Fuel problem? My mechanic is stumped!



I have a 1992 Ford E350 7.5l. Recently went to Montana on vacation. We made it from Ohio to South Dakota without a problem. We stopped to refuel and (it was about 110degrees). It wouldnt start for a couple of hours. We checked it for spark and it was ok in that respect and it was getting fuel although we didnt have a gauge to get the exact psi. We drove it to a machanic and he suggested it sounded like a fuel pump problem. We had him change the pump and filter. It ran fine for the 2000 miles. We were homebound and stopped in Indiana to refuel and the samething happend. It wouldnt start for about 2 hours (98 degrees.) It has a return fuel system and we have been told that vapor lock is rare in a system like that. But could it become vapor locked after being shutdown for fuel while the fuel isnt circulating. We thought maybe ignition problem due to the heat but we were getting a good spark while it was still hot and have checked all relays. it runs fine locally but are trying to get answers before our next road trip in 3 days(we hope haha) thanks for any input guys or gals.



Next time it happens try removing the gas cap. Expect a whoosh. If that fixes it, then you should look at the gas cap and vent system.


[b]The problem could very well be vapor lock. Especially if the fuel has any ethanol content.

To see if it is vapor lock, carry a jug of water in the vehicle. The next time the vehicle refuses to start, get out and pour some water over the fuel rails to cool them off. If the vehicle starts after doing this, you’ve confirmed it’s a vapor lock problem.



I take it that you can hear the fuel pump run when you turn the key on in these no-start situations?


I know someone who had that issue with a rented motor-home, he had the fuel pump replaced at the owners request without solving the problem. He eventually figured out it was a bad fuel tank vent and made the rest of the trip with the fuel cap loose.


I’m going to go off the wall and say the problem could still be an ignition module, no matter if there was a visible spark or not. Sometimes that spark is not as strong as it appears when trying to jump a plug gap under cylinder pressures.

The ignition module also provides a pulse to the ECM (engine computer). This pulse is what tells the ECM to provide an internal ground to trigger the fuel pump relay.

Look under the hood for the diagnostic connector plug where the DTCs are pulled and note if you have a tan wire with a green stripe in that connector.
If so, this wire splices into the lead between the fuel pump relay and the ECM.
Grounding this should energize the fuel pump and is something to consider as a test of the pump, inertia switch, etc., and narrow the problem down to the ign. module or an internal fault in the ECM.

Your vehicle (lucky you) is also one of those blessed with the TFI-IV ignition module, a cantankerous item if there ever was one. I’ve had several module failures and still had a spark present.
Hope some of that helps.