I can't tell if towing (OD off) made any difference before & after I got the "5th gear flash". I don't regret it at all for normal use though.

 

What are you guys talking about on a reflash? I have a 99 WJ and have had it for the past 3 plus years and have put over 60k on it, and it's now just at 95k. Should I be taking it in for some kind of PCM flash? This is the 1st time i've ever heard about this. Also before I bought my jeep I had it inspected by a Jeep dealer and they never mentioned anything about a reflash.

 

from what i understand the dealer can reprogram(flash) your transmission control module(tcm) and powertrain control module(pcm). this basically updates your jeeps "computer". when they update the tcm it essentially adds another gear. this will lower your rpms by a couple hundred on the highway. the test is to drive 70 mph and if your rpms are 2000 then you already have the update. if your rpms are in the 2200-2500 then you do not have the update. i have also read that when people flash their pcm it changes the air/fuel mixture and can hurt fuel economy. so i was thinkng maybe i should just have the tcm flashed.

obviously, the test will not work if you have non stock gear ratios, etc.

 

here is the most simple answer i can give you....

99-01 v8 grand cherokees had a 45rfe transmission. its a 4 speed (3+OD)
02-04 v8 grand Cherokees had a 545rfe transmission. its a 5 speed (4+OD)

Now as odd as this sounds, the transmissions are identical. the 45rfe ACTUALLY HAS 5 GEARS inside it, but the computer is set to utilize 4 gears. Later, Jeep felt that they should "unlock" 5th gear, and become standard on 02+ models. In 2002, Jeep offered to this flash under warranty, regardless of mileage for free to all wj owners. it is no longer free, but is a great idea to do if you haven't already.

 

Does this apply or not apply to my WJ because it has the 4.0, or since it is a 2004 it is already updated?

 

So do you think I should reflash my jeep? Sorry about the hijacked thread.

 

you're thinking 42re

 

looks like i need to refer to wjjeeps.com...

difference between the two? I know on mine it it will go 1-2-3-4-OD...

 

From wjjeeps.com: "MODEL 45RFE or 545RFE: (used with V8 engines only)"

link: Jeep Grand Cherokee WJ - Transmission service and maintenace

 

Add'l info: http://www.jeepforum.com/forum/f13/2000-wj-transmission-flash-5th-gear-947133/

 

So who all has done this? I think I want to get the TCM reflashed, but not sure about the PCM. I don't need to lose any more MPG than I already have.

 

well i just had it done. whole visit took less than an hour. cost 70 dollars. the service manager and transmission tech recommended i drive for a few hundred miles before towing to allow the transmission to learn the new shift points, etc. They also said my pcm had already been updated. So the owner before me must have had that done but didnt get the transmission flashed(thanks jack ***.)

anyway, just in the twenty miles driving it home it definitely runs quiter and shifts smoother. i used to have a grown/moan/roar coming from the front end at 2000-2500 rpms. that is now gone. i think this could be the best 70 dollars i have ever put into a car. especially if i get another 2-3 mpg on road trips.

i am going on a short trip this weekend. will prob put 3-4 hundred miles on it. i will let you know the results

 

Sounds good. Keep us posted on the effects.

 

sorry to butt in on a thread, but is a tcm flash the same as a tcm snip switch? im about to buy a wj that the owner installed a tcm "snip switch" and i was wondering exactly what it did/how it works. thanks!

 

just got back from weekend trip. all in all about 300 miles since having the tcm flashed. rpms are definitely down 2-300 at all speeds. it makes it much more quiet on the interstate. so much so that i noticed i was getting a lot of wind noise coming in my door.

bottom line; 200 miles at 80 mph+100 miles of city driving=18.5 avg mpg.

tcm flash is a must have for 99-00 V8. Best 70 dollars i have ever spent on a vehicle

sorry to butt in on a thread, but is a tcm flash the same as a tcm snip switch? im about to buy a wj that the owner installed a tcm "snip switch" and i was wondering exactly what it did/how it works. thanks!

i dont really know. start a thread and maybe someone else can help you

 

A buddy and me (00JGC00) did the same flash a few months ago (& write-up)as well. I've noticed that it stays in lock-up a lot longer than it use to & will eventually shift to 3rd instead of 4th when coming from lock up in 5th at freeway speeds. Depending on how long i've moderately mashed on the gas will determine if it will shift from 5th lock up to 4th, but usually just goes to 3rd. The new programming also allowed the transmission to go to lock up in 3rd w/ OD off (didn't do that before) & lock up in 4th under load while I was pulling a trailer up a slight incline.

I am not too thrilled w/ how it shifts while pulling a trailer... it seemed to want to stay in the taller gears longer & then drop to a much lower gear & wrap out the motor until it shifted into a more appropriate gear, under moderate acceleration or incline. Under normal load circumstances, it does fine, but dammit with a trailer I need momentum, haha.

When we had our TCM's flashed, it also came with an ECU flash too... Could be a placebo affect, but it feels as if it pulls better towards redline than it did before. With that being said, it shifts MUCH smoother at higher RPMs.

Overall, the better gas mileage & peace of mind that my transmission runs the way God intended, helps me sleep better at night :thumbsup:

 

Sounds good. I'll look into doing this now. At least the tcm flash.