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Discussion Starter · #1 · (Edited)
Hi all, if this isn't the right place for this, please move it. I just made an account because I'm at my wit's end with an issue I've been chasing for a while. I bought this truck a little over a year ago, 95 F250 regular cab long box 2wd with the 7.5L 460. 22X,XXX miles on the odo.

It had sat for a few years but compression test looked ok (between 155 and 140 all around). EGR and emissions were all removed. Started and ran strong, CEL, ABS, and P Brake lights all on. It had a front main seal leak and an exhaust leak where the manifold met the block. Midships tank worked great, rear tank caused it to run poorly. I jumped the test block and read the codes:

31- EGR Position below voltage
67- Neutral safety
82- Supercharge bypass
85- Canister purge
84- EGR vac fail

I brought it home, pulled the engine, had the crank polished, new main bearings, new main seal, oil pan gasket, timing kit, water pump rebuild, plugs, wires, and a clutch. All motorcraft/performance parts. I put a helicoil in the block and a new copper exhaust manifold gasket from JEGS which shut up the leak. When we started it up it had a tick from cylinder 5, ended up scoping the cylinder, finding a piece of debris fell in on the piston, taking the driver's side head off and luckily no damage to any valves so put back on with a new head gasket after having it inspected. I also took the opportunity to put a new cam and lifters in. Ran like a champ after that.

Drove it all 2020 no problems. Occasionally I'd run out of gas in the mid-ship tank so I'd switch to the rear tank and limp it to the gas station, it ran just like this on the rear tank. I ran all the old gas out of it, filled it with new gas, dry gas, etc. no change on the rear tank, so I only use it for emergencies.

This spring it slowly developed a misfire/stumble on the primary (mid-ship) tank, and within a day or two it couldn't make it out of the valley where I live so I changed the fuel filter, it was full of rusty debris. No improvement so we dropped the midships tank and put a new fuel pump in it, midships tank was pristine inside. No improvement so we swapped in a new regulator, no improvement. During this time it stopped starting so I had it towed to the local garage. They replaced ignition module, and found a broken roll pin in the distributor, replaced with a remanufactured distributor, went back to running like crap. They drove it and set timing back to exact OEM spec as it was a little advanced, during driving it "popped and went back to running strong" so they gave it back to me. It was running strong again with a very mild hiccup/stumble/hesitation under throttle.

Shortly after that it went back downhill, I dropped the Y pipe, no change. I put a new coil, new MSD low resistance wires, new distributor cap, and new Motorcraft plugs. I wiggled harnesses, looked for vacuum leaks, sprayed ether all over engine bay while running, got nothing. I listened to all the injectors with my stethoscope, disconnected fuel lines from rail to filter and blew them out with shop air and a catch can backwards, found nothing. Checked fuel pressure and I've got 40psi, had battery and alternator tested, all looked good. Put a new MAP sensor after I found a very encouraging YouTube video, no change.

I finally caved and took it to the dealer, listed what I had done above and asked for further engine management diag. Invoice reads as follows:

"Checked and found fuel pressure in spec but when disconnection the regulator there is no change. Hooked up OTC injector tester and found all injectors buzz, found varying fuel pressure drop when cycling each injector. Removed IAC and found engine will also run better but not as it should. Advised on possible IAC issue along with injector issue. Also advised on checking cam timing and drive chain for proper installation."

I removed the fuel rail and cleaned it, looked pristine inside, nothing came out. Energized all 8 injectors with 8v and sprayed carb cleaner through both ways, shop air through both ways, new o-rings and tips (rebuild kits) for all of them. Put it back together, no change. Removed IAC and it idles high but runs strong, put a new IAC and went back to running poorly.

Please help! I'm all out of money and time.

I'm waiting on a video upload then I'll link it here.
 

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I had a similar behavior about 2 years ago, mine was from a bad ground on a relay for the fuel system. Switch tanks and it ran fine, for about 6 months.

While stuck on the side of the highway, it wouldnt pull the hill and refused to stay running, I was going through the harness connectors when it started to behave (moved the right bundle enough). Managed to get to a station and finally traced it to the ground, cleaned it up, still works fine.

