91 Z28, LB9 (305) TPI, Automatic 4L60.

When cold, car does not want to upshift right at all, into any gear, with more than about 50% throttle. There is just no more acceleration, and no increase in RPMs. When its warm, the thing runs fine. Had it to two different transmission shops, and they both say its an engine performance problem, not a transmission problem.

I WAS getting an EGR code (32) after highway cruising for a while. So today I did some trouble shooting, and my service manual says ....

"Apply vaccum to EGR valve, diaphragm should move freely and hold vaccum for about 20 seconds".

"Able to hold vacuum?" No ----> "Replace valve"

Ok, first, I cant even see the damn valve, so I cant see the diaphragm.

Scondly, how much vacuum should be applied? If I apply enough, it might hold for 10 seconds, otherwise it bleeds off pretty quick. Is this an indication of a bad EGR valve, and could this be causing my drivability problem?

 

The EGR valve will not cause the problems you are experiencing.

To check the EGR valve, press on the diaphragm, then stick your finger over the hole. If the diaphragm stays put, its good. If it moves and goes back to its normal state, its bad. That's how I check them.

 

The one caveat is that the TPIs most likely have a negative backpressure EGR valve. That means that the EGR has a pilot valve within the main diaphragm. If the exhaust gas pressure (at the pintle pilot port) is too high, the EGR valve will not open (by design). This is to prevent unintended EGR operation under higher loads (acceleration, etc.). The exhaust gas pressure must be less than the pressure of the calibrated spring in the pilot valve to allow the valve to open. This would occur only at a low to moderate cruise RPM where engine load is low.



This troubleshooting flow chart might help: