Hey all, [1986 trans am, 305 TPI]

Trying to figure out what's going on with my car. It starts from cold GREAT, turns over immediately, and drives with zero issues. But if you turn the car off with coolant temp above like 160F, wait a minute, then try to start it won't fire up. The starter sounds just as fast as it does during a cold start and it's turning the engine over fine. But there's just no sign of the engine trying to fire up at all. But if I wait 5-10 minutes it will start totally fine again (coolant temp falls to 130ish?)

Any ideas? Fuel injectors are new, starter is new, new fuel filter. IAC is new. TPS is accurate 0.54V with the idle screw all the way out. No check engine lights on the car at all, and it does run great, just won't start up again if it's warm.

 

Somewhere kicking around the forums here, there is a chart of the resistance the coolant temp sender should be at different temperatures. I'd be finding that chart, and seeing if the warmed up engine temp correlates to the resistance indicated on the chart. Note that I am talking about the CTS that gives the ECM it's reading, not the one for the gauge nor the one that triggers the radiator fan relay (also not the one that controls the cold start injector) . If the ECM's CTS is off, the ECM may respond by not properly pulsing the injectors while the engine is hot (but the CSI is there when it's cold to provide the needed fuel to start).

If the ECM's CTS checks out fine both warm & cold ,perhaps checking the injectors with a noid light and checking the spark when it's hot & won't start would be the next step (along with a hot engine fuel pressure check for good measure)

 

thanks! My bf and I can check the spark with a test light, and I'll find that resistance chart for the ECU temp sensor

On the 86 305 I believe it's just the single temp sensor next to the cold start switch on the front of the engine?

 

Hi SkiingOnIce,

Yes, it'll be the one next to the cold start switch, it will have a two wire connector, with the wire colors being one black wire and one yellow wire.

 

The ignition control module under the distributor cap is known to act wonky when it gets hot, especially if the thermal paste underneath it has dried out.

 

Thanks everyone. I should give an update here, I think it ended up being the fuel pump. Car died increasingly frequently, and manually squeezing closed the fuel pump relay didn't do anything. But if it sat for a while (an hour) I could hear the pump go again. I guess I hadn't driven it around long enough for the fuel pump to stop working mid-drive. Until tonight!

Coolant temp sensor was reading correct values according to the resistance lookup table.

I will still check the module under the distributor cap. Thanks.

 

I would also check your fuel filter on the the tank side. My car (1989 tune-port 350) did this for 4 years and a fuel pump because the tank had all sorts of nasty stuff inside the original tank and it was clogging up the pump and filter. I cracked open the fuel line and found the gas to be gritty and black.

The last time it shut off, it took about 2 hours between the engine stopping and triple A bringing the car home. I was able to start it and drive into the garage. I never would have guessed the tank was bad until I was laying in bed that night and thought to crack open the fuel lines. It may be worth checking your fuel filter first to see if your gas has tank particles floating around in it. My 2 cents.

 

Thanks, I did replace the fuel filter earlier this year and it didn't seem too bad inside. But when I take the pump out I should be able to see inside the tank and look for anything weird.