Jeep GCL: Code P0171 System Too Lean (911)

[Robb]

I know, I know..................................but I need to get this fixed asap.

The wife's Jeep all of a sudden starting running like garbage tonight, and the CEL popped on. Pulled P0171 System Too Lean (Bank 1). The engine continues to run like a bucket, and the code won't clear.

It has the straight-6 in it, so I assume that bank 1 pretty much means the whole engine. If it were an O2, that wouldn't cause such a sudden change would it? And wouldn't that show an O2 code?

Anyone know where I should start with this? FP, FPR, filter, etc? I guess I should do some looking over at the Jeeper BBs..........but I trust some of you engine guys moreso than most of them.

I kinda need to get this fixed asap, because the wife is heading down to NC on Friday, and this vehicle is her only means to get there.

TIA

 

[Robb]

just a bump................and a funny pic!

$170 ?!?!?!?!

 

[Runnin'OnEmpty]

Robb, bank 1 is always the bank that has the number 1 cylinder in it. So, like you say, bank 1 is the "engine" on an I-6. If it was a V-6, it would be easier to diagnoise this code.

I don't think it's an O2 sensor. My first guess would be low fuel pressure; caused by a faulty fuel pump or fuel pressure regulator. If you can find the fuel pump relay, swap it out with another one and see if that affects the code. You could also try resetting the inertial switch, (that cuts off the pump in an accident). Older Cherokee fuel pumps are accessable without dropping the tank; not sure about the Grands.....

Another possibility is a vacuum leak. Check the vacuum "tree" for a loose hose, and the power brake booster for a leak. Since this started suddenly, maybe it's something simple like a broken or disconnected vacuum hose.......

 

[Mike 92 XLT]

www.nagca.com

 

[Runnin'OnEmpty]

Robb, I'm not sure if your model still has an EGR, but if it does, check the vacuum hose going to the EGR valve. These are exposed to a lot of heat and tend to crack or fall off, giving a vacuum leak.

 

[Robb]

Thanks Runnin!

Had a chance to look at it a little while ago, and it doesn't have an EGR system (weird!) and the vacuum lines all look good (there is only a few of them). Another weird thing........no MAF.

Since diagnostic time is so limited right now, I gotta do a little "shotgunning". And since the truck has over 120K, I might as well throw a couple of universal O2s in it and see if it helps. If that doesn't do it, I will pull out my pressure meter and start checking fuel.

 

[Mike 92 XLT]

The EGR system went away in 1990 I believe when they changed from Renix to ChryCo electronics.

I kinda doubt that it is the o2 sensors since it happened all of a sudden. Does it just idle poorly or does it run badly as well? A couple of places to look at would be the TPS and the cat. A clogged cat can result in a too-lean condition. With 120K on it, it may be toast. Also, I would check the fuel pressure first before replacing any parts. I would think it would be a fuel pump rather than the FPR, since when these fail you usually see too high a pressure resulting in a rich condition. Unless the computer is trying to compensate for that by leaning the mixure out and throwing a code. But from your description it sounds like a fuel starvation problem. Or a vacuum leak somewhere. Did you check all the lines at their termination points and not just at the tree? Another thing would be to check the battery. If the battery begins to lose power, ZJs won't idle properly and can make you think it is a sensor going bad.

EDIT: There should be a Mass Airflow Sensor on this engine.

Mike

 

[Robb]

The battery is less than one month old. I followed all of the vacuum lines directly off the manifold to all points, except the small one going through the firewall (a/c maybe?). The CAT looks to have been replaced at some point, or they used some excellent s.s. from the factory, because it, and the pipes, are super clean.

I didn't drive it enough to tell you whether the condition showed up at all ranges. I just know that it ran like a poorly tuned 2-cycle while at idle.

I don't see a MAF. There is nothing in the intake tube, and three things on the TB. 1) IAC 2)TPS and 3) looks to be a MAP maybe.

I went ahead and slapped new O2s on it. I found a local store with the universal 4-wire Bosches (with posi-loks) for $50/piece, so I said screw it and got them. The idle is better and the CEL went away (not sure how great the idle was previously). I put about 10 miles on it this afternoon with no CEL, and the wife will put about 30-40 miles on it tonight, and I will check to see how it did. After I got rid of the CEL, I went ahead and put cap/rotor/plugs/wires on it to try to clear up a small miss that it has, and it helped, but the miss is still there.

For now, the CEL seems to be cleared..................time will tell how permanant that is. I will be back if it returns.

Thanks Again For The Help Guys!!!!

 

[Runnin'OnEmpty]

Hope that fixed it, Robb. We'll keep our fingers crossed.......

That miss at idle might be a lazy injector. In fact, a bad injector could also cause a lean condition. Keep us informed on how it runs.

 

[Mike 92 XLT]

Cool Robb, hopefully that fixes it. That straight six is a great engine and you should get many, many more miles out of it. My old 4.0 XJ had over 240K when I sold it.


Mike