Would someone check my MAP math?

[Jason]

Interesting. I guess I'll have to fork over the money to have the Mech. hook up the Jeep. I had thought of disconnecting the battery again last week but never got around to it. I'll try that.
If in fact the mileage is what is triggering the light, it would be the first time this has happened and I've owned the Jeep since it had 3 miles on it, which I put on it when I test drove it. I now have over 142k on it. Like I said above, I just do not like having the check engine light on while out and about. It's like someone is telling you, "Hey Idiot! Maintain your vehicle!"

[6spdYJ]

Okay, did a little research. This brilliant device is called the Emission Maintenance Reminder. Now I can't find the mileage it's set to fire off on. IIRC, it first goes off at around 86,000 and then every 42,000ish thereafter. The way it always went for me was - replace O2 sensor and clear fault. Realize smog is due next week, maint req'd light goes on, have an anurism, get the reminder cleared, pass smog, forget about it. Fast forward two years... replace muffler. Realize smog is due next week, maint req'd light goes on, have an anurism, get the reminder cleared, pass smog, make mental note. Two more years... Replace cracked exhaust manifold and O2 sensor (again) and WAIT FOR REMINDER. No light, pass smog, send many unpleasant thoughts toward the engineer of this stupid thing. As you can see, it tends to only go off just before smog is due and you have made smog-related repairs (usually expensive). The more you spend and the more you need to pass smog with flying colors, the more likely you are to see this dumb light.

[Jason]

That's exactly what is going on with mine. All seems to point to the O2 sensor. Can't remember when I last changed it. I was told the code the scanner showed was a 51. We shall see.

[6spdYJ]

O2 sensor? Okay, let's have some fun!!! Last time I needed one, I did some looking. Get one for a 1990 Dodge Shadow with the 2.2. It's a Borg Warner OS141. It's about $30 cheaper. The difference is that the wires are about 1 1/2" shorter. Just move the wire clip and stud back one hole on the oil pan.

[6spdYJ]

Any news?

[Jason]

I'm waiting for the weekend to get back to it. Going to go the O2 sensor route first. Slowly running out of sensors to check and replace.

[6spdYJ]

Your YJ is getting newer one piece at a time...

[4wheelinmike]

I'm a little late on this but before you replace the O2 look at the tps. When I throw a MAP or a O2 sensor on mine I blast some parts wash on the CKP, test the TPS for a "dead" spot, and check for vaccum leaks. I've found that a O2 code on mine and a lot of the cars I deal with at work are only 10% real O2 faults.

The reason I say check the TPS is because the TPS and the MAP have to be happy with eachother. If one shows more then the other the others not happy. For every position of throttle theres a voltage and that voltage has to agree with the voltage of manifold pressure. after a few years of cruising down the road at 3grand, that certain point of the TPS gets worn out and that voltage is no longer 3.7vdc(for example)

And my last thought is, do you know how to read your own codes? Cycle the ignition off to on like 4 times on the last cycle leave it in the on position and count the blinking check engine. First ones 12 B+ disconect, then codes, maybe a 33 if you have no AC, then 57 for codes compleated

just my 2 cents hope I maybe helped a little bit,
Mike

[Jason]

I wanted a long "test" drive in the Jeep before I updated this post.
On Saturday, I drove the Jeep up the 330 to Big Bear. About 1/2 up just before the new section, the engine hesitated for a sec, backfired, and then drove fine the rest of the way up. Plenty of power and everything just felt fine.
Was coming back down in the afternoon and just before Arrowbear, the engine backfired 3 or 4 times with zero response from the throttle. Clicked the key off and then back on and away I went. Cycled the codes and nothing. It died a few more times down the hill. I just kept thinking, "It's all downhill to the truck. Just get me there."
Electronic ignition engines are not supposed to backfire. I think I need to check the timing and maybe clean up the fuel rail for good measures. Even though all my probems sound ignition related and not fuel.
At least this time out there was no check engine light bothering me.
Mike, no you're not late to this party. The ignition gremilins are alive and giving me fits. I did replace the O2 sensor as the voltage being read was not fluctating while on a scanner. I do belive the TPS will be my next victim.

[4wheelinmike]

MAP is also an altitude sensor. When I take mine to big bear does the same thing just because the height change. Don't touch timing if you haven't been in there before it's computer controlled

[6spdYJ]

The distributor housing sets the initiation point for the injection cycle. It's not worth messing with on a stocker. The timing is set by the Crankshaft Position Sensor. It's fixed, unless you have modified the mounting bracket for adjustability. Have you checked the Camshaft Position Sensor and Crankshaft Position Sensor? Typically when a hall effect device fails, they just go. But - once in a while they can just get flaky.

[4wheelinmike]

We have a CMP? I didn't know we had one just knew about the CKP

[Jason]

The Jeep never behaved this way in all of my past trips to Big Bear. This is why I'm looking at all possibilities.

I remember being told that the timing on these things are computer controlled and cannot be adjusted. Thanks for reminding me. At least that idea is now eliminated. I am old enough to remember how to set and adust the timing before these so called computers started running the world. I haven't used my timing light in while. It's fun to bring it out. Who knows, maybe the timing chain has stretched. Checking the timing just might shed some light. There are a lot of miles on this heep.

Any insight on checking the TPS? Voltage?

[4wheelinmike]

Key on engine off back probe the wires I don't remember what's reference and what's signal location. Ref should be a constant 5 volts dc and signal should be .5 at "idle" and 5vdc at wot. But if you have the obd1 scanner and get into PIDs try it that way

Mike

[4wheelinmike]

AND if you're backfiring it may sound like you may be rich and have an exhaust leak before the cat(assuming that your cat isn't hollow like almost everyother yj I know)