Chevyguy358

OK...I've tried to rap my head around this one for the last week. Car will run fine in open loop and once it warms up to 85 degrees C it will completely shut off. Once it shuts off, it will not start for an hour or so regardless if I unhook that batt or even reprogram it. I've datalogged the car and it shows no codes up till it cuts out. I checked for spark and there isn't any. I think its either temp dependent or closed loop. I have tried unhooking the MAF after its been in this condition (warm) in hope it would start up in open loop, but no start. I'm confused. I have datamaster logs if anyone would like to look at them, they look fine to me

95Blackhawk

A few questions:

How does it shut off? Does it shut off like you turned the key off or slowly die?

Does it die at EXACTLY 85 C EVERY time?

When did it start doing this? What did you change to make this occur?

How many times have you tried this?

What are the codes after it dies?

On a 95 stock program, the closed loop timer start at 74.75 C and then takes 52 seconds to go into closed loop.

Chevyguy358

Thanks for the info:
1. shuts off like the key was turned off
2. Within a few degrees give or take 5
3. started about a week ago, nothing done except an alignment in the last month. It did mildly overheat a day before about 230 (short period); I attributed it to a bad connection to the water pump
4. about 6-8 times, its pretty consistent and never gets into closed loop without cutting out (aka it never goes into closed loop and never gets up to temp)
5. no codes ever come up, though initially a low res code popped up for a sec with a low map (opti is newish 1500 miles and no rain) i even reflashed it with a stock tune-no luck

bw_hunter

Check the wiring harnes to the opti. Maybe the connection isn't made and it is intermittantly failing. Then check the ICM...this thing can be sensitive to temperature. Autozone can test it for you but if it's temp related it may test as god when cool...

95Blackhawk

To eliminate the PCM as the issue, try reflashing with a quicker setup to closed loop. Ex: I have mine so that it will go into closed loop at a lower temperature. Just a trial.

However, since you are saying within 5 degrees, I would say it is electrical and start tracking down the ICM. Good suggestion. I would have a voltmeter reading the ICM while it is warming up ( you can probe from the back of the connector) and see if you lose voltage as it get hotter. You could do the same for the opti encoder wires but you would be getting a code so probably not.

I had a bad wire once that would lose connectivity when the engine bay got hot and would be fine after cooldown so I think it is electrical.

Ben

Chevyguy358

I actually replaced the ICM earlier tonight and I also went ahead and programed all the parameters related to temp to be offset to the maximum value still same issue. i pulled all fuses not related to the essential functions and pulled various sensors, i.e. intake temp, pcm coolant temp, IAC, and MAF. It seems none are related to this issue as it still shut off just like normal. I think it might be the connector to the opti from pcm. Looking at the log it seems like the Ignition volts drop just after it cuts out..so i would bet that is simply due to the lower rpm.

rangers458

Do you have spark when it dies? Could be a faulty coil. Have had this issue with older cars, when it got warm, the spark would go from cold blue, to orange. Might want to check simple first.

johnnyb

have you checked your fuel pressure?

Chevyguy358

I have an extra coil I tested and both produce no spark at all when it cuts out. I have bypassed my 6al box to eliminate that variable. I have not checked my fuel pressure however when it won't start I can still clearly hear it priming and I doubt both the spark and fuel pump would fault at the same time.

JAKEJR

When I had a very similar problem on a L98 it was the ignition module. Problem was temperature related and when the engine reached normal temperature it would shut off, just as if someone had turned off the ignition key.

Of course I believe you've already checked that since you're referencing ICM which, to me, translates to Ignition Control Module.

Just brain-storming this: Can you test the MAP sensor? You did get a code on this once, right?

Sorry I couldn't help more.

So now I'm wondering "What would cause a "no spark" condition?

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!

Chevyguy358

I also have tried 2 MAP sensors, I have an extra one lying around. Same problem

Chevyguy358

ok an update...still pissing me off.The connection from the pcm to the opti connector is good. I have DC power to the A and D connectors on the ICM with the key on, nothing however in the B and C during cranking though my meter does not go down very far with the AC readings (shbox website). I am thinking PCM perhaps opti or does anyone know anything about VATS or the location of the BCM under the dash....I'm starting to get pissed off. Also if anyone is wanting to know the cost of the wiring harness from the opti to the PCM, GM is askin for $488....HAHA. Luckily I had an extra one lying around

Guest47904

How do you know it's at the transition to closed loop? Are you using a scanner that indicates it?

You say it has no codes, if that's true it wouldn't be the low voltage side of the opti since it would set a code for either of the 2 feedback signals. One code would not do anything but light the SES. The other would shut down the fuel system. So you should know it's not the opti.

I have yet to see an OBDI PCM fail. So let's focus there for the time being.

When you say you checked spark, did you check spark from the opti or from the coil? You need to check it at the coil if you haven't done so.

Here is where you need a good meter to check the IC signal on the white wire to the B terminal of the coil. If the coil has no spark then you would expect the AC signal to the white wire to have dropped out. Confirm this while cranking the engine over. By the way, the C terminal of the coil will not have anything as far as voltage there cause it is connected directly to ground. Confirm that you have a good ground there.

Now if the 1 to 4 volt AC signal is dropping out, ohm the white wire from the coil to the Black PCM connector, pin 5. FYI when ever ohming wires between two devices, disconnect one end of the wire.

Assuming now that the IC signal is dropping out. The last thing you can do is while everything is cold, when it would normally run good. Heat the PCM with a blow dryer and see if it won't start. That would definitely nail down the PCM.

Let us know what happens and we can take it to the next step.

Chevyguy358

I honestly don't know its on the transition between, it just seemed at first like the exact time and temp that closed loop usually would kick in. I now do not believe that is correct as I changed the parameters in the PCM and it still dies at the same time. Thanks for you help, I'm playin around with a few things

Chevyguy358

Anyone want to help me troubleshoot VATS?? I have it tuned out, so is there any point in checking the wiring?