stumbling on acceleration could it be coil pack? -
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post #1 of 3 Old 08-28-2010, 09:44 PM Thread Starter
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Join Date: Oct 2009
Location: Missouri
Posts: 47
stumbling on acceleration could it be coil pack?

03, turned 100,000 couple weeks ago. I had since early last year when it had 84000. To me it always seemed a little weak on acceleration and hills but it does have 3.07 gears and 31s. But now it is not just steadily slow on acceleration but seems to be stumbling, perhaps misfiring.

I put in new Autolites (standard ones, not platinum) when I purchased it. Checked them couple weeks back (16000 on them) and they look clean, fairly white. No codes, have only had 1 code some time back for throttle position (it happened after washing engine bay), but that I cleared that and it never came back. That was probably a year ago. The oil pressure sensor has also been replaced.

I had fair amount of carbon in throttle body, took it off and cleaned a couple weeks back. Took out injectors last week, cleaned them and put on new o-rings. They were clean on the inside of cone, but carboned on outside.

But as mentioned plugs had no carbon, not dark at all. All plugs consistent color.

It also seems to jerk harshly when letting off gas at times, particularly with A.C. on. Runs not very steady at steady throttle (almost like a vacuum leak), but I suppose this could be A.C. kicking on/off.

Seems like when humidity is higher (also hotter out) it runs worse. Could the coil pack be causing the problems? I have been concentrating on the fuel system, but after running seafoam in gas and Chevron stuff tank before that, plus cleaning throttle body and injectors, can't believe it is still fuel related.

Had an Oldsmobile (Quad 4) which had coil pack issues and replacement fixed it. Oreilly's said perhaps bad O2 sensor causing issues and carbon, but no codes for that. He said it don't always throw a code. He recommended the Seafoam cleaning procedure. I haven't tried that yet.

Tempted to try new coil pack rail, but those are roughly $100 or so, and hate to spend the bucks if that is not the issue.

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post #2 of 3 Old 08-28-2010, 09:56 PM
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2002 TJ Wrangler 
Join Date: May 2009
Location: Cleveland
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I'm not a huge fan of Autolites. I tend to throw them away when I come across them and install NGK's which is what Mopar did when they quit using Champions. Without a DTC or atleast some live data recordings it is hard to say what may be wrong. I have seen a fair amout of heatsoak related issues that come from the number 3 injector boiling out. This creates air pockets on restarts reulting in lack of power and misfire. This clears up after a couple minutes on it's own. The "repair" is to install and insulator around injector 3. You will notice this most in high ambient temps with the a/c on.

Outside of this you just have your usual suspects. I would start with a compression check of all the cylinders and fuel pressure readings. Coil packs don't tend to get weak, they either work or they don't.
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post #3 of 3 Old 08-28-2010, 10:40 PM Thread Starter
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Thanks. I threw away the insulator material when I took out the injectors it was pretty much rotted away. Would wrapping the injector and fuel rail in exhaust tape material work as well? I've experienced heat soak vapor lock once after driving long distance and shutting off, then upon re-start (when insulator material was still in place). The misfire went away after a few seconds.

The current problem was before removing the insulator piece anyway. Did a compression test when purchased and everything was good (don't remember numbers, thinking 160 or so). Will probably do compression test again, and maybe regap plugs. Maybe try NGK. Some on here swear by the double platinum Autolites also. Do you use standard NGK or platinum ones?

Thinking about purchasing Harbor Freight fuel pressure tester for $80 and trying to check that.

I do have a bluetooth wireless OBD2 device with just free software packages from internet. It just indicates no codes, some live data, O2 sensors show values and fluctuate between lean and rich as they probably should. Also shows regular tests including misfire, with no negative results. Haven't tried it while driving to see data, may try that.
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engine , stumbling , acceleration

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