Hello all, I have a 1991 Jeep Cherokee that had a 4.0 engine that blew up a couple of years ago. We tried fixing it by replacing the engine with another 4.0 that our friend gave us. We had run into a couple of obstacles and gave up on it for a while. Recently we had just gained the motivation to try fixing it again.

We did some checkups on fluids before we tried starting it. It didn't run but it did crank so this gave us some information about where we stood. We replaced the fuel and checked the fuel pressure, it was about 30 psi I believe which my dad said it should be about 40 psi instead, but we had tried starting it by spraying an accelerant into the air intake, and still wouldn't start so it shouldn't be a fuel problem.

We checked the sparkplugs and they seem to work. We used a tool that has a led that lights up when you crank the engine (it is used between the sparkplug and the sparkplug wire). My dad says that he has a gut feeling that it is a timing issue since it was really close to starting up a couple of times. While searching other forums, I found out that there was a distributor change some year after 1991, so we theorize that the distributor is our problem. When we did the swap-in, my dad also swapped the distributors on the new and old engines. This was because the new engine has a round 4 pin connector and the old one had a 3 pin connector so we used the old one so we didn't have to change the wiring somehow.

My question is this: is there a different timing or compatibility with these distributors and engines? How can we adapt the round 4 pin connector to our wiring?

Please be patient with me, I am not all well versed when it comes to cars, I am only almost 20 years old at this point. Thank you in advance for your responses.

 

Cruisers reference on indexing the distributor. You might be a tooth off. Also note the diagram for the plug wires. Some of the diagrams out there, notably Haynes, are wrong. http://cruiser54.com/?p=68

Fuel pressure should be 31-ish at idle and 40 with the vac line pulled or when not running. What year was the donor? 87-90 would have a different, incompatible flexplate/flywheel.

 

Is there any way to inspect the engine to find out? I don't know what year it is, I will try to reach out to my friend to see if I can get more information. I believe my dad found that link that you gave me and was talking about doing something like that. My dad was also saying that he thinks it's just off a tooth as well.

 

I took a look on at the distributor sensor connectors on RockAuto. The distributor connector on 1987-1990 is a 4-pin round. 1991->2001 are 3-pin flat. Flexplate part numbers changed at the same time after 1990 (and again between 96/97). So if indexing the distributor does work, I think you may have a mis-matched flexplate/flywheel if you didn't swap that over.

 

I just spoke with my dad, and he said that the donor engine had a flywheel on it and was from a manual and that we swapped it at the time. We are going to try to index the engine, although I don't know when.

 

Whew. I was thinking you were going to have to pull the engine out again to swap. I'm betting getting the distributor indexed will resolve the issue.