memoniz

One last thing, I would also look at your tank switch. Been through several of those also. If your switch is original, you may just want to get a new one. I'm a believer in preemptive strikes when it comes to electrical.

Shagg

You don't ever want to assume that a part is good just because it is new. And different parts can fail in different ways. The PIP sensor is used to give the fuel injectors their pulse to fire, But if you were able to start it with brake cleaner, then you had spark, which means an ignition issue is unlikely. Checking fuel pressure is a good idea, and you can visually inspect the circuit board on the ECU to check for leaky capacitors, which can cause all sorts of weird problems. if it happens again, try swapping the fuel pump relay out with something less vital, like the horn relay, and see if that relieves the issue. But other than that, you might just have to start digging in with a multimeter. Make sure everything is getting the voltage it needs, verify that all of the grounds are good, and make sure that everything is sending and/or receiving the proper signals.

300cubicinches

Thanks 👍 I recognize that I'm going to have to just dig in there and see what's going on. I'm thankful for a little bit of direction. I know I tested the rear pump fuel pressure in the past but I just can't remember what the results were. I thought this issue was behind me. I'm going to take this truck on some long trips soon so it's getting solved this weekend.

Air conditioner is blowing Ice cold after adding some freon. I was prepared to evacuate the system and replace parts, but it's holding it so I'm gonna leave it be. I'm ready for the road!

300cubicinches

I've been hesitant to drive far since the last time it shut down, but I chanced it and drove to work and back (50 miles) with no issues. I make it back home and decide to cruise town with my friend when out of nowhere the truck began to stall out. I managed to get through an intersection and to a safe parking spot, by putting it in gear and not giving any throttle. It would absolutely have died completely in the road had I given it any gas. Once I pulled over it was a beat the clock game of hooking up the fuel pressure gauge and getting second degree burns. The truck eventually stalled out after 20-30 seconds of rough idling.

Fuel pressure on the front tank was only around 15 PSI with a single turn of the key. I could build the pressure up a bit by rapidly cycling the key, enough to get it to start again but soon would die out. The rear pump had a better prime than the front but it was still not sufficient to do anything more than idle - same as normal really. Came back an hour and a half later and it still wouldn't pull a hill so I had to park it for the night and walk home. I also did change out the fuel pump and horn relays but it made no difference.

This morning I returned to pick up the truck. It cranked up and idled and drove normal. However, I am only getting ~35 PSI on the front pump and it didn't have more than 20 psi prime. A few months ago when I installed the new fuel pumps, I had at least 45 PSI.

Shagg

Well it sucks you got stranded again, but it's good to know that the problem has been narrowed down to a fuel supply issue. Now we get to find out if it is more of an electrical, or mechanical issue. Ideally, you want to see close to 60 psi of fuel pressure, and that number should rise when the fuel pressure regulator is unplugged. You'll also want to make sure both pumps have 12v and a good ground.

ThePugSmuggler

I'm not a mechanic, but speaking from my recent experience with my 92 f150 5.0, check your Injection Pressure Regulator and then your fuel filter again; both are cheap, and easy to do

Pull your dipstick, if you smell a slight fuel smell in your oil your pressure regulator could be torn.( there are no codes if that happens for my 5.0). They also use a vacuum line, this line is attached to the top and is usually a hard plastic tubing with rubber ends that over time becomes fragile, make sure it isn't broken or leaking.

Next would be the fuel filter, I know you said you replaced it, but if you attempted to use old fuel or dirty fuel (for example switching over to the second pump that hasn't been used for years) it could just be a clogged filter. You say the tanks were clean but what about the lines? did you inspect them, replace them or flush them?

I found out today the fuel filter was never changed on mine; 30 years old, 145k miles. The fuel coming out of the old filter on the tank side was dark brown, I actually drained the tank line a bit more because the filter was so clogged the sediment backed into the line a little. I didn't want this going into the new filter.

In my case I had crap acceleration, and the occasional feeling like the engine was being starved of gas. As I replaced my MAP, Airtemp sensor, idle control valve, vapor canister, purge valve etc it seemed to be more and more noticeable. I finished changing both fuel delivery parts on mine today and you would not believe the different it has made.

