New Comanche owner - Oil blow-by / Engine swap questions

[iAntix]

Hi guys! I recently purchased a 1988 MJ after searching craigslist religiously and finally found one local.

 

 

 

 

I have a 2001 Jeep XJ as my DD so I'm not new to the jeep scene; however I am new to the renix-era. The current specs on the MJ are the AW4 trans, Dana 30 front axle, Chrysler 8.25 rear with SOA Lift, long bed, and the notorious 4.0L...or so I've seen. The PO I purchased it from told me that it leaks oil like a pig, all over the engine by the airbox - including inside of it. Which from doing my own research on is known as oil blow-by. From the writeups I've seen, this is typically caused by the piston rings going bad or the CCV(?) valve hoses in the valve cover getting gummed up with junk. I did a cold compression test; both wet and dry and got the following results. 

Cylinder: PSI (Dry)                            Cylinder: PSI (Wet)

6: 95                                                   6: 130

5: 95                                                   5: 130

4: 110                                                 4: 135

3: 110-105                                          3: 155

2: 105                                                 2: 120

1: 100                                                 1: 140-150

 

Any other tips regarding this blow-by? The next thing I am going to check will be the hoses on the valve cover and see if they are gummed up and hopefully clean them. I did peek into the valve cover and it does look a bit gummy inside but I need to remove the valve cover to confirm.

 

Now onto my next question..

The PO included a 4.0 engine and trans from a 98 Cherokee; and according to him it would be a direct swap if I needed to pull the MJ engine. The spare engine turns over by hand but I don't have a lot of information on it, whether it's good or shot or if it's even a HO, to be honest. Assuming I have to pull my engine...I've read(and please correct me if I'm wrong!)  that it's possible to swap a HO engine into a renix era vehicle just by simply swapping certain accessories; for example.."You will be using the intake and exhaust manifolds from your Renix, along with all your sensors and wiring. Since the intake ports of the HO are slightly different, you use the renix gasket, and exhaust ports and identical. You will need to use your Renix distributor as it is different from the HO design. The flywheel or flexplate from the Renix must be used so that your CPS gets the correct signals. The valve cover from the renix allows you to keep your ccv system intact and requires no modifications. The HO block will have a plug in the coolant galley on the driver’s side of the block, closest to the front, which needs to be removed so your Coolant Temp Sensor can be installed in it’s place just as it is on the Renix. It requires a 5/16” square drive or a modified 3/8” drive that has been ground down to fit. Do this before installing the engine. As for the knock sensor, which is located just above the oil pan on the driver’s side of the engine about mid way, all the blocks I’ve seen are threaded for it. If not, I’ve heard they may be drilled but not tapped. Tap the hole if that’s the case." - directly from http://cruiser54.com/?p=100

 

I know this is a lengthy first post but any and all feedback is much appreciated, thanks in advance :thumbsup:

[benjy_26]

Just take the valve cover off, get new ccv hardware, clean up the insides of the cover, and you should be good to go.

[Megadan]

I don't get the Notorious part.  My renix is super reliable and a great daily driver.  Just had to put in some work to fix and clean some of the wiring and it's been a great daily driver for over 2 years now.

Follow up that compression test with a leakdown test.  See exactly where the air escapes from, because sometimes low compression can be caused by carbon buildup on valves not letting them seal properly.   If excess air comes out of the CCV hose/valve cover, then you can chalk it up to worn rings.  If air comes out the intake or exhaust, then  that motor needs a good steam cleaning (or valve seats/valves checked out)

!

As far as the HO Swap, there is an article on here that details what is necessary.  If I remember right it was written by cruiser.  Speaking of, look this over and do as many of these as you can or are needed.  http://cruiser54.com/

[DirtyComanche]

What's notorious about the 4.0L?  That it will outlast 90% of other engines?  That it actually has low end torque?  That it actually wasn't designed on a computer by somebody that never opened the hood of a vehicle nor would be able to?

 

Get new PCV parts.  Pull the valve cover and do the PCV mods and cleaning.  Put the compression tester away.  Drive it.

[Rockfrog]

Notorious? only thing bad about the 4.0L is that it runs damn near forever  ... my 88 Renix 4.0L is reliable as a rock, worn out, but still starts every time, has more pull than expected and gets me 500km to work and back each week for the last three years. the PO I suspect never changed the oil filter in about 100,000km going off the amount of coke and crap I vacuumed and scraped out of the block and VC. The only 4.0L I like better is the one in my 00 XJ, although the Renix has several of it's hand me downs. Saddest thing Chryco ever did was Kill it in '06, and try to replace it with turds. And both still get better economy than the newer Wrangler engines ... Ha!

 

But in it's current iteration, it now has parts from damn near every year 4.0L on it. So yeah, a 98 engine will work if you use the right parts and adapt those that don't directly bolt on. I would suggest using the 98 head, the 98 intake with it's far superior belt adjusting arrangement at the power steering pump bracketry. I would also use the 98 valve cover and CCV arrangement as well. But that does also mean you'll need to adapt the Renix TPS to the HO style throttle body, simple enough to do really. That's the only real hard part to mixing the parts. You may need to tap a few holes in the 98 block though, the bosses will be there but may be as yet untapped. In the end a proper mix will get you less clutter in the engine bay and a wee bit more seat of the pants to boot.