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Fuel Pressure. I have an idea ?

blu3fan

NAXJA Forum User
Location
Arizona
Hey guys
my 92 xj 4.0 has been being a punk recently and im a little stumped.
so every time it goes to start the last week. I have to crank it for 10-20 seconds.
I have confirmed. 0psi at rail when this happens.
I changed the pump about a month ago.
I can hear the pump whirring.
Filters are clear.
I think I have a blocked fuel line.
I put some fuel line cleaner in the tank...
it doesnt seem to be getting worse. but its not getting better.
any tips to fixing this ? should I Just run a new fuel line from front to rear ? and screw the metal line ?
 
I believe there should be some sort of check valve in the system, and I would wonder if yours is no longer working and is thereby allowing your lines to drain out such that your pump has to work extra duty in order to get fuel back where it belongs.

My experience is all with my '96 which is a one off illegitimate child of questionable parentage.

Your '92 should have a return line, and I believe that would allow you to install an aftermarket check valve if you were to wish to do so. However, your best bet is probably to look into your factory fuel pressure regulator and the pump itself. In fact, I would be a bit suspicious about the replacement pump.
 
I believe there should be some sort of check valve in the system, and I would wonder if yours is no longer working and is thereby allowing your lines to drain out such that your pump has to work extra duty in order to get fuel back where it belongs.

My experience is all with my '96 which is a one off illegitimate child of questionable parentage.

Your '92 should have a return line, and I believe that would allow you to install an aftermarket check valve if you were to wish to do so. However, your best bet is probably to look into your factory fuel pressure regulator and the pump itself. In fact, I would be a bit suspicious about the replacement pump.
I popped the inlet hose off. and turned the key on. heard the pump whirr.
however no fuel was in the rail. nor was coming out.
on the 92 there is an inlet. it then goes to injectors.
and there is a regulator on the return line- which then goes back into the tank.
if there was a stuck check valve in the return line fuel should have came out by my logic.
 
I popped the inlet hose off. and turned the key on. heard the pump whirr.
however no fuel was in the rail. nor was coming out.
on the 92 there is an inlet. it then goes to injectors.
and there is a regulator on the return line- which then goes back into the tank.
if there was a stuck check valve in the return line fuel should have came out by my logic.


2nd thing.
Pump was bosch.
Its pump #6 in 10 years.
so heres my thought.
this has been a thing for a while.
and its killing pumps.
im getting 45psi at rail. when she runs. but when I rev I see it drop to 20.
this would indicate psi but not volume. so im really heading towards blocked line.
the real question is. how do I clean it out ?
or has anyone else ran a new metal line ?
3rd option. cut the metal line. and attach clamps and a rubber hose.
 
There's two nylon sections near the engine. Make sure they're not kinked. Could try compressed air to blow out lines if they're clogged or run a piece of wire thru the line.
 
There's two nylon sections near the engine. Make sure they're not kinked. Could try compressed air to blow out lines if they're clogged or run a piece of wire thru the line.


I did compressed air like a year ago and a buncha crap came out.

OOOOOO !!!YOUR A GENIUS !!! I did not think of running wire through it !! THANK YOU !!!!!
 
You might even want to try something like this: https://www.amazon.com/BARSKA-Gun-Cleaning-Flexible-Pouch/dp/B009IP05NK

And WRT the check valve, it is not that it would be blocked, but rather that it be not holding the fuel. And if your lines are empty that certainly sounds like a possibility. Of course, if there is a bunch of crud in your system then that could be the reason the check valve can't seal.

Have you pulled your tank out and checked it to see how clean it is on the inside?
 
Another thing to look at, it's been reported frequently that the small section of hose that connects the pump to flange tends to leak.
 
Good point.

The hose that is for use inside the tank requires a special rating, not just fuel injection line. Line not rated for full immersion will deteriorate from the outside in.

I believe the correct spec hose is SAE 30R10.
 
Another thing to look at, it's been reported frequently that the small section of hose that connects the pump to flange tends to leak.

That is how I learned the 4.0 can idle with only 15 psi on the fuel rail. Also seen one blow out, spraying fuel inside the tank.
 
