YJ restoration project (air in fuel line?)

[Jbsmith580]

Hi all,

New to the YJ forum and I’m looking at getting some advice or a new approach to my problem.

Question is in regard to air in fuel system, I think?

1993 YJ 2.5 manual transmission. Vehicle was mine along time ago and let’s just say it’s in rough shape now as it was parked in a rural environment for over 10 years.

I got it towed to my house and tried to get it running and here are some things I found/did already seeing that I couldn’t get it to run. I admit there was no particular reason or order I did what I did to try to start it nor do I admit the way I did it was the correct way

1. Added enough fresh gas to the tank to try to dilute what very little bit was in the tank from sitting. The tank was practically empty but I knew there was SOME still in it.

2. Tried to start it, nothing.

3. Cut out the access window above the tank to get to the whole fuel unit for a replacement.

4. Replaced the whole gas tank sending unit assembly. The old one fell apart when I pulled it out of the tank, which were my suspicions.

5. Tried again to start it, nothing.

6. Found the wiring diagram for the whole jeep online, started tracing wires and I found an entire bundle of about 10 wires, near the transmission severed in half. Some fed the speedometer sensor, other wires go to the fuel pump. Butt spliced the wires back together

7. Tried to start it and it ran good for about a solid minute and just sputtered to death. Every time after I restarted it, it wouldn’t run for more than 10 seconds probably

8. Looked around online and saw that it could be a clogged filter so I got one from the parts store and replaced it.
When I put the new filter on I noticed how much gas poured out of it and the lines. I just knew air was going to be an issue.

9. Cranked the Jeep for a minute hoping to push the air out back to the tank and it won’t start now.

10. Pressed the needle valve on the Schrader valve and it seemed like a very small amount of air came out but nothing to replace the amount of fuel that came out of the line and filter when I changed the fuel filter

11. I have pressed on the schrader a couple of times and tried cranking the engine and it will fire briefly and then just resume endless cranking.
I also notice when I press on the valve, gas isn’t spraying out like I’d expect. It’s more like a trickle and it will just kind of slowly pour out of the Schrader

12. I tried jumping power to the fuel pump constantly at the relay for roughly 30 seconds and it doesn’t change the spray of gas out of the Schrader valve on the fuel rail.

Does this sound like the new pump assembly is bad already?
Fuel filter is installed in correct direction, but could that be it?
Is this just simply air in the fuel line and if it is, how do I get it out?
(Jumping the pump constantly hot doesn’t seem to help..?)

 

[Stoopid Jeep]

I would hook a fuel pressure up to the fuel rail and get a reading.
The fuel pressure gauge will have the added benefit of a fuel-purge/air-bleed button to remove any air.

Also, have you replaced the rubber lines on top of the gas tank and attached to the fuel filter?
If the fuel pump assembly fell apart, there is a good chance that those soft lines are damaged and possibly obstructed,

 

[Jbsmith580]

What pressure tester should I get? Im
Not familiar enough with reliability/affordability of fuel pressure testers. Personally I’d look for one at autozone but if I could save $20 I’d just wait for one to come delivered from the big rock candy mountain

I have not replaced any fuel lines, they’re just standard 3/8 fuel hose?

 

[Stoopid Jeep]

What pressure tester should I get? Im
Not familiar enough with reliability/affordability of fuel pressure testers. Personally I’d look for one at autozone but if I could save $20 I’d just wait for one to come delivered from the big rock candy mountain

I have not replaced any fuel lines, they’re just standard 3/8 fuel hose?

I got my gauge at Harbor Freight. one is probably as good as the next. Maybe you can rent one from Oreilleys/autozone, etc?

There are a couple specialty lines to get

For the tank vent:
https://www.quadratec.com/products/51307_03.htm

into the fuel filter:
https://www.factorychryslerparts.com/products/HOSE-FORMED~FILTER-TO-REAR-SUPPL/4418800/53004014.html

unfortunately, I have seen multiple brand new pumps fail from cheap fuel line being used. it's way more common than it should be


be sure to use clamps for fuel injection, or you'll be back in there soon.

