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  #1  
Old October 7th, 2020, 10:56
TricolorXJ TricolorXJ is offline
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1991 XJ SE - Crank no start problems

Hey all, new here and I thought I would throw my hat in the ring.
I have a 1991 Cherokee XJ SE that has been sitting for years.


I'm able to get it running with starting fluid, so I'm pretty sure/ hope the only problem is that it's not getting gas.


I just found out that I checked the power to the fuel pump wrong. I had to have someone crank the engine when I checked, and I had just turned the key to the on position and got little to no readings on the multi-meter. I will be going to recheck the power tomorrow.


I can't find anywhere that tells me where the Fuel pump fuse is. The fuel pump relay is getting power (around 12 volts), replaced it with the AC fuse and it still didn't start.



It has fresh fuel, enough coolant and oil, and I cleaned the spark plugs.


I don't have a way to post images, but there is an electronic harness to the right of the air filter box that isn't connected to anything. Is this to access the computer? Would be happy to know what that goes to/if that is normal.


Thanks!
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  #2  
Old October 8th, 2020, 22:11
TricolorXJ TricolorXJ is offline
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Re: 1991 XJ SE - Crank no start problems

As an update, I still didn't get a power reading on the multimeter going to the fuel pump. But the relay is for sure working. Still couldn't find the fuse for the fuel pump.
Any ideas on why the fuel pump may not be getting power? I may have checked it wrong, I'm not a mechanic unfortunately lol
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  #3  
Old October 9th, 2020, 19:07
Unclewolverine Unclewolverine is online now
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Re: 1991 XJ SE - Crank no start problems

If you got power at the relay and not at the pump its a bad connector or broke wire. Have you tried hotwiring the pump?
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Old October 9th, 2020, 21:59
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8Mud 8Mud is offline
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Re: 1991 XJ SE - Crank no start problems

I may be wrong, I'm old three relays control the fuel pump. ASD relay supplies power to the whole sytem, the ballast relay is power to the pump while cranking and bypasses the ballast resistor, the fuel pump relay supplies power while running through the ballast resistor.

The black green (?) wire at the ballast resistor should be hot both during cranking and running. I may be wrong on the color, one end of the resistor should be near battery voltage the other end noticeably less than battery voltage, but hot none the less. A quick check for both the fuel crank and fuel run relay.

Unclewolverine may be onto something, seen it before, the fuel pump wire/harness goes through multiple connectors (5-6?) which increases the chance for one to cause issues. The fuel pump ground can also cause issues.

If you have power at the ballast resistor, at the pump in the rear, a good ground and still no fuel try wacking the outside of the fuel tank near the pump hard a few times with a rubber mallet. When the pump sits idle for a long time, the varnish in gasoline can cause them to seize. It is sometimees possible to free the pump with a sharp blow to the side of the tank.

Another quick test, when the key is first turned to/or through the run position the fuel pump should run for a few seconds to prime the fuel rail. Turn it to run a few times, then push in the shrader valve on the fuel rail, you should get a squirt of fuel. On mine I can hear the pump run for 2-3 second when I turn the key to run, it's subtle but noticeable.

Lastly when they have been sitting for a long time the fuel filter gets gunked up. Have some extra fuel line handy and take the filter off, wash it in some solvent or gasoline, blow through it backwards. Make sure to keep track of in and out on the filter. Have something handy to plug the line from the fuel tank, it may start to siphon drain the tank with the filter removed. A new filter isn't really very expensive, I usually put one in after I've had it running for awhile, I reuse the old filter until things have cleaned themselves out some with fuel flow.
I don't have a 91 schematic, but the basics transend multiple years.
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  #5  
Old October 10th, 2020, 09:44
TricolorXJ TricolorXJ is offline
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Re: 1991 XJ SE - Crank no start problems

Thank you both for the replies,


I have not tried hotwiring it, I don't think I have the tools or the know how to do that. I'm sure there are plenty of how-tos around the internet. Not sure what you mean by "Bad connector". Do you mean the male/female power connectors that are near the fuel pump?



I will be trying to bang on the tank haha, a neighbor suggested doing that.


But as I mentioned previously, the power not getting to the pump is concerning. 8Mud, can you clarify a few things, I'm new to XJ's and car mechanics:


Is ASD the Auto Shutdown Relay? Where is the Ballast Relay located? In the relay box in the engine bay? Still haven't been able to find the fuse to the fuel pump itself.


I'll be checking the power to the ballast resistor but what does "A quick check for both the fuel crank and fuel run relay" entail?


Sorry for the 10 million questions, thanks again!


Some additional info: The 1991 XJ is a 6 cylinder 4.0, and 4x4.
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Old October 10th, 2020, 11:27
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8Mud 8Mud is offline
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Re: 1991 XJ SE - Crank no start problems

Quote:
Originally Posted by TricolorXJ View Post
Thank you both for the replies,


I have not tried hotwiring it, I don't think I have the tools or the know how to do that. I'm sure there are plenty of how-tos around the internet. Not sure what you mean by "Bad connector". Do you mean the male/female power connectors that are near the fuel pump?



I will be trying to bang on the tank haha, a neighbor suggested doing that.


But as I mentioned previously, the power not getting to the pump is concerning. 8Mud, can you clarify a few things, I'm new to XJ's and car mechanics:


Is ASD the Auto Shutdown Relay? Where is the Ballast Relay located? In the relay box in the engine bay? Still haven't been able to find the fuse to the fuel pump itself.


