I'm Stumped

[Matthew T]

I have a 1998 Expy XLT 4.6l 4x4. I had a no start condition that was preceded by a rough idle and the truck dying while driving. I replaced the fuel pump, filter and relay. The truck started and ran fine for 10 min. yesterday. Today I started the truck and it ran for about a minute and died and now will not start. Any suggestions would be greatly appreciated...

 

[1955moose]

Lets assume the motors ok for now. The fact it ran for the 10 minutes is why. First thing, let's get a fuel pressure test. Key on engine off should show 28-35 psi, if it will fire up, running pressure is 35-45, and hold that pressure. Next pull one of the front sparkplug coils up, stick a sparkplug or spark plug tester, ground against engine. Have an assistant crank engine. Be sure nice blue spark. You can rent the fuel pressure tester from any major auto parts store. One last thing, switch the fuel pump relay with one next to it. My 2000 shorted it's out. Ran fine after switched.

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[Matthew T]

The fuel pump relay is new, and I have good spark. I checked this before I replaced the fuel pump.

 

[Machete]

Too vague. Does it turn over? Or is it dead?

 

[Matthew T]

I turns over, but will not start. I replaced the fuel pump, fuel filter and fuel pump relay. It started and ran yesterday for 10 min + on 2 occasions. today it started and died in about a minute and has gone back to the crank no start condition it had previous to the fuel pump, filter and relay replacement. I can't figure out why the repair seemed to work and then didn't.

 

[ExplorerTom]

Vacuum leak.
Idle Air Control valve
Battery/alternator
Check engine codes?

Just what comes to mind based on what you’ve given us.

 

[Matthew T]

No check engine codes. battery tested fine when I diagnosed this before the repair. IAC and vacuum leak do sound like possibilities. But why would this thing run fine right after I did the fuel pump replacement? It went from a crank no start to running and is now back to the crank no start condition.

 

[stamp11127]

What you "had" before the fuel pump replacement compared to what you currently "have" can be two different things. Either the fuel or spark have dropped out. Get the facts.
What is the fuel pressure before cranking?
Is there spark while cranking?
Can you connect to the pcm with a reader?

 

[gbosin]

On a different Ford of that era I had a similar condition. PCM relay was shorting and blowing the PCM fuse. Check your fuses?

 

[grantpa]

Based on the symptoms you gave us-it ran, but now it cranks with no start, let's assume that you have spark, HAD fuel, and it has air, I'd start with addressing the fuel angle.

 

[ACEXPY]

Possubly defective new fuel pump?

 

[rjdelp7]

Bad connection at the battery.

 

[pitdexion]

Need more info. Key on is engine light on? Pcm relay/fuse is prevalent, crank sensor is possible. Is theft light on dash flashing fast? Try a different key.

 

[1955moose]

Now you know why I recommend a fuel pressure test? What fuel pump did you put in? Even the cheapest made in Shanghai ones should go at least a year, but without a pressure test, you and I are guessing. Please give us a reading, so we can advance to the next step!

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[Hawkeye07]

Fuel pressure regulator

 

[Swede252]

I know it sounds too simple, but...
My 99F150 had a similar experience, all I found was a loose fuse socket on the starter and ignition fuse, I.e. a bad fuse box... ( dash fuse box )
To fix that I slightly bent the fuse prongs opposite each other, reinstall the fuses, and never had that issue again.
Good luck.. years later a friend’s 97 had the same issue, that fixed his as well.

 

[Matthew T]

OK, I have more information. Battery is fully charged and has proper volts and starting amp. Alternator has not been checked and might need to be bench tested if can't get the vehicle to stay running. Craps out in about a minute. The fuel pressure is correct at the rail when key is turned on but, the theft system is intementantly not communicating with the key properly. I.E. it goes into theft mode ( theft light flashes rapidly for 15 mins.). I believe I have a relay, fusible link or wiring issue. It could also be the transponder antenna or ECU. I have checked the engine compartment and passenger compartment fuse boxes thoroughly (opened up both checked for bad connections or bad fuses) I will be bench testing all the applicable relays here in a minute. Next will be the steering column for a wiring issue on the antenna. Then I'll squeeze my 6'4" 300lb ass under the dash and take a look at the ecu. Any other ideas?

 

[1955moose]

How bout the key itself? Do you have a second chip key to try? They do act up and go bad sometimes. The fact that your PATS light is going wonky, says it's shutting down.

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[Matthew T]

I have a second key but its not programed to the truck. The system is not communicating well enough to program it as a pare at this point.

 

[1955moose]

Ok, on my 2000 theirs a 30 amp transceiver fuse on inside cabin fuse box. Check yours owners book. Mine is #30 fuse. Be sure you've got power, and ground, and try another 30 amp fuse. I'm sure the others have more info, electricals not my strong suit.

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