Low power/torque on 3.8 and high fuel consumption - The Unofficial BMW M5 Messageboard (m5board.com)

marekd174 · 26th June 2009, 01:52

Car is an M5T with under 200k km, no oil consumption, great compression and leakdown values.
- Car is really down on power below 4k rpm when it wakes up, but still not where is should be (I've had another 3.8 at the same time which was a lot faster and my friends 3.6 is faster).
- I cannot break the tires loose if I floor it in first.
- I also cannot get more than 450km out of the gas tank even on long highway trips (I end up filling about 85L back in)
- car seems to pick up better if gas pedal is just slightly less than mashed (put it to the floor and then back off just a tad)

I already replaced/did did the following:

- valve adjustment (3 intake valves were loose at 0.37/0.34/0.34, no difference in power delivery after being brought back to spec but ran more smoothly and is quieter)
- TB clean and sync (they open fully when gas pedal is depressed and were almost spot on to begin with)
- new Y6DC plugs
- new filters (fuel and air)
- all vacuum hoses
- cleaned crank position sensor
- new coilpacks
- new DME (to fix resonance issue as old DME had the circuit to activate it blown - resonance flap works)
- new O2 sensor
- new water temp sensor
- no DME faults logged - grrrr

I will replace the TPS next as it is relatively cheap, but I suspect that MAF might be the culprit and before I spend almost $1k I would like some opinions from others. If I unplug the MAF while the car is idling the engine will stall.

///Manuel · 26th June 2009, 06:55

That's an extensive list, it's nice to see. I would try to clean the MAF?
Have you tried disconnecting the battery for some time to reset the ECU?
Maybe it also needs a good run if it's not taken out on the highway very often.
What do the plugs look like? Does it idle ok?

roortube · 26th June 2009, 13:49

if not the MAF maybe a clogged cat??? good luck man

marekd174 · 26th June 2009, 16:03

The MAF was cleaned several times with CRC MAF cleaner, to no avail. I've disconnected the DME over the winter and in the spring took it on a 200km drive in varying conditions with no change. Plugs look like it is running a bit rich, and that coupled with the high fuel consumption, even on the highway at a steady 120km/h it burns about 20L/100km, leads me to believe it is the MAF.

I also replaced the rubber intake tube as it was cracked and that made no difference. Sometimes these cars really test my patience.

Sharkbite · 26th June 2009, 16:08

Why don't you just try the MAF from your other 3.8 ?

See if that makes a difference.

marekd174 · 26th June 2009, 16:38

Quote:

Originally Posted by Sharkbite

Why don't you just try the MAF from your other 3.8 ?

See if that makes a difference.

Unfortunately I sold the car before trying that and there isn't another 3.8 close by for me to swap MAFs with.

Luxauto · 26th June 2009, 23:44

I'm not super familiar with the engine management on these cars yet, but on other euro stuff I've worked on, a faulty coolant temperature reading will cause the car to run rich. Certain bosch systems use a coolant temp sensor to adjust the mixture, and typically when the sensors fail they read full cold, and the engine goes really rich.
Just something else to check (if it's even relevant for the 3.8 EMS) besides the likely much more expensive MAF.

marekd174 · 27th June 2009, 00:21

Quote:

Originally Posted by Luxauto

I'm not super familiar with the engine management on these cars yet, but on other euro stuff I've worked on, a faulty coolant temperature reading will cause the car to run rich. Certain bosch systems use a coolant temp sensor to adjust the mixture, and typically when the sensors fail they read full cold, and the engine goes really rich.
Just something else to check (if it's even relevant for the 3.8 EMS) besides the likely much more expensive MAF.

I've already replaced the coolant temperature sensor and it made no difference. Besides the resistance on both the new one and the old one is right in spec.

Thanks to all for the suggestions keep them coming.

Robinson · 27th June 2009, 01:34

There is a company specialized in rebuilding MAFs in US

http://www.injectionlabs.com/home.html

They take a fix price of $175. Just for your consideration.

Elekta · 27th June 2009, 03:05

Quote:

Originally Posted by marekd174

- valve adjustment (3 intake valves were loose at 0.37/0.34/0.34, no difference in power delivery after being brought back to spec but ran more smoothly and is quieter)
- TB clean and sync (they open fully when gas pedal is depressed and were almost spot on to begin with)
- new Y6DC plugs
- new filters (fuel and air)
- all vacuum hoses
- cleaned crank position sensor
- new coilpacks
- new DME (to fix resonance issue as old DME had the circuit to activate it blown - resonance flap works)
- new O2 sensor
- new water temp sensor
- no DME faults logged - grrrr

What did all this run?

I have done none of these maintenance items and I am at 93K miles. I've only done suspension and drive train. I am feeling some of the same sluggishness you mention and thought it was my clutch for the longest time, but after a recent 800 miler it's fine.

I do have a crack in my exhaust that needs to be welded and I am suspicious of the sensor and or the cat, but as yet no codes thrown. If you have done all these items and are still chasing it, is the MAF truly the last?

Zaraska doesn't have a MAF you could swap?