1985 Ford F150 5.0 EFI

On dry days (no rain or dampness) when the key is in the on position, but not in the start position, the fuel pump works as it's supposed to. You can hear it turn on and shut off within a second or two and the truck starts right up.

Conversely, on damp and/or rainy days, when the key is turned to the on position but not in the start position, the external pump turns on but runs and will sometimes take 2 to 3 minutes until it stops running. Again, the truck starts fine but only if I wait until the fuel pump stops running before I turn the key to the start position. If I don't wait until the pump stops running and try to start it, it starts up but acts like it's being starved for fuel and runs really rough for about 1 minute. After one minute or so, it seems as though it's getting enough fuel and it runs perfectly fine.

It seems to me the fuel is running back down the line and is taking a very long time to replenish. Once the pump stops running, the truck starts without any problem. Again, this only happens on damp/rainy days. I've proven that is the case over a year's time. On dry days it works as it should. On damp/rainy days, every single damp/rainy day, it doesn't work as it should. It has me scratching my head because it only happens on damp/rainy days.

My thinking is I should install a check valve somewhere to keep the fuel from running back into the tank, possibly close to where the line begins at the tank.

Any ideas on what the issue may be are welcome! Thanks!!

 

The pump system is on a timer, it doesn't have any type of pressure sensing that tells the computer anything.

I would suspect when the engine runs rough it's flooded. Check valve problems usually cause a crank crank crank condition before it will fire because it's filling up the dry fuel lines.

The pressure is regulated by the regulator on the fuel rail. Check and make sure the vacuum line going to it is ok and doesn't have fuel in it.

But the first thing I would look at for your rainy day problem is the fuel pump relay. Pull it out of it's socket and look for corrosion and socket pins that are not making good contact. If that looks ok change the relay out. You can look around and see if any of the other relays are the same and swap them.

 

I will second going down the relay path and beginning there.

 

OK - I had a spare laying around so I've already replaced it. Of course, it worked just fine, but I need it to rain again tonight (it's supposed to pour), and I'll try it first thing in the morning and let you both know.

Thanks Franklin2 and ctubis!

 

I put in a new relay yesterday. Had the same problem this morning.

Again, it seems that once there's enough fuel the pump shuts off and she will start and run perfectly. I checked the fuel regulator vacuum line and can smell fuel. I would have thought that was normal. Are you suggesting that if I can smell fuel in the vacuum line that I should replace the fuel regulator?

Thanks again for your help!

 

I would not think you should smell any fuel with the line removed. Me if it was with the truck from day 1 and was not much $ I would just replace it.


As for the relay or more the socket what shape was it in? I would pull out each (1 at a time) wire/connection to make sure they are clean and tight. You will need a tool to get them out of the socket.
That is the only way I know of to make sure it is good to use.
Dave ----

 

Yes. I will order from Rock Auto today and replace the regulator.

With regard to the relay, the female connectors are good.

Thanks!!

 

I will second Dave with the "you shouldn't be able to detect any fuel at the pressure regulator" thing... if fuel is leaking from the fuel plumbing into the vacuum plumbing, that's a problem.

But the electric pump staying on for more than a second or so is a different problem, that thing is controlled by a timer run by the computer... relays are mechanical devices that sometimes stick and that's the first path I go down... but if that's not the problem, more diagnosis is necessary....

 

Yup! I hear you. I'll change out the fuel regulator and go from there.

My ECM seems ok. No burn residue anywhere on it. No nasty smell from something burnt. No melted components anywhere.

Once the pump stops running it starts and runs perfectly. If I go to start it and the pump is still running, it's hard to start and once it is started it sounds like it's running on just a fuel cylinders, chugs, and pours out a lot of white exhaust and you can hear it sucking air into the intakes. That last until the engine is at operating temperature. Once there, the air-sucking sound stops and she runs fine.

But if I wait to start it until the pump stops running, it runs like a dream.

This has been an issue for the last year.

 

Well, I would fix what is known to be wrong - one thing at a time - and go from there.

There is some other guy out here who also couldn't find any obvious signs of computer failure (leaking capacitors, whatever) but was having weirdness apparently related to heat... he went full-steam-forward into it, he's tracking individual signals at the chip level with an oscilloscope (makes me realize I need to donate my 1970s-era Heathkit thing to the recyclers as it'll never be useful again):

https://www.ford-trucks.com/forums/1...sometimes.html

Point being, even though it's not leaking anywhere, it could still be intermittently failing....

 

Wow! That's some serious diagnostics. It'll suck if I have to replace the ECM. Ugh!

I replace the fuel regulator since I am smelling fuel in the vacuum lune that connects to it.

I rule out some other things too before I replace the ECM.

Looks like RockAuto is going to get some more business from me. Any suggestions where to get a GOOD ECM other than Rock Auto?

 

You mean to a museum ... I haven't heard of Heathkit for over 30 years probably closer to 40!
Built one of their stereo component systems many many moons ago!

-Enjoy
fh : )_~

 

Following;
The job of the pressure regulator is to send the excess pressure back to the fuel tank. When these fail, or stick, you have overpressure on the rails. This will lead to possible flooding of fuel at idle. The regulator does have a lifecycle, and does not last forever.

I'm not saying that's the only problem, for these trucks were usually not maintained concerning lifecycle of all these new early 80's components.

You mention sorcery conditions on rainy days, these trucks were built to operate in wet conditions, but years of tinkering, have defeated some of the protection from wet conditions. I would check all electrical connections related to your fuel delivery systems to ensure continuity, and a good connection. Most of these connections from the factory were filled with dielectric grease. While cleaning them with electrical contact cleaner is a good idea while troubleshooting, they should be re-greased for longer term operation after the troubleshooting brings you to a resolution.

Just because you "hear" the fuel pump running, does not mean it is running properly. Two fuel pumps in these trucks right? Low pressure in the Tank/s, and High pressure upstream from the tanks. Fuel tanks switching on the two tank models. Reservoir/Filter upstream from the high pressure pump. Filter rarely get changed.

Other factors cause the Computer/ECA to add or subtract fuel delivery to the intake.

 

Used, Junk Yard ECA's; Car-Part.com--Used Auto Parts Market
Part Search; Select Part = "Engine Computer"
Search by year.
You will need to know the E5TF-12A650-XXX, id off your current ECA.

 

Yeah... I'm reminded here that 1985.5 - 86 has a filter someplace in that sytem near the fuel tanks and that toilet tank think, Bill Vose reminded us of it a year or so ago when somebody else was having troubles in this area.