Hi all,

1992, F150, 5.0L, Auto, Dual gas tanks

When I turn the key to the on position the fuel pump runs and runs and runs. I can hear a noise from under the hood (pressure return noise?) a second or two after the pumps engage. If continuing to turn the key I can start the engine, but it runs rough and will not idle without giving it gas. Strong smell of gasoline is present.

I have tried both tanks and both tanks do the same thing.

I cannot pull codes when it is doing this because the fuel pump doesn't stop running in test mode.

Now, for the odd part. It is not consistent. The past three days the same thing has happened. However, after a bit of trying, the truck started normally and operated normally. Making several starts, stops, and driving a few miles on a 50 mile roundtrip, with store stops in between. I pulled codes last night, when it was operating properly and no error codes were present, only 111.

My thought process is that it is some control module/sensor on the engine, but not sure where to look.

Any and all help is appreciated.

Thanks,
Rick

 

Your computer(EEC) is acting up, pull it out and get the box code off the side of the connector so you can source a replacement.

 

My first thought would be a bad relay- the pumps should only run long enough to prime the fuel lines with the key in the ON position. If they continue to run it sounds like either a relay or wiring problem. The fact that it's not consistent sounds even more like a relay. It's been my experience that when sensors start going bad, it always happens until you replace it.

I would make that your first check and if that doesn't solve the problem, call around to your local parts stores- some of them will hook up a scanner for free.

 

Just tinkering around, pulled the MAP vacuum line and the truck started and ran, albeit rough at idle. Don't know if that has anything to do with anything, but the dang thing will run on its own. To me, that eliminates a fuel supply problem at least with the pumps.


Thanks,
Rick

 

I could be wrong but I believe the reason it ran is because you created a vacuum leak- when you pulled the line the engine started sucking more air and as it did so it had to pull more fuel to compensate for the extra air intake. Did the idle rev a little when you pulled the line? If so, that's what happened.

 

During the day, did try and run the truck. Fuel pump never stopped running in the run position...when starting ran rough and smell of gasoline was present. Did notice a couple of times where it sounded like the system was performing a koeo self test while doing this.

Anyway, wife stopped off on way home to get a fuel pump relay, but it was the wrong style. So, I switched out the horn relay and fuel pump relay (same part nums)...no change. Fuel pump continues to run and run and run. When I left the fuel pump relay empty, fuel pump did not run with the key in the on position.

Did notice a few additional tidbits.

Kept trying to run a koeo test...after many times of putting the key into the run position I finally hear the fuel pump stop after 1-2 secs. In the numerous times of putting the key to on, I did notice changes in the sound of the front pump, rear pump never changed. So, the koeo test begins...several times the fuel pump started running and the test just stopped right there CE light stayed on. So, I'd start the cycle again. Sometimes it began running in the early phases of the test, other times later on. Finally got it to stay off...the only codes pulled were 33 and 512 (I did take EEC relay out).

End of the night...I go out and give it one last miracle try...engine starts and runs as it should. Ran for a bit and then just stalled. I did switch between the two tanks, back and forth, looking for one to stall it. Anyway, started it back up...and it ran fine. Cycled the gas pedal...let it idle...back and forth, changing tanks, etc. It idled and ran fine for 5 minutes or so.

So, unless the horn relay and fuel pump aren't different relays...relay isn't the problem. But, what boggles my mind is how it runs perfect once the fuel pump cuts off in the on position and after I start the engine. It also boggles my mind how the fuel pump comes on in the koeo test, but yet I pull no codes for it...

Wracking my brain here on limited funds...As always any help is appreciated.

Thanks,
Rick

 

PCM.
PCM runs the tests. PCM turns the fuel pumps on or off via the fuel pump relay.
If the fuel pumps stay on when you fiorst turn it on you have a stuck relay of a bad pcm.
You've eliminated the relay.

Ever have a flakey PC? Runs fine 1 day then does nothing but crash all the time the next? Same situation here. The PCM is just a computer running special software and when its running 'normal' your fuel pumps shut off like its supposed to.

You can try cleaning the PCM connector and see if that helps. I've seen where that gets some corrosion which causes problems.

 

I have to ask, when you say "run position" do you mean the "on position"? Just want to make sure we're talking about the same thing.

Anyway, might want to check your ignition switch. Seems to me that continuous cycling on and off with the key and then finally getting it to act right is the switch, or it's a wiring issue.

And like I said, call some of your local parts stores- some of them will hook up a scanner for free.

 

Hi all,

Replace the computer and it solved that problem...onto new ones now. Argh!

Thanks for all the input.

Rick