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Discussion Starter · #1 · (Edited)
Hi guys,

I've been experiencing misfirings during cold starts (car parked for ~10 hours or more) lately. After letting the car idle for about 2-3 minutes it runs fine again. The CEL has come on a few times with the suspected error codes from misfiring.

The car is a 2006 760ia (N73, V12) with roughly 60K miles on it. Full service history and the plugs have recently been changed.

Today I decided to solve the mystery and hooked it up to my Inpa equipment. The first thing I checked were the values relating to the eccentric shaft issues on the V12s and they're all fine. Also the smoothness / balance between all 12 cylinders are within spec.

I noticed something strange when I checked the live data however...

The first problem is a very high reading relating to the MAF value (this was taken at roughly 1500rpm)

Text Font Technology Electronics Screenshot


The second problem relates to the engine cooling outlet temperature (Kühlwasseraustrittstemperatur) which shows an error of !-48.00 degrees Celsius

(Slave side)

Text Font Technology Electronic device Screenshot


This value is however plausible on the Master side, which makes me doubt that it's a sensor failure?

(Master side)

Text Font Technology Electronic device Screenshot


Really hope for some good input to this little mystery - not really sure where to start! :dunno:

// Carl
 

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What is the maf value for the side with the correct temp? Maybe the dme checks the outlet temp against the maf value for each side. Since the maf value is faulty on one side, the dme thinks the outlet temp, on that side, should be within a certain range. I'd get the maf issue sorted on the faulty side first. Maybe switch the maf sensors and see if the problem migrates to the other side on the live data feed


Sent from BimmerApp mobile app
 

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Discussion Starter · #3 ·
Thanks for the feedback! :thumbup:

I immediately made a new reading, measuring both Slave/Master during revving and during idle.

Master idle:
Text Font Screenshot Technology Electronic device


Master revving:
Text Font Technology Screenshot Electronic device


Slave idle:
Text Font Screenshot Technology Software


Slave revving:
Text Font Screenshot Technology Electronic device


Both MAF values are off (please disregard the difference in how off they are, the lower value on the Master's MAF is only due to lower revs.)

Where does this lead me? :confused:

// Carl
 

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Discussion Starter · #4 ·
Alright, ordered some parts during the weekend so that I can initiate the search for this annoying problem!

I’d already planned to replace both belts and all pulleys due to some squeaking when it’s cold.

Bit the bullet and decided to replace the thermostat (plus a new temp sensor) as well as the water pump since I have an easy access when the belts are off. I’ll also replace both PCV-valves & the temp. sensor mounted on the radiator exit hose.

Both MAF’s will be cleaned.

Hope this’ll make a difference – but still have my doubts regarding the coolant outlet temperature values.

Can’t figure out why one DME manages to get a read out and the other one not?

The tear down commences as soon as I get the parts, can’t wait! :)

// Carl
 

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Discussion Starter · #6 ·
I see thanks for that enlightenment! :thumbup:

Had kind of hoped that this sensor was one of the culprits. Why are there never any easy fixes...

Any ideas regarding the MAF values?

// Carl
 

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I see thanks for that enlightenment! :thumbup:

Had kind of hoped that this sensor was one of the culprits. Why are there never any easy fixes...

Any ideas regarding the MAF values?

// Carl
The MAF values should be pretty equal bank to bank when checked at idle only, full operating temp, and without A/C or any consumers on.

I do not think this is the cause for the misfire. This engine can have carbon on the intake valves esp. the rear two cylinders on each bank. Oil from the crankcase breather system tends to collect towards the rear of the manifold.
 

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Discussion Starter · #10 ·
Thanks for your input! Very interesting, it sounds like an endoscope inspection is the way to go?

Something I noticed is that there's more white smoke and condensation from the exhaust after a cold start than before - not sure if that's relevant?
 

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Discussion Starter · #11 ·
Thought I'd give you an update! Had some time to spare today and decided to clean the MAFs and replace the PCV valves.

As it turned out, both MAFs have already been replaced (stamped 2010 on them) and were looking like new, but cleaned them anyhow.

Next on was the PCV replacement, just three screws and some fiddling with the hoses, but it took under 10 minutes/each side.

Started the car and immediately noticed a difference in the start-up sound. Before I had like a light whistle or squeal at start-up, something I'd thought was water pump or belt related. This sound is now completely gone! The car also ran much better at idle and the throttle response was like it should again. :thumbup:

After half an hour drive on the freeway, I could also notice that the fuel consumption had been drastically improved (from 1.7 to 2.3 mpg!)

Not jumping for joy just yet, will have to wait until tomorrow when the engine is started from cold again - fingers crossed. :)
 
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