4.0 head and EFI on a 4.2 block

[N2IHC]

Hello!

First I need to say awesome post! Thanks for sharing!

I am doing this in a 258 and I have one question for ya. Should I retain the V belt set up or convert to the serpentine belt setup? is there a bonus to using one over the other? I had thought about going to the 4.0's belt set-up because it has an A/C bracket.

Thanks for any reply

[Jeep-Power]

6 & a half-dozen the other, to me.

The serpentine is nice, ideally because tension is automatically adjusted. I hear it is a more efficient setup as well.

I kept the V-belt because it was easier.

[Jeep-Power]

I got some of the OBD1 diagrams scanned in.

These are out of a 1995 Jeep Factory Service Manual (FSM) for Cherokee & Wrangler.

XJ 4.0 PCM Pinout


YJ PCM Diagram


XJ 4.0 PCM diagram


PDC Relay descriptions

[Jeep-Power]

PDC Relay circuts







FSM Description of the system

[fivestring]

Since hooking up the VSS my idle speed increases any time the jeep is moving. So when I slow to a stop and push in the clutch, the idle will be at 1200 until I stop completely, then drops to 900: OBDII. Any ideas how I can fix this?

[yuppiexj]

Since hooking up the VSS my idle speed increases any time the jeep is moving. So when I slow to a stop and push in the clutch, the idle will be at 1200 until I stop completely, then drops to 900: OBDII. Any ideas how I can fix this?

If you are running a PCM from an Automatic transmission equipped vehicle in a manual transmission equipped vehicle this is to be expected. (I assume it's a MT due to the slave cylinder references)
The high idle as you are moving is to keep the the engine from stalling when coming to a stop.
You can resolve it one of three ways
1. This behavior is by design, get used to it.
2. Swap in a MT PCM. (There's some scuttlebutt that the AT PCM has hotter timing and makes a couple more ponies(to make up for higher drivetrain losses over the MT)
3. install a clutch switch to send a "yes I'm in (neutral/park) signal" to the PCM when the clutch is depressed. (unless the pcm still does it regardless of shifter position, I will verifiy this morning in my XJ this morning)

[fivestring]

yuppiexj, thanks for the reply. Very interesting. The pcm came from an unknown source. I bought an XJ that had this pcm swapped in (MT) but did not have the VSS hooked up, so I think you are correct that this pcm came from an auto tranny setup.

So if I wired a switch to interrupt the VSS signal when I press the clutch pedal, that would tell the pcm I was at zero mph instantly, right? And in turn, would allow the rpms to drop faster during (slow, easy) shifting and coming to a stop. Very interesting indeed.

[Zorm]

yuppiex, did you ever check out the high idle thing. Great write up by the way.
I was going to swap in a 4.0 into my jeep but decided to just keep my 258/4.0 head set up and just add the 2000 intake with fuel injection. I will be using the older style injectors and fuel rail. I will also be swapping in a serp belt set up, actually did some of that today. Need to find a washer or something for the serp harmonic bal on the 258 crank
I am also wondering if I need to get a different cam since I sill be going with the 2000 intake, it has more volume that the older 4.0 intake. Had thoughts of also getting the throttle body enlarged, so cam guys, need some advice. The ecm and wire harness I have for the fuel injection all came from a 93 cherokee with auto.

thanks for any thoughts from anyone

[shukmeister]

MAN! WHAT AN AWESOME THREAD!

I have a 74 IH Scout II with the 258 AMC. I have the 7120 head and am getting set-up to go EFI. For quite a while I ran with the ford motorcraft 2bbl carb and the ignition was a chevy HEI. It was a really good set-up, but I'm going for serpentine and EFI out of a 96 Cherokee. It may take me forever, because I rarely get a kitchen pass to get out to the shop. I'll try to post my progress and frustrations. I really appreciate this site and this thread.

I have a wide-ratio T-19 4 speed manual tranny with a Dana 20 TC. Did they work the bugs out of the HESCO CPS on the front balancer, or should I swap in an AX-15 to get the CPS on the bellhousing? Can I even swap an AX-15 to a 258? Thanks!

Here's a pic of the Scout.

[Carl]

Nice looking Scout, Shukmeister. Here is something to consider. Pictured here is a HO 4.0 mated to the T18 from my 74 Scout. I made my own adapter but they are available aftermarket too. With this setup you get factory bellhousing with CPS, heavy duty T18/T19 trans, hydraulic clutch, about 30 lbs weight reduction just in the bell. The clutch is mostly stock parts. A big reason I chose this path was the CPS. I don't like the HESCO design or it's price tag. The same trans adapter would work just as well your 4.2/4.0 hybrid engine if you were so inclined.

[shukmeister]

Very nice! Definetly something to think about. I might break out the tig welder to fill up the exising trans mounting holes and then re-drill the 4.0 Bell to fit the T-19. Adapter kits aren't cheap, but I am!

[Jeep-Power]

MAN! WHAT AN AWESOME THREAD!

I really appreciate this site and this thread.

Did they work the bugs out of the HESCO CPS on the front balancer, or should I swap in an AX-15 to get the CPS on the bellhousing? Can I even swap an AX-15 to a 258? Thanks!

Skunk-

thanks- I'm glad it has been some help!

I don't know if there has been any change in the HESCO unit. From what I've read, in the past, is is an inherit problem with harmonic balancers in general. The problem just shows up because we use them to run the engine.

I don't know if I mentioned it here, but I am switching to the bellhousing mounted setup. From what folks on Strokers have said, it is a nice upgrade.

I don't know anything about Scout stuff, but I do know that most anything that will fit on a 4.0 will fit on a Jeep 258.

[rayzr]

I have just found this thread. I too am putting MPFI on my 258. I am having a "No spark" condition when I try to crank it over. I know this is the problem with getting the engine to fire. I think I have the wiring correct. Could someone help? The donor FI is off of a 95 Grand Cherokee.

Thanks,

Ray

[Jeep-Power]

Ray-

assuming you have power to all the ASD circuits, faulty crank & cam positions sensors are what have given me this issue.

Does your fuel pump run briefly when you first switch it to "run"?

[rayzr]

The fuel pump runs, and I have good pressure at the rail. I am trying to troubleshhot the CPS at this time.... I bought the harmonic balencer kit from Hesco. Do you have any info on testing the crank and cam sensors?

Thanks,
Ray