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No power to the fuel pump, 89 MJ

xjtrailrider

xjtrailrider

NAXJA Forum User
NAXJA Member
Location
Roanoke VA
Okay, I have been down this road with this truck before. When I bought it 2 years ago it was sitting dead with no fuel pressure. I traced the problem to the starter relay. I got power to the pump but it still would not work. I replaced the pump with a new unit and all was good until a month ago. I have also had a issue with the bulkhead connector dropping power to the pump and radio, nothing else. You can wiggle the connector and then it would get power back and run.

Finally last Thursday it just would not start. At first I thought the CPS but I can prime the throttle body and it will fire. I have no pressure at the rail.

I started testing and tracing the problem today. I removed, checked, tightened the pins and installed some new die-electric grease in to the bulkhead connector. I see no issues there at all. I have power to the radio now along with everything else.

I had bypassed the ballast resistor a while back. I now do not have power there when the key is in the "run" position, I do not have power at the pump but I do have a ground. I think the issue is somewhere around the starter relay again or possibly a relay or fusible link, maybe even a ignition switch. I do not have a wire schematic for the RENIX so if someone can tell me where the power to the ballast resistor is coming from I would really appreciate it. I need to get this thing running for my son since it is his only car.
 
The fuel pump gets power to prime from the fuel pump relay when the key is in the run position. When the key is in the start position power to the pump is from the starter relay (think it is a orange and black wire not sure) and bypasses the fuel pump relay and ballast resistor. When the ECU gets a good CPS pulse (engine starts), it closes the fuel relay again and then power goes through the ballast resistor to the fuel pump (if you have a ballast resistor).

The wire is orange and after the ballast resistor goes through a splice and four connectors, at least on my XJ. Any of the connectors can cause issues, I found one that was toasty and mostly burnt black. I was getting 9-10 volts in (through the ballast resistor) and 6 volts out of the connector. My fuel pump got really iffy, low voltage and likely low amperage. I jumped all the connectors to the fuel pump, solder and shrink tubing. One thing that threw me was the wire changed color to purple or something between one pair pf connectors. Might have nothing to do with your issues,but something to look at if it isn't something else.

The fuel pump relay gets power *in* on the 30 pin from a fusible link, power out is the 87 pin. I believe the 86 pin is power with key on (run and start) and the 85 grounds (switches) through the ECU.

The 86 pin is the yellow wire, same sub system and yellow wire (through a splice) that goes to the ignition module (larger yellow wire) and the alternator (and some others). Power with key on (run and start).
 
Joe_peters just posted this in another thread, it really got my attention, might help some here:

Renix fuel pump:

1. Key ON, the fuel pump is energized for a couple of seconds, then power is cut.

2. Key START, power to fuel pump from the starter.

3. Key ON, engine RUNNING, power to fuel pump from the fuel pump relay.

4. Key ON, engine running at WOT, power to fuel pump from the O2 heater relay.

Fuse? Fuse link, ignition switch, fuel pump relay and their connections all come to mind.

I think even the haynes junk manuals have the wiring drawings for this, I think 8mud posted it a few times over the years here in old no start threads.

Edit: LOL, 8mud to the rescue :)
 
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Chassis electrical diagnosis is my weakest area of my mechanical ability. Where do I start? I do not have power to the pump at any point of 8Muds description. This is the exact same issue I had 2 years ago.

I found bad and repaired/replaced;

Starter relay, as I had no power to the pump during cranking of the engine

Repaired the bulk head connector, this may still be a bad connection but I have no power before it either?

Then found the ground to be bad at the pump, made new ground

Then got power at the pump only to find that I still had no pressure. It turned out to be the elbow above the pump going into the bung was completely disintegrated. I replaced the pump and elbow with a Bosch unit and it ran great for 2 years up until this last episode.

The starter relay had burnt contacts in it on the fuel pump side. The bulk head connector is still an issue, you can wiggle it and cause the fuel pump to drop power, IF I can get power to the connector. Right now I'm dead all the way back starting at the starter relay. I ran a jumper from the battery to the down stream side of the old ballast resistor connection(mine is bypassed) and still no power to the pump under any conditions.

I'm at a loss.
 
A good place to start would be that splice where you jumped the ballast resistor.

Unplug the wire at the starter relay orange and black I believe, pull the oxygen sensor heater relay or all of them is even better. Break the splice at the ballast resistor. take an ohm reading from the orange wire to ground. This will tell you if you have an open circuit, you should get resistance but continuity through the pump to gorund. Then disconnect the fuel pump connector and do another ohm test, this will tell you if you have a short.

