Intermittent Starting Problem

[Harry P]

My 94 will usually start, no problem, runs fine. Lately, every now and again, and I think only when warm, the engine cranks fine but will not start. Fuel line inertia switch is always engaged/no issue. Switched relays of like kind, still no start. No smell of fuel after cranking. Couldn't hear system prime, but it's pretty quiet anyway. No codes stored, either. Of course, my mechanic could never duplicate this when I left it with him for four weeks last month, and suggested I check for spark if it happens again.

After this happened again - and I didn't have someone to crank the engine so I could check the spark - I kicked the underside of the gas tank / skid plate and it started right up. Based on only the assumption that the fuel pump was faulty (189k miles), I replaced that, along with severely rusted bushing at the tank and tank fuel filter.

However, with a new fuel pump, it's back with not starting despite strong cranking. Again, couldn't check spark, went back to do so an hour later and it started right up.

Anyone have any ideas? Crank position sensor? Obviously, I need to confirm spark, but I'm getting tired of being stranded for an hour here and three hours there, and I'm not looking forward to doing so just to try and diagnose what is wrong.

 

[92exp4x4]

Fuel pump relay. Its located under the hood with the other relays in the fuse box. It is fairly common for it to act up. Make sure to replace it with a quality part, like motorcraft. Some cheapies have failed within months.

 

[MrShorty]

I'd probably put a fuel pressure gauge on it next time it won't start to see if the fuel system is doing its part to start.

 

[Harry P]

Reporting back with problem solution... it was a relay, but not for the fuel pump... for the EEC.

It was a hassle figuring that out as the one time the truck was not starting, I finally realized the CEL was off with KOEO. When I switched the relay from the A/C (presumably good) with EEC and it didn't change anything. I pulled the EEC relay and bench tested it and found the relay was working intermittantly. So was the A/C relay, which made sense as I was just beginning to experience problems with that a week before (but assumed it was due to refrigerant charge being low as I have a slow leak in the system somewhere).

So two new relays at $13 a piece at the Ford dealer, we're good to go. I have changed a couple of others a few years ago (incl. fuel pump) and am thinking I should change remaining factory original relays since they are probably due to go at 16 years and 180k+ miles.

Thanks to the responders, great forum as usual. Alwasy lurking and learning stuff here.