 

[Jbsmith580]

I got mine at Harbor Freight. one is probably as good as the next. Maybe you can rent one from Oreilleys/autozone, etc?

There are a couple specialty lines to get

For the tank vent:
https://www.quadratec.com/products/51307_03.htm

into the fuel filter:
https://www.factorychryslerparts.com/products/HOSE-FORMED~FILTER-TO-REAR-SUPPL/4418800/53004014.html

unfortunately, I have seen multiple brand new pumps fail from cheap fuel line being used. it's way more common than it should be

I haven’t noticed any fuel dripping or pooling around on my concrete anywhere during all of this but I’ll check for pressure at the rail in about a day and check back here.

0 pressure would lead me to believe that the hose in the tank blew up like the one you posted or possible air in system. Although I will change hoses I don’t think those are the culprits yet because I don’t see fuel anywhere

But what could cause Low pressure? Let’s say I need 35psi and I only have 6psi

 

[JKP]

You should have dropped the tank and cleaned it out. No telling what was in there.

Pull the fuel pump back out and see if the pre filter is clogged.

If it's not spraying gas out the schrader valve when you press it with the pump running, no way it's going to run.

 

[Jbsmith580]

You should have dropped the tank and cleaned it out. No telling what was in there.

Pull the fuel pump back out and see if the pre filter is clogged.

If it's not spraying gas out the schrader valve when you press it with the pump running, no way it's going to run.

The pre-filter being the mesh-like sock around the pickup for the pump?
I’m not well versed in how exactly the fluid flows throughout that tank but I shined my light down into the tank and there’s a plastic bin that the pump is isolated from the tank.
When I pulled the old pump out it did come out in pieces but I didn’t leave anything behind.
I’ll spare some details but I got the 2-3 pieces that broke off out of the plastic bin.
If there was debris in the tank outside of the plastic container could it have made its way in there?
Nothing noticeable but I was looking down from the top with a flashlight

 

[JKP]

Yes, the sock prevents big stuff from going through the pump.

That box is to prevent fuel from sloshing away from the pump while cornering, etc.

 

[Jbsmith580]

Yes, the sock prevents big stuff from going through the pump.

That box is to prevent fuel from sloshing away from the pump while cornering, etc.

Ok, I’ll pull the pump back out and get back here in about a day or so when I get home.

I’m honestly a little suspicious of the rubber hose that was posted earlier. I did notice a difference in the one on the original pump like it was much thicker but time will tell. It could be particulate matter on that in-tank mesh filter but I don’t see how. And maybe I couldn’t see debris all that well because the inside of the tank is black plastic.

I’m kind of thinking that if that hose did explode or come loose in any kind of way, fuel is just spraying around inside the tank.

I’ll get back in a max of 2 days.

 

[Jbsmith580]

Update:

I bought a harbor freight fuel injection pump tester and hooked it to the Schrader valve on the fuel rail and I have 0 fuel pressure even with 12v jumped straight to the pump

 

[Flyer58]

Before you pull too much apart try checking the pressure at the top of the pump outside the tank and again after the fuel filter. Both my not be nessasary if the pump isn't putting I out.

 

[Jbsmith580]

Before you pull too much apart try checking the pressure at the top of the pump outside the tank and again after the fuel filter. Both my not be nessasary if the pump isn't putting I out.

The fuel pump isn’t pumping any fluid. Matter of fact it isn’t making any noise any more.
I think it’s done for. I don’t know what resistance to look for across the pump and ground though but I saw someone say somewhere that their pump to ground read 2 ohms and is working and mine is way higher than that.

I did rig a hose to the fuel line on top of the tank to an empty fuel container and jumped 12v from the battery (to be extra sure) to the pin in the relay box for the pump power, and the pump did nothing.
Even after I removed it I plugged it back into the harness and set it on the concrete and turned the key to on and heard the relay click, but the pump did absolutely nothing, no noise or gurgling no high pitch squeals it’s just dead now.

