I have a 1994 Z28 with 69k miles on it. I've been having a problem with the car stumbling badly in closed loop when it's given any medium acceleration. It seems to run fine in open loop. Could someone help me interpret the scanner data. I have been studying Injuneer's manual, but it's hard to interpret for a novice. To give you a little background, earlier this year my waterpump was leaking on the opti. I went ahead and replaced with new:

- GM optispark
- GM water pump
- MSD cap and rotor with vent kit ran to the inside of the car
- MSD coil
- GM ICM with Shoebox cooling mod
- MSD 8.5 wires and Bosch plat 4 plugs (I know...)
- Fuel filter
- 2 GM O2 sensors

Car ran great for 600 miles. Took it for an extended run (160) miles. Ran great and parked it. Problem started the next day. Since the problem I've replaced with new:

- GM EGR Valve
- GM EGR Control Module
- GM MAP Sensor
- TPS Sensor
- GM Coolant Sensor
- Opti harness

Troubleshooting by replacement is getting a bit expensive. When I initially was troubleshooting it I did find a broken ground wire on the ICM that I believe is the ground for the ECM/left fuel injector bank and repaired it. I also discovered my air pump is not working.

I've also done the following tests:

- Fuel pressure; Initial key on 42 lbs.; Simulated WOT 45-46lbs; Bleed down steady 39 lbs.
- Alternator voltage at the battery 14.54 volts
- Engine vacumm steady 18 inches

The data seems to indicate a severe lean condition on the left bank. Could someone look at the following file and steer me in the right direction? Thanks man. http://savefile.com/projects/1043601

 

Apparently savefile.com is smarter then me, I cannot figure out how to get your file from it. If you email me it to me in CSV format, I'll take a look. vince@trifectaperformance.com

 

The file download link is at the bottom of the page. It's an Autoxray file saved in Excel format.

 

The page for the file link shows "The page you are looking for is temporarily unavailable. Please try again later. ". If I can connect, I'll take a look at it.

 

There seems to be a problem with the original web site. Here's a new link to the file at a different site. Thanks!

http://www.freefileupload.net/file.p...2C+Low+RPM.xls

 

Anyone? Injuneer? Here's a working link:

http://www.freefileupload.net/file.p...2C+Low+RPM.xls

 

We spend a lot of time on private mail trying to troubleshoot this problem. Did unplugging the MAF and forcing it into SD mode help?

 

Not much in the log.... the 1-second interval between data frames doesn't help. Did you simply show the frames that corresponded to a stumble? You need to provide a higher number of frames per second, and a larger portion of the scan. I'm not looking for a 5,000 frame log, but something significantly greater than 29 frames would be a lot better.

Can you get it to give the MAP readings in kPa? Converting from voltage to kPa is not convenient.

In column S, when the EGR kicks on, the timing drops back by 3*, engine RPM has dropped 125rpm, but throttle position hasn't moved. (Hard to tell since we can't see what happened over the preceding and following 1-second interval). Is this possibly the stumble "feeling".... it would be very subtle. Appears you are describing something more severe.

 

Okay. I unplugged the MAF - no difference in how it ran.

Injuneer - here's another file. My AutoXray scanner will only let me scan down to .5 second intervals for a very short period. I captured two episodes of the stumbling issue in the following file:

http://www.freefileupload.net/file.p...g+episodes.csv

Looking at your MAP table, there doesn't appear to be a straight linear conversion factor from volts to kPa. Is that correct?

Thanks for your help.