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Unread 06-13-2009, 11:35 AM   #1
DoubleBET
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Hard shifting + no shifting = auto tranny issue?

Hey guys, yesterday I began experiencing the following issues seemingly out of the blue, in the middle of driving down my local highway:

- While accelerating from stop, the jeep would pick up speed up until around 25 mph, but not readily switch into the next gear unless I pushed down extra hard on the gas. When it did change gears, it would be a hard shift. RPMs would remain around 2200 until the shift, after which they would skyrocket to around 4500 and slowly back down.
- After the gear switch, RPMs would go back down to 2200 and stay at 2200 while the vehicle slowly accelerates. Sometimes the jeep would make another hard jump to the next gear if the pedal was floored, other times flooring it would do almost nothing, and RPMs would remain at 2200 as the jeep slowly accelerated to upwards of 55 mph. This would be a very slow acceleration, and it felt like the entire engine was straining.

It's very odd that the RPMs would stay at 2200 at higher speeds, since normally flooring it at just about any speeds would cause RPMs to shoot up to at least 3500 and the jeep would accelerate quickly. The current issue reminds me of what it feels like when I'm towing something/pulling a heavy vehicle. It's as if the engine's straining, limiting itself to 2200 RPMs to limit the strain.

Other details:
- Oil pressure is a bit low, never goes above the halfway mark, usually hovering around the 1/4 mark on the gauge. Normally it's a bit higher. Dipstick shows engine oil's slightly low but above the min.
- Before yesterday, the past few days while starting the jeep in the morning, the very first time I hit the gas, the engine sputtered/almost stalled, but was then fine. This never happened before this week.
- Transmission fluid is at the proper level but hasn't been changed in a long time. In the past my mechanic had advised me not to change it because a new (and more grainy) fluid might put extra strain on the transmission/result in harder shifting.

So that's my problem. Any thoughts? My mechanic's supposed to look at it on Tuesday. I'm quite terrified that it will be a tranny issue, in which case my jeep is probably as good as dead, since I won't have the cash to repair it

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Unread 06-13-2009, 03:05 PM   #2
CJ7-Tim
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Quote:
Originally Posted by DoubleBET View Post

- Before yesterday, the past few days while starting the jeep in the morning, the very first time I hit the gas, the engine sputtered/almost stalled, but was then fine. This never happened before this week.
- Transmission fluid is at the proper level but hasn't been changed in a long time. In the past my mechanic had advised me not to change it because a new (and more grainy) fluid might put extra strain on the transmission/result in harder shifting.
Transmissions with weird behavior ( and the strange acceleration issues ) point you in the direction of sensor issues that are confusing the TCU. Check the TPS and NSS.

Find a new mechanic. I don't how your mechanic can do any work with his head so far up his *ss. Change the transmission fluid. Trans fluid is never "grainy", only burnt and contaminated. Use only the Factory Recommend Dexron III/Mercon. Drain 3-4 quarts from the pan using the drain plug and re-fill. Do this once a week for 3-4 weeks or until the trans fluid looks and smells normal. High pressure transmission fluid flushes are what people should be referring to as they do tend to dislodge debris.
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Unread 06-13-2009, 04:36 PM   #3
DoubleBET
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Do you think an issue so dramatic as this could arise suddenly if it were a sensor? Pardon my noobishness but what are the TCU, TPS and NSS? Can a general mechanic check those or will I need to bring it to a transmission specialist?

Hmm, I see what you mean about not changing the fluid, it seems counter-intuitive. However it also seemed counter-intuitive for my mechanic to want to do less work on my car, hence making less money. So I never really questioned his advice...
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Unread 06-13-2009, 07:41 PM   #4
CJ7-Tim
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See these two links for more information -
http://www.jeepforum.com/forum/f11/cherokee-stock-specs-26256/
http://www.jeepforum.com/forum/f11/tech-faq-links-tsbs-89273/


NSS - Neutral Safety Switch, Transmission Position Sensor
TPS - Throttle Position Sensor
TCU - Transmission Control Unit

The engine computer (ECU) and the TCU work together with data from the TPS and NSS to determine shift points and transmission status. Bad data from any sensor will cause the computers to default to limp mode that is supposed to protect the engine and trans from damage.
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Unread 06-13-2009, 11:56 PM   #5
alexrule123
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Sounds like the throttle position sensor to me
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Unread 03-11-2011, 06:14 AM   #6
mayeni
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Hey
What does the NSS do?
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Unread 03-11-2011, 06:25 AM   #7
egodfrey
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Check your TPS
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Unread 03-11-2011, 08:06 AM   #8
tjwalker
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If this were mine, I'd definitely start with the throttle position sensor. Failure of this component is not uncommon and it is directly involved with transmission shifting characteristics.
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