450 SL in Denmark

Hi Peter,
I agree there are no signs of rich running to be seen on the plugs. More than 100 km should be more than sufficient to show abnormalities.

All your readings seem to be o.k. for me, too...I've read all through the thread now and thought about the symptoms.
I don't remember having read about the MPS having been confirmed to be correctly adjusted.
Has this been done?

Regards
Norbert

Hi Norbert,

The MPS could be the culprit. However, I acquired it from Volker and I am sure he was diligent in his testing before selling it. It holds vacuum.

Before I took the car for another run today I performed a smoke test to see (again) if there are any false air leaks. That was not the case. I then took it for a run and from cold and up to operating temperature it runs and pulls like a champ. When it reaches operating temperature and when accelerating moderately until ca. 2000 rpm it stumbles and jerks. Once the rpm is between 2-3000 or if I accelerate hard, it goes away. Not completely, but much better. At cruising speed (70-90) there is practically no issue. At highway speed (130) it drives and accelerates without problems.  

When I got home and with a really warm engine I performed yet a smoke test and suddenly I saw smoke coming from below and behind the throttle housing. At first I thought it came from the TPS sensor shaft, but after having carefully looked again I am pretty certain that it comes from the intake manifold behind the throttle housing. False air would certainly "confuse" the MAP sensor into believing that the engine is under load, thus sending a signal to the EDC to increase opening times, right? 

Could I perhaps be on to something?

Best, Peter  

Hi Peter,
if I had known you have a MPS from Volker, I wouldn't have considered it could be faulty.

Yes, you are correct: ECU injects more fuel when the absolute pressure in the manifold rises.
A vacuum-leak lets the pressure rise...

Regards
Norbert

Hi Peter,

sorry to hear that you are still in search of your problems and sorry for late reply due to holidays. Any false air leakage causes troubles. The lower engine load the more it will be. MPS will report wrong load to ECU and that will enrich fuel mixture.

Thanks, Volker. At least I get to clean the valley, which was full of old leaves, etc. You can clearly see that it has been hot down there and I think I'm lucky that it hasn't cause a fire.

From the picture cylinder 1 and 4 and maybe 7 do look as if something has been going on there. There are no apparent signs of leaks in the intake gaskets, but the rubber grommets between the lower and upper manifold are very hard. I have not inspected them in detail yet.

Best, Peter   

Hi Peter,

it lloks that you are on right track. Get some Dunkin Donuts and replace.