Most likely cause for a P0171 Code with M62 V8?
 

I've had my 2002 4.6is (108K miles) for a couple of months now and have been patiently sorting it out. Thankfully it hasn't really needed all that much - just a lot of little stuff. And maybe a couple of big ones…

So I thought I had it pretty much straightened out until I was driving it today and the check engine light came on. Great, now what! I just read the codes with my cheap little handheld code reader because the battery in the laptop I use for DIS/INPA is dead and my only extension cord is in use charging the battery in the old M3. I know, first world problems.

Anyway, this is the code I'm getting:
Experience tells me this is most likely a vacuum leak. And if were on an M52/52TÜ/54 I'd immediately suspect the oil separator/crankcase vent because 99% of the time, that is the source of the leak. Is there an equally likely source on the M62 V8? I'd like to know what the most likely culprit is before I order a bunch of parts and do a ton of work that it may or may not need.

I've been doing some snooping around and have seen a couple of potential problem areas, but nothing conclusive. How have others resolved this?

Could be a lot of reasons for a bank to be lean. I would do a little more diagnostic on it. Since the ECU or DME is throwing up the P0171 code I would look at how much the 02 sensor is adding fuel to bank one. You can get an App call TORQUE for free and purchase a cheap ELM 357 bluetooth scanner module to read live data. Short term fuel trim will be more than 10% above normal for the ECU or DME to throw up a P0171 code.

Couldn't I use DIS or INPA to check the fuel trims?

Yes if you know how to use those software.

Lean conditions could be a idle lean condition which is normally a vacuum leak, but a power lean condition is when you don't have enough fuel when the engine is under load. This could be due to a weak fuel pressure condition, clogged filter, or a bad MAF.

Here's a video on how to determine what type of lean condition you have.

https://search.yahoo.com/search?p=re...r=dss_yset_chr

Good info, thanks! FWIW, the CEL came on under light acceleration. That may or may not actually mean anything.

If you never changed the CCV at the rear of the intake manifold that is a normal source for a vacuum leak.

http://c1552172.r72.cf0.rackcdn.com/558324_x800.jpg

There's a Youtube video on how to replace just the diaphragm.

I am suspicious of the CCV because it's such a common source of vacuum leaks on the I6 engines. I have not replaced it yet - mostly because I'm not enthusiastic about pulling the intake manifold.

I plan to do a smoke test this weekend and see if I find anything. Maybe I'll get lucky…

Although it would be easier to replace the CCV with the intake manifold off the engine, there's a video about replacing the diaphragm with the intake still install on the engine.

https://www.youtube.com/watch?v=kKNeN8tR3wM

Interesting. Looks like it's possible to replace it without pulling the manifold. Good to know!

Did that last week. The two lowest located torx bolts are the hard ones to reach. Needs the right sized (small ones) tools, because of the water hoses there isn't too much space around. Switched the torx bolts to a allen bolts.