First off, sorry for being so vague in this post, this issue has me stumped. For the last 2 weeks on about 4-5 occasions my 96 z28 has stumbled in the first 3-5 minutes of driving, mostly during cooler weather but not always. It also died once, cranked right back up and then drove fine. It has a newer fuel pump, new ignition module, new opti and running Hypertech ECM upgrade. It also has had most of the spark plug wires new, the others are about 2 years old. I have run the autotap and have the log file when it stumbled but I do not know enough to really make sense of anything being wrong. I did notice that my oil temperature is not working. For the last 6 weeks or so my oil leak has gotten worse which I have been reading could cause problems with the oxygen sensors, but again I do not know enough to look at the readings to see if that is the issue. The car is mostly stock with only an ram air hood. Any help would be appreciated as I can not get this problem to repeat on a regular basis. Thank you in advance!!

 

Update: after swapping out another ICM from AZ and the car not even starting, I broke down and spent the money on a GM part ($90 vs $160). What a difference!! the car has been running great for the past 3 days now and at idle the engine feels smoother, ever since replacing the ICM with an aftermarket one it seems to have a slight misfire here and there but not enough to show on the AutoTap.

 

Your oil temp sensor is not showing data on AutoTap because you don't have an oil temp sensor. Only the Corvette LT1's have one.

Surprising you didn't get the codes for a shorted or open ICM, if the problem was that severe.

What oil leak do you feel is affecting the O2 sensors? As long as the oil is not falling directly on or coating the outside of the O2 sensor, it shouldn't be affecting them. If it is getting on the sensors and immediately adjacent wires, it could be affecting the sensor readings by throwing off the external ambient air reference that the thimble needs to develop a voltage based on internal (exhaust gas) O2 content.

A contaminated O2 sensor should affect the long term fuel corrections. What do yours look like in the various operating "Cells", both left and right banks? Check your data log.

Poor running at cold start, in cooler weather may be a sign of a faulty reading from the coolant temp sensor in the water pump housing. Check the readings in your data log.

If you need help understanding scanner readings, look over my online scanner writeup:

http://www.injuneer.com/ScanMast.html

If you still need help, upload your data log file to an ftp site, so others can download it and view it. Using .csv format for the file allows anyone to look at it using Excel.

What is a "Hypertech ECM upgrade"? Minor point, but the last year with an ECM = Engine control module was 93. 94 and up have a PCM = Powertrain control module. If you have a handheld Hypertech Power Programmer, do not use the "power tuning".... it has been shown in some dyno tests to reduce power. If you have a 160*F t'stat and have reprogrammed the fan on/off temps, you might actually see some added power. General consensus on the Hypertech programmers is to avoid them, and simply send your PCM to a mail order tuner (there are a couple in our supporting vendor list) for a guaranteed 10-15 HP gain, even on a stock engine.

 

Thanks Injuneer!!!! I looked at your link and that helps alot!!

As far as 02 sensors I was worried about the second one behind the catalytic convertor since it is so much lower, but they are all fine, a little dusty is all.

I did not know that about the hypertech power programming. I am actually getting a quote on swapping the LT1 for an LS1. This car is a daily driver and I cant afford any down time so I need something more dependable(?)

Thanks again for the scanner writeup!