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Old 05-10-2019, 09:08 PM
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Join Date: Mar 2011
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Engine dies while driving. Only on bumps

Looking for some pointers from the more knowledgeable on connections to check.

99 TJ 2.5L manual

Symptom: while driving the engine would sidedly die, or occasionally flash a brief CEL and the speedo would nose dive (while at speed), before recovering. Thought it might be fuel pump or CPS. Checked fuel pressure, 50 psi steady for 15 mins at idle. Checked fuel pump connector that I could get to in front of the tank, seems solid. So I go buy a new CPS and pop it in. Test drive the jeep and it almost dies. However i now notice that only when going over sharp bumps at around 25-30mph, this triggers the dying. Almost positive it’s only when the rear axle hits. In hindsight, that matches what I recall from the first few times.

I just had a shop install a ECGS 8.8 rear axle and SYE. It’s been driving fine for 2 weeks. A buddy asked for a refresher course learning manual today. He was a bit less experienced than he claimed. Lot of stalls and jerking, and at one point I heard a horrible drive shaft thump and called it a day. When I’m driving it still rolls fine so I don’t think he did any structural damage.

Given the above, the only thing I can think of is maybe the fuel pump has some sorta intermittent ghost (4 or 5 year old parts store brand, not Bosch), or there’s some electrical connection associated with the transfer case or hidden fuel pump connection that’s loose and being jarred by the bumps. Would the transfer case connections cause the engine to die? Is there some other fuel pump connection I’m missing? Anything else I’ve missed entirely?

Any help would be appreciated. This one has me stumped.

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Old 05-11-2019, 07:05 AM   #2
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Not fuel pump if gauges affected

Sounds like maybe a intermittent tub ground

Check the ground strap

Look on hinge edge of underside of hood. There should be a ground strap bolted on with other end attached to a firewall bolt

From that same firewall bolt another ground strap is attached and other end goes to a bolt on top back of engine

Check that ground from firewall to engine make sure undamaged and clean and tight on both ends

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Old 05-11-2019, 07:10 AM   #3
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I had my Jeep turning off randomly on large bumps from a heavy key chain that would literally turn off my Jeep.

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Old 05-11-2019, 12:48 PM   #4
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Maybe a long shot here but worth checking.

There is a wiring harness that passes behind the engine with very little clearance between the engine & firewall. The firewall has a bolt from the cab sticking out & the harness can rub on it causing damage. There are several wires in the harness & any of them can randomly get damaged causing any number of problems from blown fuses to loss of power. This often happens either when hitting bumps or sometimes when turning causing the engine to shift enough to push the harness into the bolt.

It is tight & hard to see back there but worth checking it. Here is a link to one such problem.


And this with 2 with the same problem & some photos/diagrams. Note posts 6 & 15.


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Old 05-11-2019, 07:21 PM   #5
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My Jeep would intermittently die when I would hit a bump due to the middle connector to the wiring harness dry rotting and not retaining the connector. A military spec zip tie (3 actually) fixed the problem.
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Old 05-12-2019, 04:53 PM
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Got some time to play with it today. I didn’t notice anything upon first glance at the firewall connector. I’ll have to take a closer look. That really seems like the likely culprit as I keep throwing parts at the jeep.

I’ve replaced the CPS, VSS, and some of the general tuneup items (cap, rotor, plugs and wires). The jeep began being a little hard starting to where you had to goose it to get it to start. Went to the local store and picked up and IAC ($80!). Popped that in and it started surging and throwing IAC codes. Put the OEM one back in and things were back to the previous state. Returned that IAC and ordered one online for 11 bucks. We’ll see if that helps at all.

I’ll take a closer look at that harness and report back. Given all the start and stopping from my buddy’s learning attempt, I could see something getting rubbed the wrong way
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Old 05-12-2019, 09:12 PM   #7
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Check main grounds.
Check alternator and fuse box leads.
Fuel pump could do this.
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Old 05-16-2019, 10:55 AM
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Checked all the main grounds, checked the engine harness, inspected the wiring in the engine bar near anything that could abrade it, nada. Took a quick clamp to squeeze the harness connections together securely, engine still died.

However, I "fixed" it by replacing the IAC. Now why on earth the IAC would kill the engine from a bump, I have no idea. I figure it would just stumble a bit. However, the jeep has not died once in the spots where I was previously able to make it die at will.

So I spent $240 throwing parts at the thing to find out it was a $11 chinese made part that corrected. Will keep an eye on it.
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Old 05-17-2019, 03:33 AM   #9
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