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Well my 75 450SE is in the shop again. I think we have finally discovered the problem causing the warm stall and bucking motor problem. A smoke test was preformed which resulted in the discovery of major leaks in the intake manifold seals. I'm having them replaced.  We also discovered leaks at the sides of the throttle body where the bar that supports the flap inside connects to the throttle body. Are there any bushings in that area that would need to be replaced or is it normal to have small leaks in this area?

The throttle body was also covered in a heavy crust of carbon. I imagine that the intale manifold is just as crusted up. Major cleaning will be undertaken.

Next the new injectors will be installed. Hopefully this will bring an end to these lingering problems.

I've often wondered about throttle body leaks. The throttle body I removed from my 450SEL (K-Jet) appeared quite worn, and there was blow-by seeping out the shaft area. The best thing would be to find a throttle body off a low mileage car.

Tim

Wow, of the things to blame out of spark, air and fuel I ruled out vac leaks in my mind, thinking that revs would run away and besides that, at WOT you should be getting full revs regardless. Or so I thought.  I'm not sure, I hope it works out Brett.  Not sure about throttle body bushes.  I'm sure there is but I haven't pulled one apart.

Replacing all those intake seals will be a major tick on the list of things to be done.  Something that the vast majority haven't done, including me, and if those leaks are there it gives false data when attempting to fault find.  There's reference to this when you read in manuals and on d-jet sites - make sure there's no vac leaks and other components are in good order.  That sort of thing.  One tends to say "yep! other things should be fine" without realising the effects of perhaps many small vac leaks present.  I'll admit I'm often guilty of that.

Well, after completing this project I will essentially have a brand new car! All the sensor have been replaced, all the vac hoses, exhaust manifold hoses, switch over valves, you name it , it's been done. I'm really hoping this work does the trick. I guess I will try getting another throttle body to see if it leaks like my old one. I talked to the Classics Center about the bushing situation and they couldn't give me  a clear cut answer on it either. 

Maybe the kind of workshop that rebuilds carburettors would be able to help with the bushing issue?

I thought of that and it may come down to do just that. Time will tell.

Finally the 450Se is out of the shop. No more bucking motor! No more warm start stall! I think I'm almost to the point of owning an excellent running W116. The fuel injectors, seals and holders were replaced with new parts from Mercedes. All of the intake seals were replaced. The original intake seals were not only leaking air but were also leaking coolant. No wonder I couldn't figure out why I kept getting little coolant leak spots on the garage floor. The throttle body seal was replaced. The throttle body was taken apart and cleaned only to discover that there are no bushings in the shaft area.The intake itself was cleaned. There was some build up in there but not bad at all.  What was also discovered was that the plug that sits in the front of the motor near the distributor had a short in one of the five wires inside. I'm not sure what those connections do  or what it is called, any ideas? Anyway, that short was corrected.The positive results of all this work is that the motor sounds and feels more solid and powerful. The stalling and bucking has gone away and the gas milage seems to have gotten better.

Unfortunately there is a negative side to all of this work. I'm not sure if the throttle linkage is adjusted correctly. The idle speed seems a bit high, 1000 RPM.s I know the RPMs at idle should be between 750 - 850. I adjusted the idle speed screw. The lowest I can get the RPMs is 950. Before I adjusted the idle screw the motor periodically would shake and I'd get a slight rough idle. The idle speed screw is also down as far as it will go and the RPMs will not decease.  The car also periodically emits heavy emission smells. So I'm thinking the motor must be set a bit too rich. Again leading me to think further adjustments of the throttle linkage is needed.

The Cruise control is now all messed up. The main cable seems to be getting caught in the main spring the of the throttle linkage causing the erratic idle of the motor. The RPMs literally will bounce from low to high making the car undriveable. What is the trick to resetting the cruse control correctly? The control unit was working perfectly before the throttle linkage was taken apart. Right now I have the cruise control disconnected.

Now the really bad issue. The oil leak in the motor has gotten worse. I think its the rear crankcase seal. The leak used to be the size of a quarter but now has tripled in side.  Am I correct in thinking that you have to drop the transmission to replace this seal?  If so,  besides the flex disk and torque converter seals in the transmission are there any other seals I should replace while the tranny is out of the car?

Thanks,

Brett

It sounds like the throttle hasn't been set up properly, or it is getting caught on something. It would be best to check it ASAP, in case of disaster.

Regarding the seals... While the tranny is out, you might as well replace the torque converter seal, front pump "o-ring" and crankshaft seal.

The Transmission's output shaft seal is something to consider as well, though it requires removal of the single use nut... It then becomes a case of "while I'm here, I might as well rebuild the whole thing"!

Tim

Wow! What type of disaster can I expect? I've been driving the car today. Now after I start it up the motor will not idle normally. Rather it continuously revs from 0 to 100 rpm. It will continue reving until I put it in gear and then it drives fine even after you put the car back in park. Shut it off and it starts all over again.

I've been looking in the service manual library for a diagram of the throttle linkage set up. Found some small illustrations but nothing that has it all broken down , springs and all , for you. Anyone known where I can find such a diagram?

Tim, I'm familiar with he torque converter seal but where is the location of the front pump "O' ring and output shaft seal?

I took another look at the throttle body linkage. It seems as though everything is set correctly .The flap in the throttle body opens and closes correctly. What I did find wrong was the adjustment of the cruise control cable. The cable was set really taught. It was so tight that it was tugging on the throttle linkage, slightly opening the flap in the throttle body. As soon as I loosened the cable I heard a click and the throttle linkage  fell into place. The motor stopped the uncontrolled RPM rev and the idle is now about 850. The air slide screw is still pretty much closed which I think is a bit strange.  So I think something must still not be adjusted correctly. I'm going to leave it alone and drive the car as is for now to see what happens. I'm more concerned with the rear main seal leak right now as that leak keeps getting larger.

The disaster I had was a result of the ignition leads jamming the throttle open. I turned the engine over and found out when it redlined instantly... the engine hadn't been started for days too. I cut the ignition very quickly!

The o ring is around the pump assembly that the torque converter seal presses into, though the bellhousing needs to be removed to replace it. That may be a little more work than you were anticipating.

It's good to hear that you pin-pointed the problem with the throttle. The fast idle must be an overly rich mixture or an air leak somewhere.

Tim

OH NO! Please no more leaks! I thought that I found them all! I have never been completely sure of myself in setting the mixture. Any pointers on how to do it properly?

Hopefully there will be no leaks. Regarding the mixture, I'm not sure how it's done with D-Jet... an exhaust gas analyzer will be needed to do it properly though.

Tim