4.0, 242 engine replacement question 1988

[mknherhappy]

I have a 1988 Comanche with a 4.0 242 I 6 motor. After several visits to two different auto repair shop, it has become very apparent that my motor is basically shot. My question that I'm hoping you all can answer for me is, what replacement motors will work for replacement without major changes? Can I only use the same make and year, or will newer years work? Sorry for my ignorance, this is a first for me. The truck is in too good of shape to just junk it, and I would like to put a different motor in. Also, any advice on where to find a replacement motor would be great.

 

Thank you all for the help,

 

Greatly appreciated.

[Zenobian_84]

Since your motor is a Renix type (1987-late 1990) any other year of Renix engine should work (from either a Cherokee or Comanche).

 

If you decide to do a Chrysler HO engine swap (1991-2001) you may have a bit more work ahead of you. IE: a few different wiring setups than what you have now; but I'm not 100% positive on this, so take my advice as you will. Someone else will probably chime in with the exact details, but that's the gist of it. I myself am not a 4.0 guru as most of the others on here are. :(

 

And obviously, any Renix engine with the same setup as your truck (stick or auto, and corresponding transmission / transfercase) will be a direct bolt on. Hope this helps! :cheers:

 

Oh, and you can probably hit up a few junkyards to find a decent motor for a decent price. Either that, or Craigslist.

[mknherhappy]

Since your motor is a Renix type (1987-late 1990) any other year of Renix engine should work (from either a Cherokee or Comanche).

 

If you decide to do a Chrysler HO engine swap (1991-2001) you may have a bit more work ahead of you. IE: a few different wiring setups than what you have now; but I'm not 100% positive on this, so take my advice as you will. Someone else will probably chime in with the exact details, but that's the gist of it. I myself am not a 4.0 guru as most of the others on here are. :(

 

And obviously, any Renix engine with the same setup as your truck (stick or auto, and corresponding transmission / transfercase) will be a direct bolt on. Hope this helps! :cheers:

 

Oh, and you can probably hit up a few junkyards to find a decent motor for a decent price. Either that, or Craigslist.

 

thank you for the input.

 

Appreciate it.

[sinkrun]

Can you tell us exactly what is wrong with you current engine? The renix era engines which you have are known for oil blow by getting in the air cleaner box. If this is the problem there are some cheap fix`s and almost all of these years that you will get used will do the same.

[mknherhappy]

Can you tell us exactly what is wrong with you current engine? The renix era engines which you have are known for oil blow by getting in the air cleaner box. If this is the problem there are some cheap fix`s and almost all of these years that you will get used will do the same.

 

 

Thank you, yes, I have the blow by, but excessive, already cleaned out the pvc lines etc. One mechanic gave up saying there is no compression to speak of, the vacuum is awful, so I took it into another shop with a well respected mechanic, and he had the same diagnosis.

 

thanks for the input.

[Eagle]

But it runs? So you need new rings and a valve job.

 

As to what's involved with the newer engines:

 

Your engine spans the 1987 through 1990 model years. In 1991 Chrysler brought out the HO version, with a different injection and ignition system. Part of the change involved the design of the head -- the ports were raised and the shape changed slightly. The lower end remained mostly unchanged. Your engine uses a knock sensor, which mounts on the lower left side of the block. The 1991 and newer engines do not use the knock sensor, but I believe the threaded boss to accept it remained on the block for several years.

 

In 1999 the 4.0L head as used in the Grand Cherokee was changed to add a boss for mounting individual coil packs at the spark plugs. This revision didn't get to the Cherokee until 2000.

 

If you don't want to rebuild your existing engine, IMHO the easiest route to follow would be a junkyard engine from a mid- to late-90s Jeep, take off the head, have your old head refurbished, and install your head on the "new" lower end.

[mknherhappy]

But it runs? So you need new rings and a valve job.

 

As to what's involved with the newer engines:

 

Your engine spans the 1987 through 1990 model years. In 1991 Chrysler brought out the HO version, with a different injection and ignition system. Part of the change involved the design of the head -- the ports were raised and the shape changed slightly. The lower end remained mostly unchanged. Your engine uses a knock sensor, which mounts on the lower left side of the block. The 1991 and newer engines do not use the knock sensor, but I believe the threaded boss to accept it remained on the block for several years.

 

In 1999 the 4.0L head as used in the Grand Cherokee was changed to add a boss for mounting individual coil packs at the spark plugs. This revision didn't get to the Cherokee until 2000.

 

If you don't want to rebuild your existing engine, IMHO the easiest route to follow would be a junkyard engine from a mid- to late-90s Jeep, take off the head, have your old head refurbished, and install your head on the "new" lower end.

 

Rings and a valve job, is this a common fix? Any idea what something like this should cost? Sorry about all the questions, I'm ignorant of most of this.

 

appreciate the input.

[Comanche County]

~$300 bucks at an engine machine shop to do a valve job, mill the head surface true, and install new valve seals and valve guides. JY engines can run about $200-250 depending on the yard.

[Dadinator]

Where are you?

I have a 4.0 motor attached to a junk cherokee I'd like to get rid of.

[cruiser54]

But it runs? So you need new rings and a valve job.

 

As to what's involved with the newer engines:

 

Your engine spans the 1987 through 1990 model years. In 1991 Chrysler brought out the HO version, with a different injection and ignition system. Part of the change involved the design of the head -- the ports were raised and the shape changed slightly. The lower end remained mostly unchanged. Your engine uses a knock sensor, which mounts on the lower left side of the block. The 1991 and newer engines do not use the knock sensor, but I believe the threaded boss to accept it remained on the block for several years.

 

In 1999 the 4.0L head as used in the Grand Cherokee was changed to add a boss for mounting individual coil packs at the spark plugs. This revision didn't get to the Cherokee until 2000.

 

If you don't want to rebuild your existing engine, IMHO the easiest route to follow would be a junkyard engine from a mid- to late-90s Jeep, take off the head, have your old head refurbished, and install your head on the "new" lower end.

 

Good advice here. I'll add something since I've done 2 mid 90s HO to Renix swaps.

 

You can use the HO head. Intake ports are off slightly. Probably no more than most factory matches between manifold ports. Use the Renix gasket.

 

Swap Renix dizzy, flywheel, valve cover, etc on to new motor..

[Dadinator]

Where are you?

I have a 4.0 motor attached to a junk cherokee I'd like to get rid of.

 

Wait... I'm guessing you're in Iowa...

[Dadinator]

Where are you?

I have a 4.0 motor attached to a junk cherokee I'd like to get rid of.

 

Wait... I'm guessing you're in Iowa...

[mknherhappy]

Where are you?

I have a 4.0 motor attached to a junk cherokee I'd like to get rid of.

 

Wait... I'm guessing you're in Iowa...

 

 

Yeah, northeast Iowa, wish it was closer