Hey everyone,

New to the forum here, found it by searching around, thought maybe I'd run a question by all of you to see if you could help me out.

I have a 1988 Ford F-250 Lariat, 7.5L 460, four-wheel drive. I have two fuel tanks on it, and I've been having a really annoying, obnoxious problem with it lately. After running it for a while, I noticed that I keep losing fuel pressure, and the truck stalls. When I try to start it, it does nothing but roll over. It just won't start. I've changed the fuel filter, I know both fuel pumps are working (I turn over the key, I can hear front, back, and high pressure pump attached to the left side frame rail kick in.) It's Fuel Injected, not EFI, hence that third pump. The problem happens alot, and it's random. I could drive for 100 miles, stop to get something to eat, come out, and it won't start.

I thought maybe it was the fuel pressure regulator, but I don't think that's the case because it still runs. I would assume that if the regulator was bad, it wouldn't run at all. I also thought that maybe it was the relay, but according to some mechanics I spoke too, if I can hear the pumps kick in when I turn the key over, then the relay is fine. The only thing I could think of is that it might be the fuel selector switch. Maybe it's going bad, shorting out or something. When I flip the switch though, it switches between fuel tanks, and the gauge reads how much fuel is in it from the sending unit.

There's a schrader-type valve up by the fuel injectors. When I push it in, it barely squirts any fuel out, if at all, so I know the pressure is low. When I push it in on a good day, it sprays out like a water fountain.

I have no idea what it could be, and all of these local garages around here can't do anything with it unless it's screwed up for them, and every time I take it to a garage, they can't get it to screw up. It's one of those dang problems...

Anyone have any ideas?

Quick Edit: Just tried starting it again - no good. Pushed on the valve, it spurted out some fuel pretty well, but still won't start. Occasionally tries to, but ultimately won't. I know the spark is good, checked the plugs/distributer cap. Can't get the sucker to start.

 

Hmm, I don't understand it. If the fuel filter is clean, the pumps work, and the truck has spark, why won't it start? It acts like it's starving for fuel, but yet it has fuel in the truck, and there appears to be fuel in the injectors when I push on the valve.

The last time the truck stalled, I popped the fuel filter off to see if it was clean, and it was. When I put the filter back on, it started right up. Maybe it's some sort of vaccum or venting problem? I tried flipping the fuel selector switch back and forth to both tanks, the sending units functioned properly, I turned over the key and heard the pumps kick in, I tried to start it - nothing. I checked to see if the high pressure pump was working - it is. Any ideas?

Edit: Could the 02 sensor be bad? Would that affect it? Maybe the fuel throttle body? Can the diaphram in the regulator improperly function on and off?

 

You need to check the pressure with a gauge when having the issue. If the check ball in the regulator isn't working, it will take a bit to build up pressure enough to start again because it will drain all of the fuel from the rails and all back into the tank.
The 88 is EFI. It has 8 injectors, does it not?
It could also be the fuel selector valve on the frame not swtiching properly and starving the high pressure pump of enough fuel.

You also need to get a noid light to see if the injectors are getting a signal from the ECM to open and close. It could be a bad EEC relay, a failing TFI module or maybe a failing ECM or even a bad chassis ground. The EEC grounds at the battery with usually a plug in the wiring before the ground cable terminal.

 

Hey, thanks for the reply.

I'll go pick up a fuel pressure testing gauge to check the fuel pressure first. What PSI range should the pressure be? Also, I found the fuel pressure regulator, so if need be, I'll replace that, too. I don't want to go and replace anything I don't have to.

It does have 8 injectors. Someone told me it wasn't EFI, which had me confused. But I'm more inclined to take YOUR word over it because you have mentioned some things to me I had not heard of, such as the TFI module. I looked around about that and some people said it would be their first guess, but check everything else, too. I found the TFI module below the distributor cap, so I'll try to test it.

I also did some looking around about an E.F.I Test Probe, which measures the pulses of the solenoids inside the fuel injectors (without having to even remove them) to test them and see if they are getting the signal from the ECM to work. I don't think the ECM itself is failing, because if that was, wouldn't it introduce a whole bunch of problems to the truck, and not just fuel injection issues? However, it seems in most cases the engine needs to be running for it to test the injectors, but I can't get my truck to start. It just cranks over and over, and all three tanks prime when I turn the key over.. I'll look into testing the EEC relay as well, and even the fuel pump relay. Found those mounted right next to the air breather by the fire wall. Also, I found the plug for the chassis ground. You were right, it's nothing more than a small plug that connects to the negative terminal on the battery.

I just need the equipment to test it, and I can start.

EDIT: I recently went out and pushed a small pin down on the schraeder valve on the fuel injector rail. -NO- fuel squirted out at all. This is a real conundrum and it's driving me insane. I'm wondering if maybe the regulator itself is bad, or the fuel tank selector valve. It may not be electrical at all, but what are your thoughts?

 

The engine does not have to be running for the noid light to flash. Just unplug an injector and plug the noid light into the plug. You can rent a noid light for free (you get your money back when you return it to say O'Reilly's) at most auto part stores.

Sounds like you may have a check valve problem with fuel drain back. Could be in the FPR or the High Pressure pump on the frame. When it does not start turn on and off the key about five times and then try to start it. If it stars then you have a drain back problem.

To check the fuel pressure with it not running ground pin #6 or short it to pin #2 of the self-test plug on the drivers fender. Hook up the fuel pressure gauge to the fuel rail and turn on the key. You should get about 40 to 45 PSI pressure. Tun the key off and see how fast the fuel pressure drops. It should drop about 5 PSI at first and then slowly drop to about 30 PSI and then to Zero if left overnight.
If the engine starts the idle fuel pressure should be about 32-34 PSI.





