--1986 F-150 302 5.0 liter V-8 Fuel Injected
--If have the TFI-IV Ignition System with the ICM mounted on distributor.
--One fuel tank with in tank low pressure fuel pump and external high pressure pump.

When the truck sits (heat soaks) after driving it, it tends to stall and die on me soon after restarting, especially in this 90+ degree summer heat. I’ve been working on this problem coming on two months now.

I posted on this same problem before, but I figured starting a new thread would eliminate confusion.

Computer Codes:
Engine off
11- system pass
Continuous codes
11- system pass
Engine Running
41- Oxygen Sensor- System indicates lean.
25- Knock Sensor- No response or little change during test

Anyway, here’s what I did to it so far, but the problem continues:
Changed coolant temperature sensor. The computer code said it was out of whack so I change it and no code for it since.
Changed TFI module (ICM) with a good Motorcraft one
Changed ignition coil/stator with a good Motorcraft one
Changed high pressure fuel pump because it consistantly made noise (buzzing/humming) after the engine had time to heat soak.
I moved the TFI module (ICM) off the distributor to a cooler spot. But since I was having trouble after all of this above, I remounted it back on the distributor hoping that would solve my problem, but NO, it did not.
I have yet to change the Oxygen sensor since I was getting this code (41) before I had this problem, plus it’s only 2 years old, but I haven’t ruled it out.

So the last thing I did today was change the fuel filter (canister type). I have a question about this. When I was changing it I noticed the bottom of the fuel filter canister was warm, but the fuel itself was cool. It just seemed odd. Also, as mentioned above, the external fuel pump hums and buzzes when the truck has time to heat soak. I decided to hot wire (jump it) the external fuel pump so it would run continuously and crawl under the truck to see what was happening. Ok, so the external pump and fuel line between the filter and pump was vibrating and making a humming buzzing noise and I noticed the fuel filter canister was warm mostly on the bottom. What would cause this? Could it be because the in tank fuel pump is not pumping or not pumping good enough? And could this be the source of my truck stalling and dying once it has time to heat soak?

Also after installing the new fuel filter I primed the fuel pump several times before trying to start it. It didn’t want to start. I primed it several more times. Started up and then died. I primed it some more, it started but it was running rough. In my experience changing this truck's fuel filter, I never had to prime it so much before it would restart.

So I guess I’m asking, is the in tank fuel pump responsible for my engine stalling and dying after it heat soaks? How can I tell for sure?

 

I did a flow test on the in tank fuel pump. The pump wasn't pumping. I will check for power to the pump tomorrow. If it's getting power and it's not pumping, it means I need to replace the pump, according to my Haynes manual.

If and when I order the in tank fuel pump, I'll likely get the entire sending unit, how do I know if I have a 17 gal tank or 19 gal tank? I have a 133 inch wheel base and a single midship gas tank, but I ain't 100% sure which sending unit to buy. I bought one before and the fuel gauge reads wrong. I'm not sure if I bought the wrong one before or if the float arm got bent putting it in. Any help is appreciated.

 

I thought only the shortbed pickups had the 16 or 17 gallon tanks. I thought all the long bed pickups had the 19 gallon tank.

 

I GOT THIS ONE! I just had similar issues with my 86' 302 EFI. My problem was not heat soak, it was a fuel delivery issue, BUT I had the same noise coming from my high pressure pump. If your truck used to have dual tanks and the selector valve is still on the frame rail make sure it is COMPLETELY bypassed. I was having trouble with mine sending fuel to the rear tank. A quick and reliable fix to bypass the valve is to go to autozone help section, there should be a package of two steel fuel lines. one 3/8" and one 5/16" both are 12" long and have the beads on both ends. These will slide right into the factory fuel lines and use the original plastic clips to hold them in place. The supply line from the tank is 3/8" while the return line is 5/16". Simply remove those lines from the selector valve and slide these steel lines into the hose end fittings.

If the selector valve is bypassed and you still have this issue, replace your fuel pressure regulator mounted on the fuel rail.

I also removed my rear fuel tank and its fuel lines. Thanks to Gary Lewis for letting me use his lift!

Once I did both of these mods my fuel pump stopped making that annoying humming sound and the truck ran SOOOO much better. My truck would hesitate and buck under 1/2 to fuel throttle or so. Now that its getting the proper fuel, it runs great. I also replaced the in tank pump for good measure. If you do that, make sure that things is mostly empty. Its awkward doing this on the driveway! Good luck

 

Thanks, Ray, but I don't think that is my problem. There's no evidence that this truck had more than one fuel tank.

