Truck won't run

[doubter123]

Well I've tried Ford-Truck Enthusiasts forum and they were no help so far so I thought I might try you guys. First of all my truck is a 1990 F150 with the 4.9 liter straight six, it has EFI and up to this point never had anything major wrong with it. What happens is when I go to start it I hear the fuel pumps kick on, and then it will fire once and then die and if I can get it to keep running it runs like s***. I have cleaned the throttle body, changed the Idle Air Control valve, checked the ecm for burn marks and now I can't come up with any reason why it won't run. So any responses that can help me fix my truck are greatly appreciated.

 

[ML-TOYS]

If it pops you may have jumped the timing out of wack

 

[doubter123]

The timing is fine the issue seems to be in the fuel pump secondary circuit (whatever that is) between the PCM and ground that's what I got from running the codes anyway

 

[devino246]

I was thinking the same thing as ML-TOYS. Sounds a lot like your timing chain jumped a tooth. Have you checked to make sure that the engine is at TDC when the rotor is pointing at #1?

What were the exact codes you got?

 

[Doc Sprocket]

I'm on board with that, too. You say the timing is fine... Valve timing? Ignition timing? Did you actually check it, or are you assuming it?

 

[doubter123]

Well the timing is fine because when we get it to run it runs fine and the chain couldn't have skipped a tooth since it is timing gears. We think we found the problem to be the ignition switch since when you hold it in the start position it will stay running but in run position it will die.

 

[Doc Sprocket]

if I can get it to keep running it runs like s***.

Well the timing is fine because when we get it to run it runs fine

Umm... Okay.

I doubt it's the ignition switch. Sounds to me like poor/weak/faulty ignition/ignition timing.

 

[devino246]

Umm... Okay.

I, too, am confused by his incoherently statement.

Well the timing is fine because when we get it to run it runs fine and the chain couldn't have skipped a tooth since it is timing gears. We think we found the problem to be the ignition switch since when you hold it in the start position it will stay running but in run position it will die.

I'm unfamiliar with the 90's Fords, but (generally) older vehicles use two separate ignition circuits: one that runs full battery cranking voltage (which is below the standard 12 volts) to the ignition system, and one that runs battery voltage through a ballast resistor to the ignition system. If the running ignition power circuit is broken (i.e. broken wire, bad ballast resistor, bad ignition switch), the engine will run while the starter is engaged, but cut off when the key is turned back to RUN.

You need a wiring diagram and a DMM and/or a test light. You'll want to verify that your ignition module is receiving power during cranking, as well as when the key is in the RUN position. You can throw parts at it, but you may end up needlessly wasting time and moneyl

 

[B man]

I thought you said when it'll run it runs bad?

 

[doubter123]

It only ran bad once the other three times we got it to run it ran fine sorry for confusing you guys. Well I am taking my ACT today and then have two graduations to go to so can't really work on it much today but I think it is what devino said so we will test the ignition power while cranking and at run position.

Also sorry for some unclear wording I am not really good at explaining things through the internet so thanks for helping me even though I can be quite confusing.

 

[doubter123]

Well fixed the problem finally, it was the ignition module. It was quite hard to find this out because everyone else with bad icm's didn't have issues like I had but I'm not complaining I'm just happy that it's fixed