I've encountered a new problem with my 95 Z28. Once it's warm, the power drops, and there is a really bad hestitation - almost a weird galloping problem. I initially thought the clutch was shot; however, since it runs fine when cold, it's probably something like a bad O2 sensor or intake / vacuum leak. Any ideas.. I tried a scan reader without success.

 

It appears that your car acts up when it gets into the closed loop mode, which would indicate a bad sensor or sensor wiring, or that the opti is heading South. A scanner, not a code reader, will be able to see if the O2 sensors are working properly (the voltage should be changing continuosly at a rapid rate). Check for retained codes. If still no codes, check fuel pressure, and fuel pressure regulator, check for ignition misfire, check for injector misfire, check grounds, including PCM ground.

 

Pete, thanks for the info. I suspect it's the optispark since the O2 sensors are reading correctly according to the scan tool, and you're absolutely about the closed loop mode. As soon as it transitions from open to closed, it immediately bogs down. If it's fuel pressure, what's the easiest way to test the system. Also, I inadvertingly broke off one of the studs on the Y exhaust while trying to change the #7 and 8 spark plugs... any way to correct that screwup other than drilling through the sheared off bolt and inserting a new bolt??

 

To test the fuel pressure ou will need a FI pressure gauge screwed on the test port on the fuel rail.

Part 1 (Pump test) Turn key to on, do not try to start. The pump will go into the prime mode and shut down within a few seconds. The fuel gauge should indicate 41 to 45 PSI. Turn the key on & off several times as the pressure may not build up with just one cycle. If the pressure fails to come up to speck, the fuel pump may be bad, or a clogged filter, or a very leaky injector.
Turn key off, the fuel pressure should hold. If it drops, you may have a leaky injector, a bad check valve in the fuel pump, or possibly a bad regulator

Part 2 (regulator test) Record the pressure acheived in the pump test. Start engine and let it idle, pressure should drop by about 10 PSI. If not the regulator is bad, or the vacuum connection is leaky.

As for the broken stud there is really no easy way besides drilling it out. What I would do is to bolt up the remaining studs and use the flange on the y pipe as a guide for the drill, Drill the broken stud out, make the hole slightly larger, and use a regular machine bolt inserted from the top of the manifold. Then the next time the bolt breaks, it will just fall off. It helps if you can get a carbide drill from a machine shop supplier, do not try to use a carbide tipped masonery drill as it will just make a lot of smoke.

 

sorry to be a pain.. but what do you recommend for gasket dressing for the water pump? Although I'm considering using the red high-temp permatex that I used recently on the rear differential, I'm concerned that might not be "sensor safe." It's strange why only some of their sealents are advertised that way. On another topic, what gasket should be used on the exhaust flange. It didn't appear to have a factory gasket, and the Fel-Pro (60988) doesn't look right.
Finally, should the oil seal behind the opti-spark be replaced? When I removed and disassembled the old opti-spark, it was basically dry but contained a small amount of oil... maybe wrapping an opti-spark in RTV around the seams would alleviate some of the moisture and oil contamination problems??

 

OK.. problem solved. It turned out to be a clogged catalytic converter and corroded EGR value. What a pain.. there's still a slight hesitation, but it's definitely about 90% better, and the exhaust has the old load tone back.