It's a 91 with 4.0 auto I've had it for bout 4 years 2 years ago on a off road trip I tried to turn it into a submarine well it didn't go well so a year later I put another engine in a used one with about 90,000 miles after getting it in and running I've.noticed a miss at idle since I installed it I've been running sea foam at first hoping maybe it just needed running because it sat up needless to say that hasn't helped I ran compression check on it these are the results
1. 70psi
2. 70
3. 125
4. 125
5. 125
6. 125

I've searched the forum quite a few times but no answer so far this is my.first post.BTW
Also I know the o2 sensor isn't working because its laying in the glove.box but pretty sure.that wouldn't make low compression on 2 cyl. I have heard it could also be blown head gaskets between 1&2 cyl other than that there is no problems beside.me gettin excited gettin it together and not changing the rear main please help

 

Low or no compression on two adjacent cylinders is most likely a blown head gasket.

If/when you pull the head, be SURE to bring it to a machine shop that specializes in this type of thing and have the head checked for cracks and also see if it needs to be resurfaced. This is money well spent and failure to have these things done has induced regret in many folks. Consider using fresh cylinder head bolts when reassembling.

Good luck!

 

That is the plan just wanted to do some research before starting on this

Also I have noticed a little.smoke !nd gas smell with indecent fuel mileage I've owned enough Cherokees to know that the gas mileage isn't great but I'm gettin like 8-10 a mile because of the problem I also developed a slight rattle not sure on that problem but I have fresh block sitting in my shop thinking bout starting the 4.6 stroker I've been dreaming about for to long

 

Gas issue would be due to the o2 sensor in your glove box. Honestly I really dont know how it runs decent at all without the 02 in.

 

STROKER STROKER STROKER

 

Probably motor time. Your usually looking for between 140 - 160 lbs cranking compression across all cylinders. Your numbers indicate at the very least a blown head gasket, as well the lack of proper fuel metering (O2 sensor in glovebox) probably galled piston/cylinder walls on the other 4, and smeared the bearings. Does this motor have oil pressure issues as well?

 

Nothing new to add to this other than if yer gonna yank the head might as well do the cylinders also. Good reason to drink beers!!!

 

The engine runs decent beside miss on idle not a lot of power kinda like a non Ho motor has good oil pressure I guess awhile back I was going down highway farther I got.the lower the oil pressure finally peggedzero so after sitting awhile me and a burt check it over couldn't find a problem so we flipped a coin and decided to try to limp it back to the house a forty five min drive because we couldn't hear any ticks or rattles so we headed home.made.it fine no trouble changed sending unit went from round 40 psi to 60-70 psi but yea I have no check engine light on with o2 sensor out