4.0L Power Improvements

[ZAEDOCK]

OK, so in trying to get back into the swing of things with my buggy project, I've been going over various power plant options that I have in my stable. I was able to pick up a nice 1993 4.0L HO earlier this year, with only 80K miles complete with everything including the ECM (it's an auto ECM - more on that later). My parts 2000 TJ is a 4.0L with the updated "smooth" manifold. Supposedly, this manifold was redesigned in 1999 when Chryco changed the ports on the head to comply with more strict emissions standards. I have heard rumors that when this manifold is swapped onto an earlier HO engine, a 15-20 HP change is possible. In my research, I found a decent write up on the swap and thought some of you 4.0L owners might be interested.

From left to right: Renix 4.0L / Early 4.0LHO / 1999+ HO


Here is the article:
http://mallcrawlin.com/forum/showthread ... NO-NUMBERS!

[nostaw]

I've got a '99+ intake sitting around, if anyone decides they want to do the swap... I was going to do it, but decided it wasn't worth the effort for my '98.

Still has a fuel rail + injectors attached.

JW

[johnsxj]

O.K. Joe, I've done the manifold swap so here's my opinion.

The old Renix system works, but it only had a four year run just in the XJ/MJ so replacement parts cost $$$$$

The H.O. '91 up has a longer production span and was in more models so replacement parts are less.

Low end, on the H.O. I didn't notice any difference between the "log" and the "horseshoe". Mid to uppper RPM, there's more umph with the horseshoe. Not sure if it's 15-20HP worth, but it's there.

On the plus side, the early H.O. fuel rail bolts right on the horseshoe. And the '96 up power steering pump set up is much easier to do belt adjustments on. Some manifold bolts are easier to get to on the log, others on the shoe. And some aftermarket headers will need to have a dimple pounded into them to clear the shoe manifold so everything sits flush on the head.

An ECM from an auto trans will work fine on an engine backed by a stick (haven't had a problem with mine).

Bottom line, if your log is working, leave it. If you gotta pull the manifold for something else, and you have or can get a "horseshoe" on the cheap (prices were really inflated on them for a while) then go ahead.

[ZAEDOCK]

An ECM from an auto trans will work fine on an engine backed by a stick (haven't had a problem with mine).

That's cool. I have the complete harness up to the firewall, so I'll need to find the right pins for the ignition. I have the fenderwell relay box too, still wired in and ready to go. The horseshoe swap will be fairly easy in my application, as the front of the chassis is completely open. I intend to keep it as-is though, for the initial start up and then swap over once everything is running correctly.

Question on your swap: I've read that they run better with the VSS (I brought it up here before and Kurt replied) and have one off a YJ in one of my spare NP231's. Did you run a couple of wires and tie it in to the bulkhead?

[johnsxj]

My situation was a little different where I was swapping from the Renix system. Fortunaely, my XJ came with cruise control that used a speedsensor behind the instrument cluster that generated the same signal pulse so I tapped into that. (I didn't want to spend the $$$ for a YJ speedsensor that would still drive a speedo cable)

That sensor you have will work fine.

[Kurt]

Joe - I could be wrong but I believe the 'puter wants so see an actual speed signal relative to the vehicle speed from the VSS for the engine to run happily.
I don't believe just hooking it up and zip tying it the the firewall is going to make it "happy".
The VSS gets power +5 or +8 Volts (depending on the year) and ground fed to it. The third wire is the VSS output with pulses relative to the vehicle speed fed back to the 'puter.

[ZAEDOCK]

Joe - I could be wrong but I believe the 'puter wants so see an actual speed signal relative to the vehicle speed from the VSS for the engine to run happily.
I don't believe just hooking it up and zip tying it the the firewall is going to make it "happy".
The VSS gets power +5 or +8 Volts (depending on the year) and ground fed to it. The third wire is the VSS output with pulses relative to the vehicle speed fed back to the 'puter.

Oh yeah Kurt! The 231 I have has the VSS in it and will be a turn'n with the t-case. All I have to do is run a 18ga 3 or 4 conductor out to the t-case from the right pins on the bulkhead. I should be able to use my YJ and XJ manuals to find the right ones. Hopefully...