There is one last remaining issue on my vehicle that's being a bugger to track down. I have an intermittent "crank no start" condition. Truck will start 5 times out of the blue, and then suddenly it won't restart 5 seconds after shut off. It will then not start for a period of time - but sometimes I come back to it, and suddenly it runs like a champ for 1-5 start ups, until if fails again.

1. I have cleaned the grounds at each connection point.
2. The vehicle will run with ether pumping into the intake in short bursts.
3. My test light indicates there is power at the fuel pump FUSE and RELAY in the fuse box under the hood. I removed the fuel relay and jumped manually with no effect (just in case I'm missing something in how it works).
4. We tried the reset switch on the passenger inside the vehicle and the ground, but it does not seem to be popped and the ground is not likely the issue.
5. I pulled the plug off at the fuel pump (less than 6 months old on a vehicle driver infrequently). The test light shows NO POWER at the fuel pump connection on all 4 wire ports in either the run or crank position.

It would seem there is something interrupting the circuit between the relay and the pump. Does anyone know this wiring? Is there a harness connection I should be looking for, or any other computer / relay between the relay and the pump? Is this the PCM being flaky?
Not sure what to do next with this very bizarre but apparently known issue. Any help would be greatly appreciated.

Thanks
sirrobocop

 

Check the codes. There may be a code even if the engine light is not on. When I had an intermittent crank/no start, it was the relay that powers up the PCM. And I had a code, a code which indicated a code erase, battery disconnect or PCM not being powered up. The first two had not happened so on the suggestion of a forum member, I replaced the PCM relay and fixed it. Get a gauge and check the fuel pressure. There is a schrader valve on the fuel rail for that purpose.

 

Thanks for the help:

RE: There are currently no codes on the vehicle. I pulled the codes first because I had a misfire issue, and I had a misfire condition in #6, (P0306) not related. It was a bad wire, I had a spare, which corrected this issue. No other codes listed. I did disconnect the battery during cleaning of the ground wires in case the no-start issue was power connection related. This cleared the log and did not alter the no start condition, however. Last, there has been no code sent to the system at any time during this or the previous intermittent failures. The vehicle just suddenly won't run.

In this case, after fixing the spark wire, I drove the vehicle for 45m, shut it off, then ran it again for 3m to move the truck, then 10m later - no start.

RE: The relay that powers up the PCM - do you mean the EEC relay in the below picture? The three relays marked in blue are all the same part number; I have rotated them around, using the horn to test each relay. None of them appear bad, and no version of the rotation cured the issue with power to the fuel pump. This is why I was wondering where the circuit goes after the fuel relay - is there something else, the crank sensor and / or PCM, that might not be passing on the "run" signal to the fuel pump? I am not familiar with the schematic (old school mechanic), but I thought that the PCM would run the fuel relay, and the fuel relay would start the fuel pump. I have not tested the crash sensor reset, but it did not appear to be popped (this would not explain the intermittent issue either). My logic center says intermittent issue, must be a flaky computer or a relay failure or ground issue. I am not sure, but a bad sensor would seem to either work, or fail, and that's it:



I'm thinking what I need to do is test for power on some particular wire on the PCM if I can get it off under the battery, or maybe there is some damaged wire enroute to the pump (seems unlikely), but I'm guessing a little bit.

RE: Shrader valve - I don't have a testor, but I'll get one. I think there is no fuel pressure - the truck will /did try to start from residual pressure, but it no longer seems to prime or catch and stay running and at the moment, although it might fire right up in the morning. The last time I started it, it ran briefly but roughly, then died out, the first time it has occurred while actually running. Ether will start it up and run the motor normal/well (relatively speaking). This seems to be confirming no fuel delivery issue, matching no power in the wire at the fuel pump plug.

Am I missing a relay that is not under the hood? Where next?

sirrobocop

 

Several things:

1. During an initial power-up, the PCM only turns on the fuel pump (via the fuel pump relay) for 2-3 seconds to prime the system. It only turns the pump back on when it determines that the engine is firing as sensed by an accelerating crank signal. It would be normal for there to be no power at the fuel pump if you measure after the priming cycle and if the engine is not running.

2. I always recommend half-splitting this electrical circuit, especially when it's intermittent. You have to be able to figure out which half (and, perhaps, successive halves) of the circuit to focus on. It saves a LOT of otherwise wasted time looking in laces where the problem isn't because of a lack of understanding how it works.

Rig up your test light to the pink/black wire at the inertia (reset) switch so you can easily see it when starting the truck. If the light always comes on regardless of whether or not the engine starts, the problem is rearward (wiring, pump, ground) or in the ignition system. If it fails to light up for the priming cycle in conjunction with a no start, then the problem is "upstream" in the control circuitry.

Once you KNOW which half of the circuit is at fault, it becomes less frustrating to troubleshoot.

 

You can also spray some starter fluid into the intake and see if it starts to confirm it's a fuel issue. Some mechanics use brake clean instead of starter fluid.

 

He already did that. See post #1, item #2.

However, due to the intermittency of the problem, it still *might* be an ignition problem but it just happened to work at that time. I'd lean very strongly towards a fuel delivery problem though, based on current information.

 

The truck did not start this morning, but it did try. Inserting the test lamp in the pink/black wire, the test light did not come on when the key was placed in the RUN position. The lamp DOES turn on and stays on when the key is in the crank position. If I understand correctly, the fault is not in the engine compartment.

What's next? A test at the ignition somewhere? Which wire at the pump should be hot, the red one? If so maybe I can trace it.

Note: I have replaced the ignition key tumbler in this truck a year ago due to wear/age, and I've replaced the entire steering column in a different F350, so I have some familiarity with the set up, mechanically speaking.

Thanks

sirrobocop

 

RE: No electric to fuel pump

I was able to find a schematic of the fuel circuit online, and determined there are no relays between the crash switch and the pump. There are two wire loom connections enroute, one under the air filter and the other at the gas tank.

After verifying that I actually had a good ground for the test light, I've traced power in the pink/black wire to the connection loom (back side) at the tank after all. So, it looks like a bad connection / continuity at the tank connection, a broken wire on top of the tank, or the replacement pump is defective. I'll have to raise the bed tomorrow and check these items.

Thanks for the help again everyone.

sirrobocop

 

Case closed. I'm making errors in my old age.

The truck fuel pump I replaced 18m ago was in my stepson's truck, which we raised the bed on. On my 1998, the spray-on bed liner prohibits easy removal of the bed, which puzzled me until it dawned on me: "Wrong truck" The fuel pump on my '98 is probably 220K/23 years old. It oughta be bad, lol.

Replaced, mission accomplished. FYI future reference: I was able to unbolt the tank straps and lay the front end on the driveway. I had to jack up the frame slightly to twist the unit out of the tank. The fuel lines require 1/2" quick-connect tool to remove them prior to unbolting the unit at the tank. Always verify your ground for your test light is actually a ground, no matter how good it looks.

Now that I understand the fuel system and wire location, it should never be a problem again. I learned a lot this round. Thanks all.

sirrobocop