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Thanks, Subford. I tried turning the key on and off several times to charge the fuel lines with the pumps, then I tried to start the truck and it didn't work. I'm assuming by FPR you mean Fuel Pressure Regulator? If so, maybe it is the check valve with fuel drain back. I'm pretty sure the high pressure pump along the frame rail is working. I turned the key over and someone told me they could see, hear, and feel the pump vibrate and turn on when I turned over the key. I'll get a noid light and fuel pressure testing gauge as soon as I can to check out the pressure and injectors to make sure they work as well.

 

Yes FPR is the Fuel Pressure Regulator.
You also need to check if you are getting fuel to the high pressure pump. If the selected pump in the tank runs OK you may have a problem with the fuel tank selector valve not letting fuel get to the high pressure pump.

 

I see. I had heard from several individuals that the fuel tank selector valve was a common issue in vehicles of that particular year and model. I'm still trying to get my hands on the pressure tester and a noid light to test things out, just to make sure there are no other problems. As of right now, there is no fuel in the fuel rail at all it seems, because when I push down on the fuel pressure release schraeder valve, no fuel comes out at all.

 

You need to get fuel squirting out of the schraeder valve before worrying about a pressure gauge and a noid light.

noid light:


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Cool, now I know what I am looking for as far as a noid light goes. So, I guess I'll have to see what's going on with the regulator, fuel tank selector valve, and/or high pressure pump before worrying about all of that, then. I'll check them out, starting with the selector valve first. Is there anyway to see if the valve is bad? Is there anyway to test to make sure the diaphragm in the regulator isn't junk?

 

First I would unplug the high pressure pump and pull the hose coming from the selector valve off the high pressure pump and stick it in a bucket.
Select a tank on the dash and then ground pin #6 or short it to pin #2 of the self-test plug on the drivers fender. Have someone turn on the key while you watch the hose in the bucket. It should shoot fuel into the bucket at about 7-12 PSI pressure.
If that tank works OK have the other tank selected and do it again.
If both tanks work OK with the selector valve then turn off the key and put the hose back on the HP pump.
Take the return hose from the FPR off the selector valve (the one that is not going to the HP pump) and aim it in a bucket. Turn on the key again and if fuel shoots out and you have no pressure at the fuel rail replace the FPR, if not replace the HP pump.

If you did not get any fuel out of the Selector valve above from either tank take the supply hose from the selected tank to the valve at the valve off and point it in a bucket, turn on the key again and if you get a good flow and about 7-12 PSI from the hose replace the valve, if not then its drop the tank time.

 

Thanks again.

I went to set to work on the recommendations you gave me, but I noticed that as my friend turned the key when I crawled under the truck, the high pressure pump wasn't working. I was certain it did, so I checked to see why. I noticed as I pushed on the wires connecting to the leads of the pump, it would turn on. I pulled the pump off and used a razor to gently slice the rubbing coating around the positive lead. Sure enough, the positive lead was not actually connected to the terminal of the pump. I crimped it back on, put the rubber coating around it and secured it with electrical tape, then put the pump back into the sleeve and onto the frame. There is now pressure in the fuel rail, and the fuel rail squirts out fuel in a steady stream. My high pressure pump wasn't even connected. I've no idea how it came disconnected, but now it works.

Now the next issue that is occuring, when I push the pedal to the floor on the truck as I drive, the whole truck will sputter and shake. The check engine light then flashes on and off. When I suddenly surge fuel with the accelerator, this happens. I think my selector valve is fine if this is the case, but I picked one up anyway. The selector valve on my truck has six ports. The reservoir is round and there are no electrical leads. The only one Autozone carries for the 1988 f250 FI with a 460 has electrical leads.

I also picked up a regulator, but it seems I won't need that either.

However, why might my truck be shuddering and sputtering like that when I give it a sudden push to the accelerator? Why does the check engine light flash? Any ideas?

Also... A problem so simple as a disconnected high pressure pump caused this much of an issue. I'm sorry for the runaround.

 

Any time the check engine light will flash (MIL in a Ford) it will set a code in CM.
You need to read your codes to find out what code is in CM.
If you do not know how to read the codes go to the link below:
Ford Fuel Injection » How To Run a Self-Test

You could have a bad TPS or lean fuel mix.

 

Hey again,

So, after some time I finally got to working on the truck again. The fuel pressure seems to be good, the truck runs, no stalling issues. However, I'm still having the problem where at times, it's a little rough to start, and when it runs and I depress the gas pedal on the truck, it stumbles, sputters, and the truck shakes a bit. I ran a self test by wiring the STI plug to the negative battery terminal and counted the check engine light flashing sequences as shown in the last post in the thread. It seems the KOEO code gave me an 11, which apparently means system pass. The CM code gave me a 35 (PFE or EVP circuit has intermittently failed above the maximum limit of 4.81 volts) and a 95 (Fuel pump secondary circuit failure. The EEC senses infinite resistance to ground from the fuel pump on the Fuel Pump Monitor circuit.).

It took me a little while to get the hang of counting the flashes, but after several tries, recounts, and double checks, this is what I came up with.

What do those CM codes mean? Could they be the reason why I, at times, get a check engine light flash here and there when I drive? How can I fix this issue with my truck stumbling and sputtering. Any help would be appreciated.

 

Sounds like your EGR valve is stuck open.