W124 economy guage and autobox

[anfieldassasin]

Hi all just quick question out of curiosity.

My 300ce economy gauage fluctuates with the E and S setting. So at idle in E the guage will go to the middle. In S it will go about a 1/4 from the black then when I accelerate and car is hot at the next traffic light when I stop, it will for a few mins stay at end (Black zone peg) but then later go back to 1/4 away from the peg in the black zone. In E it will never go to peg in the black.

My 230ce did the same.

I know it's just a vacum guage but why would the E and S switch affect the guage? The vacum line to the modulator on the gearbox does not connect to the part of the circuit for the headlight vacum that the economy guage runs on. So how are they linked??

 

[brucemillar]

Hmmm. Interesting. I suspect it is gearbox vacuum, but would like to know.

 

[anfieldassasin]

Yeah I was thinking so too but just cant figure out how the switch affects it or how's its linked to the economy guage it would seem that switching it to E causes a larger vacum leak... How I have no idea

 

[brucemillar]

Well I will own up here. I have never noticed or even checked to see if there is any difference.

I do know that in "S" the car will pull away in 1st gear if you use kick down? The reason I question that is that I only just read hat you need to use kickdown and be in "S" for 1st to engage. Previously I just thought you shifted to "S"

So if it works as you describe and that is correct? Then vacuum will need to be linked to the gearbox, the throttle/kickdown and the gauge.

Does anybody know?

 

[190]

On my W201 I'm sure the gearbox switch didn't have any impact on the economy gauge so I would think you have a leak somewhere on the auto box side. That makes sense of the symptoms because at idle you would have high vacuum (low reading on the gauge). Switch into S introduces the leak and the vacuum falls resulting in the gauge reading going up.

Frankly the switch did little for my auto box response and I used to tune the box to suite my needs using the cable adjuster at the throttle linkage. Missing out on first gear is hardly a problem as I think it engaged only a handful of times over my 21 year ownership.

 

[grober]

http://www.w124performance.com/docs/mb/other/tranny_722_Mitchell.pdf
PAGE 6

 

[anfieldassasin]

http://www.w124performance.com/docs/mb/other/tranny_722_Mitchell.pdf
PAGE 6

Thanks for that grobber interesting read but can't say I understand much of it. But the diagram on page 5 shows the vacum system connected to the manifold I guess the E and S alters the pressure level in the box (see diagrame on page 5) which in turn affects amount of vacum in manifold which then alters the level of a leak somewhere in the vacum lines that are part of the headlight and economy guage circuit as they are also connected to the manifold.

So basically from what I understand and as others have said it's not normal behaviour but I have a vacum leak somewhere in the system

 

[brucemillar]

Grober may confirm? Spraying damp start around the vacuum lines will pinpoint any leaks. The revs should flair as it sucks in the damp start.

 

[anfieldassasin]

Grober may confirm? Spraying damp start around the vacuum lines will pinpoint any leaks. The revs should flair as it sucks in the damp start.

Thanks Bruce that's one of the first things I do with my W124s when I buy them. I did this 2 months ago when I bought it and nothing no flare to indicate a leak, gave a good spray everywhere but nothing?!

No idle issues also, a little lumpy when it reaches 100 degrees and idles at 550ish in gear (but was told idle electronic so not adjustable).

Will have another look over the weekend and see if I've missed anything. Will also play with the bowden and accell cable as seems a bit sluggish on initial accel and gearbox shift up early for me and down too late for my. Liking.

 

[grober]

Usually if there are leaks it's at the short flexible rubber connectors to any vacuum units which perish or crack although the vacuum units themselves may also leak