AT my wits end here. Sorry for this lame introductory post to this wonderful place. I've been reading here a very long time but now I actually need to ask a question.
So last Sunday, after my truck (2003 f150, 4.6) ran beautifully up until at night when I go to start it to get my food. Just kept cranking. Told my brother immediately it wasn't getting any fuel.
We all deduced that it was fuel related/ fuel pump so we waited till I had time to get to it. Well we messed the relays - nothing. I changed the pump today and managed to get it fired twice but now it still wont start either.
Fuel filter changed as well. No pressure at the fuel rail before either but with the new pump it seems rather low. Plugged in a programmer to get readings from the computer and I found that the RPM doesn't go up at all when cranking leading to a no-start. Before the fuel pressure was also really low and it still is low unless I cycle the ignition.
Well the repeated cranking took its toll on the motorcraft battery, and even after charging it I don't think the voltage is enough. It drops too low, it seemed to want to start fine when it was at 14v but anything 12 or below is a no-go. This could also be either the PCM relay or the crankshaft sensor. Worst case is an electrical short somewhere which is something I can't deal with. Anyone else got themselves out of similar situation?

Also we tested the old fuel pump and it was fine. Truck only has over 128k miles.

 

What is the pressure at the rail after you turn the key on? Use a gauge, needs to be at least 28 psi.

 

1. Fully charge the battery, otherwise you'll probably waste even more time.

2. Shortcut to see if you have a fuel supply problem: Shoot some starting fluid into the MAF sensor then crank and see if it fires. If it does, you have a fuel delivery issue. If not, fuel isn't your problem.

 

I would check the crank position sensor or the wiring and connections to it, since it showed no RPMs on the scan tool when cranking it.

 

I charged the battery. Changed both the camshaft sensor AND the crankshaft sensor. Still nothing. Not getting much fuel pressure either just like before with the old pump. (which doesn't stay on long enough since it won't start at all)
Still no RPMs on the scan tool either which leads me to believe it is back at the PCM relay or fuse box. I read a similar post to mine and it ended up being the poles/grounds for the relay itself. I think mine did get a little hot. Sorry for being a little vague this has been too tedious.

 

What is the fuel pressure at the shrader valve with the key on? USE a gauge.

 

mick, you keep going the way your going about this you will never find the problem unless its luck.
WHAT is the fuel pressure at the fuel rail port after you cycle the ignition on and off 'several' times.
Does the pressure hold?
You have to either eliminate this to prove it is the problem and not jump all over the truck.
What if there is more than one issue at the same time? You would not know unless you test one area at a time.
Good luck.

 

It's 40 PSI when I cycle it. When the scanner reads 0 rpm it won't start period. It's been nearly 2 and half weeks of it not running. The only times I had it running were 2 times while it was flat in the garage. It still wouldn't continuously start even after that. I'm trying to go along the wiring and still can't find any faults or fraying either.
I just don't see it being the PCM due to that being too hefty a purchase. If it was that why would everything else still work/read on the computer and scanner? I'm hoping someone else here had the same exact conditions as me because I've tried everything short of blowing the money on a PCM or new junction box - which the connectors for the relays looked fine underneath.

 

I don't understand what your talking about for RPM.
40 psi is ok for fuel pressure.
The PCM is powering up or the fuel pump or it would not run.
Check for voltage on the coils and fuel injectors. They are needed just as much as fuel.
Then does the fuel pump run again at cranking. At least test with a voltmeter.
As it is now the RPM thing may be an indication but you have to find out why when its absent.
Ignore it and do the trouble shooting for the basics.
May even be an intermittent fuse in its holder.
Until you get a lead, it will not clear itself.
Good luck.

 

That is an illogical reason for you to rule out the PCM. Based on the ambiguous results so far, the PCM cannot definitely be excluded or included in the list of suspects.


Did you try the spray test I recommended over a week ago?

What is the state of the THEFT light during a failed starting attempt?

 

I got the PCM in the mail today. It was the PCM. I get crank signal now but I also I had to reset my PATS keys and relearn them due to replacing the PCM. What a mess this was.

 

For those wondering, the PCM failed to read an RPM signal from the even new crank sensor not because of a wiring fault but water getting into the computer itself. Unfortunately one of the many other problems my truck has is leaks which caused this mess to begin with.

I used forscan to erase the keys and get past PATS immobilzing my truck due to new PCM. It was just one of those ELM327 obd2 cables from amazon and my dell venue windows tablet. I was able to fix everything through that instead of wasting time and money at the dealer/tow truck fee.

If you have the means to do this yourself don't ever waste money at the dealer!

 

Congratulations on fixing the problem and thanks for letting us know!

 

I have a 99 ford f150 was driving one day an steped on the gas. Blow out the cylinder 8 spark plug. Messed up the coil got a new one new plugs. But now when i turn my key on my fuel pump dose not shut off after the 2 sec. I got good fuel pressure I got Spark when I spray starting fluid in it it starts but then dies can someone help I heard it might be the PCM