This is extremely interesting, a car with good fuel-flow numbers still benefiting from new MAFs. The MAF sensitivity is evidently more complex than I have thought: I thought any car with good fuel-flow numbers had good MAFs.
Do you have any new fuel-flow numbers to compare with?
Looks like eventhough you have a reading of 140L/h you might still have a bad
Respect a mans car, a man respects you. "In every detail, the M5 was a poster child of the M philosophy: superb driving dynamics, luxurious interior and above all, uncompromised performance." - BMW.ca regarding the E39 M5
1. Have you corrected for altitude/barometric pressure/temperature and humidity?
2. Numbers still low? Most of the time, with a L/H reading very low, either the fuel pump/fuel pressure regulator and/or the MAFs are shot.
Most likely the MAFs.
To check the MAFs for severe contamination:
Either run the BMW DIS / GT-1 tester procedure for MAF testing at idle and inreceased idle RPM, or use this (IMHO far more accurate and reliable) procedure to measure MAF output voltages with engine off:
(Better still use both methods: road test L/H, and direct voltage. Then compare the results.)
MAF TESTING - DIRECT VOLTAGE METHOD
0. Remove tie-wraps holding wire protection tubing in place at the MAF connectors. Pull tube back and find the applicable wires. Connect to these using insulation piercing needle-and-hook type test leads(or just plain needle type test leads if you donīt mind risking to prick yourself).
Make ceratin to have the mulitmeter set to DC volts and that you have not connected to the AMPs connectors on it. (The signals you are connecting to go straight to the DME so be careful not to short-circit anything.)
1. Ignition on
2. Engine not running
3. On each MAF measure DC voltage between
pin 3 (ground, brown wire) and pin 5 (signal, yellow wire)
4. Reading should be 1.000 +- 0.040 V. The closer to 1.000 V the better. the dirtier the MAF the higher the voltage will be.
5. If reading in step 4 is off by more than 0.020 V then measure voltage between pin 3 and pin 4 (+5V reference from DME, yellow/green wire). This reading should be 5.000 +- 0.200 V.
6. If not check the battery voltage, and connect a charger if needed and redo the tests.
7. Put the tubing back in place and secure it with new black 2.5 mm wide tie-wraps. (Make sure you have narrow enough tie-wraps to fit on hand before cutting the old ones.) To avoid sharp edges, after the tie-wraps are in place cut the excess with a flush (one side only beveled) pair of cutting pliers.
If you donīt have that kind of cutters, just cut the tie-wraps with any sharp cutter and the file the sharp corners. Only takes a minute, and might save some of your blood next time you do something in that area on the engine compartment.
The reading in step 4 should be exactly 1/5 of the reading in step 5.
If this procedure gives a reading in step 4 that is outside tolerance the MAF is definitely contaminated or otherwise damaged.
The other plausible possibility is the fuel pressure.
To measure the fuel pressure is very easy: he will need a BMW adapter for fuel pressure sensing (BMW special tool 13 5 220. This is a kit containing 13 5 221 and 13 5 222. This is common for all E39 5-series, so the dealer probably has it already) that connects to th efuel pressure regulator, and to the pressure test sensor on the DIS.
The procedure is very easy and is described in detail in TIS 13 31 029.
The thing to be aware of is that BMW states the fuel pressure as the difference between the absolute pressures in the fuel rail and in the intake tract (downstream of the throttle butterflies).
At idle the intake ports will be at -0.5 BAR. Just measure the atmosphere-relative pressure of the fuel-rail, and then add 0.5 BAR to get the reading relative to the intake ports.
In other words: hook the fuel test port up to the DIS, read the (athmosphere relative) pressure the normal way, and if it is 4.50 +- 0.05 BAR everything is fine so far.
Then disconnect the vacuum hose from the fuel pressure regulator, plug the hose, leave the fuel-regulator vacuum port open, start the engine again, and measure the fuel-rail pressure once more. It should now be 5.00 +- 0.05 BAR.
(The difference between these two readings is due to the vacuum pressure in the intake tract.)
BTW, this is a good time to measure the vacuum too while you are at it as you have access to the hose anyway.
i have a supercharged m5 with almost every dinan option. i was experiencing the low exhast rumble and lack of power at 2-3000rpm and fuel consumption was very high. the ses light came on the other day and the dealer said the fault code was cam sensor. any thoughts