Weird-Engine won't start when hot

[ajmeleng]

My 98 XLT with the V6 4.0L EFI enigne will not start in the afternoon when temp is hot but it starts fine in the morning when temp is cooler. Recently, I cleaned the MAS because it showed the classic symtoms. I changed the fuel filter and it didn't improve. During one of those times that it didn't start, I changed the coil pack and fuel pump relay. It started fine right after that. But that afternoon, it absolutely would not turn over. This morning it started just fine. I am totally stumped. Does anyone have any suggestions? Thanks in advance for any advice.

 

[Alec]

Does it try to crank?

Does the fuel pump turn on? You should hear the fuel pump whine and pressurize the system if you turn the key to "on", wait a few seconds, then start.

 

[TPLYNCH]

IF you don't hear the FP whining, try wiggling the relay (with the ignition ON) and see if it causes the FP to start running. If it does, the connections in the relay box may need to be cleaned. Remember someone had a problem with the whole bottom of the relay box moving, causing bad connections.

 

[Opera House]

Does it not crank or just not start?

I had problems with my 97 and it wouldn't crank at times. It had a strange internal corrosion in the starter solenoid mounted on the fender. I had never seen that problem before. Contacts had a beautiful powder blue coating on them.

 

[ajmeleng]

It wouldn't start again yesterday afternoon nor in the evening, but it started fine this morning. I don't really think it's the FP since it always starts, albeit during cooler temp.

I had a theft alarm with remote start installed 4 months ago. I supected this is messing up with the starter. However, I can't locate the starter nor the starter relay. They are not where the book (Haynes) saids they are.

Also, would a bad crankcase position sensor cause this?

I really appreciate all replies and suggestions.

 

[TPLYNCH]

I'd start w/ the alarm. Bad CPS could cause this problem too.

 

[Howard]

If I just look at the evidence it sounds to me like it's flooding. Are you getting lousy gas per mile as well. Possibly black smoke when you floor it. In the old days of carbs we had some Fords would have a vapour lock in very hot weather so no fuel got through. We also had some where the choke would stick open, starts great when cold and no joy when hot. So I would look very closely at the fuel supply.

 

[Rhett]

That's what I was thinking--vapor lock..hehe. But then I remembered that we're talking fuel injection. My buddies 50 Ford truck hot rod had that problem but in an EFI truck that's probably not it. Now it's probably the fuel pressure regulator.

Anther thing that crossed my mind was O2 sensor; when mine went bad, the truck would randomly die while driving when the engine was hot. Started every time though, which makes me think, ajmeleng, that it's the fuel system.

 

[ajmeleng]

Changed the Crankcase position sensor, no help. I am afraid its the Fuel pump. Had it towed to the shop this morning. Will let you know what they find. Thanks all for the tips. Just stumbled across this site recently. Great site, good info. A great big thanks for whoever put this together!