Hello

I am a novice so please excuse any dumb comments.

I have a 1984 CJ7 Laredo that has had a 4.3 Fuel Injected Vortec Motor and a 700R4 Electronic Shift transmission out of a 1996 chevrolet blazer. I have also installed a digital speedometer. I did not do the install myself and I am having some doubts as to the person I hired to do it.

The problem as I have been told is that when my digital speedometer reads that the jeep is travleing 65-70 mph down the highway - the computer is getting a reading of only 40-43 mph - there by never allowing my torque converter to come one. The person I hired for the install as spoke to AA whom the kit came from and they appear to be stumped - he thinks that it might be a problem with the gear ratio in the rear end??????

Please advise!!!!!!

Thanks
Kincaid

Your Gear ratio and tire size would definetly cause that, what was the trans out of and what is you gear and tire size.

What VSS sensor does it have in the truck and were is it mounted?

Hello

Thanks for the Help.

I do not know what the gear ratio is. I know that I have the stock axles and gears that came in a 1984 CJ7 Laredo. I am presently running 32"-33" Tires on 16x8 wheels. The transmission and motor came out of a 1996 GMC Jimmy or chevrolet blazer.

I have been told that the computer is reading a reluctor ring that is in between the transmission and the transfer case and that my speedometer is wired up to a different speed sensor on the transmission.

Thanks
Kincaid

I would agree, it sounds like you speedo is aftermarket and probably set for the tire and gear ratio. Jet makes a calibrator they call accu-speed that will allow you to adjust you transmision output signal to your ECM. I think it will allow you a good range of control on your shift points. Call them they can tell you how ta get one. Jet Performance Products 714-848-5515

Read this:
http://614streets.com/drac.html
If your system is a PCM then you can change tire size in the computer with LS1 edit:
www.carputing.com

The 700r4 trans is not an electronic trans for speed pickup,the t-case should have the cable output for the speedomoter. If using the aftermarket electronic speedo you should have a signal generator mounted where the old cable connected to the t-case, giving you your pulsed output. If they are matched there should be no problem. The 700r4 is only actuated electricly for the lockup on the convertor. Sometimes when using other pickups OR using electric shift trans, like a 4L60E or 4L80E, they have to be calibrated. As far as I know Autometer is the only aftermarket gauge that has the ability to read a stock VSS signal from the electronic GM trans. We have done a few of the swaps without issue. Here is a pick of what you should have on the back the back of the 700r4.
Our 700r4 adapted to a Toy case
http://i10.photobucket.com/albums/a102/rockfab/kimera002.jpg

Toy case cable output fitted with a Autometer pulse generator
http://i10.photobucket.com/albums/a102/rockfab/speedsensor.jpg

Autometer Ultra lite gauge setup
http://i10.photobucket.com/albums/a102/rockfab/kimera057.jpg
Now if you have the 4L60E trans you will need a reluctor ring kit, and it should be 40 pulse to work with an Autometer gauge, it the has to be calibrated by driving 1 mile at constant speed. You hit the button on the gauge when you start then hit it again when you pass the mile. Hope this helps a little.

REa read your post if all you want is the torquec convertor lockup order the switch kit from Summit then you control when it locks up. You should tie it into the brake switch so it disengages when you hit the break also.

Here's a great article on speed sensors. Newer PCM's, and even older one's can be adjusted either through PCM programming, or the DRAC module:

https://shell7.tdl.com/~jags/V8-chapters/V8-tpi-Speed-Sensors.pdf

There's no need for a special speedometer unless just to simplfy the installation. For a custom application it's acceptable, but this is the way to go without looking like you've got an AutoZone credit card.

I really appreciate all the info and help.

I have figured out the following. If the jeep is traveling 65 mph down the highway and the computer is reading from its vss only 40 mph and I take a tech II computer and manually engage the torgue converter (overdrive) - then the motor lugs bad. So I am leaning towards the real problem being the stock gear ratio of 2.73 and me running 32"-33" tires. If I use the Jet accu-speed sensor (which appears to be a great idea) it would probably solve the problem with the computer reading - but when the torque convert kicks in - it would still lug the motor real bad.

I think the solution is changing the gears and then using the accu-speed sensor to dial it in if need be. ??????????

Thanks!!!

Also

It was my mistake I do have the 4L60E Transmission - not the 700R4

The Bazer likely had ~3.73 gears, and 29"-30" tires to start
with, so your rig is way out of spec from what the computer
is thinking. Gear swap time, 2.73 are way to tall for 33" tires
look in the 3.9X and lower (higher number) gears, just to get
it to be a OK street driver.

Mike D.

You should be able to just reprogram the computer for tire size and gear like on a stock truck. And the computer read the speed correctly

Fuel Injection specialties in Texas reprogramed my ECU and removed the codes for the tranny, I know you don't want to do that but they will ask you alot of questions about your vehicle when you call them, tire size, gear ratio, tranny, about 150$. Worth the dough. Good Luck