3.6 Pentastar acceleration hesitation / hiccup - AUSJEEPOFFROAD.COM Jeep News Australia and New Zealand


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Old 03-01-2018
oscar.kruse  oscar.kruse is offline
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Default 3.6 Pentastar acceleration hesitation / hiccup

So I have an issue where sometimes during acceleration, my acceleration just cuts out for about half a second and then resumes as normal. Causes a violent jerk of the car. It is as if my foot was slipping completely off the pedal. I assure you it is not. It generally happens when I am accelerating medium to hard from the bottom of the rev range right through to the top 3rd.

Happens maybe 2 in 10 times when accelerating hard/medium.

Been happening since i purchased the car (2nd hand@ 50,000KM) which was about 10,000Km ago.

I have tried different fuels including 98, 95 and 91, seems pretty consistent.

I constantly do scans with my (Bluedriver) code reader and do not get any related codes at all.

Have checked intake pipes for any leaks and cant find anything. Air filter has been cleaned.

Car details:
2012 JKUR Manual 60,000KM
No mods to engine except AirRaid intake from and AEV snorkel
Both exhaust mufflers have been replaced with smaller ones
37s and 4.88 gearing


Any help or similar experiences with solutions would be much appreciated.


Thanks guys

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Old 04-01-2018
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Does it happen when the car accelerates through a certain rev range or does it happen as you press the peddle through a certain point. Iv'e seen something similar in my daughter's Impreza as you depressed the pedal. In that case it was a dead spot in the throttle position sensor.

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Rod.
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Old 04-01-2018
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I would check for any vacuum leaks including the brake booster, also a fuel pressure check would be worthwhile, as low fuel pressure can cause hesitation.
Has the fuel filter been replaced recently?
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Old 04-01-2018
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when was the last time the spark plugs were replaced?
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Old 05-01-2018
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It does not seem to be any specific pedal position nor any specific rev. It is always generally different. I have even had it happen going up a hill with cruise control on.

Fuel pressure might be a little tricky to check. As for the fuel filters, they are inbuilt to the pump which is located in the fuel tank. Meant to have a "life time" serviceability according to Jeep.

Brake booster vacuum leak ? How will that affect acceleration ?

I initially thought spark plugs as well but apparently they have a life of about 100-120 km. This started happening at 50km.
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Old 05-01-2018
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In built fuel filters on jeeps are allegedly good for the life of the car, in practise I find them clogged at between 150,000 -200,000kms sometimes sooner for cars operating regularly remote and getting more dirty fuel.
The jeep service instructions says on some jeep models the filter is good for the life of the car but also it should be changed for engine performance & fuel system related defect investigations and low fuel pressure problems.

Fuel pressure in my experience is one of the easiest things to check on jeeps as most models have a service fitting somewhere on the injector rail which a test gauge can be readily connected.

Lastly the brake booster is supplied vacuum from the engine manifold if it leaks this creates an air leak causing a lean mixture in one or more cylinders adjacent to the vacuum take off port this air leak will likely lead to engine stumble and misfire under load. I am surprised you needed to ask that maybe you should take the vehicle too your trusted mechanic.
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Old 05-01-2018
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Have you got the stock y pipe with the post cat loop or a loop delete fitted?
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I don't have a fuel pressure gauge so for the moment I cant really go down that path. I have checked the brake booster and other vacuum lines and cant see any leaks.

I have still got the stock Y pipe and post cat loop, its just after that where I've removed the other two mufflers and installed smaller ones.
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Old 06-01-2018
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Quote:
Originally Posted by Classic Boy View Post
In built fuel filters on jeeps are allegedly good for the life of the car, in practise I find them clogged at between 150,000 -200,000kms sometimes sooner for cars operating regularly remote and getting more dirty fuel.
Yep, mine had to be changed at the 48K service due to similar issues.
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