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Unread 03-19-2012, 08:40 AM   #1
All3Sports
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2004 KJ Liberty 
 
Join Date: May 2011
Location: atlanta, georgia
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PCM/Transmission problems

Ever since I installed my tires/lift my transmission doesn't seem to function properly. I have to literally floor it to get it to accelerate/change gears. The RPM's stay relatively low but then shoot trough the roof during slight acceleration. It just feels sluggish until it accelerates and over works itself. I know I'd lose alot of power by the lift and tires but with cruise control on it can't keep a stead speed and is either falling down to 5 mph under and floors itself to 5 mph over. Is it best to keep o/d off? Or just disconnect the battery and see if it relearns better.

Thanks in advance!

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Unread 03-19-2012, 06:06 PM   #2
tjkj2002
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You need to have the speedo calibrated,or known as a pinion reset.Only the dealership can do this and some years it can be done and others it can not,some years that it can be done will only accept some tire sizes.Your whole issue is in the speedo being incorrect and the TCM knows this by other sensor inputs.
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Unread 03-19-2012, 06:14 PM   #3
tjkj2002
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Quote:
Originally Posted by Powerslave View Post
You installed larger tires then? IT has nothing to do with the transmission, they are partially controlled by the TCM, and they have set values for shift points, and TCC lockup, by the transmission speed output sensor. Calibrating the speedometer CAN help...

There is no real compensation for large tires, unless you have the TCM shift points programmed, manfully, at higher RPMs. That's just the way it is. I got OE tires, and going up small grade hills, many of us have complained about the crap acceleration. TCC lockup occurs to early as it is, and with larger tires? Good luck...

The only way to really compensate, is to find a junked 4Cly Gasser and swap the complete rear and front ends, they have 4.10 gears in them. Stock is 3.73 gearing, and it SUCKS... It would cost you more money, and take you more time to do ring and pinion gear swaps in the diffs, over the complete axle swaps.

OR? Spend almost $300.00 on a stage II jet chip...
While regearing will help the trans will still fall flat on it's a$$ without the speedo being correct.The chip will do nothing for the issue,it's all in the speedo.

I know I went through the same thing.

3.73 gears and 265/75's,no speedo correction and couldn't get out of it's own way.4.10's and no speedo correction it had more power but the trans still hunted all the time.4.10's and the speedo corrected and very good power and no more hunting of gears and alot better mpg's.
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Unread 03-20-2012, 09:22 AM   #4
All3Sports
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So dealership for pinion reset at dealership? And it improves my MPG? Sounds good thanks for the advice.
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Unread 03-20-2012, 06:47 PM   #5
streetglideok
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Recal the speedometer, so the PCM has an idea how fast the vehicle is going. DO this AFTER you regear the diffs though.
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Unread 03-20-2012, 09:56 PM   #6
wmcreyno
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Quote:
Originally Posted by Powerslave View Post
OR? Spend almost $300.00 on a stage II jet chip...
Don't!! waste your money on jet crap.... Jet ****s are not vehicle specific tunes or anything.... they just trick the PCM into thinking the vehicle is running lean.... thus it compensates and makes the vehicle run rich and dump in more fuel..... this is a stupid way to gain power (if you even gain any) when there are custom tunes available..... B&G performance offers custom tunes for the liberty which actually change PCM programming Hypertech has also recently released a programmer for 2004 and up liberty's .... bottom line ive had a jet Chip in the past installed on my old S10 and it was ****.....
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Unread 03-22-2012, 08:01 AM   #7
tjkj2002
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Quote:
Originally Posted by Powerslave View Post
The JET chip is the real deal, I am not talking the FAKE ones all over Ebay. The Jet Chip, stage two works, I have seen it, and FELT it. Much more power, with the gas mileage suffering. It also calls for a Thermostat change, and larger exhaust.

