my fuel problem.

1987 4.0 4x4 5 speed, 231,000 miles.

I have a fuel problem, i started describing it in this thread but didn't want to hijack anymore:
http://naxja.org/forum/showthread.php?t=1009635&highlight=61scout80

my description in that thread:

61scout80 said:

...issue my 87 is having. mine doesn't quite idle, i can feather the peddle and get it up to about 1500-2000, any more throttle it stalls and any less it stumbles. let off the clutch at all when it is revved and it stalls right out. will run on carb cleaner though.

I changed the fuel filter today and it still is having the same problem. lines look ok, no leaks. i can hear the fuel pump fire up when i turn the key. My next step is to buy a pressure gauge, but that may not be until tomorrow.

mine was fine while wheeling, then i shut it off and it was game over.

Click to expand...

So today i picked up the pressure gauge. I can hear the pump prime, i can hear the fuel returning to the tank. but i only get about 5 psi at the rail. even when i pump the pedal and get the engine running at 2000 rpm i only get 5 psi at the gauge. as soon as the engine is off there is no pressure at the rail.

I'm thinking i need a fuel pump, i would love to hear other opinions before i do it.

Try pinching the return line (front) and see what happens. I haven't seen it myself yet, but others have said the fuel line inside the tank between the pump and the outlet sometime rots and most of the fuel is pumped back into the tank.
The last time I had low fuel pressure it was the ballast resistor, but it wasn't as low as yours. The time before than it was a bad connector (it was seriously cooked) near the right rear fender-well, where the harness goes from the door sill into the side panel near the spare tire.

I wonder if a bad (stuck open) pressure relief valve could let the pressure go that low? Pinching the return line would answer that.

I'll pinch off the return line tonight. Mine has no ballast resistor. I guess it was never taken in to have the TSB addressed.


is the pressure relief valve is built into the fuel pump assembly?

Just the newer ones have it in the fuel pump assy. I believe that yours is on the fuel rail and is vacuum operated. Low vacuum, higher pressure. High vacuum, lower pressure. Diaphram brakes, sucks in a lot of excess fuel into the intake.

winterbeater said:

Just the newer ones have it in the fuel pump assy. I believe that yours is on the fuel rail and is vacuum operated. Low vacuum, higher pressure. High vacuum, lower pressure. Diaphram brakes, sucks in a lot of excess fuel into the intake.

Click to expand...

ok, i call it the pressure regulator, that's where i got lost. it's on the front of the fuel rail. I need to search to see if it is replaceable and how to test it. I can see that the fuel line on the "in" side can pop off, but i'm not sure if the other side is part of the rail or removable from the rail.

61scout80 said:

ok, i call it the pressure regulator, that's where i got lost. it's on the front of the fuel rail. I need to search to see if it is replaceable and how to test it. I can see that the fuel line on the "in" side can pop off, but i'm not sure if the other side is part of the rail or removable from the rail.

Click to expand...

I had the fuel regulator go bad on my 87, it failed to high pressure, not low pressure. But to tell you the truth I don't know enough about it to make an informed guess. It's doubtful it would cause the pressure to go that low.

Still pinching the return line might tell you something, low volume will still build pressure (eventually, even if the filter is mostly plugged or a fuel line flattened or partially plugged). If the pressure doesn't come up significantly it may be a weak pump or like I mentioned an internal leak in the tank. I'd also check the voltage at the pump, compare it to the voltage in the fuel pump circuit someplace in the engine compartment. It should be pretty close to battery voltage (though there will be some line loss). The voltage can fool you, the voltage may test out *nearly* OK and a poor connection may cause low amperage, which will slow down the pump. When I found the bad connector in my 87, I actually ran a hot wire straight from the battery (after testing the pump ground) and the pump ran fine with good pressure. That tipped me off the problem was likely between the fusible link, the relay or the harness and the pump.
One tip, if you have to troubleshoot the harness running down the door sills, is that the pump wires change colors a couple of times before they get to the pump (I was troubleshooting without a schematic, I had more than a few scratch head and what the truck moments with that one).

With such low pressure I would suspect a clogged filter, pinched line, rotted pump to flange rubber fuel line, or a bad pump.

Inspect the lines front to rear, replace the filter, retest. No improvement, pull the pump and check the pump to flange hose. Replace the hose if necessary (it is only 22 years old), and then retest or just change the pump as you are in there already.

I agree that every pressure regulator failure I have seen has sent the pressure through the roof.

i do have a brand new filter on there, that was my first attempt to fix the problem. the lines looked decent when i was replacing the filter, but it's cheap enough to just replace them.

Lets say there is a clog, would a safe bet be to blow air through the line from the pressure regulator to the "out" side of the fuel filter? with the line removed from the filter, pressure regulator and in a container of course.


Edited to add: the old fuel filter was quite scummy. tipping it so fuel poured out the inlet released black fuel. it looked like coffee. but tilt it so the fuel came out the outlet it was nice and clear.

i just learned two things. first i learned that the fuel moves through the rail the opposite way i thought it did, it moved from the firewall to the radiator. i though the fuel went into the regulator first...

Second i learned that pinching the return hose only gets me an additional 1 psi. i'm going to test the voltage and a few other things now, but i think i am just delaying the inevitable fuel pump.

What fuel pump is a damn good brand? looks like checker (kragen) has bosch, delphi and airtex in the same price group. they also have a walbro for about $50 more. hopefully this link works.

http://shop.oreillyauto.com/ProductList.aspx?PartType=52&PTSet=A

Bosch 69302, I wouldn't use anything else on mine.

When you pinched off the return line the pressure should have hit about 95 psi.

Bosch has been the most often recommended. At least you don't have to drop the tank like the newer models.

the site says they can get the bosch in one day and it's $80. at least it is less than i expected to spend...

Rock Auto $72. And if you google for "Rock Auto discount", you can find the discount code for another (IIRC) 5% off. That's not including shipping.

http://info.rockauto.com/Bosch/Detail.html?69302.jpg

the summary, add expletives where you see fit. i sure did.

I drained enough fuel from the tank to get the pump assembly out. that's when i found the pic below. That's right, the hose clamp some how got loose and the hose slipped off the out going tube inside the tank. i guess the noise i thought was fuel returning to the pump was just the fuel squirting out of here.

The local checker store couldn't get the bosch pump, so i ordered the delphi. that came in and was not correct for my bracket, so i returned it. Also, while the box said delphi all over it there was a wallbro pump in there, the box was beat to hell and obviously taped back shut. Anyway, ended up returning that and coming home with the airtex...

I really didn't want the airtex, but i had to get the jeep back together. The bosch that was in there was probably fine, but i didn't want to do this twice. Hopefully that pump won't be as bad i fear it will be. anyone have experience with airtex?