Pretty much totally random. I tried to start it this morning before I left for work and it cranked right up. I turned it off and did it again and it fired right up again.

 

I think you should look @ C.O.P.'s make shure there clean and then regrease .....Maybe a plug problem ..whats your antifreeze look like ??? been using any

 

I guess I should explane why I say that...First off I'm no pro here I would say Jbrew is the man there ...

But I have a 01 5.4 screw with 75K that would not start the first time or start ruff ..after just living with it for a year I removed the cop and plugs and found some antifreeze in a 2 plug wells ..I regapped plugs and cleaned up/greased the Cops truck starts and runs fine now ...I think the antifreeze came from a thermostat gasket that was leaking and replace before the problem started

One more note I did have a miss that was very noticable but would not throw a code witch is what lead me to looking @ tha cops

 

Mine doesnt have a miss at all - the truck is running like a top, plenty of power, etc. The COPs were all checked about 15000 miles ago - new plugs, boots, greased COPs, etc.

 

Pretty sure you have an intermittant fuel delivery or IAC issue.

Try this... when the truck is stumbling and trying to start, give it just a hint of gas pedal. If it pops off and goes to running then chances are pretty good it's a flaky IAC.

Brad

 

If you replace the throttle position sensor, the issue will go away. Sometimes these sensors send no signal to the pcm. The result is the pcm doesn't set anything up for the engine to fire. I've seen sensors like this show no codes, nothing, just no start.

 

The engine would still turn over, but just wouldn't start? Where is that sensor located and is it difficult to change?

Truck isn't throwing any codes whatsover and the issue is totally intermittent...

 

Yea , Iduno, something getting lazy every now and again lol. I haven't seen a TPS issue without a DTC , - yet! Definitely not saying that isn't the problem.

But yea, I think it goes MAF TPS Trans on start. The PCM needs to hear from those three I know for sure ans well as others.

But before that you have a starter interrupt relay. I have a diagram of that , I'll go dig it up, - old galleries aren't working, but I have it in another location. It'll take a few minutes, - I post it.

Yea , it's here, - the interrupt is toward the top of the diagram -



You mighty wanna check that one or just replace both since it's cheap and these problems can be a PITA. Or,- locate both relays and when it acts up again, put your hand on the relays. Their usually warm to hot when bad.


Btw , this is for a 98 model. Yours IS DIFFERENT, but this should still give you and idea of whats going on when you turn the key..

 

Qualified "Maybe" on the TPS.

Problem is, if it's dead and sending nothing while the engine is being cranked the computer should see a circuit without an in-range signal and set a code. If it's not quite far enough out of range to set a code, it should still crank, but the performance will be off.

If the TPS is completely dead the computer should sense the lack of signal on that circuit and default to limp-home mode. In that case engine should at least still crank (limp-home = base fuel mapping).

It may well be the TPS, but I'd be leery of blanket-statementing it. I'd also be looking at a couple other things a little higher up on the probability scale. There are some pretty exraordinary things that must happen for the TPS to be out of whack enough to cause a no-crank without setting a code.

The lack of codes makes me think it's still a fueling or idle-air management issue. I think you still need to get a handle on what the fuel pressure is doing during the no-starts.

Brad

 

Thats what the Ford tech was trying to do, but it never would do a no-start when he had it. He kept a fuel pressure gauge on it constantly (taped to the windshield), but the truck never would act up. I guess I need to bring it back down there and have them keep it even longer this time. Its such an aggravation because it could go several weeks between the times it acts up. I really don't need my truck to be gone that long, but I guess I don't have much of a choice.

 

You should be able to rig up your own guage.

Just thought of something... crank position sensor. If the CPS is getting flaky it could be throwing spurious timing codes and causing no-start problems. Had that on and SHO I used to have. A replacement CPS wasn't quite aligned properly and it would cut out at the darndest times. It was usually when it was only partially warmed up, or when cold fluids were introduced into the warm engine and the differential expansion tweaked the sensor gap (every time I changed the oil it wouldn't fire for ten or fifteen minutes until the temperature normalized). In that case it was all-or-nothing, run perfect or not at all situation. In other words it worked or it didn't - no stumbling start thing. Never set a code.

Brad

 

Thanks JBrew! You mentioned two different relays a couple of times in that post, but only referenced the Starter Interrupt Relay specifically - what is the other relay I need to locate?

Where would the starter interrupt relay be located under the hood?

 

I'm trying to locate a place locally to purchase a fuel pressure test gauge that I can use to watch the pressure myself instead of leaving it down at the shop for an unknown amount of time...

 

I have seen TPS's go bad like this before sometimes they get stuck in the wide open throttle reading but when it happens they usually wont start a lot more than they will.

 

If I were you I would change the crank position sensor and the pigtail.