I have a 2003 F150 5.4L. About once every couple weeks, and I don't know why, my truck won't start. It turns over and is trying, but it won't fire up. If I go back a few hours later, sometimes it starts. Also, if I jump start it, it usually starts (sometimes it doesn't though)

I pulled off the fuse cover and noticed that relay #2 (the one for the PCM) was really hot. I could touch it, but it is very hot. It is also yellow and all the other relays are black. That makes me think it has been replaced before. Does that usually get hot when starting the truck?

Do those symptoms match what would happen if that relay was bad?

Thanks for your help!

 

Few things to check in this thread :

https://www.f150online.com/forums/v8...e-my-cure.html

Start with checking if PATS is having an issue ( i.e. have another RFID key or an RFID transponder like a Mobil Speed Pass ).

Once you know PATS is testing out correctly, move on to the list in the above thread ( PATS is noted in there )

 

There are some great ideas in that post. Thank you for linking to it. I'll start down the list you have there. I'll report back here when I figure it out for future readers. I'm trying to figure out one of your ideas though - What is IAC stand for? TB is throttle body, correct?

 

Sorry IAC = Idle Air Control.

On the 97-03 5.4 there is a solenoid on the back of the intake, that when the throttle is closed, it opens to let air into the throttle body.

If it is closed, the engine won't get air at idle.

 

Mr SScully i think that post you made about your cure for no start just crank should be made a sticky!!!!!!!!!!!! BIG TIME!!!!!

 

Long day today and not much progress. Here's what happened:
-Checked all the fuses inside the cab and under the hood - double check fuel pump specific ones. Everything fine.
-Checked the relays - I took the relay from the trailor tow battery charge relay and put in in where the fuel pump relay is. Wouldn't start.
-So I swapped the PCM relay into the Fuel pump relay just to be sure the relay was good, and the battery was dead from trying to turn it over so many times. So I hooked it up to my wifes car to jump it. Wouldn't start.
-So I put all the relays back in their original position. I left my wife's car running and connected to my battery for about 10 minutes and tried again (with relays in original position) and it started right up.
-So I disconnected everything and cleaned up my stuff while my truck ran to recharge the battery a bit. (probably 10 minutes) Turned off the truck and went inside for a sandwich. Came back out and it started right up. Let it run for a couple minutes and turned it off. Went inside and showered and got ready for work. Got in the truck about 30 min later to leave for work and it wouldn't start again. (crank, no start)
-Swore, got on my motorcycle and left for work. I just got home (10 hours later) and it still won't start.

Could a battery be strong enough to turn the engine over for 2+ minutes, but not strong enough for it to actually fire up? Can someone test a battery to see if that's the problem, or should I just go buy a new one? I think the battery seems plenty strong because the engine will crank for a long time before the battery dies.

I'm frustrated because I can't reproduce the problem consistently. And I'm tired. I'll sleep on it and see what I can figure out tomorrow.

 

Check fuses F18 & F23 to ensure that both are 15A fuses, not oversized. If they are correct, then replace the PCM Power Relay.

While you have each out, inspect the female receptacle pins for excessive corrosion or heat damage.

 

How did you check the fuses ?
- Pull and stare method or using a meter to check + VDC on the pins on the back while installed ?

Have you had a chance to check the battery cables ( at the starter and at the battery and engine block ) ?

Did the PATS test out when you turn the key from off to run ( do not start ) or is the theft light flashing when you have the crank no start ?

If you jumper the fuel pump relay normally open contacts in the relay socket, does the fuel pump run ?
- This should bypass the PCM turning the fuel pump off after 4 ( 6? ) times of crank no start as it is direct powering it.

Might want to put the battery on a charger overnight, you are getting after it pretty good, and you don't need to kill the battery by running it too low.

 

Sorry I have disappeared for a few days. I've been working stupid, long hours, so I've just been riding my motorcycle to work until I get some time to work on this. I spent a few hours yesterday going through more of your ideas.

First I put a new fuel filter in. Probably not the problem, but it was time anyways.

Then I went through your list, SSCULLY
- PATS is working. I have tested it using several different methods I found on the forum. The theft light does not flash.
- I checked the battery cables and cleaned the terminals to be sure.
- For the fuses, I did the pull and stare method. I thought I would try the relay first, then go through with a meter.
- I have not yet jumpered the fuel pump relay. I was going to do that next, but the battery died, so I connected it to my wife's car to put a little charge in the battery and the truck fired right up.

So the good news is, it started. The bad news is, I'm not sure I did anything. Sometimes it just fixes itself and then dies again in a couple weeks. Time will tell.

So I think I'm on hold until it doesn't start again. It's hard to tell what to fix while it's working.

You guys have been awesome. Thanks so much for your help. I may be back if it stops working again (hopefully not).

 

The dreaded intemittant fuel pump failure again?

 

It died again yesterday, so I checked the fuel pump. That was the problem. I put a new one in today and it works. What a pain in the butt. Hopefully that really was the problem and it's not just another false positive.

I don't understand why the fuel pump only worked sometimes though. I thought once it died, it was dead. Whatever - I'm just glad it works now. I might put my foot through my windshield if I go out there tomorrow and it won't start again.

You guys have been awesome. Thanks so much for all the help!

 

You will be fine. I don't know why it just does't die completely, but they do.

 

I guess I am joining a big club of folks that have or are expieriencing a periodic non starting situation. I thought it was the battery and did not even have the old one tested. I went and bought an Interstate 850 cranking amp and stiil, this morning left for work, drove to the gas station for gas, and it took 9 tries till it caught, cranked and connected. It always turns over with vigor. I am far from being a mechanic so I need to rely on basic help before spending money at the mechanic.

 

If it always cranks with vigor, it cannot be the battery or cables.

Check PATS first.

 

How does somebody that only drives my Screw, do a PATS test?