Explorer will not start once it is warm. Please help.

[filburn]

I have a stock 1992 ford explorer 4x4 with a 4.0 liter engine and automatic transmission. It has 176,000 miles on it and I have only owned it for 10k of those, so I do not know its entire maintenance record.

Here is the problem:
Car starts when cold every time without fail. Once the car is at operating temp and turned off, it has about a 50/50 chance of starting up again. The car cranks fine. starter, solenoid, battery and all that work fine. It peters out once I let off the ignition and the engine tries to take off on its own but it just can't. It sounds like it is going to start every time as in it turns over, but just sputters and nothing. After waiting 20-45 minutes it will start. Once it decides it wants to run, it idles very roughly at first only. I give it some throttle to keep it going and it will eventually run. Once the engine gets going again it runs and idles fine. It absolutely runs 100% (accelerates great/idles great at stop lights).

Troubleshooting I have done:
I searched the forums and found a lot of great information. I did find a couple posts that were very similar, but had some different symptoms. I carefully cleaned the MAF sensor and the car ran the exact same. I changed the air filter. I changed the fuel filter and that didn’t do it. I cleaned the IAC so it moves freely and that didn’t fix it either. My fuel pressure at the rail reads about 20psi when charged with the car off and it reads 30psi when the car is running.

Any suggestions would be appreciated, but keep in mind the car runs fine once it has been started. So it has to be independent of the engine running mechanics and is temperature sensitive.


Thanks for reading,

 

[Joe Dirt]

Mine is doing a similar thing, but only if you short-key it. That is, when warm, I have to keep the starter engaged a little longer to make sure it starts without sputtering. If it sputters, it stalls out, then won't start for 5-10 minutes. I think I may have bad/loose/leaking intake gaskets. I've checked everything else, and will be replacing those when it warms up outside.

 

[Willard]

I have had a similar issue, just not near as bad, for years now. Once in a great while (like once a month) I will start it and it will run funky for about 30 seconds. Then it clears up. Only does it when it's hot and I wait a certain amount of time after turning it off.

The only thing that comes to mind with yours is that maybe the fuel pump is on it's way out. If you run the pump before you start it when this would happen, does it sound the same as it would if it was cold? I'm just wondering if the fuel pump is having trouble getting going, and once it does, all is well.

 

[MrShorty]

One possibility I see, that has come up before on hard warm starts is a bad fuel pressure regulator (FPR). One failure mode of the FPR is for the diaphragm to leak fuel, which gets into the intake via the vacuum line attached to the FPR. While the engine is running, this leak isn't bad enough (yet) to effect driveability, but when you shut the engine off, the fuel pressure bleeds off (which is suggested by your 20 psi reading before starting, if the system were holding pressure like it should, that should be near 40 psi) and all that excess fuel in the intake makes for hard warm starts and rough running until the excess fuel can be flushed out. If the engine stays off long enough, the excess fuel has time to dissipate normally. First thing I'd do would be to start the engine, then pull the vacuum line to the FPR and see if there is gas in that vacuum line.

Second thing I would do would be a more careful fuel pressure test. What is the fuel pressure when it won't start/runs rough and what is the fuel pressure when it runs just fine? Sometimes the fuel pump relay works fine cold, but doesn't work hot.