I tried searching couldn't find no answers. I have 91 Z 28 305 TPI less than 90,000 miles. The car is hard to start cold or hot motor just spins some time it starts some times it dosen't. You can remove the battery cable it will start but run rough. When you shut it off it will not restart. When it is running it runs very rough and will not turn over 3500 RPM. The plug wires, dist cap, plugs, fuel filter, pcv, egr, and vacum lines have been replaced. The fuel presure was checked and was good. There are no check engine lights or codes.




Thanks Dennis

 

Basically there are two areas that will not code but cause this, One is the fuel system, the Second is the Ignition system.

Always start simple, double check and confirm everything...

Does it miss? Only at idle only or all the way thru the rpms to 3500?(If at idle only look to vacuum routing or vac leaks in intake, T/B etc. If all the time look to the ignition.
You replaced the plug wires, did you double check for the correct firing order?(1-8-4-3-6-5-7-2)Trace them carefully from the cap to the plug.
Did you locate the correct number one cylinder?(front on drivers' side or engine, on the distributor cap it's also the front on the drivers' sideand it's rotation is "clockwise".)
Confirm good spark at the end of every plug wire.(Just snap the wire onto a used plug and ground it to the motor.)

Confirm vacuum hose routing by the under hood diagram.

Do a compression check.
A quick way to see if low compression is causing a "Hard Start" problem is to squirt oil into all of the spark plug holes and the try to start it. If it quickly fires up but won't restart easily when you shut it off, then the rings are probably stuck in the piston ring grooves. This is caused from running way too rich too long. The carbon builds up in the groves and eventually the rings will hang up.

There are more complicated tests dealing with leaky injectors, worn cam lobes etc, but try some of these first.