e38 M62B44TU stalls on hot soon after start

[Michal740i]

Good Morning bmw owners.
Few months ago my 740i starts to stall on hot engine as soon as engine starts. Cranking is normal and starting also, but immediately (about 1 sec) after start revs drop down, and engine stops working. I noticed that those symptoms generally occur when the outside temperature is very high (> 86 F) and goes down significantly to time of next startup (for example in underground car park 2 hours after parking). In such circumstances the temperature indicated with external temp sensor often differs from the temperature read from MAF built-in temp sensor. Is this ok? INPA throws no error codes. I have analyzed a lot of superb articles written by Timm and other people (thank you all) but I did not find an answer what can cause such behavior? I have 2 new OEM Camshaft sensors, new OEM crankshaft sensor, new OEM MAF, used OEM EDK replaced, checked continuity of cables from these sensors to DME, but I can not find any solution because those checked stuff is ok. Moreover I am sure that there is no air leak, because I replaced all intake gaskets and crankcase vent valve on intake manifold. Mixture is not lean.
I have a method for starting engine when that situation occurs (gently press the acceleration pedal as soon as engine starts and hold down for a while - then everything is ok) but that is annoying. Please help! I would appreciate every suggestion or idea.
INPA reading from analog value is ok except slightly negative additive mixture correction (-4.0 but that does not light up the check-engine light). Multiplicative is ok.

[Sobek]

This is a semi regular issue for the M60 motors as they have two temperature sensors on the coolant manifold, which can become faulty as such that they cause rough running / stalling and inability to hold an idle only once the car is up to temperature. It's as simple as replacing one or both of the cheap little sensors and off you go. I am not sure if the same condition can affect the M62 motors however, as they run a slightly different setup. Maybe another member with experience on the topic can offer insight into that. If you were driving an M60 powered E38, I would immediately be looking at that, as your temperature reading differences would be a clear indicator.

[Michal740i]

Thank you for reply Sobek. The most interesting is that idle is very stable, when I manage to maintain running engine after hot start. Idle after cold start is also stable. Revs without AC on is about 600 so according to Timm's info about M62TU it's ok. Moreover coolant temperature is proper and idle is stable even in heavy traffic during hot weather. I runned roughness test in DIS and INPA and values are good (the most interesting is that INPA roughness test shows deviations on other cylinders than DIS, but they are small:

In DIS allowed deviation values on cylinders are up to 1.5 - mine is near zeros on all cylinders except 8th (0.3).
The thing which doesn't allow me to sleep is why is it so hard to maintain running engine soon after starting, when it's hot? I replaced spark plugs to iridium and they should be still good (replaced 5k miles ago). I also checked plug holes if they are no oil near them, but it's ok too. Maybe you are right that temperature sensor (outside) is the cause. Cooling system I think is not the cause - I had leakages from multiple locations last year and replaced valley pan, o-rings, gaskets, few hoses, radiator, thermostat, expansion tank with OEM cap and auxiliary pump with valves. I also checked water pump and it was ok.

[georgebest]

Thank you for reply Sobek. The most interesting is that idle is very stable, when I manage to maintain running engine after hot start. Idle after cold start is also stable. Revs without AC on is about 600 so according to Timm's info about M62TU it's ok. Moreover coolant temperature is proper and idle is stable even in heavy traffic during hot weather. I runned roughness test in DIS and INPA and values are good (the most interesting is that INPA roughness test shows deviations on other cylinders than DIS, but they are small:

In DIS allowed deviation values on cylinders are up to 1.5 - mine is near zeros on all cylinders except 8th (0.3).
The thing which doesn't allow me to sleep is why is it so hard to maintain running engine soon after starting, when it's hot? I replaced spark plugs to iridium and they should be still good (replaced 5k miles ago). I also checked plug holes if they are no oil near them, but it's ok too. Maybe you are right that temperature sensor (outside) is the cause. Cooling system I think is not the cause - I had leakages from multiple locations last year and replaced valley pan, o-rings, gaskets, few hoses, radiator, thermostat, expansion tank with OEM cap and auxiliary pump with valves. I also checked water pump and it was ok.