I’m off tomorrow and have to return it to the big rock candy mountain via UPS pickup but I’ll get up early enough to jump 12v- and 12v+ straight from the battery to further prove to myself it’s gone

 

[ytradio]

The fuel pump isn’t pumping any fluid. Matter of fact it isn’t making any noise any more.
I think it’s done for. I don’t know what resistance to look for across the pump and ground though but I saw someone say somewhere that their pump to ground read 2 ohms and is working and mine is way higher than that.

I did rig a hose to the fuel line on top of the tank to an empty fuel container and jumped 12v from the battery (to be extra sure) to the pin in the relay box for the pump power, and the pump did nothing.
Even after I removed it I plugged it back into the harness and set it on the concrete and turned the key to on and heard the relay click, but the pump did absolutely nothing, no noise or gurgling no high pitch squeals it’s just dead now.

I’m off tomorrow and have to return it to the big rock candy mountain via UPS pickup but I’ll get up early enough to jump 12v- and 12v+ straight from the battery to further prove to myself it’s gone

If you already have it out try blowing compressed air back through the pump. If it was showing a high amp draw and not pumping that is an indicator that it has plugged.

 

[Jbsmith580]

If you already have it out try blowing compressed air back through the pump. If it was showing a high amp draw and not pumping that is an indicator that it has plugged.

I didn’t actually read amps, I was looking at resistance to ground and trying to compare online what it should be. I don’t know what the resistance or amps should read anyway I’ll check on the new pump when it’s arrives though

 

[Jbsmith580]

I didn’t actually read amps, I was looking at resistance to ground and trying to compare online what it should be. I don’t know what the resistance or amps should read anyway I’ll check on the new pump when it’s arrives though

I’ll go ahead and leave this here though incase there’s anyone out there going through this same thing.

My tank was fairly clean, no debris in the plastic box the pump sits in. The mesh pre filter had no signs of anything on it other than fuel.

I’ll be back on in roughly a week with results of the new fuel pump

 

[deadpool1]

done many barn cars, restores and sold many, (not my day job) !,
seen it all, all kinds of failures. for 59 years doing this, (i did 4wd car flips for 10 years)
the tests are easy. using real tools.
inspections too.
one way to learn is DOING. and asking for help , you did. Bravo that. !
live help is 100x best, after all online we are blind, can't see damage and is there.

This EFI system has rules (MPI 4 injectors and PCM)
rule #1 is ASD< the ASD relay must close,and stay closed cranking or the pump relay and ASD relay both disabled, by PCM on purpose.

a voltmeter is needed, as is learn the 3 key on test for DTC blink out error codes.
hearing a pump run means near zero, only PSI matters on EFI. (electronic fuel injection) same with dribble tests. if not a drop the pump is dead. sure.

the PCM cuts ASD for these reasons, and the fuel pump too, the 2 relays use the same wire to energize them.
PCM does that .
the FSM is free to see, ask for it, free PDF to have , hold and read, for sure chapter 8w full car schematics.

1. ASD drops dead (and pump relay) if PCM sees CMP or CKP dead. ( cam or crank sensors dead, or cam chain snapped off)
2. ASD dies for 02 sensor shorted so unplug it. a free easy no tools test
3. ASD drops out if HV spark coil goes shorted (primary pins)
4. ASD drops out if any overloads sensed , at output pin of the ASD relay main contacts.PCM monitors this pin all the time key on.
5. this sensed wire (buss) feed is called A142 in the schematics, nothing on this wire feed can be shorted. ever.
   

this is first, not pulling gas tanks, in my book taking a bath in fuel is last. benzene is nasty stuff.

the fuel LINES 2, one is full 36psi pressure cranked. the other is the FPR return line
the return line sure can have air in it any time pump is off line. key off . it simply drain to the tank and is now full of air.
The pressure like primes each time the key is turned on and this prime means all air from pump to 4 injectors are purged of all air in this line.
keyon3 times and all air is gone. (pump and FPR both good ok?)
the supply goes to filter then to fuel rail
then the FPR uses the return line to return fuel to the tank and forms fuel loop.
the pump must pump for 3 seconds keyed on, each time, the pressure at the rail is 36psi, dibble tests do not prove 36psi ever. thus the tools.
that is my nut shell tests. EFI,

most barn cars found ive ever seen the injectors are all fully or 1/2 clogged. hopeless .
and all fuel lines filters and take a filth mess and gas there nasty smelling and full of slime.
and lots more,

