AMXJ

Looking for some ideas as to what is going on with my 91 4.0L XJ. I have worked on and built a lot of V8's as well as a couple of AMC/Jeep 6 Cyl. engines but this problem has me stumped!!

My Jeep has been running great and trouble free for years. Since buying it in 2008 I have rebuilt just about everything on my Jeep and service it on a regular basis. A couple of week ago it all of a sudden started running rough and I also noticed at htat time it developed a rocker arm noise that had not been there. Long story short the cam shaft lost (rounded) one lobe. I replaced the cam and lifters with a Melling stock replacement cam and Melling lifters and now my Jeep won't start. It cranks over fine no popping or backfiring or anything like that so (without taking it back apart again) I'm 99.9* sure the timing gears and chain are installed correctly. I had re-checked the alignment of the timing marks on the crank and cam gears several times to be sure they were perfect before bolting the cover back on. (BTW it also has a Cloyse double roller timing chain and gears.) Along with the cam and lifters I decided to replace the Dodge Neon injectors with some rebuilt K Suspension injectors since they are highly recommended (and fairly priced) by a lot of 4.0L Jeep people.

I have pretty much checked all of the basics. It is getting fuel, and spark but I did notice spark at the coil and spark plugs seems a bit weak compared to the high-performance engines I have built and worked on. The thing that gets me is it was running so good right before the cam lobe went flat. I was only about 2 miles from home, so I slowly limped it home and took it apart to find the bad cam. Cam and lifter change was pretty straight forward but now it won't even start so that I can run the cam in.

Anyone have any ideas what I should be looking at or for on this? I love this little Jeep and really want to get it back up and running right again soon.

Thanks in advance for any input or ideas you might be able to share with me on this problem!!!
Dennis

exasemech

Distributor timing/sync off?

Don't ask me how I know... Porsche engine.

bluejeep2001

That was my first guess also...might have dist set to nbr 1 but motor is on nbr 6 tdc compression. If after you verify thats good and no help...check compression across the board

AMXJ

Thanks for the suggestions, but wouldn't it be popping and farting while cranking it over if that were the case??

Thanks again!!
Dennis

exasemech

​​​​​​
No
Not necessarily.

dmoe69

Have you done a compression check? The 4.0 is sensitive to changes in dimensions of the valve train. Also, you didn't say if you installed OEM or aftermarket rockers, or if you installed an aftermarket valve cover, both could be relevant.

AMXJ

I didn't do a compression test because it was running so good right before the cam lobe went flat. I have always run OEM rockers and the rocker cover is stock as well.

I haven't had any time to dive into it much yet but will post more when I am able to.

Thanks to everyone for the response!!
Dennis