If you finished checking your fuel system and it is all working correctly, maybe move on to the air side of what is needed for combustion, check hoses, MAP sensor, idle control valve, air temp sensor and air intake filter/hoses.

Best of luck mate! Half the fun of owning these old trucks is fixing them. ;D
Let us know when you figure out what is going on!

300cubicinches

I agree with you, I enjoy working on this truck for the most part.

The fuel pressure regulator does not appear to be an easy check on this vehicle. Its hiding under the intake manifold plenum like everything on this vehicle. It looks like a Bosch brand and has some corrosion on it - original perhaps?

I did a fuel pressure test after work yesterday with the engine cold

Front pump: KOEO - Pump primes but only builds up to 25-30 PSI unless I cycle the key a few times. It won't pressurize beyond ~53 PSI. Upon starting, pressure dropped down to the mid 40s and stayed in that range during idle and when applying throttle.

Rear pump: KOEO - Seems to prime a little faster/better, quickly builds up to 35/40 PSI and will start, but the pressure quickly falls off and it will die even at idle.

Didn't have the opportunity to run a voltage drop test for the fuel pump relay but I will hopefully get to that this weekend.

I also discovered a badly frayed ground wire that is mounted to the drivers side fender just above the ICM. I'm going to fix that this evening.

ThePugSmuggler

Hmmm so it works fine on the front pump? Then it most likely is not the pressure regulator. Mine is located on the top, backside of the 5.0.
This is where my pressure regulator is at.



Did you check your Reservoir Tank Selector Valve? Only thing I can think of that would allow your front tank to flow fine but not the rear tank. That is where the system switches between tanks into a single fuel line to the fuel filter.

And don't forget that you are priming the line when you test the front tank. If you switch to the rear tank after that the system is still primed. Trip your inertia switch, run the truck till it dies. then reset the inertia switch, then test the pressure on the second tank priming the lines and then running it. If it builds slowly when you prime it then the issue could be from the Reservoir Tank Selector Valve to the rear tank or the electrical components.

Once again, I'm not a mechanic, but just some ideas if you haven't thought of them. As for the ground, it aint pretty but that shouldn't be your issue. However, when I got my truck, half of the electrical did not work. I checked everything even fuses and it all looked fine. Decided to just replace every single fuse with new ones and sure enough everything worked perfectly. After when I looked at the old fuses they were not visually popped but when I tested them they were bad. Something to consider there as well. I also snag a few relays from my local pick-n-pull while I'm there. Doesn't hurt to have some spares.

300cubicinches

I appreciate the reply.

I posted this thread because the front pump has started to intermittently fail and I rely upon that one to get around. I don't really care if the rear pump works or not, but I figured it might be useful information in determining what is going on with the front fuel pump.

The fuel pressure on the front pump is falling off when the truck has been driven for awhile. Perhaps it is only now presenting itself because the weather is getting warmer. Rear pump is problematic 100% of the time.

I couldn't tell where the broken ground wire goes without tearing apart the loom, but it is very close to the power distribution box and PCM so I figured it might be important.

ThePugSmuggler

Oh! Well in that case I'd lean back towards the pressure regulator. If it is not working properly your fuel rail wont have the correct pressure for your injectors. Then fuel filter again, and fuses/relay. You could try swapping a relay out just to see. Other then that I'm at a loss :/

There are a few things you can do to test the regulator, pull the oil dipstick, if it smells like gas it could mean the diaphragm is torn. Check the vacuum line on it as well to make sure it isn't compromised. Another test is to find the valve on the fuel rail, while the engine is off lay a rag over the valve and press a small hex key into it to release the fuel pressure from the fuel rail. If only a tiny bit comes out with little to no pressure, replace the regulator. It was a bitch to do on the 5.0 too, had to lay over the engine and unscrew 3 small screws from the bottom of the regulator which is toward the back of the block. 100% had to be done by feel, and had to watch videos and look at pictures to get familiar with it.

Best of luck man! If you figure it out let me know!