runs great, for 5 minutes

Jamie C.

Member
Oct 26, 2021
7
2
13
65
Wisconsin
Hello, I have a 91 lx with the 5.0 engine. I took it out of the garage and a few blocks from my house it started to sputter and died. I got it home in my garage and let it sit for an hour. I started it up and it runs smooth for about 5 minutes and then starts to weeze and dies. I'm not a mechanic but I've changed the plugs, wires, coil, cap rotor (it needed these anyway!) the fuel filter, ignition control module and the fuel pressure regulator (it had gas squirting out of it when I pulled the vacuum line off) it has a brand new motorcraft battery too. I checked the fuel pressure when it's running and it's at 37 psi. I did notice that it doesn't maintain pressure in the line when it shuts down, not sure if it is supposed to. the timing is right on. I'm at the end of my "knowledge" and was wondering if anyone here could offer any suggestions. thsnk you in advance! 20200820_151950.jpg 20200820_152351.jpg
 
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90sickfox

Wasn't a pretty sight...and I've got big hands
SN Certified Technician
Mar 2, 2015
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Very clean car !!!

Grab yourself a Ford EECiv scanner. It plugs in behind the drivers strut tower and will flash or read codes. This will help to point you in a direction.

Screenshot_20211026-231832_Amazon Shopping.jpg


These codes will greatly help us help you.

There are a bunch of things that could cause that issue. There are several connectors that cause issues. Main one is the ignition switch electrical connector on the column. Unplugging it will easily tell you if you have an issue there. It will be melted if it's going bad or the plastic and metal part it plugs into will be loose. Usually it doesn't cause your issue but it's a good thing to check anyway.
 
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ChaseRoads

do I need to lube this area?
Oct 29, 2020
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I agree with the scanner, but it sounds like the fuel pump is failing. after it dies, will it start back up? if not, maybe see if some fuel or starting fluid will get it back to life.
 

Jamie C.

Member
Oct 26, 2021
7
2
13
65
Wisconsin
Very clean car !!!

Grab yourself a Ford EECiv scanner. It plugs in behind the drivers strut tower and will flash or read codes. This will help to point you in a direction.

Screenshot_20211026-231832_Amazon Shopping.jpg


These codes will greatly help us help you.

There are a bunch of things that could cause that issue. There are several connectors that cause issues. Main one is the ignition switch electrical connector on the column. Unplugging it will easily tell you if you have an issue there. It will be melted if it's going bad or the plastic and metal part it plugs into will be loose. Usually it doesn't cause your issue but it's a good thing to check anyway.
I got my scanner this evening, I'll give it a try tomorrow and let you know if anything comes up. it says to run it until it reaches operating temperature, I'm not sure if I'll be able to get it to run that long! I noticed that after I shut the car off there is no pressure in the fuel rail at the schrader valve, is that normal? I appreciate everyone's help.
 

manicmechanic007

Mustang Master
Sep 26, 2017
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396
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You had better check the fuel pressure when it dies
The pressure should still be there when it dies
If not that is the problem
Fuel pump failure
Seldom sets a code
Possibly a lean code in memory
What do you mean you are not a mechanic
if you are smart enough to install and use a fuel pressure gauge
You are ahead (smarter) than 90 percent of the people on the planet
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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There is a check valve-doohickey that is supposed to hold the pressure after the engine is shut down, if it bleeds down right after the engine is turned off it's no big deal, the pressure readings while the engine is running should be steady, most, if not all problems can be resolved by the 'surging idle checklist'.
 

manicmechanic007

Mustang Master
Sep 26, 2017
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That doohickey you refer to is part of the pump module
It is supposed to hold pressure and bleed max 5psi in 24 hours
Otherwise you have long crank times because it has to build pressure to start
The hinky dinky is a one way valve with a built in damper
Used to see the hose that connects it to the pump inside the tank split and fail once in a while
Causes a no start not a dying condition
IMHO you need a new fuel pump Jamie C
You can put a new pump in your sender real easy on a Mustang
Buy a new sock
 

manicmechanic007

Mustang Master
Sep 26, 2017
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396
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They have been calling them fuel pump module assemblies for a while now
There is a lot to them these days
Some of them look like a Jarvik heart
The ones for a Chrysler 300 or other saddle tank styles like Contour or T-Bird
 

90sickfox

Wasn't a pretty sight...and I've got big hands
SN Certified Technician
Mar 2, 2015
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I agree with above. It isn't normal for the pressure to be gone right after cutting off. There's also a connector in the back behind the bumper that can be problematic. It has the fuel pump and sender power and ground wires running through it. The thing hangs right at the back of the pump. You can also check for power there to see if the pump is getting a signal while someone cranks the car over. Just turning the key on will show no voltage by the time you get there. ( only primes for a couple seconds ).

