1991 F150 - Loses power after engine warms up
06-21-2016, 09:18 PM
#1
Member
Thread Starter
1991 F150 - Loses power after engine warms up
1991 F150 - Inline 6, Dual tanks...
Last week - I finally rolled over 100,000 miles in my (formerly) dependable F150 flatbed.
Last year - I replaced both front and rear fuel tanks and pumps (there are only 2 pumps on my truck - not a 3rd pump under the hood as far as I can tell)
Last week - When at speed (i.e.55-65mph) - and after the engine is warm - I started getting an intermittent happening of the engine cutting out... No power at all... At first - I could wait and slow down, and the engine would regain power. Now - not so much - until it cools off.
At first I thought it could be the ignition coil - so I checked it, and had a LOT of corrosion on the high-voltage connector - so easy fix - replaced the coil - but it didn't fix the problem.
Today - I got to the job-site just fine (about an hour drive from home) .. but on the way home this evening - the engine shut down again - this time on a major Dallas freeway. Luckily I was able to coast and exit the freeway with no traffic.
The CEL came on, and it wouldn't start. popped the hood, made sure the battery connections were good - and on a whim - switched to the rear tank. It fired up! (ran rough, but it fired up - I usually don't use the rear tank because the 1 year old pump is not putting out enough PSI of fuel to run well - I just have not replaced it yet).
So that tells me that the problem may very well be related to the front fuel pump, front fuel pump wiring (switch in dash), or the fuel pump relay... or possibly as a last resort, the ECM computer...
Any other ideas for me to trace down?
On a the F150 with dual tanks - is there 1 fuel pump relay? Or are there 2 relays? I'll (Hanes and Chilton manuals don't say).
This only seems to happen when it is HOT. Engine up to temp... The tank is not out of gas - but it sure acts that way...
As a strange thing - I also had to change the headlight switch last week, as my dash lights fuse blew... replacing the fuse didnt fix that - so I changed the switch - and all is working now with the dash lights.
Anything else to track down?
Rex S.
Last week - I finally rolled over 100,000 miles in my (formerly) dependable F150 flatbed.
Last year - I replaced both front and rear fuel tanks and pumps (there are only 2 pumps on my truck - not a 3rd pump under the hood as far as I can tell)
Last week - When at speed (i.e.55-65mph) - and after the engine is warm - I started getting an intermittent happening of the engine cutting out... No power at all... At first - I could wait and slow down, and the engine would regain power. Now - not so much - until it cools off.
At first I thought it could be the ignition coil - so I checked it, and had a LOT of corrosion on the high-voltage connector - so easy fix - replaced the coil - but it didn't fix the problem.
Today - I got to the job-site just fine (about an hour drive from home) .. but on the way home this evening - the engine shut down again - this time on a major Dallas freeway. Luckily I was able to coast and exit the freeway with no traffic.
The CEL came on, and it wouldn't start. popped the hood, made sure the battery connections were good - and on a whim - switched to the rear tank. It fired up! (ran rough, but it fired up - I usually don't use the rear tank because the 1 year old pump is not putting out enough PSI of fuel to run well - I just have not replaced it yet).
So that tells me that the problem may very well be related to the front fuel pump, front fuel pump wiring (switch in dash), or the fuel pump relay... or possibly as a last resort, the ECM computer...
Any other ideas for me to trace down?
On a the F150 with dual tanks - is there 1 fuel pump relay? Or are there 2 relays? I'll (Hanes and Chilton manuals don't say).
This only seems to happen when it is HOT. Engine up to temp... The tank is not out of gas - but it sure acts that way...
As a strange thing - I also had to change the headlight switch last week, as my dash lights fuse blew... replacing the fuse didnt fix that - so I changed the switch - and all is working now with the dash lights.
Anything else to track down?
Rex S.
06-25-2016, 08:26 PM
#2
Generally there is only one relay.
If you had a 3rd fuel pump it would be located on the driver's side frame rail, near abouts the back of the door.
2 things to consider is 1- if the CEL came on there is a code to read, which will help with diagnosis, and 2 - if you suspect fuel pump pressure, a fuel pressure gauge would be a wise investment.
I know they have loan-a-tool programs at some parts stores but personal opinion; by the time you pay the gas and waste the time to get it and then take it back you're halfway to paying for one that can sit in your toolbox in case it acts up again. I've also found that it's useful on my wife's car, my friend's jeep, my son's ranger and lots of other vehicles too.
If you had a 3rd fuel pump it would be located on the driver's side frame rail, near abouts the back of the door.
2 things to consider is 1- if the CEL came on there is a code to read, which will help with diagnosis, and 2 - if you suspect fuel pump pressure, a fuel pressure gauge would be a wise investment.
I know they have loan-a-tool programs at some parts stores but personal opinion; by the time you pay the gas and waste the time to get it and then take it back you're halfway to paying for one that can sit in your toolbox in case it acts up again. I've also found that it's useful on my wife's car, my friend's jeep, my son's ranger and lots of other vehicles too.
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Rex Smith (06-30-2016)
06-30-2016, 10:11 PM
#3
Member
Thread Starter
As time and power shutdowns continue to occur - I cannot help but wonder if the 1-year old fuel pump, or a wiring connector, or maybe the selector switch could be overheating at some point, and opening the circuit for my front tank.
Any experience with new fuel pumps shutting down intermittently - but seemingly in the heat of the day in a hot place like Texas?
