I have been reading up on the forums here and decided I want to do the 4.0HO head swap on to my 88 4.2 258. I have a donor 96 Grand Cherokee that I can get all the parts from I believe.
I have a 7120 head from a 95 Grand Cherokee and was told that will work.. I was thinking about switching over to fuel injection as well while I'm at it.
My question is... Will the harness, intake, ECU, etc work from a 95 Grand Cherokee? Everything I read on here says to get the 7120 head, intake/exhaust manifold, ECU, and harness from an XJ. Can anyone tell me if It will work, or why not if the head is the same, which parts will or will not work if so..
I've found that putting a 4.0 head on a 258 is alot of hype, might be different with the FI. I have a built 258 and installed a clearwater 4.0 head with offy intake and holley 470 4 barrel, I was disapointed at the gain. For kicks and giggles, I had my 258 head P&P'ed, I installed it back on my 258 with the other performance parts and it was a screamer. It had a much better lowend torque cuvre and responed better throughout the rpm range with the comp cam. I lost a little on the topend, but the engine responded better up to 4,800 rpm's where I mostly operate. The FI may make a difference, but with a carb and an old school build, a ported 258 head works better, or at least it did for me.
1987 wrangler, 258 I-6, 5-speed.
2007 liberty sport 4X4, automatic
2009 ford ranger 4x4 FX4 OFF/ROAD, 5-speed
That's interesting Wendell. I found significant gains when I put a '94 4.0 Cherokee head, junk-yard stock except for welding the cooling ports closed, and using the old Carter carb and intake. I did have to make some oddball washers (teardrop shaped, sort of) to hold the intake, and I used the 4.0 exhaust manifold & modified 4.2 downpipe to save money. Other than buffing the surface clean there was no machining at all. It ran great, could even bump a short wheelie on stock 235 tires & 3.07's. I did notice my block still had crosshatching with 150k on it, so it's likely that it was freshened.
To OP; the biggest problem I see is the crank sensor. You'll need some sort of pickup - either changing the flywheel out to the 4.0 flywheel (IF that will work, I don't know), then you'll need to find a way to mount a crank sensor in the right position, and notch the transmission bellhousing if needed. I think you'd be farther along to put the whole 4.0 block in from the '96, as it will have all the correct sensor mounting bosses and the engine mounts I believe bolt up to each other. As for wiring, I'd find a '95 harness and computer. Might cost a couple hundred (if that) but then you'd have a 'correct' 4.0 YJ with all the wiring colors being correct for any future diagnostics. The bends in the wiring would be correct too, plus it'd all be plug-n-play so save you a lot of time splicing it.
You didn't mention which transmission you're going with. As I recall the transmission is ECU controlled for the GC, so you might get a check engine light if you're running a manual. I do a lot of automotive electrical work but I'm not Max when it comes to what-fits-where... wait for him to chime in
Thanks for the info guys. I'm going to stick with the 4.2 motor, I was in the middle of rebuilding it when I saw the thread about the head swap and got curious.
The 4.0 motor in the donor Grand Cherokee has a bad bottom end and block thats not rebuildable, but the intake, ECU, wiring etc are all still good. I just wasn't sure if there was a reason all the info on the swap referred to using parts from an XJ (other them more room to work) simpler harness or location of connectors etc.
Im going to put the 4.0 head on with my Weber for the time being until I can find a little more info if this will definately work.. It will be nice to see how much of an improvement the head makes carbed and then with the fuel injection after...
Ill put everything off on the side in my garage for now till I get all the parts and the verdict is decided.. I think I have everything needed but the fuel pump and VSS sensors, if the Grands harness works. Worse case maybe Ill have to pull a new harness out of an XJ?