I'll be checking the power to the ballast resistor but what does "A quick check for both the fuel crank and fuel run relay" entail?


Sorry for the 10 million questions, thanks again!


Some additional info: The 1991 XJ is a 6 cylinder 4.0, and 4x4.
I'm not real familiar with the 91 and don't have a schematic handy so some of this is guesswork.
The ASD relay is the auto shut down relay, the ECU (engine control unit/computer) gets a pulse signal from the CPS (crank position sensor) as the motor turns over and closes the fuel pump relay when the engine fires up. The ECU closes the Ballast relay (in the PDC power distribution center just behind the battery). during cranking, this bypasses the ballast resistor and gives full power to the pump to compensate for the power drain needed to run the starter motor. Under normal running the power from fuel pump relay to the pump goes through the ballast resistor which cuts down the voltage a bit. I hope my explanation is clear.
The ballast resistor is located on the inside of the drivers side fender well on most models, not sure for the 91. A white ceramic block maybe two inches long. There should be power there during both cranking and running. You can bridge or jumper the ballast resistor, it is largely useless anyway, it was installed to quiet the feul pump some for sissy drivers.
You have spark so the CPS is likely good, when bad you will have no spark or fuel, the ASD relay won't close. You have spark so the ASD relay is likely good, it also supplies power to the ignition coil.
The harness for the fuel pump and other stuff runs down the drivers side under the inside door sill. That harness has many connectors along it's length any one of which can be corroded, loose or have a poor contact inside a connector that can generate enough heat to discolor or partially melt the plastic connector (happened to me). The connector that melted on one of my XJ's was the one just before the rear fender well, but there are others just as vulerable to failure.

I have no idea where the fuel pump fuse is on the 91 on some later models it was the "2" fuse. But most years the PDC fuse layout changed most every year. There should be a fuse and relay diagram in the cover for the PDC. Or in the owners manual.
Sorry about typos, spilled coffee in my keyboard, makes typing interesting.

No problem with the questions, I just hope my explanations make sense. XJ acronyms and part names can be confussing, expecially because some have evolved over the years. I still use ECU (Engine control unit) the new name is PCM (powertrain control module). I learned automotive electrical on main battle tanks in the military, enough wiring in one tank to build a fleet of XJ's . I've been working on XJ's since 87. Things that seem common to me might be greek to you.
If you have a wiring problem this can turn into a real can of worms, can be labor intensive and may take hours (or days). I always found it to be challenging and interesting, some people get frustrated.
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  #7  
Old October 10th, 2020, 13:13
TricolorXJ TricolorXJ is offline
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Re: 1991 XJ SE - Crank no start problems

Thanks for the next plan of action and wealth of info 8Mud!


I'll get a chance to work on it early this week. What I'll plan to do is check that ECU fuse (which I believe is the fuel pump fuse among other things).


Then I'll check to see if the ballast resistor is getting power going to it and from it.


Then I will do some wire following from the fuel pump up to the engine to see if I can find any corroded connections and to check the power on those connections.


If the ballast resistor IS getting power how might I bridge that? I don't mind a loud fuel pump if I can get this baby running! Plus I can't even find ballast resistors on Oreilly's, etc. Would I need to get some splicing tools and learn to use them to bypass it?



Any website recommendations on finding OEM XJ parts or at least quality parts? Kind of considering buying fuel pump and filter anyways since its probably gunked up.
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  #8  
Old October 14th, 2020, 20:29
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Rob Mayercik Rob Mayercik is offline
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Re: 1991 XJ SE - Crank no start problems

The standard crimp-on spade connectors should match the terminals on the resistor, so making a plug-in jumper should be easy. I just cut the harness connectors off and used a butt splice.

30s stock should work ok, but may need a couple washers under the steering stops.
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  #9  
Old October 16th, 2020, 21:58
TricolorXJ TricolorXJ is offline
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Re: 1991 XJ SE - Crank no start problems

Hey thanks for the replies!


Here's the update : So I got the old fuel pump out and it had lost its filter and had a bunch of black goop on it. Had a broken hose fall off of it, so it was ready to be replaced.


Unfortunately, I could not get the new one to fit in there so I wasn't able to crank it today. I tried fitting it all sorts of ways but could not get those two notches to fit into the fuel tank female receptors.


I saw a video and it looked like one guy didn't make the notches fit and just put the retaining ring back on somehow anyways. I didn't get that far.


I did try to remove the tank but could not get one of the large bolts to budge on the fuel tank shield. Actually bent a socket extender and thought I was moving the bolt


Next time I go back I'll bring some wd-40 for those bolts. In the meantime I'll be researching putting that pump back in, maybe there's a secret. I was also worried there was sludge/parts of the old fuel pump blocking the new pump's entry. And that was the main reason for trying to remove the fuel tank.


Any insights would be greatly appreciated!
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  #10  
Old October 22nd, 2020, 15:19
TricolorXJ TricolorXJ is offline
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Re: 1991 XJ SE - Crank no start problems

Update, was able to get some gunk out but still not fitting. Iíve decided to drop the tank and clean it but didnít have time today. Any recommendations on getting those big rusty bolts for the tank shield off? Hopefully I can get the fuel pump to fit once that tank is out or maybe it will be the wrong part...will keep updating.
Any advice welcome
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