You might even want to try something like this: https://www.amazon.com/BARSKA-Gun-Cleaning-Flexible-Pouch/dp/B009IP05NK

And WRT the check valve, it is not that it would be blocked, but rather that it be not holding the fuel. And if your lines are empty that certainly sounds like a possibility. Of course, if there is a bunch of crud in your system then that could be the reason the check valve can't seal.

Have you pulled your tank out and checked it to see how clean it is on the inside?


so the history on the car.
she sat with about 1/3 tank of gas for 5 years.
when I got her up and running I found rust in the tank.
it clogged a pump screen.
so I pulled the tank and found nothing left. tank was fine. so unsure where the big bit of rust came from.
I think whatever was growing/rusting in the tank spread to the lines.

what came out was brown/rust last year.
I pulled the pump and the screen is clean.
the filter is clean.
yet I still have 0 fuel at the rail.
crank for 10-20 seconds. car starts. runs fine.
pull rail
rail full with fuel.

so tonight im going to my friends house use bailing wire and a compressor and see if I can clear it.
ill post updates.
 
okay
it wouldnt start at all.
reading 0psi.
so I removed the fuel filter.
hit cranked it. no fuel.
pump is not getting voltage or its dead. or hose came off.
I can hear it. so about to pull it now.
meh. its always something. Just Empty Every Pocket
 
well well..
this explains a lot.
Strainer had fallen off the pump.
I think the pump is dead haha.
new one arrives by 5pm.
 
OK, first, how much fuel is in the tank? Does this happen only at below a certain level?

I ask because there is a fairly common failure that can cause this symptom. There is a short length of hose inside the tank, between the fuel pump and the mounting. They are notorious for cracking or coming off.

Also, I did not check all the thread, but have you replaced the fuel filter?

Adding more fuel when this happens, tends to help boost the fuel pressure due to not having the leaking hose, in air, but rather in gas.

From what I have seen in my years of fighting XJ's is that if you can hear the pump, the pump is probably fine. another thing to try is to disco the hose right at the tank and see if you get fuel out when it primes. Beware of fire!

I have also seen clogged fuel lines and even ones pinched by a rock.
 
OK, first, how much fuel is in the tank? Does this happen only at below a certain level?

I ask because there is a fairly common failure that can cause this symptom. There is a short length of hose inside the tank, between the fuel pump and the mounting. They are notorious for cracking or coming off.

Also, I did not check all the thread, but have you replaced the fuel filter?

Adding more fuel when this happens, tends to help boost the fuel pressure due to not having the leaking hose, in air, but rather in gas.

From what I have seen in my years of fighting XJ's is that if you can hear the pump, the pump is probably fine. another thing to try is to disco the hose right at the tank and see if you get fuel out when it primes. Beware of fire!

I have also seen clogged fuel lines and even ones pinched by a rock.
so its odd you ask about the fuel level.
currently its lowish. maybe 1/3 of a tank.
and Upon reaching around the tank. I feel that the strainer lowers the pump enough that I do not believe without the strainer attached it could get any.
My pumps sender doesnt work. it reads empty or 1/3 on the gauge.

I already bought the new pump. but its $70 with the fuel gauge so im not worried.
But I think the pump is fine. and its just sitting too high without the strainer to get any fuel.
 
So Actually.
Im still not done with this.

Died today.
Would not start.
0 psi at rail. no fuel.

wiggled power wires on battery.
pulled fuse. put it back in.
pulled the fuel pump out took less than 30 seconds. Im getting good at this now. Turns out you can pull the pump without unhooking anything !. NOTE FOR FUTURE GENERATIONS !!!

wiggled the wires on the fuel pump.
still didnt start.
I then pulled the rear drivers side quarterpannel.
loosened the ground.
re tightened it.


car started.
I have no clue what fixed it.
maybe the ground.
idk.
so mad....
 
Best I can see is keep track of factors involved when it pulls this stunt, assuming it repeats its tricks.

Some of these things get challenging to track down, but given time you will eventually pinpoint the root cause.
 
Im super worried its my harness failing.


I will run a manual 12v to the fuel pump next. and if it happens I can start isolating.
so much meh tho...
 
Harnesses do not generally fail.

Unless your vehicle is a flood salvage vehicle I would not jump to that degree of failure.

A bad ground could well explain it.

I could also be something like a loose pin in a plug.

Keep collecting data and you will eventually get it nailed down.
 
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