This is an update on one of my older post about my truck not starting regularly. Basically what would happen is it would start fine and then every now and then it would just crank but wouldn't start. I assumed it was a fuel pump problem because I would prime the fuel system and it would start fine. So last weekend I put on a fuel pressure gauge and checked it while it was running, off, priming etc. Anyway everything checked out fine and it had the correct pressure all the time. I know it is not a leaky injector because I left the gauge on there and it held pressure for a good 1-2 hours before starting to go down. I am now thinking it is a bad relay or a connection, which is not letting the fuel pump prime the engine before it starts. I am going to look into it some more but I was wondering if anybody else has a idea of what it is and what I have to do to fix it. I don't have any codes, I checked right before I put the gauge on and it has not check engine light on. Once the truck is running it has no fuel problems like stuttering or bad power. Is there a bulletin for this problem, any extra advice would help.

 

Not sure of your meaning here, but the fuel pump doesn't 'prime' the engine, as in 'spray fuel' when you cycle the key. It is the fuel pump that gets 'primed' when you cycle the key. It causes the fuel pump to run 2 or 3 seconds to be sure there is enough pressure in the fuel rail to overcome atmospheric pressure in the intake manifold at first crank.

When it cranks and fails to start, keep an eye on the check engine light. If the light stays on while cranking the PCM is waiting for a Crank sensor signal. If the light goes out while cranking, that is an indication that the PCM has seen the crank sensor signal. Then it might be looking for the Cam position sensor so it can figure out 'when' to fire 'which' injector.

 

There is a Starter Relay mounted on the firewall same side as battery. Mine was having issues and would start intermittently. Got worse over time. A way to test, is when it is not starting lay a screwdriver shaft across the two contact bolts (holding onto the plastic insulated handle) and see if it starts.



Don

 

The check engine light doesn't not come on at all. What I was wondering was that is there something that is causing the engine to crank but not fire. The fuel pressure was fine and there are no dtcs or check engine lights. It doesn't happens that often but it is very random. Temperature has no affect on the problem, happens in the summer, fall, winter and spring.

 

Again, I'm not sure of your meaning here. Are you saying the Check Engine light doesn't come on at all, not even when the key is in the bulb check position or while cranking the engine?

Or do you mean the Check Engine light doesn't come on while you are driving?

Yes. A missing crank sensor signal will allow the engine to crank but the PCM can't figure out when to fire which plug. And a missing cam sensor is needed for the PCM to figure out which injector to fire when.

Also, extra keys or metalic thingys on key rings have can cause the PATs to get confused as to which key is being used.

 

+1 on the confused PAT... I now run with ignition key and house key only.

 

I meant it doesn't come on while driving, it just did it this morning wouldn't start ,at first then it fired after cranking, then turning key off and then cranking again quickly and it fired right up. This is the only way it will fire when it is acting up, if I just cranked it on one cycle it would never fire up.

 

how long had it sat before you fired it up this morning? it sounds like the fuel pressure is draining off, the fact that when you turn the key to run and "prime" the system which is just running the pump to build pressure in the line, the fuel pump has a drain back valve which sounds like it's going bad.

the pump itself is fine and has nothing to do with the lose of pressure when parked however you have to replace it as a unit

 

My expedition was having the same issue and the dealer was thinking it was the fuel pump. After 2 days of testing, they found out that the computer system needed to be updated. They need to perform TSB 06-13-09 Reprogram PCM. There is an issue with the computer setting on the idle that causes the car to not always start on first attempt.

 

Mine does the samething once in a while. But I notice that when I turn the key on it takes a few seconds for the Fuel Gauge needle to move.

 

My 03 was doing the same thing for a while. Had it at the dealer for over a week and they eventually said it was an intermittent problem with the fuel pump pressure. They replaced the pump and it was working fine until recently. The problem is now happening again intermittently. Which model years was the TSB for?