Hi, new to this forum.
I have a '91 f150 dual tank 5.0
This past week it started running rough, and has gotten worse. Also when running it dumps fuel from the front tank underneath the truck, I'm pretty sure that the relay is out so I'll have to drain that. This morning I replaced all the plugs and wires hoping to fix the rough idle, but amazingly, it got worse. It won't even idle now unless I give it some gas.

Anyone know what might be causing the idle issue? The fuel leaks seems like a separate issue but could they be related? Any ideas are appreciated thanks.

 

I double checked the wires, replaced the rubber grommet on the gas tank which was rotted out. The truck will stay idling now, but still shakes and randomly surges. Not sure if some kind of sensor is out or what.

 

When you say shakes do you mean not running on all the cyls ?
How does it run when you raise the RPM ?
How many miles are on the speedometer?
Did you gap the plugs before installing them?
When replacing the plugs did you pull all the wires off where two of them could have been switched?
Is it possible one of the plugs got cracked when tightening?

 

It's a pretty rough shake at idle, calms down a little when I give it gas but still shakes/vibrates. I did gap the plugs when I installed them, I did 1 wire at a time and even double checked those plus the sequence afterwards.
It started shaking slightly about a week ago, got slightly worse everyday which is why I switched the plugs/wires out.
It has 187k miles

 

Have you checked the dist cap for cracks/moisture and condition of the rotor? It would be helpful if you could determine which cyl is misfiring. Whatever you do don't consider removing plug wires with the engine running to locate the miss because that leaves high voltage with no place to go and it can wipe out the ign module. You can use an old spark plug with each plug wire connected to it and have the plug lying on the engine so the spark can get to some metal to complete the circuit. You would get a double misfire until you hit the one cyl that has a problem at which point you would get no change.

 

I'll try that this morning Hanky, thank you. I'm sure the dist cap is the original.
I'll let you know how it turns out.

 

Well said hanky !!

 

It turned out to be my harmonic balancer, it was off. Replaced it and she runs smooth now.
But after a few days it started another issue.
Sometimes when I start it, it kicks over than immediately dies. Then it'll start right up. When I go to put it in gear it dies. If I give it gas it still dies.
I have replaced the ERG valve, the IAC, I will put it on jacks and test the torque converter today.
Is there any other things it may be? If it's not the TC than I am stumped. I am ready to strap some dynamite to it and be done lol

 

It might be a good idea to check all the electrical connections you moved . Sometimes a poor connection will prevent full voltage or ground being available and once running the alternator can compensate for that, the problem goes away until the next restart. A good part of the time after a repair is done, things like this happen and it is usually something simple that was either overlooked or disturbed and the problem now shows itself.