It's almost like I'm losing pressure in the fuel injection system somewhere. If I let the rig sit a while and turn the key to "on", the fuel pump runs for several minutes and then shuts off, as if it's building up pressure in the system. The engine then starts and runs fine. If the engine has been running a while, and I shut it off, and then immediately re-start it, the fuel pump runs just a couple seconds and shuts off. And then it starts and runs fine.

Crazy huh???????

 

Tom, one thing to check start the engine let it run for a little while then shut it off, and let it sit about an hour then without turning on the key check the fuel preasure (or install a gauge run it then shut it off and watch the gauge it will probably fall off a little but shouldn't drop to zero in an hour if it does you probably have an injector that is going bad)
Also as 53 said yes the relay could be causing some of this this would be a good canidate for the replace with known good component, if you can find someone with a vehicle of the same year and engine trade it out, and see if it cures your problem if so buy a new one and replace yours like I posted earlier this is actually a part of fords diagnostic proceedures in thier manuals.

 

Hi again,

I've got a new fuel pump relay installed, and the fuel pump is still acting like it was before. Haven't had a chance to try a new/borrowed ignition relay yet. I wanted to start cheap, and work my way from there.

But I'll recheck the fuel pressure as you suggest to see if I have an injector going bad.

Thanks again for the suggestions----I am persistant and I will fix this thing!!!!!

Tom

 

Tom,
I dont know if your rig is diesel or not, (I forgot) But, in my gas engine on my 1990 bronco with fuel injection, when I turn the ignition to "on", the fuel pump turns on for a few SECONDS, not minutes, but then it also shuts off. It is like it is building up pressure, then turns off. HOWEVER, when I do that, I can do it again within seconds, and the fuel pump again turns back on for a few seconds. I think the way they work(and I may be wrong...if I am, let me know someone) is that they turn off not because of a preset presure, but because there is no ignition on. They turn on, then if the vehicle doesnt start, they turn off....However, if the vehicle starts, they stay on. You said the fuel pressure is around 40 PSI(?) or so. This sounds normal or around normal and should not cause the problems you are experiencing. I am thinking it may still be that ignition relay, making your fuel pump shut off at odd times and restart at odd times. I wouldnt be surprised if it is the culprit even if the reaqson isnt "sticking contacts". Even I'm getting frustrated with this thing, and I'm not even getting my knuckles busted and dirt under my nails. Keep up the tenacity, and you'll get it.

 

Thank you all for your inputs. Here's an update:

I put in a new fuel filter today, but that yielded no change in my symptoms. Fuel pump still ran for several minutes with key "on".

No mention of a "fuel pressure sensor" in any of my Ford books. Only a "fuel pressure regulator" that I replaced about 5K miles ago. It checked out OK now though.

My son is a mechanic at Ford, but he's a young guy---and says that he has not worked on an older rig like mine (ouch). He's gonna ask the "older guys" in the shop if they have any ideas.

Anyway, I hooked up a fuel pressure gauge again last night, left it hooked to the fuel rail overnight, and here's what I got:

Fuel pressure with key "off", after rig sitting idle overnight: about 5 PSI, maybe a bit less.

Key to "on": gauge moved slowly from 5 PSI up to about 30 PSI, but fuel pump continued running.

Fuel pump eventually stopped running after about 11 minutes at a little over 30 PSI. The engine then started and ran fine.

About thirty-forty minutes later, pressure had dropped to about 20 PSI.

About five hours later pressure had dropped to about 5 PSI. It has held steady at about 5 PSI.

(One very strange thing happened this afternoon while I was doing fuel pressure tests. On one occasion, after the fuel pump had stopped running after pressure reached about 30 PSI, it started running again! With nothing at all being touched!)

Tom

 

Tom,
I think the probalem may actually be the pump, and not the regulator. It should jump to max pressure almost immediatly after the pump turns on. It shouldnt take any more than two seconds at all under any circumstances. Another thought is that there could be some kind of blockage somewhere in the line. Did you say you had already replaced the fuel filter recently? Have you checked your fuel to see if there may be water in the lines yet? Just some more ideas. You've probably already gone through them, but hey, at least now I'm TRYING to be helpful.

 

one other thing there is probably 2 pumps on that rig one in the tank and one on the frame they both need to be working it is something to check out because that is taking way to long to reach full preasure. my guess would be that the lift pump in the tank isn't operating at all and the high preasure pump on the frame is having to do all the work. Just another possibility.

 

Hi 53wa2fl,

I replaced the fuel filter about 1K miles ago, and I put a new one on this morning. The fuel pump pressure definitely does not "jump" to maximum pressure when I turn the key to "on". It gradually works its way from about 5 PSI to about 30 PSI when I turn the key to "on". I don't think I have a problem with water in the lines, because my generator, which uses the same gas tank, but has its own fuel pump, starts and runs perfectly. Maybe my fuel pump has indeed crapped out?


Hi monsterbaby,

I have gone over every inch of fuel line, all the way from the fuel tank, the fuel filter, the fuel pressure regulator, up to the FI rail on the engine. (Not a fun job crawling about 30 feet from the back of the motorhome to the front.) I can easily hear the in-tank electric fuel pump running inside the tank at the rear of the motorhome, however I have not seen an external fuel pump anywhere on the frame rails. This is a motorhome, and they do WIERD things on motorhome chassis! So if my in-tank electric fuel pump is going bad, then it looks like I better budget for a new one. I guess if it's gotta go it's better doing it here under controlled conditions, and not in the middle of nowhere!


To all who have given inputs: Thanks again for ALL the suggestions!

 

I dont know about the R.V fuel pumps as I havent ever owned one, but....on my bronco, there is only one pump. It is in the tank, and man....what a bugger to put in and get out. Try to run the rig to just about empty.....or else! I'm thinking your pump may have indeed started going bad. However, I would run a pressure test closer to the tank if at all possible. Maybe we're getting lucky and closing in on this problem?!

 

yeah we had to replace the in tank fule pump on a 94 f150 it had a full tank so i took the bed off it was actually less work the bed it pretty light. but an a motorhome you gotta crawl under it. yuk if it was lifted up you could stand under it.

 

Fimding a lift large enough for a motorhome is darn near impossible. I had to crawl under my bronco to do mine also...uggh what a pain. The good news is that once it's done, it's DONE and it (hopefully) works just fine. Actually, once you get the tank off the rig, it is actually a pretty straightforward job. Putting the tank back up is a bear...but hey, it can't all be easy cheesy.

 

My fuel pump just barely gives me 30 PSI, with the engine on, or with the engine off and the fuel pump running.

I was finally able to contact the original owner of our rig and learned that I still have the OEM fuel pump---the one that has the extremely high failure rate. So I bought a new fuel pump and wire harness adaptor from a Ford dealer near here.

There's a guy who works on RVs near here and he said he's changed out several of these fuel pumps. So it looks like he and I will be getting under the rig to change out the fuel pump. I guess that at 58K miles, the OEM fuel pump was already running
on borrowed time, and was destined to fail at any time.

Thanks for all your help troubleshooting this problem, and I'll let you know the results of changing out the fuel pump.

 

glad to hear you got that information, hope it cures your problem, and please let us know for sure so if someone else comes up with this problem we can pass it along.

 

I would interested to know if that cures your problem also...Good Luck Tom.

 

map sensor might be bad,it will also cause it to run rich