GC5.2 ZJ: Slow acceleration from tranny or differential??

Hi all,

Two things I want to ask about, and forgive my ignorance in accurately describing the following issues.

First, my 93 5.2 GC (220K) doesn't have the "snap" it should, 90% of the time, throughout the speedometer range. Off the line it's decent, but the accelerator pedal doesn't really seem as "sensitive"/"responsive" as it should be even then. (I acquired the 93 w/209K and did tranny service (pan, filter, new fluid), new water pump/timing chain among other things).

For example, at 20 mph, when I give a moderate push (30%-60% pedal), it doesn't drop to a lower gear and "crank-up" the RPMs for that "burst" one would expect. Instead after about 2 seconds, it seems the engine RPM's "jump" up" slightly (like a delay), not the amount one would expect though. The only time(s) the "gear drops/RPM's jump" as expected is when I push practically 85% of the way on the pedal-- then it moves, and when the RPMs hit high (4K? 5K?) it shifts to a higher gear/RPM's drop back as expected-- *BUT*, after that speed "brust" if then I do not COMPLETELY let off the pedal (all the way), the engine will shift to a lower gear and momentarily spike the RPMs up again past 5K!, seemingly "out of control" (scary-- that makes one completely release the pedal..)

I also have a 95 ZJ 5.2 (175K) which completely flies as expected with a moderate pushing on the accelerator, off the line, and throughout the driving range, so I'd assume the engines are similar if not identical.

The other issue, which may be related is that I've never changed the differential fluid, and I don't know when/if it had been done before on this vehicle, and I wonder if that could possibly be contributing to the above problem in any way.

With respect to the differential, if I start up in the morning on a spring day for example (not a cold day when idle would be raised by the IAC valve), and I warm for only 30 seconds or so and switch into drive, and let the idle move the vehicle, it takes maybe 5-10 seconds before the Jeep starts to creep forward. This happens sometimes. Now this ZJ has a low idle to begin with (~620, dunno why), but I don't think that's the issue. It seems that once the car is warmed for 5 minutes or so this doesn't happen at all. This also could be an issue with the parking brake because when I first drive off (at a moderate rate) I hear a 1 second "rub" from the vehicle.

I also wonder on such a high mileage vehicle, if there's any risk to getting the differentials completely changed/flushed, and having the differential box "cleaned out" with carb/brake cleaner or the like. I've heard/read that doing flushes on "high mileage" tranny's can remove benficial "varnish", and I wonder if a similar principle applies here, if my differential hasn't been serviced for a very long time/ever.

I'm also considering putting in a bottle of Lucas Transmission Fix into the tranny just beacuse.. How much tranny fluid would I need to siphon out and do I add the whole bottle of Lucas? Is there any chance I could hurt the tranny further by adding the Lucas?

Thanks in advance.

Reply to
jimboe via CarKB.com
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Try cleaning the Throttle Position Sensor:

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Some stuff about how yourtransmission shift points are controlled:
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God Bless America, Bill O|||||||Omailto: snipped-for-privacy@aol.com
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Reply to
L.W. (Bill) Hughes III

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