This is one of the best roughness I have seen, tho 0 on so many cylinders is probably strange. Or it's just a perfect engine. Sorry, i have no idea what is causing your issue.

[Michal740i]

Thanks George, I take care of my car and do it my best. Idle is so perfect that sometimes am not sure about is it running or not
Today I inspected cables which connect into outside temp sensor. And what is really strange... previous owner did something there. I found broken sensor plug, and unprofessionally tied cables... I decided to check continuation of these. After disassembly of IKE clocks, I looked into bentley and checked harness location, etc. And that was the point. Custom cables connected to sensor were swapped... I connected them properly according to bentley's book and finally both temperature readings are the same! Now I must drive in different temperature conditions, but I think that this can be a solution!

[Michal740i]

Hello guys, unfortunately temp sensor did not solve the problem. Yesterday engine started and failed down soon after start (engine was hot, I started engine about 1 hour after parking). I had to increase revs immediately after engine start, and after about 5 seconds it calmed down and engine managed to maintain correct revs (~600rpm). What do you think guys what is the reason? I checked error codes after all at home but INPA shows NO ERRORS. I also checked analog values and noticed the only strange values on long-term (additive) adaptations which was slightly negative (-3.5) on both banks. Could it be connected to hot-stalling issue? Maybe cats are choked? What do you think?

[Timm]

That sounds SO much like a Chinese MAF - are you sure you weren't sold a dud?

P.S. Additive values that small are fine.

[Michal740i]

Thank you for response Timm. Well, the new MAF sensor seems to be ok (Bosch 0 280 217 814) I bought it from trusted seller in Poland - moreover I remember that before MAF change the same symptom (stalling on hot soon after start) was occuring - I am absolutely sure. So the MAF can be ruled out. I also checked all wirings between DME - MAF and DME - throttle with continuity tester and everything is ok. I checked continuity on cold engine only. Maybe that's a point?
P.S. I also replaced fuel filter with pressure regulator - still no improvement.

[Michal740i]

I have done some research today. First of all wiring continuation check: from dual temperature sensor to instrument cluster and DME, as Sobek advised. Checked wiring diagram in bentley and small resistance was noticed at dual temp sensor ground leading to DME unit (1.1 Ohm). I fixed connector and now multimeter shows 0.1 Ohm which is very good.
Second decided to do some test of MAF as Timm said.
I checked wiring continuation to DME unit on hot engine and three of five wires had resistance greater than 1 Ohm and less than 2 Ohm. Other two was 0.3 Ohm. Is it possible that these readings can affect engine? On the other hand INPA shows no error. Today hot engine started very well. Then I shut it down, disconnected MAF and once again started engine. Engine started by identical way (maybe except slightly deeper revs dropdown, similar to that specific behavior, when the story began, BUT engine did not die. 600 revs maintained). Of course hot film mass sensor error occured after that. I shut down engine, cleared error, connected MAF and started once again. No difference, engine started the same way (shallower revs dropdown). No error codes. My mind goes blank.
Finally the resistance of crankshaft position sensor was checked. Because of cannot get to it from bottom I decided to measure resistance directly between pins of DME: 32 and 46 of X60003 harness (according to bentley's manual). I got 750 Ohms. Then I tested my old GOOD crankshaft pos sensor (replaced earlier, in search of the main issue solution - unluckily without success) - it showed only 635 Ohms... Why...? Maybe wires between sensor in my car and DME give over 100 Ohms resistance, or maybe new sensor which currently is installed in my car (replaced few months ago, bought from authorized BMW parts seller) has greater resistance than used one. I came to few conclusions today:
1. MAF seems to be good (slightly noticeable engine characteristics when MAF connected and disconnected. INPA reading on idle: 21.5kg/h. Research done on hot engine (105 C)
2. Dual temp sensor seems to be good after cleaning connector - that was good point, Sobek. I will see is that causing problem in next few days while driving.
3. Resistance on crankshaft sensor is suspicious. I will try to measure resistance directly on sensor pins because it will be much more accurate.
Ideas are slowly running out. I really appreciate every your suggestion guys - please help.