The fried wires on the old starter relay may be a short. Could be the harness rubbing on a seam in the frame or body someplace that is an, on again, off again event. I had one of those in my instrument lighting circuit.

Best guess would be a harness, splice or connector problem between the ballast resistor and the pump. Could be one of those connectors is melting down and some of the poles (pins) are making contact that shouldn't be. Or the splice is iffy and making heat.

Unplug the fuel wire from the starter relay turn the key to start and see if you have power there. As far as I know there is no fuse and nothing but a short piece of red wire and the starter relay itself between the battery and the fuel pin on the starter relay.

The guy that taught me to troubleshoot electrical systems back in the 60's (on the M-48 main battle tanks, your talking hundreds of yards of wire here), taught me to think of myself as a mouse and I'm on a path through the electrical system and to check all the stops (connectors) on my path to where ever I (the electricity) needs to be. Jumping from point to point with no real overview of the whole system is often frustrating and fruitless. I usually start in the middle and work first towards the power source or at the one end, the power source, and work towards where the current needs to be. There are usually events that happen on that path, relays that close, switches that need to be thrown and in the end a component that needs to work, A step by step systematic approach often gives better results than just jumping to possible trouble spots, swapping out components and hoping to get lucky. Time consuming, but I always rationalize the time spent as a learning process that will sooner or later come in handy again, you have to have patience.
 
I am really baffled by this. I pulled the O2 sensor heat relay and ran mine with out it for a year with no problem, before I found and fixed the shorted wires to the O2 sensor (Driveshaft ate the wires).

I think that O2 heater relay is energized all the time in the run position feeding power to the O2 heater (except at WOT according to Joe_peters?, which is also when the ECU switches to rich mode, bypassing the O2 sensor closed loop mode), keeping the O2 sensor hot, so I guess it is NO, but that means it powers the full pump with the ECU turning off that relay? Now I can see bypassing the ballast resistor at WOT to feed full voltage to fuel pump at WOT, but something must be cutting power to C228 with the engine off? Ignition switch perhaps?

8Mud said:
Click to expand...
 
Ecomike said:
I am really baffled by this. I pulled the O2 sensor heat relay and ran mine with out it for a year with no problem, before I found and fixed the shorted wires to the O2 sensor (Driveshaft ate the wires).

I think that O2 heater relay is energized all the time in the run position feeding power to the O2 heater (except at WOT according to Joe_peters?, which is also when the ECU switches to rich mode, bypassing the O2 sensor closed loop mode), keeping the O2 sensor hot, so I guess it is NO, but that means it powers the full pump with the ECU turning off that relay? Now I can see bypassing the ballast resistor at WOT to feed full voltage to fuel pump at WOT, but something must be cutting power to C228 with the engine off? Ignition switch perhaps?
Click to expand...

My guess is in 88, when they added the ballast resistor because of fuel pump noise complaints, they needed a quick fix for possible fuel starvation during WOT. They also designed the XJ for the European market and some places over here, there are no speed limits. Few quicker ways to lunch a motor than to run it at full throttle, lean, for long periods. Necessary parts and pieces like the pistons melt when the motor runs too lean. European models also got colder plugs.

Maybe the ECU defaults to full rich at WOT and the O2 sensor is unnecessary, darned if I know.
 
8Mud said:
A good place to start would be that splice where you jumped the ballast resistor.

Unplug the wire at the starter relay orange and black I believe, pull the oxygen sensor heater relay or all of them is even better. Break the splice at the ballast resistor. take an ohm reading from the orange wire to ground. This will tell you if you have an open circuit, you should get resistance but continuity through the pump to gorund. Then disconnect the fuel pump connector and do another ohm test, this will tell you if you have a short.

The fried wires on the old starter relay may be a short. Could be the harness rubbing on a seam in the frame or body someplace that is an, on again, off again event. I had one of those in my instrument lighting circuit.

Best guess would be a harness, splice or connector problem between the ballast resistor and the pump. Could be one of those connectors is melting down and some of the poles (pins) are making contact that shouldn't be. Or the splice is iffy and making heat.

Unplug the fuel wire from the starter relay turn the key to start and see if you have power there. As far as I know there is no fuse and nothing but a short piece of red wire and the starter relay itself between the battery and the fuel pin on the starter relay.

