KE7JFF

First Time Poster, long time reader here.

I recently bought a 1994 XJ with the 4.0 I6 from a questionable guy of criagslist for $950. The XJ itself was running really bad when we picked it up, but with my father's assistance, we replaced the plugs, wires, rotor, cap, valve cover gasket, air filter, fuel filter, and even the battery and it was sounding and running better, but still was occasionally misfiring at idle, but I could live with that. At this point, I thought had a excellent XJ

Since I am in the State of Oregon, we have to take our vehicles in for an emissions inspection and this XJ was due for sure (I was running it on a trip permit for the time being). I took it in last Friday for the test and I failed. Hydrocarbons were at 2109 (State Standard is 220) and the CO was at 2.109 (standard is 1).

So since then, me and my father have been testing out and replacing parts. We have so far replaced, the O2 Sensor (it was showing no change in voltage) Thermostat (it had NONE! WTF), Fuel Regulator (the old one was not doing its job per the FSM) and the PCV valve (it was pretty ratty). The 3rd cylinder pressure however is a bit low (at 90; others are at 120). We also cleaned out the fuel injectors and changed out the o-rings.

The MAP sensor, IAC, CTS, Igniton Coil, all checked out as OK. We also did a oil change.

Before we did the fuel regulator swap out yesterday, we took it again to DEQ. Still was at the same HC and CO level. Was very disappointing.

We replaced the fuel regulator and the idle is better, but not where it should be. Also seems to be using less fuel to get moving than before.
My father suggested when I do the test again today, I should remove one of the plugs on one of the fuel injectors so that fuel would be reduced going out, we got kind of somewhere. My first test was at 1500 HC and 2.059 CO. Since my HC was below 1800, I could do a second idle test after running the car in park up to 2500 RPMs. The second test showed 739 HCs with the same CO. So we are getting somewhere.

I just don't know what else to check at this point. Its some sort of fuel combustion issue, but we don't know where else to go.

Anyone have ideas?

MAN00XJ

Im assuming with all the work you've done, and all the voltage you have tested, you have a manual. Check the timing. It may be a little retarded, probably not too advanced, but check it anyway.

mike albo

sounds like your not getting enough spark to fully ignite all the fuel,check the coil output

mike albo

the timeing is fixed none adjustable on all cherokees

CherokeeEnthusiast

check the coil. could have been causing the occasional misfire and could be your not buring all your fuel. Also try swapping out your ecm.

Willys55

A faulty fuel pressure regulator or even a restricted fuel return line to the tank can ramp up the fuel pressure and cause it to run rich

The91XJ

You could also try "heet", an additive from auto parts stores. I've heard two bottles with a damn near empty tank will bring down your numbers. I don't know if there's any truth to this but i found on another forum that 2 gallons of Denatured Alchy from Home Depot/Lowes to an empty tank will pass with flying colors. All measurements will be at least half of what they usually are. Good luck man, smog inspections suck, i've been there before.

KE7JFF

As I said, we replaced the fuel regulator already. The Igition coil was checked and it checks out OK on the primary and the secondary. And yes, the timing is not adjustable in the XJ per the FSM I have.

The plugs are brand new. They are NGK brand; I know from reading here, its suggested to use Champion. However Champion and NGK are both the cheapest plugs and have almost the same construction. So I don't know what that would do for me.

KE7JFF

I'm thinking I might just try to replace the cat. The XJ has 176,000 on it now so I think it might be worth a swap.

MAN00XJ

Like stated above, the timing is non-adjustable, but... If the the computer is faulty, that could mess with your timing, and many other things.. if all else fails, find another computer from another cherokee in a scrap yard, or trade yours in on a new one from an auto parts store.

KE7JFF

Thats something I am leaning toward too..I wish I knew someone who had an XJ nearby...most of my friends either have an YJ or ZJs.

KE7JFF

Well now I am having fun with the exhaust system...I have the cat almost off from the muffler, but I am hearing something loose inside the muffler too...GRRR. I'm going to have a friend tomorrow remove and install the cat for me since he has the better tools and a 2 point lift to get the job done. But I think I might need a new muffler too.

MAN00XJ

Sounds like a good time to put on a magnaflow

Eli Lilly

With the HC that high I wonder if cylinder 3 has a bad valve?

-E

KE7JFF

Well now get a load of this. My friend removed the old cat and exhaust finally and THE CAT WAS HOLLOW! Yup, thats right, the questionable guy removed the GUT of the cat so I HAD NOTHING.