I have recently acquired a 1994 z28 with 5.7 litre 6 speed manual....When driving it for about hour and it starts to have trouble taking off and runs rough...I have to keep the rpms up to 2500 to 3000 to keep it running......I recently changed the plugs, wires, oil, and coolant.....It has excellent fuel pressure....I do know that it has sat for most of the past year.....

The other day I pulled it inot the driveway and the catalytic converter was bright cherry red....I didnt drive it for too long then....So i took out the catalytic converter and it sure wasnt clogged and can't see a clog up in front of it or behind it.....if you have any ideas please let me know!!!!

 

You might want to add a signature line with any mods you have on the car, it helps out. How many miles are on the engine? Any smoke, noises or smells? Did you flush the fuel out of the tank/lines before you started it after it set up for so long? Did you change the fuel filter? I'd check the basics before going too far into it. Also, did it throw any codes?

If this is your first LT1, welcome aboard, they are a blast!!

 

Hey, sorry....it has absolutley no upgrades and 155k miles.....It does misfire after becoming hot and if I drive it and then turn it off and restart it before it completely cools down it runs rough right off the bat as well as misfires.....

 

Sounds like the Opti or coil.

 

A red-hot catalytic convertor indicates raw fuel has gotten into the cat. Your misfire could be leading to this but it would have to be pretty bad to get the cat that red. Check the injectors for leaks by lifting the fuel rail and turning the ignition switch to on without starting the engine. Dripping fuel indicates bad injectors....

The miss can be an ignition problem but the red cat indicated fuel to me....

 

How did you check fuel pressure? Did you do a leak down test as well? In other words, did the fuel pressure hold after you shut if off or did it drop to zero? FYI, there is a fuel primer connector that is better to use for checking for fuel leaks, pressure etc... here is the link to Shoebox's site (BTW, if you haven't checked out his site, it's a MUST!)

http://shbox.com/1/fuel_pump_prime.jpg

I agree with BW_hunter but unless a fuel pressure leak down test shows bad, IMO I wouldn't pull the fuel rails. Just my .02

Another thing to check is the coil. Shoebox's site has info on that as well. I don't think a bad coil will light up your Cat but could be a cause for misfires. Do you have the ability to scan the PCM and look at the parameters? If not, check this link out and search on here for more info.

http://www.aldlcable.com/

You'll need a cable and software (laptop of course). Your 94 should be OBD1. A datalog can tell you alot.

Looks like you are new to the forum. Trust me when I tell you, the people on this forum have tons of experience. They've never let me down or left me with a broken car Keep us posted. I am curious about the glowing cats.

 

What is "excellent fuel pressure"? What is the pressure at idle, with and without the vacuum compensation line connected? Did you check the vacuum compensation line for fuel? If the fuel pressure diaphragm is damaged, raw fuel would be running into the intake manifold.

And as noted, misfires do make it run rich. The unused air from the misfiring cylinder hits the O2 sensor(s) and the O2 sensor tells the PCM the engine is running lean, and the PCM adds excess fuel that the engine doesn't need. An exhaust leak before the O2 sensor will also cause it to run rich. Could be faulty O2 sensors.

Heat soak could be contributing to the misfires. Check the IC Module. Shoebox has a fix to move the ICM away from the hot head. Check the PCM for Opti codes, in case the optical cam position sensor is heat soaking.

 

i agree that is seems like a secondary ignition issue, wires plugs or opti

check it for codes to make sure you do not have any clues