P0171 with no P0174

[mattkins99]

Am I correct in assuming this would be a failed intake manifold gasket? I'm seeing a lack of power at higher rpm too.

-Matt

[bastereo]

Are those system lean codes? We don't have them memorized...

Intake manifold gaskets would be a possibility and without checking anything it would be quite the assumption to jump to that. Could be a vacuum leak anywhere that effects just one bank or an oxygen sensor that is biased lean, or many other possibilities.

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[mattkins99]

sorry, yes, this is a system lean code (I was typing on a tablet touch screen last night so my post was shorter than it should have been.)

I checked the intake system from the MAF up to the throttle body, and everything seems good (connections are tight and I saw no cracks) I cleaned the MAF for good measure but SES light came back within a few minutes after a reset and a drive around the block. Also, the fuel filter is less than a year old. Because I was only getting one bank lean I was didn't think this was likely but it's something I can do before throwing parts at it.

I hadn't thought about an O2 sensor being faulty but not throwing it's own code.... hmm... would that cause low/no power at higher RPMs? This would have to be a pre-cat sensor right? I might order some just because....

[mattkins99]

So to close the loop on this, I replaced the gaskets, checked the hoses. The vent hoses both looked good but the smaller oil return hose that connects under the manifold was in bad shaped and simply pulled apart when I detached it from the CVV. I couldn't get to the shorter oil return host that connects to the bottom of the oil separator, but as best I could tell, it was in OK shape.

After I buttoned everything back and cleared the codes again, the P0171 came back... but then I got the P0174 code too which I wasn't getting before. I was a bit worried that I'd missed something or screwed the car up worse, but I decided after reading in another thread that the MAFs are the same in the 4.4 engines as well as the M5 that I'd swap in one of the MAFs from my M5, clear the codes and see how it goes.

Well, no codes, I passed emissions and OMG was the X5 down own power! I never noticed because my daily driver is an M5 and I figured with the smaller engine and a lot more weight... the X5 was just a pig but holy cow!

[mattkins99]

Oh, and by replaced the gaskets, I mean the intake gaskets to each cylinder, the throttle body gasket and the CVV gasket.

[smarkwilson]

So throwing parts at it solved the problem but didn't pin point the exact problem have ing the same problem in my wife's x5 now and I had the problem on my 540 that turned out to be intake gasket and a broken CCV tube that some one tried fixing before

[upallnight]

P0171 and P0174 are lean bank codes which always means a vacuum leak. In my case the seal between the DISA valve and the intake manifold was the culprit. If I had brought it to the stealers or an indy they would have replaced the DISA valve at a cost of $200 for parts plus labor. Going on the internet (Thanks Al Gore for inventing it) I was able to find a hack that several owners had use. They scrapped the old seal from the DISA valve and replace it with a o-ring. A 3 bucks fix versus a 200+ bucks fix.

[Dshain80]

Originally Posted by upallnight

P0171 and P0174 are lean bank codes which always means a vacuum leak. In my case the seal between the DISA valve and the intake manifold was the culprit. If I had brought it to the stealers or an indy they would have replaced the DISA valve at a cost of $200 for parts plus labor. Going on the internet (Thanks Al Gore for inventing it) I was able to find a hack that several owners had use. They scrapped the old seal from the DISA valve and replace it with a o-ring. A 3 bucks fix versus a 200+ bucks fix.

Would this be a possible same case for the 3.0 ? I am getting the sme codes.

[upallnight]

Originally Posted by Dshain80

Would this be a possible same case for the 3.0 ? I am getting the sme codes.

My X is also a 3.0 engine. So yes that could be a possible same case for your X.

[upallnight]

Originally Posted by mattkins99

Am I correct in assuming this would be a failed intake manifold gasket? I'm seeing a lack of power at higher rpm too.

-Matt

Sounds more like a DISA Valve with a busted pin. Better not drive or start the X until you have a chance to remove and inspect the DISA Valve. If that loose pin get suck into the engine, you're in for a costly engine rebuild.