Hangs up when coasting....what gives?
 

200k+ 560sl, runs drives fine except sometimes when I take my foot off the gas coasting downhill, I get this mild hesitation like I would if I am tapping the brakes a little. I experimented with taking it out of gear entirely to see if it was wheel related or not and in Neutral there is no sympton.

Almost has to be transmission related? But....what? Not really looking toward a big ticket tranny rebuild.

Thanks for your input.

J. Boggs

I experience the same thing when coasting with the cruise control on (and the target speed is less than my current speed when the coasting begins).

In gear, throttle closed, engine speed above idle, EHA should shut down the injectors. The engine should exert a smooth drag. Follow Bribenz' advice, and check too for idle air leaks.

Steve

Sorry Sbourg, your talking over my head.
 

Can you dumb that down for me a little?

Thanks.

J. Boggs

What I am saying is that to conserve gas, the engine management shuts down the injectors when you take your foot off the throttle, then turns them back on when you slow down to near idle. It does this by modulating the EHA to reduce secondary fuel pressure to below the cutoff pressure of the injector check valves. It uses several indicators to determine when to do this, one of which is the throttle position switch, on the throttle valve shaft pivot. When that switch makes poor contact, the EHA will switch pressure up and down, causing the engine to surge.

Steve

Thanks
 

I think I got that.

JBoggs

I like this on my 300e. gives the feel of 'engine braking' as when driving a manual car. I use it to control the car better going downhill etc, so it doesn't 'run' away and I can save on the brakes. My wife's dodge will go flying foot on or off the gas, and you need to use the brakes all the time. that car is also a lot lighter than the benz though :)

Yes, and when decel shutoff is not working it pulls your fuel mileage down about 30%, at least it did for me.

23MPG became 17 MPG.

That might explain it then
 

I disconnected the EHA and went for about 4-5 miles and on decel it didn't drag a bit-I am anxious to see the gas mileage improve.

But what does that say about the root cause-the EHA is new, less that 1000 miles cause the old one was cracked (and it had the same decel issue before). I assume I don't want to run EHA-less for too long, so what is the correction? Lambda adjustment, throttle switch?

Thanks.

JBoggs

OK, let me be clear. WITHOUT the EHA you will have no deceleration shutoff and your fuel mileage will be WORSE. You will not improve your mileage by disconnecting the EHA.

You WANT to feel it drag, as you described.

The first thing I would check is that all linkage is moving freely, the decel microswitch is good and the throttle switch is good, in that order.

OK, got it
 

but, based on a round-the-block ride with the EHA disconnected if feels normal, like driving any other car. Before I disconnected it, it had a drag but it pulsed randomly-like I said, like very ligh toe tap on the brake-not at all constant.

I see what you are saying, the EHA creates the drag by reducing the fuel to the injectors-weird that mine seem improved. I guess the gas consumption will tell alot. I'm gonna drive it EHA-less tomorrow just to see what happens.

I have another symptom posted elsewhere manifested by a rough idle and one cylinder apparently not firing properly, so I suppose it's all inter-related.

What is the part number for the decel microswitch?