Low Fuel Pressure 1989 LX 5.0

[Mikael88fedon]

Im in need of some guidance. Below is the story so far and its a bit long

Went to drive car home from work (car ran like a champ to work). As i was leaving the parking lot of where i work the car started having issues trying to stall on me and i was able to play with the throttle to get me somewhere safe.

When i try to restart the car it would run for a few seconds and die. I was able to keep it running by increasing the idle and started highway back home but as soon as i hit some red light hesitation came and i was able to pull into a oreilies and it died. It wouldnt start but after a while i could get it to run for a few seconds.

Got it towed back to the house and started investigating. Started up fine and idled and when started dying i replaced the fuel pump relay and did not fix

Got a fuel pressure guage hooked up and when cold and i start it it reads 29psi. When it warms up at high idle it hovers about 20psi but when i bring the idle back down it slowly drops to 10psi then under and the engine dies.

Unhooking the Vac line from the fuel pressure regulator does not chamge the fuel pressure at all.

Stopped and picked up a fuel filter but unsure if will fix. Any help is appreciated

 

[General karthief]

If the filter does not fix it you will be dropping the tank and replacing the pump.
get a new grommet for the filler tube where it goes into the tank too.

 

[Mikael88fedon]

Thats my fear that the pump is bad. Hoping it was something easy to fix like a pressure regulator or fuel filters. Will see when changing the filter

 

[General karthief]

It could be the fpr but I doubt it. Pull the vacuum line from the regulator and smell it. If you smell gas it's bad.
if the car has a lot of miles or if you don't know if the pump has ever been changed it is a good idea anyway.
remember the filler neck to tank has a rubber grommet that likely will need changing too.

 

[Mustang5L5]

Most likely, the rubber hose on the fuel pump split. Have seen it happen. Result is less than full pressure

 

[jrichker]

Check fuel pressure:
The local auto parts store may rent or loan a fuel pressure test gauge if you don't have one.
Disconnect the vacuum line from the fuel pressure regulator. Check it for evidence of fuel present in the line by removing it and blowing air through it. If you find fuel, the fuel pressure regulator has failed. Reinstall the line; leave the fuel pressure regulator end of the vacuum line disconnected. Then cap or plug the open end of the vacuum line and stow it out of the way.
Connect the fuel pressure test gauge to the Schrader port located just behind the alternator.
Turn the ignition switch on & start the engine. Observe the pressure: you should see 38-41 PSI at idle.
Turn the ignition off; reconnect the vacuum line to the fuel pressure regulator. Then disconnect the fuel pressure test gauge. Watch out for squirting gas when you do this.

Fuel pump pressure test
Disconnect the larger of the two fuel lines up by the Schrader valve. It is the return line and does not have the Schrader valve on it. Find a piece of rubber fuel hose and clamp it on the return line coming from the regulator. Stick a bolt in the other end of the hose and make sure that all your connections are tight and leak proof as possible. When this powers up, you don't want fuel squirting everywhere. Hook up the fuel pressure test gauge. Turn the ignition switch on and watch for leaks. You may want to use a helper inside the car to cut the switch off quickly if you have a leak. To trick the fuel pump into running, find the ECC test connector and jump the connector in the Upper RH corner to ground.

Caution!!! You have blocked the return line for the fuel pump! Pressure will rise very quickly past safe levels with a good pump
If the pressure goes up past 55 PSI, the pump is good and the fuel pressure regulator is bad. If the fuel pressure does not hit 55 PSI or more in a few seconds, the pump is bad or you have electrical problems.

 

[Dan02gt]

Most likely, the rubber hose on the fuel pump split. Have seen it happen. Result is less than full pressure

That's my bet too.

 

[Mikael88fedon]

Great news.
Replaced fuel filter and was not issue. Before dropping tank decided to replace fuel pressure regulator since current one looks like no name adjustable

And it fixed my issue. Staying at 29 psi and not dropping

Thanks to everyone for the help

 

[General karthief]

Thats better, what is your pressure now with the vacuum line unhooked and plugged?
should be around 40lbs unplugged, 34 or so plugged in.

 

[Mikael88fedon]

Looks about 30 plugged and 35 unplugged. I can check unplugged again to see if a little higher than 35

 

[General karthief]

That sounds like an acceptable range, I would like to see it closer to 40-42 with the vacuum line off, but that is me.
Just curious, what's the pressure koeo with the fuel pump jumped at the test connection?

 

[Blown88GT]

That sounds like an acceptable range, I would like to see it closer to 40-42 with the vacuum line off, but that is me.
Just curious, what's the pressure koeo with the fuel pump jumped at the test connection?

No, not you. Fuel pressure is still too low.

 

[General karthief]

No, not you. Fuel pressure is still too low.

it's me I tell ya! I have ID to prove it!
and yes it is still low, I agree.

 

[Mikael88fedon]

Checked again and was 32 plugged and 38 unplugged. Didnt jump it yet

 

[FastDriver]

That's good to go. Should be 39... technically

That's the order I do 'em in. Filter, then regulator, then pump. It's more a matter of ease of work & cost than likelihood. Just did this on a friend's SN95 a couple weeks ago, and it turned out to be the pump itself.