Lonehowl

So, I bought an 89 XJ (Renix engine) from a guy back in September 2017. Smog was due, but he didnt want to mess with it cause he bought a new JK. It had previously smogged in May 17. I bought it cause it had some goodies already on it like lockers, etc. I figured I could figure out how to get it to pass smog here in California.. It had the notorious low idle, then would kind of perk up for a short bit, then low idle again. Running real rich. it was a gross polluter right off the bat. I replaced sensors etc. but nothing worked till I put a new cat on and screwed in a new O2 sensor (dont remember what brand now). Perked right up, I could tell it ran better, so I took it down to get smogged and it passed with super low numbers. That was in Late October 17. Been driving the heck out of it since.

So yesterday out of the blue, I start it up and its idling weird again, and smells a little rich, like its in open loop and not closing. Im thinking the O2 sensor is suspect again. I will put on in tonight to see what happens.
My question is, would there be a reason a Cherokee would go thru O2 sensors often? Bad sensors (NTK's) ? Voltage have something to do with it? Bad/weak relay? Ive done the Cruiser54 ground refresh etc., so I guess Im looking for ideas on what to look at going forward.
Thanks all!
Mark

EDIT: Put a new O2 snsor in this evening and runs like a champ again. Not sure what is happening?

89Laredo

Have you tested any of the other sensors? Do you have a scanner? Is there 12v for the heater at the oxygen sensor plug?

NTK is the recommended sensor.

Lonehowl

I have not tested any sensors that I recall, no scanner..and have not tested for 12v at plug. Which wire on plug do I test? Any specific sensors I need to test?
Thank you,
Mark

cruiser54

Also be sure the hose from throttle body to MAP is perfect.

I'd check for 12 volts at the oxygen sensor heater as suggested.

Lonehowl

Thanks Cruiser, so are we talking about having 12V from one of the 3 wires in the harness plug? Which wire is it?
Thanks.

cruiser54

Red.

Lonehowl

Shoulda known that lol, thank you sir.
Mark

cruiser54

LOL. You got my drift....

Lonehowl

Another question..when you pull the vacuum line off of the map sensor, is it supposed to kill the engine, or should it keep running?
Thanks,
Mark

cruiser54

It can stay running, but should get blubbery.

Lonehowl

Hmmm, ok, mine dies, every time.

cruiser54

They can die if you unplug the electrical plug. blubber if you pull the vacuum line.

Lonehowl

Well, dang...it instantly dies when I pull the vac line off. Not sure why? Anything in particular that stands out that would cause that? Should I worry about it?

cruiser54

cuz it's running pig rich..........

Lonehowl

But it passes smog fine? With low numbers even...goes into closed loop etc. (per my smog guy). Running rich, would that be the only reason?