This happened all of a sudden today on my '88 Cherokee Pioneer with the 4.0L. When I attempted to start the engine at a store parking lot, I heard what sounded like a misfire as it was about to start. Not loud, but you could hear it. It started on the second cranking, but the engine wasn’t happy. The vacuum gauge normally reads ~15 inches of mercury at idle, but now it was reading 10-11. There was an audible hissing sound coming from the top of the engine when there was none before. Although the engine wasn’t running roughly (no shuddering), it lacked power. I was able to drive it home and during the trip, I felt a miss now and then. The engine did not stall at any point. If I step on the gas when idling, the response is not what you'd expect. No misfire, but it struggles to gain rpm.



I had a similar occurrence a number of years ago when the engine lacked power and had a low vacuum reading, but there was no hissing sound. Back then they found a collapsed fuel pump hose inside the tank, plus the O2 and crank sensors had gone bad. The hissing sound is a new phenomenon. I bought it brand new in January of '88 and have kept it all these years. Could the timing chain have jumped a tooth?

 

That's got to be the craziest leap of non-logic I have ever heard on this, or any other vehicle forum.




Try looking for a vacuum leak.


https://www.youtube.com/results?sear...+a+vacuum+leak

 

Somewhat embarrassed, but I found the problem.

It turned out to be the vacuum plug where the MAP sensor tube goes into the throttle body. It had popped loose. Plugged it back in, problem solved.

 

Woulda been my first recommendation. Kinda common. There is a fix for it.

http://cruiser54.com/?p=280

 

Mark what's the deal here ?? Not much of a help after cutting the guy down for theorizing what the problem might be he's just looking for help and not this kind I'm sure..
This is the 4th thread I've read today where you come across like a grumpy old ***** and are probably running new members off by the herds..
I'm here to learn about XJs while I build mine and there's plenty of WRONG info wading through the old posts you keep telling everyone to search through so keep that in mind when there's a call for help...
Mabe you should go get the XJ in your sig running and take a break from posting for a while or sell it and buy a Subaru or something...
Flame away buddy I got big shoulders but I bet I'm not the only one thinking what I posted just the one that did it...

 

Corky, you are right and I am wrong. Thank you for calling me out.