Jeep Wrangler Forum banner

Wiring upgrade.... 90 YJ to OBDII

6K views 7 replies 5 participants last post by  JMickey 
#1 ·
I'm Considering upgrading my YJ to OBDII......
I know..why would I do a thing like that?

I'm starting with a 90 YJ fitted with 98 4.0 w/ 4.6 stroker kit build....with Weber 38 DGES and Nutter Bypass and a 4.2 distributor... Runs okay but mileage and power is embarrassing...

First ..... I think I want modern MPFI...
Second .... I want owner diagnostics capability...
And third .... OEM style repair parts available from my local NAPA...

The Burning Question Is, which wiring harness will swap over and how do I determine which PCM to start with?

I'm thinking 97, 98, 99 TJ under hood wiring harness w/fuse box and PCM. What other years or set ups would work...is a 2000 or newer harness and PCM usable?
And if I might be so bold, how do I connect to my YJ chassis Harness?

Here is to the Jeep Brain Trust,
Thanks in Advance.
Gene S.
 
See less See more
#2 ·
I myself don't see where MPI and owner diagnostics is going to increase your mileage or performance. I would just go with an HEI distributor/10mm plug wires/ gap plugs to .050 and wake up that motor.

But to try and answer your questions...The vehicles that you stated are compatible. As far as connecting it to your chassis harness, it would need to be pinned out wire by wire in the engine side of the fuse box.
 
#3 ·
Sounds ambitious, I'll give you that. Plenty of guys have seen plenty of performance out of a stroker. There are benefits, as you noted, when going to modern technology but they should not be necessary. If you go that route, the wiring to tie into the Jeep isn't that bad. I swapped an mpfi 5.2 into mine and am by no means a wiring expert. Get schematics for your jeep and for the year of your harness and go to town.
 
#4 ·
Daddyjeep and OIIIOforlife,
Thanks for the info. Every bit helps guide me.
I am under the impression that late model fuel injection will greatly increase fuel mileage. Having the OBDII will reduce my need for dealership visits to shake out computer controlled component problems..
I will be feeding the stroker with a Weber 38 DGES through my 4.2 intake until I get everything else worked out and ready to convert.
Thanks again.
 
#5 ·
The MPI isn't going to change your fuel mileage by any drastic numbers. It might increase by 3-5 mpg, if you are lucky.

As far as the need to visit the dealership? You stated that it has the nutter bypass done, so the computer has been cut out of the equation. No need to ever visit the dealership.

Switching to OBDII will require the install of many sensors as well as changing over to a bell housing that is compatible to mount a crank sensor in it. And probably a flywheel that has the parts on it that the CPS reads.

It is way more complicated than just slapping MPI on it and hooking up some wires. If I were doing it, I would seriously consider selling the current jeep and buying a TJ if you really want to be OBDII.
 
#6 ·
3-5 mpg increase? That would be disappointing. I have a complete 98 4.0 for the stroker. Everything, flywheel and forward... I was under the impression that on carburetor the 4.6 at best would make 200 to 230 hp. But with proper operating setup it would make as much as 270 hp... Its so hard to know what is truth and what is opinion... Currently I get 9 MPG... 15 MPG would be nice... 17 would really be great.
Any future suggestions are welcome.
Thanks.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top