DirtyDaveW

Here I am with a completely new ignition (Coil, ICM, Opti, New PCM) and the '94 Z28 A4 was driving fine last night. Parked it in the driveway, went inside the house and went to sleep. I get up this morning and, after getting myself and the kids ready for (high) school, I go out to warm up the car. WTH? It won't start and the SES light is on again. I grab the laptop with LT1edit/PCMCOMM on it and hook 'er up. Hmm. Haven't EVER seen this one before. DTC 41 EST Open error. I've googled and found several hits but only one that was somewhat directly associated with our cars. It was on www.camaroz28.com and the question and answer seemed to point to a problem with the knock sensor. I checked the resistance and it was 3.5K or somesuch. Well within the correct reading. I then looked up the wiring diagram I'd downloaded from shoebox and the Knock Sensor feed (dark blue wire on the "D" connector to the PCM) said that the 'key on' voltage should be 1.6 volts. But when I measured mine, I get 2.6 volts. This is with a fully charged battery, not running, just Key in the ON position. Anyone out there have any clues, tips on what I can start the process of elimination? At this point I'm going to pull the PCM out of it's cavity, disconnect the "D"(Blue) connector and check the volts at the Pin (D22) to see if the 2.6 voltage is present there. The main issue is that not only am I'm getting the SES but there's NO spark. All the other voltages/fuses are intact and have been evaluated.

David K. Wilson

'96 Z28 355 LT1 M6 4.10

'94 Z28 383 LT1 A4 3.42

turbo_Z

Im betting on some bad connection with the coil, ICM.

Injuneer

I don't think its related to the knock sensor.... problems with that would set DTC 43.

DTC 41 is related to the IC Module control circuit.

Your knock sensor sounds fine.... key on, harness wire connected to sensor, the voltage at the KS pin should be in the range of 1.5-3.5V. With the harness wire disconnected from the sensor, you should be 5V from the harness wire to the block.

I think you're looking in the wrong place.

DirtyDaveW

Thanks for the reply. I'm going out now with the Multimeter, some jumper wires and some hope that I can find something definitive.

DirtyDaveW

Well, using shoebox's really nice wiring diagrams, I checked all four PCM connectors with the key on and compared the voltages to the ones listed. The only one that is weird is;
Connector: RED
Pin Number: A13
Pin designation: Tach output
Wire color: White
Normal voltage with Key on, motor not running: zero volts
Measured voltage under this condition: 8.06 volts
WTH?

DirtyDaveW

There is a device called an "ICM (ignition control module)" that receives an A/C (alternating current) voltage that fluctuates between 1 and 4 volts. When the voltage drops to 1 volt, that's the car's computer demanding a spark be sent to the distributor. Well, sometimes I would measure it with the connector off and it was getting the right voltages (1 to 4 volts). I'd then reconnect it and it still wouldn't run.

However, today when I pushed a straight pin into the fully connected connector and hooked up the multimeter to it and then cranked the motor, the car would start.

?????

So once it was running, I began to suspect the actual connector and began grabbing the connector housing and wiggling it. The motor would stumble sometimes, others, it would flat die.

So after doing this a few iterations to prove I could reproduce the problem, I pulled the connector apart and looked to see if the crucial white wire was broken inside the housing.

Nope, it was fine.

I then rotated the connector to look at the point where the female and male pins slide over each other...

aha.....

The female side of the white wire pin was just this much ' ' farther apart than the other 3 female pin holes.

Using a pinpointed voltage detector probe, I pried the white wires pin housing closer together.

I then reinserted the ICM's connector and started the car.

After that, I wiggled the ICM connector housing over and over and it NEVER stumbled or died.

So it looks like "Turbo_Z" correctly analyzed the problem in general. Thanks for everyones input.