Correlation between high engine temps and stalling?

[screedchan]

I have a 1994 E420, which just passed 120,000 miles. I recently had the major service completed, and due to an infrequent stalling problem, my mechanic cleaned out the throttle body. Also, the car was running about 105-110 C in traffic, so we changed out the thermostat, having replaced the radiator some time ago. Sadly, the car still runs hot, and it still stalls from time to time. The last time I posted about the stalling problem, many people suggested an OVP relay, but I later found out that this model does not have an OVP relay. Is there anything else which could cause the stalling, and is the stalling related to the overly high engine temps? As far as I can tell, the stalling does not occur when the car is cold.

I have already replaced the spark plugs and the fuel filter. Hoping someone might have some suggestions which I can pass on to my mechanic. Thanks in advance.

[screedchan]

Also, how hot is too hot for this engine? I figured by the markings on the gauge that anything inbetween 80 and 100 C was acceptable. I tried adding the Redline waterwetter, but it did not seem to make much of a difference. Thanks.

[JimF]

Here's a couple of things to think about:

Does it idle smoothly? If no, maybe dirty/plugged injectors; have injectors power cleaned with BG; also check fuel pressure regulator.

Re hot temp: WW must have right percentage to work properly. Check that it's about 60/40 ratio (water to AF).

[stevebfl]

Do your auxilary fans work when it gets so hot? They should be on much earlier due to the A/C.

The corresponding device on your car, to the OVP, is the Base Module. It has four fuses in it. It has self-diagnostics. Your tech should look at the lower partial versus upper partial adaptation numbers (on the LH controller). Based upon a bunch of testing I would worry about the differences between the two. In other words, if you get lower partial numbers of .85 and upper partial numbers at .91 then there is a reason why the mixture is richer at low flow rates.

There has been some really good info given by JimF and Willy about adaptation problems in early 119 engine. I would encourage you to search for the thread.

I can offer a story about a 600SEL that I learned a lot about. The car had been a dealer with the check engine light on. Code 19 on the diagnostic module. It was found that the lower partial adaptation values were at .85 on the left side and .91 on the right. Upper partial values were .89 left side and .93 on the right. The first time I reset the values with my scanner to "1" it took two days of intermittant driving to get the car to relearn itself. Upon doing some research I found the criteria for the car to relearn itself. The car must be held to 1600-2200rpms at a load of 40kg/hr to 80kg/hr. The upper partial must be driven for a period at 3500-4500rpms (not sure about the upper rpm) at a load of 150-300kg/hr. I found that I could zero the adaptation values and relearn both sides on my dyno in about five minutes. After doing this repeatedly I got consistant numbers like above that increasingly got lower on the lower partial as the car got hotter.

It was really special to be doing this on a 600 as there are two mirrored systems. I moved the air mass meter from side to side and found that the measurements moved with the device. I got a new unit and the values went to an even .94 on both lower and upper partials. We managed to fix this car without new controllers as the dealer would have done.

The real kick is that the reason the dealer would have changed the controller is that MB has changed the software in the new units to allow adaptations for much greater range at least double the old one. The old controller would set the light when adaptations bottomed at .85 or at the other end 1.15. The new controller may go to as low as .68 or as high as 1.32. This would be a good idea but it seems outrageous that they make people buy a $2000 piece of hardware just to get the software improvement. Both BMW and Volvo have done similar software improvements with either chip installation or straight software downloads. Volvo gets less than 50 bucks for their updates (parts only - the labor is probably more).

[JimF]

Steve, thanks for that post. Very, very informative.

I've wondered what the new 'sw' limits were; could tell that the limits were increased because 'hex' numbers were larger, both positively and negatively. But MB really increased the limits quite a bit. No wonder the CE due to DTC 19 was fixed.

Are you saying the the MAF sensor was the 'cause' on the 600SEL? So replacing it, fixed the problem?

May I add this 'gist' of this info to my page under LH-SFI menu?

[stevebfl]

"Are you saying the the MAF sensor was the 'cause' on the 600SEL? So replacing it, fixed the problem? "

That is what I am saying. The problem was that given the conditions the computer was running out of ability to compensate. The MB fix (I might have forgot to say that the dealer had diagnosed the problem to require two new controllers - about $3400) is too give the controller a much larger ability to correct. You can quote me if you like. I am guessing on some of this. I am not sure how wide the window is now. I think it is as large as I said.

Also since I haven't improved on the cars abilities, it is still suseptable to any other seemingly minor mixture glitch. I am sure that the air mass meter had degraded, but it probably would have been acceptable for a long time with the more capable controller software. When I first decided to try and solve the mixture problem I wanted badly to change the fuel pressure. I am sure I could have fixed the car by reducing the fuel pressure by 5psi across the board. There are people making adjustable pressure regulators for use on cars with OBDII software and added Turbos or superchargers. I am keeping a new eye out for such a device.

[screedchan]

I should have included in my original post that I have already gone round and round with Willy regarding the new computer chip for my E420. I, too, was plagued by the dreaded "check engine" light for error 19, but a new chip bearing the software for the replacement computer seems to have slayed that beast, as the check engine light has not been a problem for well over a month. So I should consider a new MAF sensor?

[screedchan]

In response to JimF, the car seems to idle smoothly in most instances, other than when the car stalls, obviously. I thought that it might be a plugged fuel filter, but that was just replaced. I believe that I am runnning 50/50 in the radiator with Mercedes red coolant, perhaps a bit more water since I usually just top off with water when low in the reservoir. The aux fans do kick on when the car goes over 100 C. I'm just wondering what the normal operating temperature range is for this vehicle, because maybe the temps I am seeing are not excessive.