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Old 21st February 2014, 19:34   #1
JUNGLISTluder
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S62 running too rich

So my M5 has been running progressively more rich over the past year and now it is pretty obvious that something is wrong. There is no SES light and the engine runs smooth but read below and let me know what you think.

Engine Mods:
  • PowerChip ECU Tune (Matt did it a couple years ago)
  • Tubi midpipe and muffler deletes

Symptoms:
  • Used to get 280-300 miles per tank with normal mixed driving; now I get 220-250 miles per tank with the same driving style
  • My exhaust tips are always black and sooty; even after washing they will be black in a couple days
  • The car briefly hiccups/stumbles when pressing the accelerator before taking off
  • Doesn't quite feel like the engine is making full power

In an effort to fix the problem I have done the following:
  • New OEM M5 MAF sensors
  • New precat 02 sensors
  • New fuel filter
  • New spark plugs
  • New air filters
  • Cleaned oil seperators
  • Fuel pressure test (high 60s at idle; low 70s when revving)
  • New thermostat
  • New ECU and sender temp sensors
  • Fuel pump relay
  • ECU reset via OBD2 scanner and battery disconnect
  • New rear tires
  • 4-wheel alignment (within spec)
  • Techron concentrate treatment

Here are the things I have not replaced but could potentially have an impact:
  • Cam Position Sensors (CPSs)
  • Fuel pump
  • Vanos seals

What am I missing? What would affect the A/F ratio and cause the engine to run rich but not trigger the SES light? Is it my PC tune? Would the vanos cause this? I don't think it's my fuel pump because I have solid fuel pressure. Is it the difference between summer/winter fuel blends? Am I just crazy? Thoughts???
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Old 21st February 2014, 20:11   #2
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Quote:
Originally Posted by JUNGLISTluder View Post
So my M5 has been running progressively more rich over the past year and now it is pretty obvious that something is wrong. There is no SES light and the engine runs smooth but read below and let me know what you think.

Engine Mods:
  • PowerChip ECU Tune (Matt did it a couple years ago)
  • Tubi midpipe and muffler deletes

Symptoms:
  • Used to get 280-300 miles per tank with normal mixed driving; now I get 220-250 miles per tank with the same driving style
  • My exhaust tips are always black and sooty; even after washing they will be black in a couple days
  • The car briefly hiccups/stumbles when pressing the accelerator before taking off
  • Doesn't quite feel like the engine is making full power

In an effort to fix the problem I have done the following:
  • New OEM M5 MAF sensors
  • New precat 02 sensors
  • New fuel filter
  • New spark plugs
  • New air filters
  • Cleaned oil seperators
  • Fuel pressure test (high 60s at idle; low 70s when revving)
  • New thermostat
  • New ECU and sender temp sensors
  • Fuel pump relay
  • ECU reset via OBD2 scanner and battery disconnect
  • New rear tires
  • 4-wheel alignment (within spec)
  • Techron concentrate treatment

Here are the things I have not replaced but could potentially have an impact:
  • Cam Position Sensors (CPSs)
  • Fuel pump
  • Vanos seals

What am I missing? What would affect the A/F ratio and cause the engine to run rich but not trigger the SES light? Is it my PC tune? Would the vanos cause this? I don't think it's my fuel pump because I have solid fuel pressure. Is it the difference between summer/winter fuel blends? Am I just crazy? Thoughts???
Surprised the new rear tires didn't help!!! (j/k).

After changing parts, like spark plugs, pre cat O2's, any improvement? If you are running rich, it is not the fuel pump.

Assuming tune is good, (did you have the issue before the tune????) I would think there is an unmetered air leak after the MAF's. So the car sees more air than it is getting, hence running rich. Can Matt return the tune to stock temporarily to eliminate that issue?

You might check the two pipes going into the front of the plenum, there is a small rubber gasket on each side that is easy to mangle (ask me how I know!!).

Why not do some dyno pulls and get your AFR's and the AFR curve? Might be helpful.

Regards,
Jerry
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Old 21st February 2014, 20:17   #3
ard
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Surprised you dont have fuel trim numbers... diagnosing based on soot and miles per tank isnt optimal.


See this:

Failed emissions...with a twist?

Stop replacing parts, do some diagnosing.....

IMO
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Old 22nd February 2014, 04:17   #4
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Im averaging about 24mpg at 65mpg, 21mpg at 85mph, 23mpg 45mph city. Sound about right? I've watched my fuel trims and they're normaly almost zero. That sounds right to me. My car does have a very.. hard to explain... digital stepper motor feeling throttle. Very small movements yield abrupt response but only at lower rpms.

Rao?
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Old 22nd February 2014, 05:06   #5
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Did your car come with the tune? I'd start there.
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Old 22nd February 2014, 05:26   #6
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Speaking of running rich!
Changed my pre-Cat O2 sensors tonight.
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Old 22nd February 2014, 05:43   #7
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Try the CPS sensors. Rock auto sells the Intermotor brand. I have been using them for years with no issues. My exhaust ones actually had the BMW stamp. Go for new O2 sensors as well. I bought Denso ones. They're a good OEM.
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Old 22nd February 2014, 05:50   #8
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Quote:
Originally Posted by bcampbe7 View Post
Speaking of running rich!
Changed my pre-Cat O2 sensors tonight.
Wow, were you getting an SES light at all? I found the Bosch sensors on eBay from reputable sellers for $50 shipped each. Not bad. Bosch 13477 I believe it is. Theyre not knockoffs either. $100 isnt a bad investment.

Other than the seller telling you it has a tune, how would I know? Throwing it on a dyno isn't very precise for knowing if it has a tune - before someone suggests that lol. I'll happily throw it on the dyno though for fun

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Old 22nd February 2014, 06:20   #9
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And before I go any further: how far and what kind of mileage are you guys getting in those conditions? Granted I have 19" wheels amd BBK F&R and that affects everything so that's why I'm wondering about where everyone else is. I brake early for traffic lights to avoid stop starts in traffic and I se cruise control on the freeway when traffic permits and my heart isn't feeling the need for speed.
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Old 22nd February 2014, 18:02   #10
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Would also be interested in seeing how you solve this. I feel like my car is the same way at low rpm. I have no lights and the car runs like a champ so its not something I want to dump money into.

Jerry you have a good point. The two rubber gaskets on the inlets to the plenum are a huge source for added air post-MAF. I have replaced the 2 on the MAF's, just need to do the plenum ones now.
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