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The damn clockspring can cause engine to run lean

RaymondT

TJ Enthusiast
Supporting Member
Joined
Aug 13, 2016
Messages
596
Location
Summerland, B.C.
I've been living with a 2.5 that's been a little cranky below 2300 rpm. Always assumed (like many others) that it's just a characteristic of the old AMC designed motor. The right conditions cause it to buck at 2000rpm while pulling a hill and suddenly giving it a little more throttle. Now before you 4.0 owners write this off as a 4-banger problem, bear in mind we have the same harnesses, clockspring, and ECM design. 2 extra cylinders might mask the problem. And please note, no codes or check-engine light is set.

It was only when an ABS light started coming on that I ended up changing the clockspring. While doing some web-surfing on this problem, it was evident many others had the 2000rpm jerk. There were other suggested fixes such as injector wiring mixed up or sensors - for some, it fixed the problem but many others it did not. Some dumped loads of $$$ changing every sensor on the engine. Then I found a post from @Jerry Bransford that explained it the best. A failing clockspring with an intermittent break in one of the wires can back-feed noise down to common grounding point in the ECM. This noise causes an error in the TPS signal to the ECM resulting in the wrong pulse duration to the injectors (= lean!).

What a difference this has made in the idle - 2200 range. This engine now runs as good as the day it came off the lot.
 

Chris

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Sep 28, 2015
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Salem, Oregon
No kidding? I would have never guessed that. Good information from @Jerry Bransford. Thanks for sharing this. I think this is one of those posts people are going to stumble upon down the road and be thankful it exists.

How did you determine the clock spring was actually bad though?
 
OP
RaymondT

RaymondT

TJ Enthusiast
Supporting Member
Joined
Aug 13, 2016
Messages
596
Location
Summerland, B.C.
No kidding? I would have never guessed that. Good information from @Jerry Bransford. Thanks for sharing this. I think this is one of those posts people are going to stumble upon down the road and be thankful it exists.

How did you determine the clock spring was actually bad though?
The ABS light started coming on after the system check and on a few times, when the steering wheel was moved. But for two years, the engine didn't run it's best at time below 2K. Some days, it was quite lively, other times, it just seemed cranky - like an engine miss but more subtle.
 

Chris

Administrator
Staff Member
Joined
Sep 28, 2015
Messages
40,682
Location
Salem, Oregon
The ABS light started coming on after the system check and on a few times, when the steering wheel was moved. But for two years, the engine didn't run it's best at time below 2K. Some days, it was quite lively, other times, it just seemed cranky - like an engine miss but more subtle.
Wow, 2 years? That would have driven me crazy.

And of course the last place I would have ever thought to look was the clock spring, sheesh!

Always carry a spare I guess.
 

Rollin20z

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Joined
May 9, 2019
Messages
224
Location
King George VA
Too weird that I read this and now recall mine giving a buck every now and then and sometimes while coming to stoplight or such stopping idle will stay up around 12-1300 rpm's and seem to stay there and even a quick throttle jab doesn't knock it back down but then it'll just return to normal. Only been happening past couple weeks and only bucked a couple times and rpm's acting up a couple times more. No lights or anything popping up so I guess I have been just forgetting about reading on it to find out whats causing it. I'll keep a closer eye on it and go from there. Thanks though as I neither would've ever thought of clock spring. I guess just like I never thought my plug on my hazard switch would've been not fully seated causing me to have no brake lights either but still have hazards. 😕
 
OP
RaymondT

RaymondT

TJ Enthusiast
Supporting Member
Joined
Aug 13, 2016
Messages
596
Location
Summerland, B.C.
One of the clues that this might be an issue is how it starts. With the clockspring replaced, it's back to normal. Starts instantly and revs up to 12-1300rpm and then settles down after a few seconds. With the faulty clockspring, it cranks a few seconds longer, and just comes up to idle 800-850 where it finally smooths out.