DIS Errors P0171 & P0174 - Do Smoke Test First!
 

Guys, like a few other users, I have had the engine management light showing on my dashboard for a while and when hooked up to a DIS scanner, i got the error codes P0171 & P0174, meaning the fuel mixture is to lean, or in other words, getting to much air, so compensating with extra fuel. After much reading, I tried cleaning the MAF sensor with cleaner, but this didnt fix the issue. Therefore more reading and ended up swapping out the MAF sensor, But again still the error light was showing. Then i read about a smoke test where you blast smoke into the ait intake and if there are any split pipes, the smoke will come out. Therefore, I tried this, this morning, and i have a split pipe (see picture, its split on the ribbed bent section). So possibly, cleaning and replacing the MAF sensor was a pointless exercise. Therefore, before you do anything else, run a smoke test.

The rubber bellow is a well known area for a vacuum leak if it hasn't been changed within the last 50,000 miles. MAF will not produce a vacuum leak. The MAF just determine the amount of air that flow through the intake. The amount of air is determine by a hot wire or hot film that is heated and the DME determines how long it take to cool the wire.

If you had search this website you would have found that most 3.0 owners experience a lean condition when that boot cracks or tears. I know of only one poster on this website that will tell you to clean or replace a MAF as a fix for a lean condition.

I stand corrected, but to be honest, i search here, there & everywhere, and only found conflicting solutions or unresolved issues.

From what I've read, that is one of the most common points for the boot to break, especially the smaller elbow feeding into the ICV. How did you go about the smoke test as a diy?

Jam Jar
2 x Short lengths of garden hose
Kiddies swimming pool pump
Smoke Pellets (used to smoke test chimneys).
Lots of tape
Old T-Shirt

Made 2 holes in the Jam Jar lid and inserted hose (used tape to cover holes), connected pump to one length of hose with lots of tape, removed air filter box\maf and inserted other length of hose down the pipe, blocked up hole with t-shirt to prevent smoke coming out, lit pellet and placed in jar, added lid and switched on pump. the smoke was then forced out of the hose into the air install pipe and as it happens can out the split pipe. Becareful the jar gets very hot.

And I must admit, I did do the happy dance in the garden when I saw smoke coming out of the split pipe.

Great job. Thanks for going into the details

Thanks for this thread.

My Service Engine Soon light came on the other day.
I pulled codes = P0171 and P0174.
Searched this site, found this thread.
I've been waiting for an excuse to build a smoke machine, but figured I'd just do a quick visual inspection first.

I immediately noticed a ~1" long tear in the ~1" diameter hose of part 8 in the diagram above (BMW PN 13541440102). So I taped it up with electrical tape, reset the codes, and a new part is on order right now.

BTW, service records show that this exact part was replaced at the dealer 5 years and 26k miles ago. Is it possible for it to tear like that so soon? It actually makes me doubt the service records now - not that the PO was trying to trick me, but that he was constantly getting ripped off by the dealer.

Glad you found my thread helpful.

SF doesn't have EXTREME temp swings... but rubber bits on BMW's are known to crack in 5 years time under the right conditions. Especially if you are in extreme temp areas like south Texas. I regularly clean under hood and "condition" (detail shine) the rubber pieces. Not sure if this has helped me, but I don't usually have to replace the same rubber piece twice in the period I own a BMW. I also only use OE quality replacements... no URO, Karlin, etc. type brands for these type of components. That said, my convertible is starting to show signs of a cracking intake boot once again... last one was replaced back in 2010 or 2011, would have to check my records.