:: Automatic stalling

[Qube]

e39. Second time in three days.

First time is stopped on a slight incline. Started to turn right up slight incline (90 deg turn) and immediately stalled. Surprised me a bit as I thought power steering died but then realized car stalled when batt and engine light was on. Neutral to restart and on my way.

Second time was stopped flat, then turn right onto slight incline (90 deg turn) and stalled. Same drill.

From home, I have to exit the parking garage from flat to right up a much steeper incline with no issues yet. The two incidents were going up a very slight incline.

Removed rear seat to sniff for gas to no avail. Per e30 forum "If you smell gas from the rear...it will most likely be your fuel pump's rubber gasket that is messed up...not an expensive fix..."

I don't recall turning right onto slight inclines otherwise in my travels. Today I did a somewhat sharp right (110 deg?) with no issues, but full passenger load.

Suggestions? Oh, pulled codes, but no codes. I reset the oil light though :)

Probably unrelated... right rear signal LED failed. Put in a regular bulb works fine. Swap the bulb and/or holder to other side works so contacts are fine. More troubleshooting needed for this one involving multimeter (polarity, voltage, etc).

[rob101]

Check your MAF signal. a friend of mine had similar problems (except much worse than yours, sounds like the mixtures out so when it load it up it stalls. but could be a problem with power steering. does it idle at the right speed normally?
this is just a hunch probably more of a BUMP until the professionals arrive

[Qube]

Yep. Steers normally. It's probably just a byproduct of stalling.

"Check your MAF signal." Explain that a tad bit more if you could? :)

Tacking this on: http://www.bimmerfest.com/forums/showthread.php?t=95089

[Qube]

Obvious things first. Cleaning the MAF tomorrow...

While not an S62, still valid...


The MAFs (Mass AirFlow meters) are located in the M5 and Z8 air intake tubes. The MAFs report to the Engine Electronics (DME aka ECU) the amount of air that is drawn into the engine, and what temperature this air is. The DME uses this to calculate how much fuel to inject.

Vital as the MAFs are, those have to be _really_ bad before you actually get a stored fault-code.

The functional test by the BMW tester just tests the MAFs at idle with the car standing still. IMH experience that says absolutely nothing about how they perform at WOT (Wide Open Throttle).

I think there is an economical (warranty) reason why BMW does not want the MAF fault code to trigger as soon as the MAFs start to be less-than-perfect, rather than only when there is extremely poor MAF function.

MAFs typically last 50000 miles before getting so contaminated it affects S62 engine performance.

There are two methods to test the MAFs yourself:

Method A - using the instrument cluster of the car *********

Read post #11 in:

http://www.m5board.com/vbulletin/showthread.php?t=1898

Follow those instructions, and select the mode for fuel consumption per hour.
With the engine fully warmed up, drive several WOT (wide open throttle) accelerations. Notice the fuel flow per hour numbers. If everything is ok the numbers should increase continously to about 140 litres per hour at WOT at 7000 RPM. (don´t worry about bouncing into the rev-limiter)

The fuel-flow is directly proportional to the MAF reading reported to the Engine Electronics, so if the Fuel-flow is correct, the MAFs are most likely correct too.

To be able to compare your fuel-flow readings with other people´s readings,
you need to correct the data for temperature, barometric pressure and altitude. This is easy: look at the table attached at the bottom of this sheet.

Look up the two factors matching your temperature, barometric pressure and altitude. Then multiply the reading from the instrument cluster with both those factors. The result will match what the fuel flow number would have been at sea-level, +20 deg C and normal barometric pressure.

Method B - using an OBD-II scan-tool *******************

1. Get a graphing and data-logging OBD-II scantool. If you already have a laptop PC, it will cost you about US$ 100 to buy one. Worth every cent. (I use the one called "ISO" from www.obd-2.com which I am very pleased with)

2. Plug it into the car and go for a drive

3. Look at the graph for CLV (calculated load value). This is basically the MAF signal expressed in percent of the expected maximum at each RPM.
When you accelerate WOT this number should immediately go to 100% and stay there until you release the throttle or hit the rev-limiter .

