CEL - both banks running lean

[Tarron]

I did a search on this and really didn't find an answer. I had a CEL come on a little over a week ago just before leaving for Canyonlands and two days after changing the plugs. Hoped that it was just a random error so just disconnected the battery to clear it. After the computer reprogrammed itself the X ran fine with no CEL. Got back on Friday after 1100 highway and 120 off-road miles and it was still running fine getting 20-21 mpg on the highway. Started it this morning and the CEL was back. Took it to Advanced Auto Parts and the codes indicated that both banks are running lean. It just turned over 40,000 miles during the trip and the only thing out of the ordinary was a little idle problem during the first start of the day in Canyonlands. It would start and go up to 2000 rpm then down to 450-500 then back to 2000 and then idle fine. Once it went so low that it died and I had to restart it. Advanced AP cleared the codes and the CEL hasn't returned but how long would it take to get another CEL with this problem? Any ideas what is wrong?

 

[BradE.]

The computer must recognize the same fault in 2 consecutive drive cycles before it will set the CEL.

Sounds too me like your O2's might be having a slow response problem that is intermittent. That means they are probably getting ready to crap out soon. Check the wiring to each O2 and make sure the connectors are tight and there is nothing loose. Also make sure the O2's themselves are not loose.

Other than that, start saving your $$$$ because O2's are not cheap.

 

[tenikiwon]

Do a search on the O2s. Mine were replaced after I bought it so I've never done anything with them, but I don't think they cost that much or are that difficult to do. there are 4 in mine (1997).

 

[BradE.]

O2's are over $50 each.

 

[yob_yeknom]

Both banks lean at the same time? Too much of a coincidence if it was both O2's going at the same time. I think you have a fuel delivery problem, or a vaccuum leak. Either you're not getting enough fuel, or you're getting too much unmetered air.

Change your fuel filter (can't hurt with 40K miles anyways) and see if that solves the problem. It more than likely will.

 

[Tarron]

Thanks, I'll do a search on replacing the fuel filter as I seem to remember that it takes a special tool to remove it.

 

[Robert]

What were the actual code numbers? There are about 15 different codes that relate to being too lean. All mean a different problem.

For example:

P0171 (short term fuel trim too lean bank 1) + P0174 (short term fuel trim too lean bank 2) + SOHC = ONP 00M12.

Do a search for 00M12 and your questions will be answered.

 

[mikeh]

Since you just did your plugs I would look at possibly one of the plugs getting intermittent spark problems. Did you do your wires also?? I would almost say that you didn't get a boot all the way back on.

That's my call and I'm sticking to it

Good Luck,
mikeh

 

[Robert]

I would think that if it were a problem with a spark plug not firing he would get a rich condition and only on the bank with the bad spark plug/boot. If the spark plug doesn't fire, you'll dump raw fuel into the exhaust.

 

[Tarron]

No code numbers

Unfortunately, the auto parts guy was in a hurry and just said the codes meant that both banks were running lean and then cleared them. Next time, and I'm sure there will be a next time after reading all the rough idle/00M12 information (Thanks Robert), I'll make sure to write down all the codes. It makes sense now that the worst of the idle problems came at about 18-20 degrees early one morning when camping, as here at home it's always in the garage at 32-40 degrees when I start it.

 

[Bill Kemp]

I would think it has to do with a vacume line being disturbed during the spark plug change. I knocked one off once and it through a cel. The othe time I didnt screw down the air tube connection at the throttle body and that made it idel poorly at times.
Unless you poured a bunch of old gas in I wouldnt thing it was the filter but you never know..
Good luck.

 

[Tarron]

Checked the vacuum lines and they all look fine. I would think that the rough idle would continue if one was leaking but mine stops as soon as the engine runs for a couple of minutes. I'm waiting for the CEL to return and then call Ford so they can fix it (I hope).

 

[Tarron]

It's finally cold enough.

Last week the CEL came on again and the codes were PO 171 and PO 174 so I called my local Ford dealer about the ONP OOM12 fix. They said sure come on down BUT be sure and have $130 with you in case that isn't the problem and we troubleshoot something else as being wrong. The CEL has only come on three times and the two times I read the codes they were 171 & 174 so...the questions is could there be something else that they could blame it on so they can grab my cash? At the moment I don't have a spare $130 to give away and from the posts I've read here it sounds just like I have the ONP OOM12 problem, but I'd rather change something as preventative maintenance with the money than just give it away. Thanks.

 

[Robert]

Unfortunately you are at the mercy of the dealer. Those are the two codes I had when my o-rings leaked. They are also the same two codes the original TSB listed. If you have access to an OBD-II scanner that will let you monitor the short term fuel trims on your Explorer you can verify it yourself before taking it to the dealer. If not, then you pretty much have to be willing to pay them the money if they find that something esle is wrong. It mostly depends on how good your dealer is. If he is an A-hole then he will look for another reason for the codes. If he is good then he will look for reasons why it is the o-rings. It sure starts them off on the wrong foot though when he tells you up front that be prepared to give them money if they find something else wrong.