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Old 09-19-2009, 03:32 PM
Jeremy5848's Avatar
Jeremy5848 Jeremy5848 is offline
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Join Date: Mar 2006
Location: Sonoma Wine Country
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Not a boost gauge!

Actually, I have a "real" boost gauge in the ashtray slot. The "economy" gauge you see in my cluster is plumbed into the vacuum line that goes to the transmission. As I put my foot more into the accelerator, the gauge moves towards the red zone, much as it does in a gasser.

As you know, Mercedes designed (I suppose the factory doesn't "jury-rig?") the VCV and blue flying saucer to simulate gasser intake manifold vacuum so they could use the same transmission control for gasser and diesel alike. Thus, the vacuum line to a 722.3 or 722.4 transmission (and maybe others?) looks like gasser intake manifold vacuum and you can use the same gauge.

The 'economy' gauge is unmodified; it was part of the 4-gauge section in a 1989 300E cluster. Since that car has "unleaded fuel required" written on its gauge face, I swapped the face from a 1984 300SE, which pre-dated the unleaded warning. No other modifications were required; the fuel, oil pressure, and coolant temp gauges are identical to their diesel counterparts.

As a bonus, the 1989 4-gauge section has a little red twist-in fuse that the 1987 version lacks. I don't know what it is supposed to protect but I sleep better knowing it's there.

I posted a thread when I did the installation:

Another diesel use for the gasser "Economy" gauge

So is it really useful? Well, I do notice it moving and I suppose it's a reminder to use as little right foot as possible, hence improving fuel economy a bit. Should the vacuum system fail, I'll have something to look at when my shifts suddenly (or gradually) become harsh. And it's fun to mess with peoples' minds when they see something unexpected.

Jeremy
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Our all-Diesel family
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