The guy that taught me to troubleshoot electrical systems back in the 60's (on the M-48 main battle tanks, your talking hundreds of yards of wire here), taught me to think of myself as a mouse and I'm on a path through the electrical system and to check all the stops (connectors) on my path to where ever I (the electricity) needs to be. Jumping from point to point with no real overview of the whole system is often frustrating and fruitless. I usually start in the middle and work first towards the power source or at the one end, the power source, and work towards where the current needs to be. There are usually events that happen on that path, relays that close, switches that need to be thrown and in the end a component that needs to work, A step by step systematic approach often gives better results than just jumping to possible trouble spots, swapping out components and hoping to get lucky. Time consuming, but I always rationalize the time spent as a learning process that will sooner or later come in handy again, you have to have patience.
Click to expand...

Great advice! I'm heading out to the garage now.
 
.....So i go out to the garage and before I do any of the diagnostic work mentioned above by 8Mud and Eco, I decide to see if it will start. As soon as I turned the key to "run" the fuel pressure came up, i heard all of the relay's doing their thing and as soon as I turn the key to start after 4 revolutions it fires up and runs perfect.

WTH!

This is what it has done now for the last month or so. Runs fine for a day or two, shut it off and no restart until it WANTS TO!!! Sometimes its a few minutes, in this case it has been 5 days without any fuel pressure then out of no where I have a full 30psi at idle and 39 with the FPR unplugged.

I need to find this issue and I'm now leaning towards the ignition switch. This one is new(2 years old) and its a BDW brand.

This is making me bat**** crazy:mad:
 
Check the mounting and adjustment of the ignition switch on the column. If good, I would then start renewing grounds and connections in the engine compartment.
 
joe_peters said:
Check the mounting and adjustment of the ignition switch on the column. If good, I would then start renewing grounds and connections in the engine compartment.
Click to expand...

Thanks Joe, All of my grounds have been upgraded and I just re-checked them 2 days ago. Is there one in particular that will affect the fuel pump relay? I checked the ground at the fule pump and its good and I added another ground strap from the chassis to the fuel pump bung.

I just got home from running errands and decided to try to start it up. It would not start, no fuel pressure. IF I can get it to start it will run and never shut off but if I cut it off and go to restart it, cold or hot, it may or may not start.:doh:

When I left the house at 7:15 pm my fuel pressure gauge read 30psi key off, when I got home at 9pm it reads 0. Typical of the RENIX era, the check valve is long gone. But I will say this MJ starts up on less cranks than my 90 XJ(when the MJ starts)
 
How is the ground at the tank--seen those deteriorate badly.

You are going to need a second pair of eyeballs.

Use a test light at the fuel pump by the tank--check for power on when you first turn the key to the ON position. If the test light lights and the pump primes, then try to start the engine. If not--repair what is wrong before moving on.
 
joe_peters said:
How is the ground at the tank--seen those deteriorate badly.

You are going to need a second pair of eyeballs.

Use a test light at the fuel pump by the tank--check for power on when you first turn the key to the ON position. If the test light lights and the pump primes, then try to start the engine. If not--repair what is wrong before moving on.
Click to expand...

I've done this, if i get power to the pump, it always starts and runs. My meter is telling me I have a good solid ground at the pump connector and on the bung. It will either get power and runs or it doesn't. Time to start tracing wires and bypassing connectors.
 
Ever done this?

I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals making sure they haven’t retracted into the plastic holder, and then plugging it back together. There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one. Also be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.
ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then plug them back in. I do this on every Renix Jeep I purchase or work on for someone else.
Revised 07/23/2012
 
So I opened up the main engine wire harness where it goes into the bulkhead connector to check splice A in the schematic. The splice is like new, still had that funky factory duct tape wrapped around it LOL!

I hook my test light to that splice and to a the nearest ground(which I also checked, it was good at the splice as well) I turn the key and I get a light!

But still no fuel pressure....Hmmm.

I ran a jumper directly from the splice to the connector at the fuel pump, turn the key, get a bright light but no fuel pressure.

I reconnected the connector and try again-no fuel pressure.

I took a dead blow hammer and pounded the bottom of the tank, turn the key and BINGO! Fuel pressure!

It appears that either I have a bad pump or a bad connection at the pump. So the tank will come out next.

So, 8Mud, Joe and Eco, if I run a direct connection from the splice A to the fuel pump connector what will it hurt? This will eliminate several connections and I can run the wire in a loom down the frame rail with the fuel lines to the pump. Not ideal but as it is right now that orange wire goes through the bulk head connector, into a loom behind the fuse block, down along the door seal and across the floor board and out the bottom of the cab. There are many potential places for an issue down the road and I would like to eliminate all of them now while I'm at it.

Your thoughts?
 
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