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Hitting fuel tank switches?

Tiny
F2507.5L
  • MEMBER
  • 1991 FORD F-250
  • 7.5L
  • V8
  • 4WD
  • AUTOMATIC
  • 180,000 MILES
My truck cuts out if I press the gas pedal more than 1/3 throttle and it stalls when I'm sitting at a stop for too long. If I hit my dual tank selector switch to from the tank, then back to rear all problems go away for a minute or two then I must repeat. I have replaced the switch all other engine sensors except the thermostat or crank sensor.
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Friday, September 30th, 2022 AT 6:10 PM

9 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
Hi,

When it stalls, is it easy to restart the engine? Since switching the tanks allows it to run properly, it could be fuel related.

Do me a favor. Check to see if there are diagnostics codes stored in the computer.

Here is a link that explains how to retrieve them:

https://www.2carpros.com/articles/ford-lincoln-mercury-obd1-1995-and-earlier-diagnostic-trouble-code-definition-and-retrieval

Let me know what you find.

Take care,

Joe
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Friday, September 30th, 2022 AT 11:01 PM
Tiny
F2507.5L
  • MEMBER
  • 5 POSTS
My truck has had an EGR deleted and a (twisted smog module) from 460 EFI guys to mimic all the sensors that were deleted. So no codes it is fuel related for sure the idle is high and rough it also has a timing gears installed 3 years ago and I assume it should still be correct. I drained the gas tank, and it had water in it, but I cleaned that all out still not running right. It starts very easily every time.
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Saturday, October 1st, 2022 AT 6:49 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
Hi,

I agree the timing should be fine. If it is fuel related, do you ever notice any dark smoke (gray or black) from the exhaust? Also, have you checked fuel pressure?

I'm trying to think of things that could cause it to work when you switch tanks. I'm wondering if when switching, the supply of fuel is briefly reduced. It's a theory.

Let me know.

Joe
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Saturday, October 1st, 2022 AT 2:18 PM
Tiny
F2507.5L
  • MEMBER
  • 5 POSTS
Yes, black smoke when it revs up it smokes a lot if I unplug the map sensor and it smelled like gas pretty bad until I changed the o2 sensor I checked the TPS voltage it sits at.96 at idle while running if I unplug my IAC nothing changes and my front tank has a bad fuel pump 17psi pressure rear has 43psi and 50psi if I unplug the vacuum line from the fpr. I have heard something about the harmonic balancer slipping and throwing off timing. I put a new dizzy in it about 8 months ago, new wires last week and plugs, I checked the EEC 4 and one cap looked a tiny bit swollen on top but no black on the connections is there a way to run an external fuel tank to test if it's a clog in the fuel lines?
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Saturday, October 1st, 2022 AT 4:09 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
Hi,

I don't think it's clogged. When you checked the fuel pressure regulator vacuum hose, did you check to see if there was a vacuum to it with the engine running? Also, was there any evidence of fuel in the vacuum hose?

Interestingly, the pressure you indicated is high. Actually, 43 is on the high end with the engine off, but 50 is too high regardless of if the engine is running or not when checked. That would explain the black smoke. It's getting too much fuel. See pic 1 below.

Let me know if you checked the regulator.

Take care,

Joe

See pic below.
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Saturday, October 1st, 2022 AT 8:42 PM
Tiny
F2507.5L
  • MEMBER
  • 5 POSTS
Yes, I checked it koeo40 PSI and 50 if it's hot under the hood running pressure is 38PSI, but it falls off after a short priceless than 20 until I flip the switch and it goes back up. I replaced switch still doing same thing maybe it's the valve.
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Thursday, October 6th, 2022 AT 2:11 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
Hi,

That is about the only thing left. I know years ago; the OEM valve was recalled because it would overfill the opposite tank. I attached the recall below just so you have it as a reference.

Let me know your thoughts.

Joe
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Friday, October 7th, 2022 AT 6:56 PM
Tiny
F2507.5L
  • MEMBER
  • 5 POSTS
I haven't done anything to it but drive it the last couple days and it's seemingly getting better, I can drive without hitting switch. I'm looking for that valve but I can't find it where might I look or do you have a picture?
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Tuesday, October 11th, 2022 AT 5:52 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,192 POSTS
Hi,

I can't seem to find a pic in my manual. However, they are normally on the inside of the frame rail after the fuel filter and before the engine compartment. If you follow the fuel lines from the tanks toward the engine compartment, you should find it.

I found a pic online and attached it below.

Let me know.

Joe

See pic.
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Tuesday, October 11th, 2022 AT 7:01 PM

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