Trouble pinpointing 99 XJ Fuel System Issues
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Year: 1999
Model: Cherokee
Engine: 4.0 L
Trouble pinpointing 99 XJ Fuel System Issues
I started having issues since I dropped my fuel tank and put in a new Carter fuel pump assembly. At first the new pump seemed to be working great. Seems like the problem started when the Jeep wouldn't start up on the first try. Knowing the battery was at the end of it's life, I assumed that was the problem and replaced it along with the cables. After that replacement I've still had to prime the system and the engine wont start up until the 2nd, 3rd or 4th try (and recently, sometimes not at all). It smells like it's been running rich and I've got P0171: "System too lean" and 1494: "Leak detection pump switch or mechanical failure" error codes. (Recently replaced the EVAP purge solenoid and all the rubber elbows to pass smog, so I'm not sure if the second one is related.)
Sometimes the Jeep will drive fine—usually first thing in the morning. After that it all goes downhill: on acceleration, the engine starts to sputter and feels like it's about to stall, I get no power and sometimes it will suddenly lurch forward. I started getting P0300: "Random/multiple cylinder misfire detected" codes, especially when idling in traffic. Had to get towed home the last time after I stalled at a stop sign.
I went out and rented a fuel pressure test gauge to get a better idea of what's going on.
1st test of fuel pressure:
Sometimes the Jeep will drive fine—usually first thing in the morning. After that it all goes downhill: on acceleration, the engine starts to sputter and feels like it's about to stall, I get no power and sometimes it will suddenly lurch forward. I started getting P0300: "Random/multiple cylinder misfire detected" codes, especially when idling in traffic. Had to get towed home the last time after I stalled at a stop sign.
I went out and rented a fuel pressure test gauge to get a better idea of what's going on.
1st test of fuel pressure:
- Primed the fuel rail by turning the jeep on and off: got about 10psi
- Shorted the fuel pump relay with a piece of wire: got about 20psi
- Turned the engine over: ~30psi
- Foot on the gas: drops to 20psi
- Turn the Jeep off: pressure drops to 0 immediately
- Test to see if fuel pressure leak is in the back of the system by clamping off the fuel hose that connects to the front of the fuel rail: same thing, drops off immediately
- Prime with keys in the ignition: less than 10psi
- Prime by shorting the pump relay: about 10psi
- Trying to start it up: almost no pressure (<10psi), starts up and immediately dies
Last edited by coffeeCola; 03-13-2019 at 07:08 PM.
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Year: My Jeep is a GMC
I went out and rented a fuel pressure test gauge to get a better idea of what's going on.
1st test of fuel pressure:
1st test of fuel pressure:
- Primed the fuel rail by turning the jeep on and off: got about 10psi
- Shorted the fuel pump relay with a piece of wire: got about 20psi
- Turned the engine over: ~30psi
- Foot on the gas: drops to 20psi
- Turn the Jeep off: pressure drops to 0 immediately
- Test to see if fuel pressure leak is in the back of the system by clamping off the fuel hose that connects to the front of the fuel rail: same thing, drops off immediately.
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Year: 1999
Model: Cherokee
Engine: 4.0 L
I'm a little out of my depth with how to test the voltage. What's the procedure? Is it just attaching the test leads of a voltmeter to the positive and negative wires to see if there is a significant difference to the battery voltage when I turn the key?
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Year: 1999
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Engine: 4.0 L
Couldn't voltage drop make the pump perform poorly? It's under warranty, but I want to make sure it's a dud before I go through the trouble of dropping the tank to take it out and put in a new one.
I tried testing the voltage on the fuel pump harness using the below photo/diagram I found over on this thread (Cherokee Forums – Low Fuel Pressure plus p0122 code). I attached the positive lead to a safety pin I stuffed in the the back of Pin Cavity 1 and then attached the negative lead to the undercarriage, but couldn't come up with anything on the multimeter when I shorted the relay. Thinking maybe I didn't get a good enough ground.
I tried testing the voltage on the fuel pump harness using the below photo/diagram I found over on this thread (Cherokee Forums – Low Fuel Pressure plus p0122 code). I attached the positive lead to a safety pin I stuffed in the the back of Pin Cavity 1 and then attached the negative lead to the undercarriage, but couldn't come up with anything on the multimeter when I shorted the relay. Thinking maybe I didn't get a good enough ground.
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Year: 1992
Model: Cherokee
Engine: 4.0L L6 PowerTech (stock)
Couldn't voltage drop make the pump perform poorly? It's under warranty, but I want to make sure it's a dud before I go through the trouble of dropping the tank to take it out and put in a new one.
I tried testing the voltage on the fuel pump harness using the below photo/diagram I found over on this thread (Cherokee Forums – Low Fuel Pressure plus p0122 code). I attached the positive lead to a safety pin I stuffed in the the back of Pin Cavity 1 and then attached the negative lead to the undercarriage, but couldn't come up with anything on the multimeter when I shorted the relay. Thinking maybe I didn't get a good enough ground.
I tried testing the voltage on the fuel pump harness using the below photo/diagram I found over on this thread (Cherokee Forums – Low Fuel Pressure plus p0122 code). I attached the positive lead to a safety pin I stuffed in the the back of Pin Cavity 1 and then attached the negative lead to the undercarriage, but couldn't come up with anything on the multimeter when I shorted the relay. Thinking maybe I didn't get a good enough ground.
Yes, underpowered pumps produce less pressure at the rail and push less volume thru the lines.
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#9
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Year: 1995
Model: Cherokee(XJ)
Engine: I6 4.0L
I missed the part where you mentioned "this started after installing a new Carter pump".
So either you boogered up the wiring/connector when installing the pump, or the pump is junk (and with Carter brand, I happen to suspect the latter.)
Once you have some reliable numbers on the voltage, if it's leaning towards the pump, replace it with a Bosch if possible.
So either you boogered up the wiring/connector when installing the pump, or the pump is junk (and with Carter brand, I happen to suspect the latter.)
Once you have some reliable numbers on the voltage, if it's leaning towards the pump, replace it with a Bosch if possible.
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Year: 1999
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Engine: 4.0 L
In case anyone else with the same issue stumbles on this thread, replacing the fuel pump fixed this issue.
The 2nd Carter fuel pump that came as a warranty replacement isn't reading the fuel level, but at least it's holding pressure.
The 2nd Carter fuel pump that came as a warranty replacement isn't reading the fuel level, but at least it's holding pressure.
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