 

[Jbsmith580]

done many barn cars, restores and sold many, (not my day job) !,
seen it all, all kinds of failures. for 59 years doing this, (i did 4wd car flips for 10 years)
the tests are easy. using real tools.
inspections too.
one way to learn is DOING. and asking for help , you did. Bravo that. !
live help is 100x best, after all online we are blind, can't see damage and is there.

This EFI system has rules (MPI 4 injectors and PCM)
rule #1 is ASD< the ASD relay must close,and stay closed cranking or the pump relay and ASD relay both disabled, by PCM on purpose.

a voltmeter is needed, as is learn the 3 key on test for DTC blink out error codes.
hearing a pump run means near zero, only PSI matters on EFI. (electronic fuel injection) same with dribble tests. if not a drop the pump is dead. sure.

the PCM cuts ASD for these reasons, and the fuel pump too, the 2 relays use the same wire to energize them.
PCM does that .
the FSM is free to see, ask for it, free PDF to have , hold and read, for sure chapter 8w full car schematics.

1. ASD drops dead (and pump relay) if PCM sees CMP or CKP dead. ( cam or crank sensors dead, or cam chain snapped off)
2. ASD dies for 02 sensor shorted so unplug it. a free easy no tools test
3. ASD drops out if HV spark coil goes shorted (primary pins)
4. ASD drops out if any overloads sensed , at output pin of the ASD relay main contacts.PCM monitors this pin all the time key on.
5. this sensed wire (buss) feed is called A142 in the schematics, nothing on this wire feed can be shorted. ever.

this is first, not pulling gas tanks, in my book taking a bath in fuel is last. benzene is nasty stuff.

the fuel LINES 2, one is full 36psi pressure cranked. the other is the FPR return line
the return line sure can have air in it any time pump is off line. key off . it simply drain to the tank and is now full of air.
The pressure like primes each time the key is turned on and this prime means all air from pump to 4 injectors are purged of all air in this line.
keyon3 times and all air is gone. (pump and FPR both good ok?)
the supply goes to filter then to fuel rail
then the FPR uses the return line to return fuel to the tank and forms fuel loop.
the pump must pump for 3 seconds keyed on, each time, the pressure at the rail is 36psi, dibble tests do not prove 36psi ever. thus the tools.
that is my nut shell tests. EFI,

most barn cars found ive ever seen the injectors are all fully or 1/2 clogged. hopeless .
and all fuel lines filters and take a filth mess and gas there nasty smelling and full of slime.
and lots more,

Thank you for the details. I just worked an 8 hour shift today so I got the new fuel pump in and purged the air with the key on/off a couple of times and it’s doing great.

It’s still a project and I have more I have to do to it but the engine runs!

 

[deadpool1]

GREAT NEWS (TRUMPETS BLARE) THANKS FOR SHARING TOO.!
keep in mind, the old 90s jeeps did not have year 2000 E10 fuel upgrades.
we know for fact pump /tank parts melt or deform with E10 fuel since year 2000.
USA, rules on fuel, 1% of stations had it 2000 and has expanded to E10 and now E15 joe bidumb
the new pump is E10 good.
for sure spectra premium brand pump. SP3xx? is good.
the plastic tank is good to go E10 up.

ULTRA-POWER SP736H
this at rockauto is really SPectra brand, and ISO9001 certified too. it will not fail for E10. the stock jeep pumps all failed. until cured later.

THE GUY ABOVE POSTING REAL EFI FUEL HOSE CLAMP IS WINNER"tHanks". NEVER USE CARB HOSE CLAMPS ON EFI SYSTEMS. EVER.
UNLESS DRIVING A ROCKET , IS A GOAL.
EFI PRESSURES CAN HIT 100 PSI, use only legit clamps.