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89 MJ, no fuel pressure except when the key is in "run"

xjtrailrider

NAXJA Forum User
NAXJA Member
Location
Roanoke VA
I thought I would start another thread. My other one started out to be one problem but was actually another


I have fuel pressure when the key is in "run" but no pressure when the key is in "start"

Here is what I have done; Cleaned grounds, checked synch sensor, replaced CPS(still had the original in it), checked all relays except started relay, checked the index on the distributor, checked injector pulse on all six injectors, I have strong spark.

If I "prime" the TB it will start and run as long as keep fuel going in the TB, there is no pressure on the rail until the engine dies then I get pressure. I can hear the pump running with the key in run but not in crank.

The pump "primes" but never shuts off like my other RENIX XJ does

I suspect the starter relay but I can't find one locally to try

The Jeep has sat for 3 months, the fuel smells okay but I added a can of Heet to it anyway.

Help me get this beast running!
 
You should have a small cream colored resistor on the fenderwell. Called a ballast resistor.

It is there to reduce noise on the fuel pump circuit.

When this resistor goes bad, you will have fuel pressure when the key is in the "start" position, as the ballast resistor is bypassed in this position. However, when the key is released and goes back to the "on" position, the ballast resistor is back in circuit and you will lose fuel pressure.

Try bypassing this resistor with a piece of wire. Or measure the resistor (it will be stamped as to the spec resistance) and replace if necessary. (they're only a few bucks)

Need to rule this out early in this process.
 
Any way you can check the voltage on the pump while its being started to see if it is dropping voltage at that point? If not I'll help you tomorrow morning when I ride down.

I wish the jeep was here at the house but its at Fitch's house. I hate working on the ground!
 
You should have a small cream colored resistor on the fenderwell. Called a ballast resistor.

It is there to reduce noise on the fuel pump circuit.

When this resistor goes bad, you will have fuel pressure when the key is in the "start" position, as the ballast resistor is bypassed in this position. However, when the key is released and goes back to the "on" position, the ballast resistor is back in circuit and you will lose fuel pressure.

Try bypassing this resistor with a piece of wire. Or measure the resistor (it will be stamped as to the spec resistance) and replace if necessary. (they're only a few bucks)

Need to rule this out early in this process.

The resistor is bypassed. That was the first thing I tried!
 
The resistor is bypassed. That was the first thing I tried!

If you have power to the pump when the key is in the full "start" position, but that power is gone when the key is released, and you already have the ballast resistor bypassed, the likely suspect is the ignition switch in the column.
 
The resistor is bypassed. That was the first thing I tried!

1) You know the pump is good.

2) It is very odd the that pump never shuts off in the run, pre start mode, then fails to run in the continue running mode, but the continue running mode does use a different circuit. The fact that it never shuts off in the pre start mode may be a clue, perhaps the wiring is no longer stock?????

3) I would check the wiring diagrams at this point, and check the voltage at the ballast resistor (monitor it while some one else starts it) to see if it is ever hot, and when is it hot, feeding into the resistor. If there is power at the ballast resistor, then the wire from there to the fuel pump is bad, otherwise......
 
If you have power to the pump when the key is in the full "start" position, but that power is gone when the key is released, and you already have the ballast resistor bypassed, the likely suspect is the ignition switch in the column.

I sort of disagree, here is why. He said it does keep running if he manually adds fuel to the throttle body after starting it. In the run after start mode, I think the ECU powers the fuel pump via a fuel pump relay through the ballast resistor, not through the ignition switch or the fuse panel.
 
Does it have an alarm system?
 
Does it have an alarm system?

LOL, who puts an alarm system on an 89 MJ? LOL

With my luck they would steal the ALARM!!!!! LOL, and leave me stuck with the Old jeep!
 
Its the fuel pump. I remembered to take my gauge with me today. I have "0" psi with the key on but there is fuel flow. When the key is turned to start the amp draw from the starter shuts the failing pump the rest of the way down.

I have a Bosch on the way in the am

Learned a good lesson from this, just because you have fuel in the rail it doesn't mean you have enough pressure and flow to run the Jeep!

Thanks for everyones help
 
87-90 fuel pumps problem Renix by Ecomike
http://www.naxja.org/forum/showthread.php?t=1048534
I had a non working fuel pump about 18 months ago, 20,000 miles ago on my 87 XJ Wagoneer. I cleaned the fuel pump QC male/female connectors and ground/external connection at the rear of the face plate on the outer housing and the fuel pump has worked ever since. 2 weeks ago the same thing happened to my daughter's 89 XJ. I cleaned the same connectors on it and that fuel has worked ever since.
Most people would have replaced the fuel pumps. I think it may partly be a grounding issue over time.

-------------------------------
Grimm Jeeper posted I just swapped out my a Renix pump I was sure was bad, even though I could hear it working the truck would die every time I touched the gas pedal and would barely idle. Turns out the feed hose was rotted out inside the tank (from the pump to the hard-line that passes through the plate). Next time I'm starting with the fuel pump instead of swapping in all my spare sensors and such.
 
87-90 fuel pumps problem Renix by Ecomike
http://www.naxja.org/forum/showthread.php?t=1048534
I had a non working fuel pump about 18 months ago, 20,000 miles ago on my 87 XJ Wagoneer. I cleaned the fuel pump QC male/female connectors and ground/external connection at the rear of the face plate on the outer housing and the fuel pump has worked ever since. 2 weeks ago the same thing happened to my daughter's 89 XJ. I cleaned the same connectors on it and that fuel has worked ever since.
Most people would have replaced the fuel pumps. I think it may partly be a grounding issue over time.
-------------------------------
Grimm Jeeper posted I just swapped out my a Renix pump I was sure was bad, even though I could hear it working the truck would die every time I touched the gas pedal and would barely idle. Turns out the feed hose was rotted out inside the tank (from the pump to the hard-line that passes through the plate). Next time I'm starting with the fuel pump instead of swapping in all my spare sensors and such.

Good advice here. Even if you do replace the fuel pump, be sure to do what is suggested above.
 
Good advice here. Even if you do replace the fuel pump, be sure to do what is suggested above.

X2 had one where the connector near the rear fender well (inside) was making poor contact. Volts X Amps = Watts, Watts are what makes it run. One or the other (volts or amps) low or missing and it can fool you into replacing a good pump. I usually double check the ground and run a wire straight from the battery to the pump, before I do anything else.
Many timers I've found wires that are in a position prone to wiggling or vibration, fatigue through the copper strands in a wire, under the insulation. They can be rough to find, but if you jump the harness and test, and it functions (whatever component) at least you know you have a choke point to find.
 
I put the new pump in and all is well, runs awesome!

A pump had been put in it years ago but it was a botched job. The elbow was left loose and popped off and no pressure was able to make it to the rail. I went with a Bosch unit.

Thanks for everyones help/suggestions!
 
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