5.0L warm start issue

[JimM]

I have a new-to-me 99 Mountaineer 5.0L V8 AWD with 175K on it. I have put 1K miles on it in the month that I have owned it.

It starts up normally when cold. When warm it will crank without firing for an extended period of time unless I apply some throttle.

The engine spins at normal speed before starting whether hot or cold, eliminating battery, cable, solenoid and starter issues, and it runs fine hot or cold once running.

It gets acceptable mileage 16-19 mpg, there is no CEL and no codes when scanned.

I have previously owned this drivetrain combination in Explorers but have never exprienced this difference in starting when warm.

 

[Turdle]

If you turn the key to the on position you will hear the fuel pump prime for about 2 seconds.

The next time you do a warm start, prime the pump 3-4 times, then crank the engine over. If this results in an instant start, I would suspect the fuel pump-regulator assembly is getting weak. Post up your results please.

 

[gatzdon]

Classic symptom of a failing Engine Coolant Temp Sensor (not to be confused with the temp gauge sensor).

Luckily you have a '99, so it's easy to check out with a cheap OBD2 adapter ($10-$20 on Amazon) and Forscan Lite (~$5 on App Store). Don't even have to start the vehicle. Just turn the key on and see what Engine Coolant Temp the PCM is reading. If it's more than 25 degrees colder than the real temperature, you will have a hard time starting/driving a warm engine.

I gave a write up here on how to check it.

http://www.explorerforum.com/forums...ng-when-hot-but-starts-fine-when-cold.435965/

 

[Dave98XLT]

Good afternoon;

My 98 SOHC is exhiibiting some startup weirdness and no codes are being set.

1. It chugs and dies on warm restart sometimes. My OBD2 adapter is reading 56C coolant temp after sitting 2 hours.

2. Sometimes when cold it won't start either. Suspecting the CPK sensor too. Again, no codes...

Recently changed the TPS and the IAC valve. Since then, these other things have started happening!!!

 

[CDW6212R]

Check the fuel pressure with and without the vacuum line on the FPR, but first what is it when the key is first turned on? A tune up is a good idea if things haven't been done in a while. The fuel filter and plugs/wires I'd wonder about.

Do you notice the "THEFT" light when the key is turned on, that should never flash with the proper key. If it flashes, then the fuel pump is disabled at that time.

 

[Dave98XLT]

The tune-up is fresh and the theft light is not flashing. I can run a fuel pressure test.

Where is the fuel pump/regulator located if I have to replace it?

 

[CDW6212R]

Find the fuel rail, and the FPR is on that, to the left rear. The FPR is rarely ever bad, but the pump and injectors get tired when old. Given the tune up items mentioned so far, I'd expect it to be the pump or injectors, or possibly the CMP sensor etc.