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1987 - 1996 F150 & Larger F-Series Trucks 1987 - 1996 Ford F-150, F-250, F-350 and larger pickups - including the 1997 heavy-duty F250/F350+ trucks

I'm stumped

 
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Old 04-17-2019, 04:04 PM
pbeamtn
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I'm stumped

I'm about out of ideas on my '90 F250 5.8L. It keeps dying on me while driving, but idles fine. I have had it sputter and die, but it starts right back up and keeps going. This weekend, it sputtered and died, and I tried to nurse it home, but it came to a point where it would no longer run. After it sat for a bit, it started up and idles fine, but I was afraid to drive it very far. In its recent past, I have replaced the fuel tanks and pumps, fuel pressure regulator, ignition module, and MAP sensor. The engine was rebuilt about 2 years ago, and I have had some sporadic problems, but this one has me stumped. I once again replaced the fuel pressure regulator and fuel filter, did a small test drive (about 3 miles) and it died on me twice. I could start it up and keep going. With the new regulator, I initially measured 34 psi, but now I measure 25. It only goes to 35 with the vacuum pulled. I don't understand how I could lose 10 psi with a 15 minute drive. I'm not entirely trusting my Harbor Freight gauge, but it is suspicious. What am I missing?
 
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Old 04-17-2019, 04:10 PM
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pull the codes from the computer,see if it shows anything. Even if there is no CEL on, it may have stored codes.
 
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Old 04-18-2019, 07:42 AM
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Is the pressure the same for both tanks ?
 
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Old 04-18-2019, 08:12 AM
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Good suggestions! When you get frustrated, it becomes harder to think clearly. I will shortly go and check whether any codes were stored. My rear tank is nearly empty so I when I did switch the engine would barely run.

I am getting suspicious of my tank selector valve. My truck is a late 89 or early 90, and I think they changed the valve in 90. I need to look underneath and see what I have as I have seen some YouTube videos on cleaning that valve. I may even bypass it to eliminate a variable. I feel like I have been chasing this gremlin for a while and the fuel tanks may not have been the root cause -- well, one was leaking so it had to be changed. It seems like when I touch the fuel system things are better for a while, and then the problem comes back. I will now focus on the things that are still 30 years old.
 
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Old 04-18-2019, 08:19 AM
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You have replaced the fuel filter as well, right?
 
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Old 04-18-2019, 08:33 AM
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Yes. I could not remember if I replaced it before or after the fuel tanks and pumps, so I got a new one and replaced it before putting on the new regulator.
 
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Old 04-18-2019, 08:36 AM
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Originally Posted by pbeamtn View Post
. My rear tank is nearly empty so I when I did switch the engine would barely run.
I am getting suspicious of my tank selector valve. My truck is a late 89 or early 90, and I think they changed the valve in 90.
I suggest you put 4 gals of high-test in the rear tank & add a bottle of ISO HEET Gas-line antifreeze to soak up the water that separated from the Ethanol in your tank. This way you can compare the pressure from each pump.

1990 MY was the first year with High Pressure pumps in the tanks and no High Pressure Pump on the fuel rail. Also they did away with the switching valve this year in the gasoline models, so yeah, check to see what you have..
 
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Old 04-18-2019, 08:55 AM
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I would almost bet it is water. I do have the "newer" dual tank system that does not have the big reservoir on the frame. I also don't have any fault codes other than my disconnected air system being inoperative. I will get some fresh fuel in the other tank and some additive before I do anything else.
 
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Old 04-18-2019, 09:14 AM
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Originally Posted by pbeamtn View Post
I would almost bet it is water. I will get some fresh fuel in the other tank and some additive before I do anything else.
Try to find the ISO HEET product, it's basically Isopropanol and soaks up water very well. Dump it in the tank first, then add 3-4 gal 93 octane fuel.
The Octane level of fuel degrades as well over time, so depending how long it's been, the octane level in the tank now could be well below 89.
Same for the Ethanol Phase Separation, the longer it sits without being refreshed, the more the separation.
Other snake oils like SeaFoam do little soaking up of water.
 
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Old 04-18-2019, 09:43 AM
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I found this article ( https://cropwatch.unl.edu/ethanol-an...oval-additives) that indicated HEET was 1 of only 2 products tested that actually absorbs water. It may take me till tomorrow to get that plus some fresh gas in the tank.
 
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Old 04-18-2019, 09:10 PM
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Originally Posted by pbeamtn View Post
good link.
see attached, looks like the same crowd;
EDIT; lol, ok, same as the link in your link.....
 
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Old 04-19-2019, 02:53 PM
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Update: Getting the rear tank usable was a little more work. I was not using it because after I changed it I noticed a leak from the top of the tank and I just didn't feel like messing with it at the time. (I just use this truck locally, so two tanks is really not needed.) Last night I removed the rear tank and found that I had not properly put the metal seal ring in place -- one of the tabs was not engaged, so the sealing gasket did not have even pressure. I put in some Heat and some fresh 93 octane fuel in each tank and went for a drive. For a couple of miles everything was fine, but then it died on me. I switched to the rear tank and everything was fine. I switched to the front and drove a bit farther. It started bucking on me so I switched to the rear tank and it ran fine. I definitely have some problem with my front tank, which I would not expect for a new tank and new pump that I installed in November.
 
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Old 04-19-2019, 04:44 PM
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See post # 3.
 
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Old 04-19-2019, 04:58 PM
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I measured once and they were both the same -- ~ 32 psi. I think the front one cuts out or acts up occasionally. I'm having trouble catching it when I can see something. Today, I could only get it to act up when driving, and it died at 15 mph when it was really not under load. A fuel pressure gauge in the cab would be handy, but I'm not sure I want to run a fuel line inside.
 
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Old 04-19-2019, 06:26 PM
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Originally Posted by pbeamtn View Post
I measured once and they were both the same -- ~ 32 psi.
They are rarely the same, so I'm wondering if you have a restriction somewhere, or a Gauge issue?

When reporting Pressures, post both tanks, with and without vacuum applied to the Fuel Pressure Regulator for a complete picture.

Did you receive the correct parts when you replaced the pumps?
 

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