I'm stumped. I have a 2002 Z28 with manual transmission. It starts fine. Until it has been run for 30 minutes or more. Then, sometimes, it won't start until after 30 minutes. Sometimes it will, sometimes it won't.

Here's what I know and what I've done:

The starter itself works fine.
The battery is new.
Even when it won't start, the dash lights, radio, etc., all work.
The condition doesn't depend on the weather or amount of fuel in the tank. I thought it was vapor lock but it doesn't matter if the tank is full or empty or if the day is hot or cold.
I always fully depress the clutch.

I have replaced the starter and ignition relays (I was really hoping this was it but alas, no).
I've had a new key cylinder installed and have tried with both keys.
I don't see any loose wires or signs of wear.

When I stop the car, if I run a 30 minute errand the car might not start. If it doesn't, it will be 30 minutes after I first try it before it will start.
If I stop the car, try to start it and it won't start, I can then run my errand and find that it will start 30 minutes later. It seems to be tied somehow to when I try to start it - it sounds like some sort of security issue. (new keys and cylinder haven't solved this though)

Finally, I'm not keen to take it to the stealership because they can run up a bill trying things.

Help!

 

When you try to start does it crank at all or no if theres no crank only few things it can be and sounds like you have tried most of them already always check battery cables in and out TWICE. i have had 2 of them bite me at work for that. also when it happens if theres no crank check voltage going to the starter if its good trigger beat on the starter and see if that goes. if it does replace the starter seen hundreds of solendoids and/or gear sets bad in starters

 

I had this same problem on my 72 c/10, it caught on fire one day randomly while driving and after I replaced all the burned wires and other burned parts (thank goodness i had a fire extinguisher) the problem went away and never came back probably a bare wire causing an intermittent short of some kind, it is odd though how it only does it when it's warm, mine only did it when it was warm too.

 

It looks like whatever I do next will require a tester of some sort. Voltage to the starter seems like the first thing to check. I don't think I'll go the light it on fire route. lol Glad that eventually worked out for you. Tough way to fix a problem.

 

it's hard to test for a problem that's only there SOMETIMES, I never found out what it was, but after it all burned and I replaced everything the problem was gone.

 

Goes with out a doubt it is a thermo problem, but yes you may need a meter at this point. You can get a digital meter for $10 from most places, Harbor freight and tools being my choice.

When it stalls do you have any fuel pressure, spark? Lots of vehicles use the oil pressure switch as an emergence fuel pump cut off switch, say, in a wreck the oil pressure drops and it cuts off the fuel pump. The fuel pump relay could also be on its way out if oil pressure and fuel relay fail or are intermittently failing you get no code! Here is a really bad thought the fuel pump could also be failing but lets no go down that path yet!!

If you have no spark then you need to find the test for the coil pack and related components, I need to order the OEM factory maintenance books Haynes and Chilton’s are a joke, can’t help you yet!!

Some Camaro’s I’ve been told use a fuel pump reset switch in the trunk area; I thought it was just Fords and others, it could also be failing? If you have one which still I doubt the problem could be there, again do you have fuel pressure or spark after it stalls? I will not know for sure about the fuel pump reset switches until I can get into the Dealer on Monday and brain drain them.

Make sure the EMC ground is clean and tight, also the engine and battery grounding straps. Also does the engine while running surge making a sucking air/vacuum sound, check that you have nothing lose even slightly, cracks in any rubber even small ones between the MAS and throttle body. Then your looking for dirty connections you said they are tight but when you separate them is there any dust past the rubber seal between the male and female. Clean with electrical parts cleaner (not cheap but carb cleaner has lubricant) and use electrical connections grease (couple of bucks at most places), seal them up tight! Really pay close attention to any electrical connection which are covered in grease, oil and grim, clean, separate and grease also clean where the wires go into the connectors and grease.

This could keep going and going, and I haven’t even gotten to the modules yet, if one has a thermal problem, that’s when a Dealer may be expedient.

 

Steelhorse - lots of thoughts there and I appreciate it. The car doesn't stall. Does that change any of your input? There are no idiot lights on when it won't start. It seems like there would be an indicator for some of your suggestions - oil pressure.
The engine compartment is clean and it's been well maintained. Were in SC so don't have the northern corrosion issues.

 

I assumed a stall, my fault; I would still include testing the fuel relay and oil pressure sensor, but would also include the injector relay. They all go to whether or not you’re getting any fuel when it will not start?

Have you run any tests as far as fuel being delivered or spark? Besides the other tests and poss fixes I mentioned before I would test temperature sensors, they are simple ohm tests.

Then if you find you have fuel and spark while it will still not start look to the intake modules from the MAF up to the throttle valve, I have three and they are controlling little bast&*ds.

Also if you have fuel and spark then include the cam and the crank sensors could easily be adjusting the spark for a cold engine, which goes to a temperature sensor, fault module. Also I have noticed on most every vehicles these have a tendency to be drenched in oil and grease. They tend to also be susceptible by their location to being sand blasted by air coming under the vehicle exposing and stripping wires. A potential starting of a short could give the computer the wrong info and misadjust just about every component on the car, again also look for oil drenched connectors.

So I did assume a stall but you still have not mentioned if it is receiving fuel and getting a spark?

 

I am still including the fuel relay becuse it primes the fuel system before a start, if it is shorting when hot it would not prime the pump. The computer would assume a problem and not activate the pump.

 

so the car will not turn over at all like the starter is not working? and while its doing it the lights and everything works? its an 02 so im sorta out of my area but if it turns over have u checked for spark at the plug wire.