MJ Fuel Delivery Problem - JeepForum.com
 
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post #1 of 4 Old 04-22-2019, 10:46 PM Thread Starter
shivlesNbits
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MJ Fuel Delivery Problem

I run a 1986 Jeep Comanche 2.5l and my fuel delivery is messed up it seems. I have bench tested the pump, which starts up immediately, checked the filter to make sure it wasn't clogged, and the only thing I seem to have an issue with is the relay itself.

Here's the issue: I have to use a jumper wire on the fuel pump relay socket to get the fuel pump to engage on its own. The main ground for the pump is super shiny and clean, but when I have the original relay in the socket, it just constantly clicks, and when I have a new relay in the socket, nothing happens at all. The only way the fuel pump primes is by a fused jumper cable from pin 30 to pin 87.

At first, when the original relay was in the relay socket, I could pour fuel into the throttle body, and it would start up like a champ, only to die after the fuel had been burned off. Now, it's starting to struggle to even do that with the original relay in.

With the jumper cable priming the fuel tank, the engine will not fire at all. It will constantly try to crank, but it will not fire for some reason.

I have not tried the fuel pressure yet, but that is on my list for the next time I see my truck. Also may check spark plugs to see if they got fuel-logged from the fuel pump constantly priming before cutting it off.

If anyone has any words of wisdom, I'm all ears. I've been trying to remedy the problem for four days..


1986 Jeep Comanche 2.5L 5-speed manual 4x4

2002 Jeep Wrangler 2.5L 5-speed manual 4x4
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post #2 of 4 Old 05-10-2019, 11:55 PM Thread Starter
shivlesNbits
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Bump, bumpbumpbump bump...

1986 Jeep Comanche 2.5L 5-speed manual 4x4

2002 Jeep Wrangler 2.5L 5-speed manual 4x4
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post #3 of 4 Old 05-16-2019, 11:17 PM
Luuca
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Confused. you said throttle body. Does your 2.5l have TB Injection or a carb?

duh.. checked the stock specs and yes TBI.. ok then

If you have detected an issue with the relay, it is possible that the relay wiring on the bottom of the relay box is corroded or bad.

Before you do that though,..

rent or borrow a fuel pressure tester. Not sure if the 86 has a schraeder valve or not but it may. see how much fuel pressure you have at crank. if it's low, it could be that the problem is the wiring between the pump and the relay - based upon you stating that the pump tested good.

Since you can get it to run with a jumper, I would suspect the relays you are using are bad. you can swap in the horn relay or another new relay and test it.

I'd take a good look at the relay box wiring underneath. it may be cracked and not allowing a new relay without corrosion to make good contact.

strange one. WIsh I was more help, but I have never worked on a TBI system.

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post #4 of 4 Old 05-18-2019, 04:21 PM Thread Starter
shivlesNbits
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Thanks for the info, Luuca. Even though you don't have much experience with the TBI, I appreciate the comments. I'll have to inspect the fuel pump relay socket more and see if there's something going on there.

1986 Jeep Comanche 2.5L 5-speed manual 4x4

2002 Jeep Wrangler 2.5L 5-speed manual 4x4
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