[Michal740i]

After dynamic driving on hot engine adaptations got crazy! Today I checked analog values 2 according to Timm's diagnosis info and something goes wrong and came into terrifying conclusion:
The more revving up engine during drive, the worse negative additive mixture adaptation occur (Today was -5.93ms on bank 1 and -6.01ms on bank 2: but it still does not lit up "check engine" control on instrument cluster).
Is it still ok?
EDIT: Do you think that both catalytic converters are clogged?

[Timm]

Those values are still within limits, most members here will have values far outside those. Blocked cats usually cause misfires at full throttle - and can be checked by a garage using the back-pressure test at the Lambda points.

[Michal740i]

Yeah Timm, absolutely you are right. My issue is related with idle only, thanks. My latest trace leads me into failed DME unit. I think it could broke when I discovered cooling water between pins after strange engine behavior including fail-safe mode (fixed it thank to you - https://www.meeknet.co.uk/e31/BMW_M6...e_Problems.htm MANY THANKS by the way). Moreover, One of pins leading to MAF (nr 7 in X60003) is made from a piece of wire (instead of DME unit pin)... I think that this can be a culprit, particularly that you wrote about a failed MAF. Furthermore the oldest software version is inside my DME unit (checked with DIS) and according to realoem there was over a dozen software corrections after that. So I have at least 3 reason to replace DME unit and upgrade software by the way. I just have bought newer unit (used, but matched with my car) and in early September bmw programmist will reprogram and adjust it to car. We will see what will happen.

[Michal740i]

Ok guys, problem solved. The culprit was old DME unit. After recoding newer one to my EWS and after software upgrade everything is good. Engine starts almost the same way on hot and cold. Never stalled again after that! :-)

[Timm]

Thanks for letting us know - always good to hear what the real cause was!

[purplecty]

Ok guys, problem solved. The culprit was old DME unit. After recoding newer one to my EWS and after software upgrade everything is good. Engine starts almost the same way on hot and cold. Never stalled again after that! :-)

Did you get a new DME or a used one and had the ISN reset?

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[Michal740i]

Used one, but programming it via OBD did not succeed - motronic programmer was necessary.

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[Michal740i]

I have to admit that exchanging DME unit helped a lot, but UNFORTUNATELY few weeks ago stalling soon after hot start returned :-( (after remaining hot for 2 hours in air-conditioned car park). I decided to replace throttle assy, because everything else has been exchanged in the last 2 years... (even throttle, but I get used one). Moreover DIS/GT1 says that faulty throttle can be detected by measuring resistance between pins 4-6 of throttle (potentiometer no.2 resistance). That value should be in the range 1.84-2.76 Ohm. Mine was 2.75 so I thought that it can be the real culprit. I get new VDO throttle assembly, deleted adaptations of DME (including EDK), executed new throttle adaptation by turning the key to ignition pos. for 30s, then key off. Then 10 sec waiting and finally engine start. I let it running for few minutes to allow DME unit learning new adaptations. Next day I got into car and move the same way as earlier, finishing in the same car-park. I let it there for almost the same time, temperature outside was nearly the same as earlier. Finally I got into car. Tried to start it... and GOT IT!!! Issue did not come back! Engine started perfectly, running wth revs up to ~1400 and then slightly fell down to ~600. It maintained these revs without any hesitations!
SO GUYS. Please check your throttle in M62TU if your engine dies soon after start! Check resistance of throttle between pins 4 and 6! Check the value! It should not be greater than 2.76 Ohm, but I noticed that values closer to 2 Ohms means better. Before measuring remember to disconnect battery, or at least get your key out of ignition switch! I hope that it will help you like me. Regards! :-)

[Timm]

Great stuff! We are slowly seeing a change from the 'usual' culprits to new, more exciting problems!

[purplecty]

Great stuff! We are slowly seeing a change from the 'usual' culprits to new, more exciting problems!

The older they get the more newer issues are appearing...

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