If the key is turned on and you get pressure up front but it bleeds off right away there's a problem with the pump or the regulator.
 

Jamie C.

Member
Oct 26, 2021
7
2
13
65
Wisconsin
hello, I put the code reader on the car (I actually read the instructions!) and it doesn't do anything but display 000's. there is a square (not flashing) and a triangle on the display which the manual says means it's hooked up to the computer and if the square is flashing means its receiving codes. I put the fuel pressure gauge on it, when I turn the key on it goes up to 20 one time and 70 the next! I started the car and it settled down to 40 psi. it ran for a few minutes and sputtered and died. the fuel pressure dropped to zero in a few seconds. I pulled a plug out and here is what it looks like. usually when I turn the key on I can hear the fuel pump whine for a few seconds, now every once in a while it stays whining and reads 70 on the gauge. I was thinking of selling my car because I put 300 miles on it in the last 10 years but I don't want to sell a car with problems. I appreciate all the suggestions you all have made!
 

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manicmechanic007

Mustang Master
Sep 26, 2017
1,406
396
93
62
Replace the fuel pump
Drive the car around enough to get it up to operating temperature
Then recheck the spark plugs
Not too concerned about the plugs yet as per the dying condition
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
22,468
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polk county florida
They have been calling them fuel pump module assemblies for a while now
There is a lot to them these days
Some of them look like a Jarvik heart
The ones for a Chrysler 300 or other saddle tank styles like Contour or T-Bird
Never heard of anything in the fuel tank of a fox mustang called a 'fuel pump module '.
:shrug:
 

Jamie C.

Member
Oct 26, 2021
7
2
13
65
Wisconsin
Replace the fuel pump
Drive the car around enough to get it up to operating temperature
Then recheck the spark plugs
Not too concerned about the plugs yet as per the dying condition
thank you, what would be causing it to load up and sputter after 4 or 5 minutes? I'm just asking because I'm lost!
 

Jamie C.

Member
Oct 26, 2021
7
2
13
65
Wisconsin
thank you, what would be causing it to load up and sputter after 4 or 5 minutes? I'm just asking because I'm lost!
thank you, what would be causing it to load up and sputter after 4 or 5 minutes? I'm just asking because I'm lost!
also, would you just replace it with a factory type replacement? is there any reason to "upgrade" to a different fuel pump? thanks again!
 

Jamie C.

Member
Oct 26, 2021
7
2
13
65
Wisconsin
I agree with above. It isn't normal for the pressure to be gone right after cutting off. There's also a connector in the back behind the bumper that can be problematic. It has the fuel pump and sender power and ground wires running through it. The thing hangs right at the back of the pump. You can also check for power there to see if the pump is getting a signal while someone cranks the car over. Just turning the key on will show no voltage by the time you get there. ( only primes for a couple seconds ).

If the key is turned on and you get pressure up front but it bleeds off right away there's a problem with the pump or the regulator.
I did replace the fuel pressure regulator (lots of swearing!) the original one had fuel coming out of it when I pulled the vacuum line off.
 
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Jamie C.

Member
Oct 26, 2021
7
2
13
65
Wisconsin
hello, I just wanted to update my issue. I replaced the fuel pump and the problem still exists. for some reason the OBD1 scanner is not showing anything. someone told me you can use a jumper wire to get the car to flash out codes by jumping two posts on the OBD1 plugs. has anyone heard of that? Also, it seems to run crappy when it gets up to operating temperature, is it possible it could be the barometric sensor which is located on the firewall? I'm above my skill level here, any suggestions are appreciated!
 

manicmechanic007

Mustang Master
Sep 26, 2017
1,406
396
93
62
Jamie C,
Substitute a known good MAP sensor
Most all good Ford drivability techs have one in their toolbox because the pinpoint tests are horrible for the MAP sensor and related codes
It (the MAP sensor) sure could be your problem but you need to get the no code output figured out first
There are one or two fuses that have to be good for the processor to output codes thru the self test connector
First test for the map is to inspect the vacuum line for debris (they have thick film inside them that comes apart occasionally)
That plugs up the vacuum line and sets a MAP code
You should be looking for a Star tester or a Super Star II to test codes on your 1991
A NGS would be optimal but you probably will have to pay too much to get one of those (mine was 6500 with all the goodies) cards etc
Have a Ford tech in your area check your Mustang for codes with his star tester or NGS
Thanks, Paul
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
22,468
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polk county florida
In case this was not mentioned before:
And how to pull codes without a reader:
Note: if you cannot get codes from the computer likely there is a problem with the computer and needs to be checked out. I have used the ecuexchange several times, it's quick and not that expensive. You can find them on flea, ahh, I mean Ebay.
Most mechanic shops are confused when dealing with our computers and will tell you they won't tell you anything useful. BS. You just have to think harder, or more, I don't know, think'n gives me a headache. :jester: