Is the term MAF a misnomer? - The Unofficial BMW M5 Messageboard (m5board.com)

bimmernut1 · 4th October 2006, 04:53

I've read through about every link on this subject and have a question. When I read how this system works, it appears that the sensor itself does not measure mass flow but instead volumetric flow (e.g. SCFH). True mass flow is only obtained when the volumetric flow is converted to mass (e.g. lbs/hr) by the car's computer using the ambient air pressure and temperature readings. This mass flow appears to be the flow that fuel flow is ratioed against, not the output from the MAF itself. Is this assumption correct? If so it should be called a VAF (volumetric air flow).

On a related note all I see points to the fact that the MAFs should be treated as a maintenance item. That is, assuming you can get them from David rather than the dealer's high price, shouldn't they just be replaced at say 50k miles regardless of how the car "appears" to run. If other electrical items like O2 sensors and spark plugs have a recommended replacement interval, shouldn't the MAFs as well since they can gradually lose efficiency which is only detected by the test procedure. I don't see many total MAF failures, most appear to just gradually perform poorly. I can see not doing this at the dealer's cost but if the cost is reasonable, I think they should just be replaced at some given interval (what that interval is is uncertain to me however). Could BMW's 4 year 50k mile warranty be the reason they don't recommend replacing them within that period? I'm not cynical by the way.

Nabio · 4th October 2006, 05:04

When BMWNA marketing began offering extended maintenance a lot of normal maintenance items turned into "lifetime" or "only if it throws a code" replace items. I don't know if the MAFs fall under this category (although the dealer will replace them under CPO if they throw a code I think) but the fuel filter is an example of an item you should replace optimally every 30k. Clearly it's not a "lifetime" item as BMW seems to think.

bimmernut1 · 4th October 2006, 05:19

Quote:

Originally Posted by Nabio

When BMWNA marketing began offering extended maintenance a lot of normal maintenance items turned into "lifetime" or "only if it throws a code" replace items. I don't know if the MAFs fall under this category (although the dealer will replace them under CPO if they throw a code I think) but the fuel filter is an example of an item you should replace optimally every 30k. Clearly it's not a "lifetime" item as BMW seems to think.

That's a good point. I would love to see a list of items that have increased recommended intervals "after" the marketing of zero maintenance began. Perhaps some are a result of improvements in technology, but I bet some are just a result of BMW not wanting to pay during the 4/50 period.

StevenZ · 4th October 2006, 06:25

Quote:

Originally Posted by Nabio

When BMWNA marketing began offering extended maintenance a lot of normal maintenance items turned into "lifetime" or "only if it throws a code" replace items. I don't know if the MAFs fall under this category (although the dealer will replace them under CPO if they throw a code I think) but the fuel filter is an example of an item you should replace optimally every 30k. Clearly it's not a "lifetime" item as BMW seems to think.

The fuel filter is an often overlooked maintenance item. After you run your tank to empty a few times you should probably change the fuel filter. You are basically cleaning your fuel tank into your fuel filter. You don't want that crud to get to your engine.

If you keep your tank at or above 1/4 full with quality fuel you can probably change this filter every 50 - 60K miles. I've never seen a filter that lasts forever!

StevenZ · 4th October 2006, 06:29

Quote:

Originally Posted by bimmernut1

That's a good point. I would love to see a list of items that have increased recommended intervals "after" the marketing of zero maintenance began. Perhaps some are a result of improvements in technology, but I bet some are just a result of BMW not wanting to pay during the 4/50 period.

Add transmission oil and differential oil to this list. They don't last forever either. I change transmission oil at 50K miles and differential oil at 65K miles. If you drive your car especially hard change them sooner.