jamoon

94 Z28 starts fine when cold, runs good until it heats up. Shut it off it won't start again, sounds like it's flooded. We can smell gas after it has been running a while. Changed the coil, had the ICM tested. Could this be the FPR or optispark? We did smell fuel when we checked the oil.

Injuneer

Have you scanned it for codes? Have you checked the fuel pressure? Did you check for raw fuel in the vacuum compensation line to the FPR?

Could be as simple as a faulty coolant temp sensor. Could be faulty O2 sensor(s) or wiring.

When you had the ICM tested did they heat it up with an external device, to make sure it isn't heat soaking and breaking down?

mrmint69

What all has been done to the car or is it stock?

jamoon

There's a new water pump and opti. Fuel pressure was good. New plugs and wires, new vacuum hose to FPR. No codes.

jamoon

No mods

jamoon

When it sits for a while it will start up and run very smooth.

mrmint69

I had a leaky injector and it acted that way. I only found it by disconnecting the fuel rail with the injectors hooked up but out of the manifold. Then turn key without starting and see if any leak. Lots of other things it could be.

jamoon

There were no RPM's when we tried to start it after driving it today. We will try to look at some of the wiring tomorrow. We had to replace the vacuum line to the FPR because a mouse had chewed through it. Maybe got into other wires.

Injuneer

How did you scan it for codes?

jamoon

Yes no codes

jamoon

took it to a shop

Injuneer

I would test the injectors for leakage as described above. I would also test the coolant temp sensor - the one in the water pump for the PCM.

4th Gen LT1 F-body Tech Articles

If a leaking injector is flooding the engine, it may still start when the engine is cold and it needs a richer mixture to start, but will not start when the engine is hot and doesn't need the extra fuel. Ditto with the coolant temp sensor. If it's not telling the PCM the engine is hot, and the PCM thinks the engine is cool, it may be setting the mixture too rich to start.

Both of the above would cause it to smell rich. Another possibility is a faulty O2 sensor telling the PCM the mixture is lean when it isn't, and the PCM pouring fuel in that the engine doesn't need. This will often show up as an OK cold start, but as soon as the engine warms up and the PCM goes into closed loop and the O2 sensor could cause it to run too rich.

Then there are "heat soak" items - things that can fail when they warm up - fuel pump, IC module, and the optical cam position sensor module in the Opti. The reason I asked about codes is because the ICM and the Opti will set codes, and shut down the engine. Those codes do NOT turn on the SES light. Hopefully your "shop" knew that they had to use the correct OBD-I scanner to read the codes, and didn't assume that they could read the codes by shorting the ALDL pins and flashing the codes on the SES light. 1993 was the last year that worked.

jamoon

I might have figured out the problem. There's an aftermarket alarm on the car (on it when we bought it). When trying to start after driving, it's not showing RPM's. The tach wire has to be hooked up to the diagnostic plug on the alarm, if it's not it will crank but not start. Wondering if there's something in the diagnostic plug that causing the problem. Red LED light will flash very fast when trying to start. Let me know what you think

jeremyhurt

Maf

Injuneer

The alarm has a "diagnostic plug", and a tach wire has to be hooked up to it, in order for the car to start. What "tach wire" are you using? The tach is driven off the white wire from pin A13 in the PCM. Is that the wire you are attempting to hook up to the diagnostic plug on the alarm? Never heard of anything like that.

You indicate "it's not showing RPM's". Do you mean your tach doesn't show RPM? The tach is driven by the PCM, which gets its signal fomr the optical module in the Opti distributor. Still sounds like that may be your problem.