the ECM side yet.

I love the idea of the voltage divider. I'll give that a try tonight if I get a chance.

Thanks for all of your help so far!

I got it running! It was a bad connection at the ignition module the whole time.

I took 4 leads that I cut off some capacitors and soldered them onto the 4 pins in the ignition module. I did this so I could introduce 3v from the voltage splitter without cutting the harness or backprobing. I plugged the connector onto the new extended leads and decided to give it one more try. It fired right up and code 41 hasn't come back since. The new leads were a little larger diamater, so they made a stronger connection.

Thanks again for all you help with this.