Code 0171

Earlier this summer I got this 98' Cherokee Sport 4.0L W/ 184K on it. It runs great when cold, and usually gets 24 hwy, and averages 19 city. So far so good.

Occasionally, when it has been running at cruise for some time then idling, it will run rough - the RPMs will drop, then pick up suddenly and run OK. Sometimes it stays running rough, and the tail pipe emissions smell like sulfer and it throws this 0171 code.

I looked up the code, and it read something like "lean", but which appearantly means "can not lean" because of the emissions.

I read the plugs, and they are a nice brown/tan color. Obviously somebody isn't happy in mudville, but where to look for what appears to be an intermittent trouble.

Oh, and I'm not sure this is related... The oil guage is all over the map. When at a steady cruise RPM, that thing is floating thoughout the range. All other guages are fine, and the engine sounds normal.

Clearing the code with a scanner usually results in a few weeks of clear guages, until I take another long trip ( hour or two one way), then it sometimes throws a code.

So, has anyone experienced this code, or run across this trouble?

Ron

Both my books say fuel system too lean. Hence the awesome fuel mileage!
Maybe O2 sensor?
There are two on yours. Most likely the one closest to your engine.

Maybe check the o2 sensor wiring for burn-through, that might give you an intermittent issue when things are extra hot, like after a long trip.

IC, i guess I was interpretting the 0171 as a too rich, but infact it's too lean... Ah So.

That doesn't quite explain the sulfer smell. That's usually caused by too much fuel present (rich).

Or the oil pressure guage dancing around... But when I get a chance, I'll re-visit the Bank One sensor for wiring issues and see what we've got. A burn though would certainly account for the intermittent code issue.

If anyone else has ideas, just hop in and lay'em on me. I'll get a chance to revisit this after I get the Wrangler back on it's feet, so there's a bit of time.

Ron

Zuki-Ron said:

IC, i guess I was interpretting the 0171 as a too rich, but infact it's too lean... Ah So.

That doesn't quite explain the sulfer smell. That's usually caused by too much fuel present (rich).

Or the oil pressure guage dancing around... But when I get a chance, I'll re-visit the Bank One sensor for wiring issues and see what we've got. A burn though would certainly account for the intermittent code issue.

If anyone else has ideas, just hop in and lay'em on me. I'll get a chance to revisit this after I get the Wrangler back on it's feet, so there's a bit of time.

Ron

Click to expand...

Yeah, it is a weird code, it is telling you that the PCM is running the engine REALLY rich based on a LEAN code from one of the sensors. The PCM is really doing its best to richen the air fuel mixture based on a LEAN input. When you find the intermittent cause of the lean input you will have it.

As for the gauge, don't know. I have seen the wires not properly attached after a filter change, and that would allow the resistance signal to the gauge to fluctuate wildly. Might start there.

Good luck.

Yah, I'm getting tons of conflicting data on this code. Some say it says "too lean", others say "Can not lean". I'm inclined to go with my nose and say that the engine is running rich, but the PCM thinks it is running lean, which Joe, is what you said.

It ran fine today, and no codes. Of course it wasn't a really long drive, just 15 miles.

Ron

Just a guess- but when there is a gross misfire the unburned fuel in the exhaust is picked up by the 02 as a lean condition even though it's really rich enough to torch the cat. I'd look closely at the ignition system on this one.

Check for vacuum leaks. Their might be a leak only when its warm and is letting unmeasured air into the engine causing a lean miss fire accounting for the rich smell and the computer seeing a lean mix at the o2 sensor.

This is a follow up...

The Oil pressure issue was solved by replacing the bad sender unit.

On to the 0171 problem.

I spent a lot of time with a volt meter, a vacuum guage, and a manual trying to figure out what ws going on; but in the end, it was really solved by a trip to the junkyard.

In desparation, had resolved to replace all the electronics on the Throttle Body. I looked around, and without fail, every single XJ (and quite a few Grands) had the IAC motor removed.
Hmmmm....

I grabbed a IAC motor off a 96', and when I got home, I found it didn't fit (connections) :doh: However, after removing mine and examining how it worked, I did find that mine was stripped out.

The stepper motor runs a shaft back and forth that holds a plunger which covers a air inlet port on the TB. The plastic holding the shaft from spinning was stripped, and since the stepper could not move the plunger in and out, the mixture at idle was almost always wrong.

I manually adjusted it for best idle when warm and left it unplugged until I bought a new one.
No more stinky idle/rough part throttle operation, and the gas milage is unchanged!

arty: