Wiring harness up grade

[MJholic]

I have a 1989 MJ long bed 4.0 2wd with a 5 speed soon to be 4wd. I was at the junk yard checking out 2 MJ trucks for parts (tail lights where gone of course) and one of them is a 91 or 92 because it has the injection module by the air cleaner and has the open cooling radiator system. It looks just like my 1995 XJ under the hood. I'm thinking of doing a fuel injection swap with wiring harness and all sensors throttle body etc. Couple of questions. Will I get more HP out of my 89 4.0? Are the injectors in the junk yard truck the 4 port ones that are talked about running smooth and get better mileage? Do I need to get the entire wiring harness out of the truck or just from the firewall block forward? I didn't see a fuel pump resistor in the junk yard truck does that mean I need to switch fuel pumps also? I seem to remember there might not be a return line from the fuel rail. I forgot to look at the junk yard truck. If there is only one line going to the fuel rail then I assume it means that I need the fuel pump for sure. And if that's the case should I just go ahead and get the tank. Seems like I read that the fuel pump mounts might be different. The junk yard truck is 4.0 2wd 4 speed manual. Comments?

[johnj92131]

You have a nice, stock, well running 1989 - Right?  That give you nice knock sensor to back off the timing when you have a bit of knock.  It also lets you have better gas mileage than you will get with a 91+ MJ under exactly the same conditions.  Your cam and cam timing is set to give you more low end torque than the H.O. engine.  Lastly, why would you want to "jury rig" or "bastardize" your trucks wiring?

 

You will never see the 13 extra horsepower in the H.O. engine with the changes you are asking about.  The extra 13 horses come at the very top of the RPM range and are there because of the bigger intake ports of the H.O. head, plus the camshaft timing changes.

 

Get your truck in good shape, do the 4x4 conversion and enjoy it.  When you are ready to rebuild the engine, strongly consider a stroker crank, set the piston to cylinder quench very tight - like ..035 and bump the compression up to about 9.3 for regular gas, (higher for premium). Or consider an engine conversion to an aluminum block 5.3 ltr Chevrolet truck engine with the latest electronic engine management.  That gets rid of a good 100 lbs from the front wheels, 325 hp minimum, a torque curve that is essentially flat from 1500 to 5500 (90% of peak torque).  You can use regular gas or E85.

[MJholic]

Thanks for the info. My 95 XJ has the HO engine so there is only 15 HP difference between it and my 89? What about the 4 port injectors? Got a part number for them? Is there a thread for the Chevrolet engine conversion you mentioned? My 89 from Tennessee has 100 k on it so it will be awhile before that engine will need anything but I do have 2 or 3 more projects in mind. 

[johnj92131]

Did not have any special thread in mind.  Just looking at recent Chevy/GMC truck.  Wondering if I really want to spend the money on the Comanche to install a new stroker engine.  Or should I just move on from the 25 year old truck.

[Megadan]

The way I see it, if it ain't broke, don't fix it.  If you have a swap in mind then I would research everything you need to do and buy for it, gather all your parts, and wait for something to give or plan on a time after you have all the parts and research done.  If you want to do a stroker, build one up on the side so you can drive and enjoy what you have now.