Chevrolet Repair: 91 Camaro 3.1 V6 Manual Trans- Driveability, vacuum leaks, exhaust leaks

Question
Hi Mark,

I have been working on this car for a long time. Have been
having hesitation problems, and with a stick shift, that is
aggravating.

I checked and fixed all possible vacuum leaks, changed every
sensor (IAC,TPS,EGR,MAP,Air Management Valve on A.I.R. Pump,O2
sensor, etc), still no avail. It was due for a smog check, so I wanted to
make sure all exhaust leaks were fixed. I pulled the heads, had them
magnafluxed and vacuum checked (all OK). The reason I pulled
the heads was that one of the exhaust manifold bolts had
broken off in the head, and needed to be extracted. When I put
the left exhaust manifold on, the bolts didn't line up-it had
shrunk by about 1/2 inch. New manifold, put gaskets on (the
original didn't have gaskets). Problem seemed better, but is still
there. It actually is pretty good when warm (closed loop), but
horrible when cold (open loop). I experimented by disconnecting
the O2 sensor, no change-even when warm, it seems better, same as
when O2 is connected.

I have replaced everything except the ECM, wondering if it is
that? To put it on a diagnostic scope is around $150. I figured I
could change $150. worth of parts, and fix it... apparently not.

The original injectors were running rich, a few showing less
than 8 ohms resistance. They have been replaced.

Any thoughts? Or am I doomed to get the diagnostic run, and
probably still pay another $200 for parts?

Thanks for any help,

Bob

Answer
Hi Bob, I remember having this problem with the 3.1 in the early 90's. We used to clean the intake valves(they would have carbon on them)because the carbon would soke up the gas and make it run lean. Sometimes this worked....the only thing I know that worked for me was to increase fuel pressure to the injectors. This might not be a option for you because of the smog test. I would run 60 psi to the injectors and it run great. To increase the pressure I pinched off the return line, I know it sounds bad but it worked and only had to do a couple cars. My boss was all about it because they ran so good.

Sorry I can't help more

Mark