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Unread 09-25-2014, 03:41 AM   #1
herrmc
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1986 CJ7 
 
Join Date: Aug 2011
Location: Agra, Ok
Posts: 32
81 CJ7 258 is dead - Advice on replacement

- I am going to ramble... will try to keep it to a minimum -

- I have 5 Jeeps
81 CJ7 - bone stock with 258
81 CJ7 - bad block... lots of mods - this thread is about this jeep
86 CJ7 - Nice trail jeep, Mopar EFI, several other moderate mods.
94 YJ --> rollover - bought for the 4.0 - MPFI
08 JK --> not relevant to this thread... but didn't want it to feel left out.
...

I have a CNC Mll ... and CNC plasma ... relevance is I can make some parts if needed.

... I have several "orphaned" Engines (mostly chevy small blocks)... (I do have a 396 big block... but can't see it being a good choice for my jeep)

- I originally purchased the 94 YJ to put the 4.0 and FI in my stock 81 cj7... but the 258 and carb in it just won't mis-behave ... I mostly just use it around the farm.

- I just (last week) purchased another 81 CJ7 (setup for rocks)...
--- 37" tires
--- Dana 44 front and rear (Detroit in Rear, EZ Locker in front)
----- I do not yet know the gears in the Diffs...
--- Has the Dana 300, twin stick, (was told it has 4:1 conversion)
--- T-176 transmission
--- The 258 in it was fairly fresh... but it broke a piston skirt, and damaged the block cylinder beyond reasonable repair... Previous owner removed the 258 and dis-assembled... about 6 months ago.

--- the bad 258 had been fitted with a TBI ... I have that on-hand

++++++++++++++++

I have several options for the replacement engine .... I am leaning toward using the 4.0 from the YJ (it had 122,000 miles ... and ran good... I think it had some intermittent PCM issues though).

Options:
- 4.0 from the YJ Rollover
- 1994 RAM 1500 truck I have, with either 318 or 360? (FI) 94,000 runs good.
- Chevy small blocks.... 305, several 350's, one 400 SB, and.. one of the 350's is from a 98 truck... MPFI .. but the engine would need a rebuild.

++++++++++++++++

Over the last couple of days, I have removed the Fenders, Hood, Tub from the YJ .... the PCM and Wiring harness removed as well.... I am now ready to dismantle and remove the 4.0 .... Plan to clean it up, run compression tests on each cylinder... and probably crack open the Oil pan and take a look at the bearings??? (I am old school chevy engine experienced... this will be my first time in a jeep engine)..... From those tests will decide if internal work is needed..... clean it up, paint it nice.... then put it in the (new to me) 81

- I have read a couple of threads about the viability of swapping in the 4.0 .... I don't see anything there that scares me much.... I am interested in feedback from those that have been there ....

...

Attaching 3 pictures -
1.) the YJ a couple of days ago before I started on it
2.) the YJ tonight
3.) the new to me 81 on the trailer...

94-yj-before-dismantle.jpg   94-yj-progress-dismantle.jpg   81-crawler.jpg  
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Unread 09-25-2014, 09:27 AM   #2
RenoF250
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1985 CJ7 
 
Join Date: Sep 2011
Location: Foresthill, CA
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Assuming the 4.0 is good that sounds like a good path to take. I did it and it was not that hard. You will have to come up with a solution for the CPS, I had already put in an AX-15. Other than that, the wiring, and fuel pump, it is pretty much drop-in. My donor engine had over 200k on it and the lower end was in great shape. I could have easily gotten away with just doing the head and changing the timing chain.
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Unread 09-25-2014, 10:17 AM   #3
CJShayne
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1986 CJ7 
 
Join Date: Jun 2012
Location: Roswell, ga
Posts: 105
Not to hijack your thread, but how do you like your Mopar EFI in your 86? I've been thinking about this upgrade for mine as well....
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Unread 09-25-2014, 02:45 PM   #4
herrmc
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Location: Agra, Ok
Posts: 32
Quote:
Originally Posted by CJShayne View Post
Not to hijack your thread, but how do you like your Mopar EFI in your 86? I've been thinking about this upgrade for mine as well....
-- Shayne,
- I love it..... the conversion was already done when I purchased the Jeep... runs like a top.... I have taken it to the Ouray area twice.... and it handled the altitude... and the angles much better than my Carb'd jeep.....
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Unread 09-25-2014, 02:48 PM   #5
herrmc
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Quote:
Originally Posted by RenoF250 View Post
Assuming the 4.0 is good that sounds like a good path to take. I did it and it was not that hard. You will have to come up with a solution for the CPS, I had already put in an AX-15. Other than that, the wiring, and fuel pump, it is pretty much drop-in. My donor engine had over 200k on it and the lower end was in great shape. I could have easily gotten away with just doing the head and changing the timing chain.
- I had the benefit of getting the donor engine in a running vehicle.... It ran very well.... the only problem I had was that it would randomly die... and not start... then later would run just fine..... I am pretty sure that it was/is a PCM problem.... I have read that some of them have some loose connections on the inside....
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Unread 09-25-2014, 02:55 PM   #6
herrmc
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Location: Agra, Ok
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I forgot to mention.... an added bonus (I hope)....

---- The 81 that I just purchased with the bad engine...... was setup with the TBI (howell).... Since I will not be using it in the jeep it came in.... I will have it to transfer to the stock 81 if desired....
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Unread 09-25-2014, 03:43 PM   #7
dirtdudeaz
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1983 CJ7 
 
Join Date: Jan 2013
Location: Lake Stevens, Washington
Posts: 495
What is your plans for the jeep? Keep it set up for rocks and what not? comfortable driver?

I am kinda leaning towards your chevy small block options and swap in an automatic as well. This may be the better option for offroading. If it's around town or cruising, do the 4.0 and keep the T-176
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Unread 09-25-2014, 05:21 PM   #8
swatson454
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Location: Dripping Springs, TX (soon)
Posts: 5,041
How 'bout taking the guts out of the 4.2 with the bad block and building a stroker?


Shawn
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Unread 09-25-2014, 07:42 PM   #9
RenoF250
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Quote:
Originally Posted by herrmc View Post
- I had the benefit of getting the donor engine in a running vehicle.... It ran very well.... the only problem I had was that it would randomly die... and not start... then later would run just fine..... I am pretty sure that it was/is a PCM problem.... I have read that some of them have some loose connections on the inside....
My donor would run good and die fairly quickly, turned out to be a plugged cat. The PCM is potted in rubber, not likely there is any loose connections. I have heard of problems with bad caps causing the fuel pump to never turn on but I don't remember seeing anything with intermittent quitting.
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Unread 09-25-2014, 07:44 PM   #10
RenoF250
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Quote:
Originally Posted by swatson454 View Post
How 'bout taking the guts out of the 4.2 with the bad block and building a stroker?


Shawn
If I had it to do over, I think I would have put the 4.0 in, run it awhile and then turned it into a stroker.
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Unread 09-26-2014, 08:52 PM   #11
81azcj7
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1981 CJ7 
 
Join Date: Aug 2010
Location: Phoenix, Az
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I would stay with a solid 4.2 lower, put a #7120 4.0 head on it then use the howel tbi. You will have plenty of power, low end and good gas millage
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