86 Ranger Fuel Pressure Loss

[Doc Holiday]

86 Ranger 4x4 with 3 litre engine. Runs fine when engine is cold. When engine heats up is starts to mis-fire then after about 15 minute when engine is at full temperature, it w'ont run at all. Had it to a garage and they said the complete fuel system needs replacing - about $1000. Vehicle isn't worth that input. Fuel pressure is 35 psi when cold then falls to 5 pse about the time the engine is hot.
-Is the problem sludge in the tank as suggested by the garage? If so, is there any way to clean the tank without pulling it.
-Is is a weak fuel pump? If so, will an inline fuel pump suffice instead of replacing the in tank pump. Any recommendations?
Thanks for any help offered.

 

[410Fortune]

your in tank fuel pump is likely shot

sluge in the tank is BS
Entire fuel system for $1000? Does that include new injectors, new pumps, new pressure regulator and labor? WAJ

If the pressure drops to 5 psi when the engine is hot, either your pump is old and shot or your pressure regulator is bad.

You can test the pressure regulator, an easy way is to pull the vacuum line and see if there is gas in it, if so its torn

I am leaning towards the in tank fuel pump
You have two fuel pumps in 1986
the one mounted inside the tank is a "boost pump" and the one on the frame rail is the high pressure pump.
If the boost pump is not feeding the high pressure pump it would cause the condition you describe.

The in tank replacement is about $85 new and the labor takes about an hour max.

In 1986 your Ranger has a 2.9L V6, no such thing as a 3.0L back then, there is a BIG difference.

The shop you took it too sounds shady to me, I have seen the inside of many Ford gas tanks from older trucks, there is never any "sluge" in any of them, varnish maybe if fuel is left to sit, but sluge = no way. Its a "line" the shop uses to try and get your truck in on their rack so they can charge you whatever they want, "oh yeah the entire system needs to be replaced, that will be about $1000" dont be surprised if $1000 turns into $2000 real quick...

here's what I would do (and have done many times)
Fuel pressure test (you did that, it drops to 5 psi at hot idle = no bueno)
check pressure regulator vacuum line for fuel
unplug vacuum from regulator at idle and see if the idle jumps up, if it does likely the regulator is fine (probably is since it holds 35# at idle when cool)
Listen to both fuel pumps

If a pump is going south alot of times you will hear a whine.
Its quite possible the pump in your tank is NOT EVEN RUNNING, listen for it

park the truck on a hill with the gas tank down hill, let it sit and see if starting is difficult

If it starts see if the pressure drops while idliing on the hill

On my 88 when I had a problem like what you describe my in tank boost pump was on its way out. I replaced it for $85 and it still works great today!

 

[Doc Holiday]

Thanks for the advise. I will try you suggestions in a few days (can't do it now because I can't get into my garage) and will post the results. Thanks again.

 

[SalsShittyTruck]

Fun similar problem and resolution story:
88 2wd ranger with the 2.9L. Starts up fine, starts out driving fine, once hot sputters/dies upon accelerating. Fuel pressure at the rail reads 30 at idle, 40 with regulator disconnected. Fuel pressure when driving bounces erratically between 0-40.
Now comes the funny part- unplug the electrical connector on the in-tank pump... exact same performance. This beast was running on only the external high pressure pump! In tank pump (original) was missing it's sock, looked like it had tried to swallow a fine wire-brush, and was seized. Replaced the in tank pump and fuel pressure now reads 30 +/- 5 while driving, and changes smoothly. Who knew it could run so good on only one pump!!! If it ran worse it would have been much easier to diagnose!!!
Posting because I saw a thread somewhere else about a guy who decided it was the ECU (without evidence) and scrapped his truck. We almost thought it was a control circuit problem too because the voltage to the pump wasn't a steady 12v (which we expected... but might not be what it's supposed to get. Couldn't find specs for this.)

 

[410Fortune]

I converted my 88 BII to use a single in tank pump, sending unit from a 90 Bronco II with a Walbro 180 lph pump
I simply put a second fuel filter where the old high pressure pump was mounted on the frame rail.
Works excellent

 

[roscoe 0202]

on my 86 bronco II when the lowpressure pump went out I replaced it and about two weeks later same thing had to replace high pressure pump worked until I sold the car
the84 I'm building right now with a 4.0 transplant I used a 90 fuel pump sender in a 86 or newer tank and changed the sender for the different ohms of the older fords

roscoe