And thanks to you, Franklin. Based on some gas tank measurements online at RockAuto's website, I confirmed that my tank is a 19 gallon one.

 

Well, if your external fuel pump is making that humming noise it is either trying too hard to suck gas or pushing too hard. Once I replaced my fuel pressure regulator it ran great and the pump noise was gone. Bypassing the selector valve was just yet another one of my problems...good luck. I highly recommend that fuel pressure regulator though...

 

As I mentioned earlier, yesterday I did a flow test on the in tank pump, but the pump DID NOT pump any fuel nor did I hear it running. (I should mentioned that the external pump is consistently getting power and running.)

Ok, so this morning I checked for power going to the in tank pump. It was getting voltage (11 volts, as it should) and the pump DID pump fuel. I was hoping for power to the pump and no pumping, because that would have meant a bad pump, then all I would have to do is buy and install one and problem solved, but no.

I let the truck run for a while and turned it off and let it sit. I checked voltage again. I was still getting power (11 volts), but this time the pump DID NOT pump.

Does this mean the pump is going bad or what? As long as the pump is getting power, doesn't that mean the problem is with the pump and not some problem in the circuit?

I want to be sure before spending money on a new pump. Thanks again.

 

Well, I guess I'm buying a new in tank pump. I tested the pump again. It was getting power but it wasn't pumping. Hopefully, this will correct my stalling and dying problem. Perhaps it wasn't related to heat at all. We will see. I will post an update once I install the new pump.

 

You know, I had some weird things happen with my in tank pump as well. I had my wife turn the key to run while I had my ear on the tank, I heard nothing, same as with the engine running. I then thought "well that pump must be bad". So I replaced it. Well, after doing that and before I put the tank back up into place I turned the key to run and listened for it to at least prime...nothing. BUT when I started the motor I could hear it running inside the tank. So, you might have to have the engine running before that in tank pump will actually continuosly run. I dunno.

If your in tank pump don't fix your problem, move to the fuel pressure regulator on the fuel rail....I think $20 or so at Oriellys

 

In my Haynes manual it has instructions on how to hotwire the fuel pumps to get them to run continuously. Basically, you attach one end of a jumper wire (I used a testing light thingy with a long cord that has an alligator clip on one end of it.) to connect to fuel pump lead on the DLC connector (the computer code connector) and the other end is attached to a good ground source (I attached the alligator clip to the A/C compressor). Then you turn the key to the ON position and listen for the pumps. You can also check for voltage to the pumps at this point. I was getting voltage (power) to both pumps but only the in tank one wasn't pumping. I did a flow test on the in tank pump, where you pull off the supply fuel line just before the fuel reservoir and check the rate of flow. Like I said it didn't flow because the pump wasn't working, but was getting power. So, according to my Haynes manual, that means the pump is bad and the solution is to get a new pump. My concern is I know I can cause the engine to die if I get it hot and allow it to heat soak (let it sit for about 15 minutes after shutting it off). I'm just wondering if heat soaking it exacerbates the fuel problem, somehow affecting the flow of fuel even more or if I'm having two problems at once. Basically what I'm saying is, I still believe heat is playing a role in my truck dying on me, but I'm hoping that is it all related to this fuel pump and not something else.

 

I bet it will run like a champ once you get that new pump in. Im curious, does your reservoir have 6 ports? If so, then you had dual tanks at one time. Oh wait, is yours a short or long bed? I don't have a clue if the short beds had a dual tank option or not, but if its long then you may have had duals if you have a 6 port selector vavle/reservoir thingy.

 

No, it doesn't have 6 ports, just 4 ports. At first you had me a little curious about whether or not the truck had two tanks at one time, but I had this truck since 2000 and the previous two owners kept good records, and they had no mention of removing any gas tank. Anyway, I sure appreciate your help and positive vibe.

 

If you have power going to the pump and it is not working, why do you have a problem installing a new one? Its obvious that that could be at least one issue. I also had really strange fuel delivery issues, but all my pumps were working. My fuel cutoff relay would go crazy when my truck would stall, not start or run really rough. Turns out it was computer on the fritz. Installed a refurb and have not one issue for a year now. Not saying this is your problem but if the pump isnt your only issue than maybe look into your computer.