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94 XJ wants out of the running rich club!!

awdsully

NAXJA Forum User
Location
Fort Collins, CO
I know there are many different threads with discussion on this problem, but nothing has really been helpful to my particular case so I have to ask for some helpful advice!

Specifics:
1994 Cherokee Country 4.0HO ODO shows 218k but previous owner claims motor was rebuilt.
Anyway, car started having a rough idle by dropping to about 500rpm and acting like it wanted to stall and occasionally would, especially when throttle was applied.

When throttle is applied from idle, it stumbles and eventually climbs to rpm. Leaving a really rich smell. After about 1500rpm it runs perfect.
To start I did a simple tune up with plugs, plug wires, dist cap, rotor, and a fuel filter. Also ran BG44k through her. Helped a little but still horrible gas mileage and rough idle running rich.

More recently I have done Throttle Position Sensor, MAP sensor, cleaned all around the throttle body and IAC. Also replaced O2 sensor, compression tested and all around 140lbs, and lowest being 130lbs. Fuel pressures came back fine, and there seem to be no vacuum leaks.

Ive currently got the injectors sitting in B12 injector cleaner, and after playing with a meter they all read about the same voltage.

I'm out of ideas! Please help!!
Thank you!
 
Grab yourself 3-4' of vinyl tubing (or hose), stick one end in one of your ears and then move the other end CAREFULLY around the exhaust manifold upstream from the O2 sensor. NOTE: an exhaust leak will be LOUD, be careful of your hearing and moving engine parts/heat.
 
What do you mean by "done" the TPS, MAP...

Cap, rotor, plugs and plug wires? CPS???

What do the spark plugs look like, they can tell you a lot!!!

Sensor grounds???? Battery contacts at the posts?

How rich is it running?

You test the injectors with a 9 volt battery and jumper wires!!!
 
I found a small crack in the header, right where they separate below the upstream O2...

I will try to find more with the tubing trick, I can hear a air whistle/ wining noise at idle, which I would like to find and address, so thanks for the tip!

I pulled plugs and they look great, no fouling, darkness or anything. There is also no soot in the tailpipe, but it is definitely running rich.

Sorry by done I mean replaced, the map was from a donor vehicle, but everything else were new replacements.
 
The HEEP is still running really rich, backfiring a lot more, and breaking up/ falling on its face in low rpm in gear. Any other thoughts? The exhaust is leaking, I just do not know if it is bad enough to cause this problem.
I am going to check timing and see if it helps anything.
Thanks!
 
Check the vacuum line from the Map to the throttle body. Is it loose or damaged? They often come loose that throttle body and cause your new problem.

If the MAP is good, and the vacuum line is good, and the cap, rotor, Dizzy, plug wires and battery contacts /sensor grounds are good (clean, tight and no shorted harness wires or bad plug wires), I would suspect a dying CPS now.

You can disconnect the O2 sensor to make sure it is not the problem before swapping the CPS.

Rare problem is a dying HV spark coil.

Have you test the fuel pressure with gauge? A lot of reports lately of the pump outlet hose in the tank going bad and loosing fuel pressure!!!
 
Any updates on this thread? I'm currently in the same boat with my '96 xj... Had a pretty embarrassing night with mine last night--pulled another car out of 6" inch deep mud at a friend's house, hung out for a bit, and then mine refused to start until I gave it a full nother hour to chill out.
 
Long time no update, I broke down and took it to a shop and they told me to put in different plugs... I was reluctant to believe since it was my 3rd set in 3k miles but I had been putting platinums in and they told me to use copper plugs and it fixed majority of the issues!
Hope this helps
 
Long time no update, I broke down and took it to a shop and they told me to put in different plugs... I was reluctant to believe since it was my 3rd set in 3k miles but I had been putting platinums in and they told me to use copper plugs and it fixed majority of the issues!
Hope this helps

What exactly were the issues you were having? I am very curious!!!! Any idea if there are issues like low compression versus Jeep OEM spec for new engines. Running rich? Oil fouling from leaky valve seals? Was the problem immediate with new platinum plugs or did they foul over time?
 
Long time no update, I broke down and took it to a shop and they told me to put in different plugs... I was reluctant to believe since it was my 3rd set in 3k miles but I had been putting platinums in and they told me to use copper plugs and it fixed majority of the issues!
Hope this helps

Also, which platinums were you using? Single, double, multiple grounds??? Brand, part number?
 
Ah, Ha!!!!! From post #1!!!!

compression tested and all around 140lbs, and lowest being 130lbs

So how about the oil leak question? Any sign the plugs were fouling at all in any way? Brand, part number, style of Platinum?
 
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