There is no way that I can think of to check voltage at the pump when it happens. as it's when I'm driving - and usually on a busy highway. (unless I wire in a meter as close to the pump as possible and run the leads up to the cab?) That may isolate whether the voltage is lost before the pump... or within the pump.
Both tanks supply lines run to a y-connector, which then goes to the fuel filter, then direct to the fuel rail/pressure regulator. The return lines also go to a y-connector near the tanks, then straight to each tanks' fuel return. So -according to the Haynes manual - there *is no* mechanical fuel selector valve to check - or to be bad. Each in-tank has it's own return.
When the pump shuts down - I can switch to the rear pump, and continue on (but it's a rough ride, as the rear pump is only putting out about 27psi - and I believe the regulator needs more in the 60-80psi to regulate down to running pressure of about 45-60psi.
(and yes - I already have a replacement pump for my rear tank... Just need to install it....)
Thoughts? Continue diagnosing? Or simply go ahead and replace the selector switch AND the front pump that is intermittent as well?
Any experience with new fuel pumps shutting down intermittently - but seemingly in the heat of the day in a hot place like Texas?
There is no way that I can think of to check voltage at the pump when it happens. as it's when I'm driving - and usually on a busy highway. (unless I wire in a meter as close to the pump as possible and run the leads up to the cab?) That may isolate whether the voltage is lost before the pump... or within the pump.
Both tanks supply lines run to a y-connector, which then goes to the fuel filter, then direct to the fuel rail/pressure regulator. The return lines also go to a y-connector near the tanks, then straight to each tanks' fuel return. So -according to the Haynes manual - there *is no* mechanical fuel selector valve to check - or to be bad. Each in-tank has it's own return.
When the pump shuts down - I can switch to the rear pump, and continue on (but it's a rough ride, as the rear pump is only putting out about 27psi - and I believe the regulator needs more in the 60-80psi to regulate down to running pressure of about 45-60psi.
(and yes - I already have a replacement pump for my rear tank... Just need to install it....)
Thoughts? Continue diagnosing? Or simply go ahead and replace the selector switch AND the front pump that is intermittent as well?
06-30-2016, 10:23 PM
#4
Member
Thread Starter
Thank Chris
Yes - CEL Has come on a few times. And today it came on when I was on teh rear (known low psi) tank. I would bet it would be giving me a lean-condition code with a low psi. Thoughts? Autozone cannot read a truck so old - so I need to research how to get the codes to display. (jumper something & count CEL engine flashes?)
I had tested my trucks' pressure last year. And front tank was at the low-end of good PSI (when running in the parking lot at AutoZone - rear tank was bouncing around 27psi) Currently - unknown. Can do it again - but honestly - the truck shuts down - my gut instinct is that the front tank's pump is simply not getting the voltage it needs - or is shutting down internally.
Yes - CEL Has come on a few times. And today it came on when I was on teh rear (known low psi) tank. I would bet it would be giving me a lean-condition code with a low psi. Thoughts? Autozone cannot read a truck so old - so I need to research how to get the codes to display. (jumper something & count CEL engine flashes?)
I had tested my trucks' pressure last year. And front tank was at the low-end of good PSI (when running in the parking lot at AutoZone - rear tank was bouncing around 27psi) Currently - unknown. Can do it again - but honestly - the truck shuts down - my gut instinct is that the front tank's pump is simply not getting the voltage it needs - or is shutting down internally.
Generally there is only one relay.
If you had a 3rd fuel pump it would be located on the driver's side frame rail, near abouts the back of the door.
2 things to consider is 1- if the CEL came on there is a code to read, which will help with diagnosis, and 2 - if you suspect fuel pump pressure, a fuel pressure gauge would be a wise investment.
I know they have loan-a-tool programs at some parts stores but personal opinion; by the time you pay the gas and waste the time to get it and then take it back you're halfway to paying for one that can sit in your toolbox in case it acts up again. I've also found that it's useful on my wife's car, my friend's jeep, my son's ranger and lots of other vehicles too.
If you had a 3rd fuel pump it would be located on the driver's side frame rail, near abouts the back of the door.
2 things to consider is 1- if the CEL came on there is a code to read, which will help with diagnosis, and 2 - if you suspect fuel pump pressure, a fuel pressure gauge would be a wise investment.
I know they have loan-a-tool programs at some parts stores but personal opinion; by the time you pay the gas and waste the time to get it and then take it back you're halfway to paying for one that can sit in your toolbox in case it acts up again. I've also found that it's useful on my wife's car, my friend's jeep, my son's ranger and lots of other vehicles too.
07-09-2016, 11:12 PM
#5
Member
Thread Starter
As a courtesy follow-up...
Last week, I changed the fuel pumps on BOTH of my tanks. Also changed was the dash-mounted tank selector switch (as well as the fuel filter).
After a full week of use - I am confident that my problems have been remedied. The truck runs strong - on both tanks - and has not randomly shut down when it is hot out.
I *may* do a post-mortem inspection of the pump - to see if there's anything internal to it that may be causing it to have randomly shut off... But that's only if I make time.
Thanks for the suggestions & ideas.
Last week, I changed the fuel pumps on BOTH of my tanks. Also changed was the dash-mounted tank selector switch (as well as the fuel filter).
After a full week of use - I am confident that my problems have been remedied. The truck runs strong - on both tanks - and has not randomly shut down when it is hot out.
I *may* do a post-mortem inspection of the pump - to see if there's anything internal to it that may be causing it to have randomly shut off... But that's only if I make time.
Thanks for the suggestions & ideas.