4. If the CLV reading it is low at all RPMs, try new air filters.

5. If it is ok at low RPMs, but lower at higher RPMs, try the MAF cleaning procedure and the retest immediately. If this improves the numbers you know 100% there is (or if the cleaning was very successful used to be) a MAF problem. This does not say it is the only problem, but the car can never run better than its MAFs.

Symptoms of bad MAFs ************************

In degree of malfunction of the MAFs possible symptoms are:

High Lambda values at idle (lean air-fuel-mixture)
Engine hesitation at high RPM
Engine misfire at high RPM
Engine going into limp-home mode at high RPM

MAF cleaning procedure ************************

http://www.louv.tv/cars/m5/MAF/
(by m5board member Louv)

How the MAFs work ***************************

The MAFs have a non-heated temperature sensor and heated temperature sensor. The latter is made of a very thin wire of platinum metal. The wire is heated to about 200 deg C, and its temperature is continously monitored and the heating current is controlled so as to keep the wire at this temperature. The more air that passes the wire on its way into the engine, the more the wire will be cooled. The electrical current needed to maintain the sensor wire at 200 deg C, is directly proportional to the amount of air that passes it, and also depends on the temperature of the air (hence the non-heated temperature sensor).

The electrical current and the air temperature are measured, and the corresponding air-flow is calculated and reported to the engine electronics.

How MAFs clean themseves ***********

Once in a while the MAFs will run a very high electrical current for a few seconds through the platinum sensor wire, so the wire gets red-hot (1000 deg C). This burns off much of the contaminants, and probably help keep the MAFs working much longer between manual cleaning or replacment intervals.

How MAFs fail *********************

With time the MAF platinum-wire gets fouled with contaminants settling from the rapidly passing intake-air. These contaminants acts as thermal insulation on the wire. The effect is that the wire will not be cooled as much as it should by the air-flow, and thus reports too low air-flow to the engine electronics. The engine electronics in turn uses this too low air-flow number when calculating how much fuel to inject. The fuel injection will be to low, and the air-fuel mixture in the cylinders of the engine will be lean.

Many M5 owners have reported K&N oiled intake air filters to cause MAF contamination.

What to do if the L/H fuel flow numbers are low?
************************************

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:

CHECKING MAFS
************

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 don´t 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 don´t 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.

FUEL PRESSURE
************

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 would be a good time to measure the vacuum too while you are at it as you have access to the hose anyway.

[rob101]

well i don't know for the e39, but the e36 bentley has data on Mass air flow sensor testing in the fuel injection section of the manual. tests with a ohmmeter basically. good luck, it is just one of the many things. have you noticed any roughness like a little bit of a buck if you step off the throttle quickly? or popping in the exhaust on overrun. its hard to know, but these were some of the other tell tales my friend had. i know i get that because i have a vacuum leak but thats mainly because i have a vacuum leak lol. the car kind of feels different when the mixture is not-right.

[Ferret]

My E34 540i used to stall if you steer, have your foot slightly on the brake (ie foot just touching the pedal, not actually braking) and bring the clutch out at the same time... it was because of the hydraulic brake assistance and the load on the (excessively lean running) engine.

Now I've sorted out the intake manifold leaks, it's not even threatened to do it once :D

You may have a mixture problem - the hydraulic pumps on the v8's can take a lot out of the engine and if it's not running properly to start with can cause it to crap out. How's your power steering fluid? Is it low - and/or is the reservoir a low point under the stall out conditions?

[Qube]

I would, Ferret... cept it's an auto :) I'll check the PS fluid. All fluid was changed fresh a few months back.

[Qube]

Cleaned the MAF. Didn't look all that dirty, but I can't really see into the plate area.

In a nutshell, placebo effect tells me that I don't seem to have to press as hard on gas to go. We'll see. CPS looks like an easy swap.

[MBXB]

Check the throttle switch?