Wrangler 2.5L Kicking and Bucking at higher RPMs - JeepForum.com

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post #1 of 4 Old 03-25-2007, 04:21 PM Thread Starter
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1997 TJ Wrangler 
Join Date: Mar 2007
Location: Reno Nevada
Posts: 27
Wrangler 2.5L Kicking and Bucking at higher RPMs

1995 Wrangler 2.5L + 31” Tires on D35 4.10

Oil pressure: 50psi
Temperature: 190
Volts: 15.5
Fuel: Full
Speed: Irrelevant (30 through 70)
Miles: 151,000
Altitude: 5200ft
Grade: Flat
Conditions: 20% Humidity, 70°F, Sunny
Road: Street or Highway
Oil Grade: 10w40

Sitting in my driveway, rev motor to 4000 RPM, purrs like a kitten.
Rolling downhill, downshift so the new gear is 3500-4000 RPM, purrs like a kitten.
Very slowly accelerate past 3300ish – 4000ish, purrs like a kitten.
Accelerate normally or aggressively past 3300ish and the RPM needle drops something like 1000 RPM instantly. If I leave my foot on the gas the RPM’s will ‘bounce’ between the two and the Jeep will lurch and buck.

When I bought this Jeep it had 33” tires. I swapped them out for 31” tires. I live up a 4 mile highway with a 5% grade. I don’t have the power to hold 55-60 in fourth so I ride it high in third. Like between 3000 and 4000 RPM. I did this for about a week without issue. I changed the oil, transmission fluid, transfer case fluid, air cleaner, spark plugs, and checked the timing. I took the Jeep for a test drive down and then back up that hill without issue. I took it out wheeling for several hours without issue. The next day I am on an onramp getting up to speed when I first feel the motor ‘buck’. I took my foot off the gas and clutch and limped it home not knowing what might have happened. I was high RMP at the time. I was looking at merging traffic and not at my gauges so I don’t know the exact RPM. There is the possibility that I went past redline. I looked the motor over and broke out the timing light again. The timing was the same as before, 13° BTDC. I suspected that I may have purchased the wrong spark plugs so I put the old ones back in. The Jeep still has the problem.

Any information on what might be the issue here as well has suggestions on how to fix it.
Advice on the timing: my Haynes says I don’t need to adjust it on a fuel injected motor and even if I could I can’t get the bolt to come loose that holds the distributor in place.

Last edited by MrHappy; 03-25-2007 at 07:01 PM.
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post #2 of 4 Old 03-25-2007, 11:41 PM Thread Starter
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Location: Reno Nevada
Posts: 27
I couldn't get over the fact that it seemed the problem is related to the ignition timing so I went over all the systems involved. It turns out that one of the bolts fell out of the crank posision sensor located on the bell housing, and the remaining bolt was very loose. I replace the missing bolt and tightened them both up and no the Jeep runs great. Still gutless, but running great.
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post #3 of 4 Old 03-26-2007, 10:26 AM
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my 2.5l did the same thing, it was the fuel filter(located inside the tank )
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post #4 of 4 Old 03-26-2007, 12:34 PM Thread Starter
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Location: Reno Nevada
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Oh, I forgot to mention that I changed the fuel filte too. It was one that is just ahead of the rear tire on the body frame. I think I will get some injector cleaner and add it to my tank. the Jeep is running fine now but it can't hurt i suppose.
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