Novak Conversions Jeep Wrangler JK radiators

JKU hesitates and sputters when accelerating at low RPMs

whiff

whiff

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Rowlett, TX
2008 JKU X, 6 speed stick, no major mods, just 18 in wheels and big brakes all around, 211k mi. Hesitates/sputters only when accelerating at lower rpm, like 1k to 2k. Goes away, nearly completely once operating temp is reached. No codes. Short term fuel trims are zero, long term trims at 6 and 6.5. Recent swrvice in last three months: new cats and O2 sensors, plugs, wires, and ignition module, crabk zensor, pcv valve, spray clean throttle body. Use only 93 octane fuel since 150k mi. Every 5k full synthetic oil, uses about a quart every 2500 mi. Runs silently smooth, other than hesitation. Next steps?
 
whiff said:
Hesitates/sputters only when accelerating at lower rpm, like 1k to 2k. Goes away, nearly completely once operating temp is reached.
Click to expand...
Some clarification please. Is this a WOT acceleration and you only get the hesitation initially, or a more typical part-throttle accel? Do you get this if you are already moving and try to accelerate from a low rpm or only from a standing start?

Without knowing the answers above, my first thought is the throttle body. You said you cleaned it and, admittedly, I'm not familiar with the 08 specifics. I assume that is an electronic throttle body? With 211k the actuator motor may be getting tired and losing control/accuracy at lower opening angles. Inaccuracies with airflow at certain operating points (low load, off idle, etc) really play havoc with the control systems ability to compensate for stability.

If you are gently tipping into the throttle and it's doing this try a more aggressive acceleration - WOT, or close to it, and see if it still happens.
 
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"spray clean throttle body"

I would almost always first start with a more through cleaning and possibly new injectors. That many miles means you have some build up in the injector and it may not be nebulizing the fuel well until it is under greater pressure. Especially, in a cold start state, that thing has to do double work trying to manage a cold engine and low throttle response.

My two cents (worth about .5 in current economy).
 
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tJKrider said:
Some clarification please. Is this a WOT acceleration and you only get the hesitation initially, or a more typical part-throttle accel? Do you get this if you are already moving and try to accelerate from a low rpm or only from a standing start?

Without knowing the answers above, my first thought is the throttle body. You said you cleaned it and, admittedly, I'm not familiar with the 08 specifics. I assume that is an electronic throttle body? With 211k the actuator motor may be getting tired and losing control/accuracy at lower opening angles. Inaccuracies with airflow at certain operating points (low load, off idle, etc) really play havoc with the control systems ability to compensate for stability.

If you are gently tipping into the throttle and it's doing this try a more aggressive acceleration - WOT, or close to it, and see if it still happens.
Click to expand...
It happens from.standing start when cold, then only when accelerating from slow rolling in 2nd and third at temp . I did not remove throttle body when spray cleaning, so back sidw may need it. Will try... Thanks!!!
 
tJKrider said:
Some clarification please. Is this a WOT acceleration and you only get the hesitation initially, or a more typical part-throttle accel? Do you get this if you are already moving and try to accelerate from a low rpm or only from a standing start?

Without knowing the answers above, my first thought is the throttle body. You said you cleaned it and, admittedly, I'm not familiar with the 08 specifics. I assume that is an electronic throttle body? With 211k the actuator motor may be getting tired and losing control/accuracy at lower opening angles. Inaccuracies with airflow at certain operating points (low load, off idle, etc) really play havoc with the control systems ability to compensate for stability.

If you are gently tipping into the throttle and it's doing this try a more aggressive acceleration - WOT, or close to it, and see if it still happens.
Click to expand...
And it does not happen at high rpm accel.
 
Still chasing this sputter/hesitation...
1 Thoroughly cleaned throttle body, front and back. A bit of improvement resulted.
2 Replaced crankshaft position sensor. A bit of improvement again, but not perfect.
3. Replaced camshaft sensor. Again, a bit of improvement, but still hesitates a vit on low rpm accel when cold.
4. Replaced EGR valve. Good improvement, but then threw code for catalyst inefficiency on bank 1. Cats are only about 18 mos old.
5 Replaced downstream O2 sensor, cleared code. Still hesitating. Watched live sensor activity from cold to warm and all vary within spec voltages. Code did not return.
6. Threw code for misfire cylinder 4.
I don't mind throwing those parts at it, as it's at 218,000 miles and they're all originals, but I'm thinking fuel injectors now. They too are original. Keeping in mind that it runs perfectly smoothly, better than new, once thoroughly warmed up, and I did plugs, wires, and ignition module in the summer. Thoughts?
 
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