4.0 head and EFI on a 4.2 block

[Jeep-Power]

Yeah-- I wasn't too happy about it. To HESCO's credit-- they did give me a break on the replacement.

The scans are on the to-do pile, along with everything else.

[DOUG]

I have read and reread this thread a 1/2 dozen times and I'm ready to take the plunge. Swapping a 4.0 head/efi onto the 258 in my Scrambler.
I'll be sending the head to the machine shop this week, then to purchase the needed parts to complete the install.

[DOUG]

Forgot to ask a question...which motor was the gasket set and new pushrods bought for? (or maybe they are the same P/Ns?)

[Jeep-Power]

Doug-

Buy a head gasket for the model/year head you have.

As far as I know, the 4.2 & 4.0 share the identical pushrods. On the first head swap I
did, 4.2 push-rods were used (because I had them). On Toms' swap, 4.0 rods were used.

While on topic: On the first head swap, 4.2 rockers, bridges, etc were used on the 4.0 head. They are interchangeable.

[akecj7]

Have you had any drivabiliy issues using the stock PCM? I posted over at hesco and they said there are issue when using a stock computer with the conversion. Thanks for the help and exellent thread.

[Jeep-Power]

curious.

That's all I've used. No issues. They work fine, for me.

What issues did they describe?

[akecj7]

curious.

That's all I've used. No issues. They work fine, for me.

What issues did they describe?

This is what LEEE said on the Hesco forum
"The main thing is all the codes that cause drive ability problems have been eliminated. The timing curves are set for performance, the fuel window is wider for compatibility."

As far as what causes issue not sure. How many conversion have you done? Are you a PCM from an automatic or a manual? I will be running a th400 with a reverse pattern manual valve body. If useing a stock computer works that would same me a bunch of money which will help get my heep back on the road. Thanks for the help.

[Jeep-Power]

I've done two conversions.

They were both initially run with automatic PCM's on manual transmission Jeeps.

I have since picked up a second computer for mine (backup) and have switched it in & out numerous times. They all work fine.

I am sure HESCO's computer works better than the OEM setup, but I'm VERY happy with the junkyard PCM's we've used.

[akecj7]

Thanks good to know. This saves me about 300 bucks. Thanks again for the help.

[fivestring]

I found a big difference between the 4.2 (not sure of year, possibly a 1990) and 4.0 (1996) pushrods. I measured spring preload and it was over 1/4" with the 4.0 rods. The 4.2 rods were significantly shorter ( I forget the measured difference and the spring preload measurement on these) but I ended up using the shorter ones and the Jeep runs fine.

I am running an OBDII system. I need to know if the ecm is supposed to have a 12v supply that is always on so it can retain the learned info. I feel the motor is relearning settings every time I fire it up. It starts rough like there is a big cam in it, then after 30 seconds or so it settles into a smooth idle.

If the ecm is supposed to have a non-interrupted 12v supply, which wire would it be? I have posted the pinout for these computers here:
http://www.jeepforum.com/forum/f12/newe ... e-1111789/

[Jeep-Power]

fivestring-

Yeah-- I'm not sure of the years/pushrod specs. I did measure the ones I had in my 4.2 against the ones that came out of the donor 4.0 OBD1 engine-- they were visibly (I didn't use a micrometer or anything) the same exact size.

It looks like:
pin #22 is for Fused battery-- constant 12V supply.
pin #2 is fused ignition (switched) positive 12V.
pin #6 is ground

[fivestring]

Thanks for the confirmation Jeep Power. I suspected number 22 was the rascal I was lookng for. I will test to see if it's getting 12v when the key is off.

[fivestring]

I just checked that wire and I am getting 12v there all the time. I think my rough initial idle may be related to a fuel pressure leakdown issue I am having. The pressure bleeds off to around 25lbs within about 30 minutes

Does anyone know how to shim the regulators to adjust fuel pressure? I have heard you can do this easily as opposed to buying an adjustable regulator.

I am using the '96 fuel pump which has a built-in regulator on the pump but my fuel rail also has a regulator on it so it is not original with this '96 motor. Right now the return line is plugged as you don't run one with the '96 systems.

I am thinking of going with a Ford truck external pump to get the 49 lbs of pressure needed and I will need to adjust the regulator to 49 lbs.

Any other thoughts on what would cause a very rough idle ever time it starts up cold? The only other issue I am having as far as performance is a 'flat' spot in acceleration around 2800 rpms then above that it seems fine.

[4.whoa]

Are you having a fuel pressure drop @2800? Before you crank it up, let the fuel pump prime or pump up for a few seconds and see if that fixes the rough idle.

My xj sometimes has a rough idle @ start up.It's losing a little water,and i think thats why.if i bleed the water press off when i park it, it usually doesn't do it.

[92tank]

my jeep run rough on start up with the stock injectors, then cleared up. but after i put the new ones in that issue went away. just food for thought