I've got a '94 XJ 4.0L. I've got 99+ intake, CAI, ford #19 injectors with high fuel pressure reg, 63mm TB. I've been getting bad gas milage latley so, I checked all the sensors, and they are all fine. I was running NGK plugs, and had some lite pinging going on, so I decided to go with a slightly colder plug, autolite. I have them gaped at 41.

So, my problem is that after I changed the plugs out, the check engine light came on and the truck ran like hell. Sounded like it was trying to suck in more air then needed. I ran the colds for the light, and it came back with o2 failure. So, I replaced the o2, all seemed fine. I then drove 50 miles home, and the check engine light come on again, this time is was the o2 detected a lean setting.

I'm not sure if this would have anything to do with the plugs, I know older XJ's can be picky on plugs, but it seems to have a slight stumble every now and again at idle, and doesn't like to start right away.

What do you guys think? I may go get some OE champion plugs and swap them out.

Thanks,
J

 

JMO, go with OEM. you have some mods to deal with and may need to adjust heat range accordingly but that's my suggestion.

 

Also, and I just thought of this, I took the ECM connector off and cleaned it with the electrical cleaner, when I screwed the screw back in the ECM, I over torqued it, and heard a crack noise, I hope it was just the connector, and not the ECM.

Thanks,
J

 

Check fuel pressure........is the HP Reg new?

 

I would go with a normal grade NGK plug sounds like u have other issues.. could be fuel related..

does the rig run good now just have the check engine light or what?

 

Yes the HP fuel reg in new.

and she does run pretty good, has a slight stumble while at idle.

I'm guessing it's not the o2, since it is doing it's job. by reporting the lean condition.

 

I read my code as a bad oxy as well I replaced it and still have the code... I read it again and it was an EGR code...

I would pull the egr and clean it.. Thats what I am gonna do first.. clean it then change it if the problem does not go away... my car has a bit of a stumble at idle but nothing bad and runs great!

 

My '94 doesn't have an EGR. I will check the fuel pressure today, what should the pressure be?

 

So, I've been fighting with this all day now, and it's kickin' my *****. I keep getting code 51, which is o2 indacted a lean, abnormally rich correction. What the hell does that mean? I'm leaning towards, that the /ecm just needs to relearn itself. Does this sound right to you guys?

It runs really good, just stumbles at idle now.

Thanks,
J

 

with the new HP Reg. it should be around 49Psi

 

Alright guys, need you help.

So far, I've regapped the plugs to .37.
Changed the MAT, and CTS.
Put stock T-stat in, (195^)
checked for vacuum leaks, there are none that I could find.
Checked all the plug wires, all are good.
New cap and rotor, needed it.
New o2 sensor.
Fuel pressure good.

Checked the MAP, got 5v, on one leg, and 1.437v on the other, Seems right? Book says 5v, and around 2v, (not sure how much "around" is?)

It run, hard to start warm and hot, feels like it almost wants to stall out then recovers, but only maybe every 1 minute or so.

Still getting the code 51, o2 sensor indicating lean air\fuel mixture abnormally rich correction

What do you guys think should be next?

 

change the parts

 

Don't have many parts left to change out....What would you suggest? I may try the MAP tomorrow.

What am I missing?

I found what I needed to change. And a great thread, using the search feature!! Imagin that.

Thanks Finney98xj.

I figured I'd repost a link:

https://www.cherokeeforum.com/f2/jee...di-obdii-3341/

Thanks,
J