MoniqueTriana

Hi,
I have a 95 Cherokee 4.0 6 2 wheel drive with some rich fuel burning issues. I had never had problems with emissions in the past but am not passing emissions. I have concluded that the fuel is burning rich, so I replaced all hoses (some were cracked) and replaced cap and rotor and plugs. It seemed to run better so I decided to take it back to emissions before replacing more costly items like the o2 sensor or fuel pressure regulator since I do not seem to have any sputtering, problems starting, high idling and it drives fine. I started it and let it run to get the cat hot, and noticed that I had some hard running while pressing the gas. I decided to check the plugs and the first one I pulled was hard to take out and cracked on the ceramic. All the others looked burn already (they have only been in and havent driven anywhere but it being on in the driveway and driven around neighborhood.) I see this is because rich fuel burning. Can anyone give me any ideas what could be the issue if I am not having any problems with idle, sputtering or performance. Is the 02 sensor or Fuel regulator easy to replace, could it be a bad fuel pump? Fuel injector? it does not run bad or have any symptoms to fit any of these issues it could be.
Thanks everyone

opie1988

you may have leaking injectors. pull them and replace O rings and clean them

MoniqueTriana

OK Ill try that. Thank you. If that is the case wll it give a heavy carbon smell like it has from the exhaust? And fry out and crack new plugs that havent had any drive time just idling in the driveway?

salad

What plugs did you install? No amount of running rich will cause them to die that spectacularly...

MoniqueTriana

Mid grade auto lite from autozone,(bout $3 per) same I used before and worked great. They arent completely destroyed, one was cracked completely on the white ceramic and some looked very worn and blackened. Ive let it idle in the driveway after replacing hoses and replacing the radiator, drove it around neighborhood, only put about 7 miles on it. They just looked more worn than they should have been and smelt burnt and I could feel at unease when i accelerated in park and thought it felt like plug issues so I checked them. The rotor looked a little burnt also, and I replaced that and the cap at same time.

salad

Yikes.

You should be running Champion RC12ECC or NGK ZFR5N, AutoLites have mixed reviews in this engine.

Any change of a photo of the plug ends?

Have you tested the TPS or MAP? Any idea what the operating temperature is?

O2 sensor isn't that expensive, $35 on RockAuto.com for an NTK (the OE brand) last I looked.

jakecarder

Post pictures of the spark plugs. We need to see what you mean by burnt plugs. Are they completely brown and black? Even if they have 1000 miles on them, they should still be fairly white and new looking. If one is cracked the only thing I can think of is either wrong plugs, to long causing contact with piston( if that's possible with the 4.0, seen it happen in an old v8 with wrong plugs) or spark is too hot. Each brand/part number plug is different. Even tho autozones computer says it will work more often then none they don't. Their computer basically tells you its the same thread type amd will make the engine run. Dosent go into detail about that specific plug. I don't know the real wording, terminology or even how to say this but think of it as heat and volts. Spark plugs needs x amount of volts to make a spark at x temperature and each one is different. The jeeps ignition system only puts out x amount of volts and if it don't match the spark plugs you picked there will be problems. If you feed to much to them it could cause it to crack. If your feeding it not enough the spark will not be the right temperature and not ignite all the fuel sprayed in the chamber. Then un burnded fuel still in liquid form goes out the exhaust, ruins o2 sensors and catalytic converters. Unburned fuel also shows up as running rich. Now dont quote me on all this. I could be completly wrong I'm just a guy on my computer.. when I was getting sparkplugs for my 2000 I came across that info a few times on here and random web sites. Remember the jeep 4.0 absolutely has to have factory spec replacement spark plugs. All the new fancy triple spark sparkplugs womt work because basically the 4.0 was deaigned 30 years ago and used in tractors. There made by champion and can be picked up from any parts store or jeep dealer.

partsguyct

Check the map sensor hose for small cracks