Hi All,
I'm new to forum, but impressed with what I've read so far.

My 87 XJ has a 2.5 liter TBI, auto trans, 136,000 miles. I'm having a problem with it misfiring intermittently. It's most noticeable at an idle and especially at a steady light to medium throttle. Under hard acceleration not so much, if at all. I just replaced the coil, cap, rotor, plugs, (wires are fairly recent), and fuel filter to no avail. The O2 sensor and EGR were replaced about 6K miles ago. Haven't put a fuel pressure gauge on it yet (loaned mine to a friend).

This problem rared it's ugly head occasionally 10 days ago and has progressively gotten more steady.

Any help with diagnosing this would be greatly appreciated.

Thanks,
Bob

 

Do you have A/C?

If so, #1 plug wire will rub against the compressor and arc out.


I have one plug set that has an angled boot that clears the compressor.........cannot find another set like it.



Just one possibility.

 

BTW, you only run at 15lbs of fuel pressure..........not likely a fuel problem if you do not experience it at all rpms.

 

The 2.5 is very sensitive to vacuum problems.

Clean out your vacuum ports and check or replace the line to your MAP.......make a new one with steel brake line.

 

http://cruiser54.com/?cat=2


Not all this applies to you directly but go through his tips.

Clean grounds.....replace ALL your battery/starter/ground cables........eliminate your C101.....etc......

All MUST dos.

 

Yessirree. That firewall ground is particularly critical on the 2.5s.

 

Thanks guys!

No AC. Wish it had it. But then again, it's already woefully under-powered I feel.

Honestly don't think it's a fuel issue, but would like to eliminate the possibility just for surety. (Still haven't gotten my gauge back....Grrr.)

Haven't had time to do Cruiser's suggested C101 and MAP vac line fixes yet. The next few days I will and will let you know how I make out.

Cheers,
Bob

 

I refreshed the C101 and.......SUCCESS! Complete elimination is next.
I certainly wouldn't have figured this out without your tips. And can't thank you enough.

Cruiser's other tips will be attended to in the near future.

Thanks again,
Bob

 

You made my day Bob!!

Be sure to check the lines/nipples that Jeep Driver suggested also.

Also, make sure the intake manifold bolts haven't loosened up.

 

I will Cruiser.

Quick question;
Are the NAPA part numbers you have listed the same for a 2.5 as a 4.0?
On my 2.5 the lower port on the throttle body port goes to the top of the valve cover and the upper goes to the MAP sensor. The upper is a smaller diameter than the lower.

Your fix says to tap the lower port 1/8 NPT. I assume this applies to the 4.0.

Cheers,
Bob

 

All that stuff is different.

You can be the pioneer here on the 2.5!! You're on the road to success. Keep us in the loop.

 

Nice hit Pete! Bob, not that any Jeep might not suffer this, but older might be more prone. Doing Bumper work on my 84 last week, I found the vacuum ball worn through. Myself, and a now diciest smog guy, never nailed it down. I needed to pay a "dirty" shop $150 extra to smog it, many years ago. Just capping, or vac testing that large tube off intake vacuum to the ball is something to rule out.