Never threw any codes or lights, every weekend for those 6 months I was looking for reasons why the rear tank would not give fuel, everything checked out properly everytime.
 

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Discussion Starter · #3 · (Edited)
That sounds promising, I had considered it may have had more grounds than just the one heavy one that I found when I took the engine out. I had considered adding one to the firewall, but obviously there could be bad areas in the harness too. Any chance you could snap a pic of the area you had trouble with? I'd really appreciate it! Are we talking near the rear by the fuel pumps or in the engine bay?

I have to limp the truck around right now to get to work but I hate every minute of it. It requires ether to start once it's hot most of the time. It engine brakes smoothly downhill but as soon as you try to give it throttle again it starts in with the stumbling.

Here's a video:
 

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Wouldn't hurt to put another ground from the intake manifold to the firewall and one to batt negative, like @causticuc said it could be a ground, and since it happens when the engine gets hot it could be caused by losing ground due to heat expansion? With all the electronics on the engine grounds are really critical.. Won't hurt and it's worth a try..
 

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Discussion Starter · #5 ·
Wouldn't hurt to put another ground from the intake manifold to the firewall and one to batt negative, like @causticuc said it could be a ground, and since it happens when the engine gets hot it could be caused by losing ground due to heat expansion? With all the electronics on the engine grounds are really critical.. Won't hurt and it's worth a try..
Sure, my current ground goes from between the alternator/block on that bolt, to the battery negative with a #4 stranded copper wire. I suppose the manifold sits on a fat layer of sealant and gasket, couldn't hurt to add one up there. Dealer diag. says the entire electronic system for fuel injection is working properly, but pressure drops when firing individual injectors are different. I pulled the injectors, opened them with ~8v from a power supply, blew carb cleaner and shop air through both ways, and put new o-rings/tips on them, however they are finely tuned pieces of equipment and they may be packed up with gunk inside. I have a completely new set on the way.
 

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not sure if you have done this or not, but i had an issue similar to this with my '96. it ended up that in the fuel pumps if one is messed up then it runs like **** on that tank, if they are both messed up, it will cause this exact problem you are referring to. it ended up being a one way valve in each of the fuel pumps. the mid tank would work sometimes in mine, but if it ran below a half tank of gas, it would start losing power and eventually it just wouldnt run. i think you should replace both fuel pumps and check the wires on them especially the ground.
 

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"popped and went back to running strong"
Any luck on this issue? Have you looked into the tank selector valve? I am working on a truck with similar symptoms... VERY similar symptoms. That might as well be a video I shot. Last night I took apart the tank selector valve for cleaning and testing. There is a diaphragm that "pops" up and down on a detent system, actuated by pressure from whichever in tank low pressure pump turns on. So fuel pushes the diaphragm, from one of two tanks in one of two directions and it moves valves for feed and return between the two tanks, and the detent locks it in one of two positions... except when it doesn't. In my case I found disintegrated o rings, tons of crud, sticky valves and more.

Here is the thing... after cleaning everything seemed to be working fine but when tested wasn't. Blowing air at 5-6 lbs through one inlet only opened the valve half way... into the other would not move it at all. It's supposed to only need 5-6 lbs of pressure to switch... mine needed much, much more. So a low pressure in tank pump might not switch the valves completely...

What happens when it is half way between both tanks? VERY high resistance to flow. Random leaking into the feed line from other tank. Returning to wrong tanks return line or both return lines. All kinds of fuel supply problems.

Also it's worth noting that even when mine WAS locked in for primary tank the same symptoms persisted. AUX tank position worked great if I locked it that direction manually. Oh and fuel pressure readings appeared normal at the fuel rail this whole time. So basically I manually popped and locked mine into place for the tank I plan to use until I get this replaced.

Hope that helps. At least gives you something else to investigate. Now while I wait for the RTV to dry I might go ground my intake manifold just in case. Good luck!
 

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A 95 truck with a 460 with the original PCM would have 3 digit codes, not 2 digit ones. 2 digit codes ended in 92 or possibly 93, and those earlier PCMs would normally have had the gray ICM and a diode for the E4OD solenoid block moved between the solenoid block and the PCM, as well as a slightly less sophisticated sontrol system.
 
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