TO the other, regearing would work just fine. I work at a performance shop, I know what regearing will do. You will be able to ask the owner of an H2 SUT we regeared, with no ECM modifications. If you have not done the math, then again: Insert exclamatory remarks here.. The SUT us getting huge tires, plus almost 200Lbs of Dynamat, so, the over 5.xx gearing will make due.

Again, why this stuff works for me ant no YOU ALL? Well, that's something to figure out on your own. I never have any issues with my mods... Must be that I accidentally do it right... Sucks to me me, huh? Yep, I guess so, but my **** runs...
The PCM will "learn" around the Jet stage II chip,I know I have one.The only reason I have it is becasue of the increased trans line pressure which does not get learned around.Basically the same as doing the resistor mod on the 45RFE/545RFE.

Changing the gear ratio on a KJ does not effect the speedo,adding larger/smaller tires does,again I know by personal experiance.I went from 3.73's to 4.10's,nad now have 5.13's.
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Unread 03-23-2012, 08:51 PM   #8
wmcreyno
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Quote:
Originally Posted by Powerslave View Post
Again, why this stuff works for me ant no YOU ALL? Well, that's something to figure out on your own. I never have any issues with my mods... Must be that I accidentally do it right... Sucks to me me, huh? Yep, I guess so, but my **** runs...
Not to be a smartass but no one was saying your mods do not work.... the jet chip is just not the best option... and you said you accidentally do it right? implying that we do not know what we are doing..... plugging a stupid jet "chip" into a socket on the PCM doesn't really take a rocket scientist.... all i was saying is that why would you waste your money on a chip that essentially tricks the PCM into making the vehicle run Richer.... when for about 50 more bucks you can buy the hypertech programmer which actually changes the PCM programming..... AND my **** runs as well i ran this chip on my old S10 and saw basically no gains..... that s10 was pretty modified.... I SOLD THE JET CHIP and ended up doing much more expensive mods... i was running an aftermarket cam, custom dual exhaust, CAI, E-FANS, underdrive pulleys and a custom tune... and i wouldn't bash what TJKJ2002 has to say... as he has a KJ that is completely custom in and out and probably one of the nicest jeeps i have ever seen.... he knows what he is talking about... I wasn't bashing you i was just telling my first hand experience with a JET chip
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Unread 03-24-2012, 06:39 AM   #9
tjkj2002
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Quote:
Originally Posted by Powerslave View Post
I said accidentally, because according to said PROs, it doesn't work, so I must be "accidentally" doing something right for it to work where they have failed.

I work in a performance shop: www.dynamicsracing.com - I know how to get more out of nothing...

The Jet Chip Power control module sandwiches between the harness, and the ECM. Doesn't matter what the ECM sends out, the module intercepts and outputs it's own data curve. So, say the jet unit puts out data based on a curve of 10, but the ECM sends in a 5, it adds five to keep the output it wants. So, the ECM adjusts and sends out a 3, the unit adds 7, to keep it at the constant. The ECM will only compensate to a point, then stop. So, 25HP is 25HP, no matter how you slice it.

The ECM can relearn all it wants, then change its data to so-called "compensate", but the information sent out the system is still coming from the jet chip control module. I do not mean a stupid CHIP, or IAT mod, this is a power control module that replaces the data output from the ECM, with a data curve from the module. Oh, they work, believe it, or not, like rippley says... The Stage 2 module is more aggressive, and you need to change the thermostat to 180 degrees, and have a free flowing exhaust. This one does simply dump more high octane required fuel into the motor... These engines are all configured conservatively from the factory, they can put out more than it comes with off the line.

Then again, it all may be accidental, or God likes me, and makes it work, just for little ole' me...
The JET chip changes the inputs recieved by the PCM,it does not change the outputs.After awhile the PCM learns that the inputs are out of normal range and adjusts back into normal range,basically ignoring some inputs.One guy over on LOST has dyno proof the stage 1 chip actually netted a 5hp loss over stock.

Oh and you can not get something for nothing when it comes to engines.
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