4.0 in 86 cj7

bigred78 · 07-15-2009, 12:38 AM

I have recently obtained a 1988 YJ with a fuel injected 4.0 in it and automatic tranny. The engine sounds pretty good. When i type in the VIN it says the YJ came with a 258. But im not sure if its right or not. The jeep is very very rusty. I have a 1986 cj7 with the amc 258 in it.
I would like to take the 4.0 outta the yj and put in my cj. I have been reading the posts and overwhelmed by the information. My friend is a mechanic, so i wouldnt be doin it myself.
A couple questions that i have are:
Would i need to buy anything else, or would everything i need be in the yj?
Can i use the stock cj7 guages?
Does the 4.0 bolt up to a 86 5 speed tranny?
New motor mounts?
Is there some sort of step by step or best by step guide anyone has wrote?
Thanks in advance
Sean

NewdRiver_ · 07-15-2009, 01:22 AM

YJ's had the 258 4.2L until 90. Starting in 91, they had the 242 4.0L

Few things I know of but not all the details:

-4.0L cylinder head will bolt onto the 4.2L block, giving it fuel injection and slightly higher compression I think.
-4.2L crank and rods can be put into the 4.0L to stroke it to 4.6L
-90% sure the T-5 trans will bolt up but there is some issue with the CPS
-A gauge is pretty much a gauge unless it's a fuel gauge.
-4.0L will bolt into 4.2L mounts. They are pretty much the same casting.

bigred78 · 07-15-2009, 08:33 AM

Maybe that would be a option for me, that is putting the head and fuel injection on. Its gets really cold here in the winter and the carb wont cut it. Dont you have to plug holes and stuff in the 4.0l head? Is there any writeups about this anywhere?
Thanks
Sean

**jeepskate** · 07-15-2009, 08:38 AM

I'd recommend that you spend a whole lot of time over on www.cjoffroad.com in the 4.0 swap forum. It's been around for several years and is the largest single source of info on 4.0 and head swaps.

1986cj · 07-15-2009, 11:01 AM

I would try to find out what year the 4.0 is, whole moter swap would be worth it, just the head swap and inj to your motor, if it is a 91 or later I would go for it, early xj motor I would hold off and look for something that is obd1 and stay away from the early Renix myself. They say a lot of parts for the Renix is getting harder to come by, and not much interchanges with the obd1.

CSP · 07-16-2009, 09:36 AM

I wouldn't mess with just a head and EFI swap. It's easier and more reliable just to swap the entire 4.0 in.

07-15-2009, 08:33 AM	#3
bigred78 Registered User Join Date: Jun 2009 Location: Goose Bay Posts: 59 Profile Gallery Classifieds My Jeeps	Maybe that would be a option for me, that is putting the head and fuel injection on. Its gets really cold here in the winter and the carb wont cut it. Dont you have to plug holes and stuff in the 4.0l head? Is there any writeups about this anywhere? Thanks Sean

07-16-2009, 09:36 AM	#6
CSP Registered User Join Date: Aug 2002 Location: Colorado Posts: 6,322 Profile Gallery Classifieds My Jeeps	I wouldn't mess with just a head and EFI swap. It's easier and more reliable just to swap the entire 4.0 in.