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Old 08-07-2001, 07:57 PM
Posts: n/a
"Economy" panel meter

On a 1989 300E, with 103 engine.... I get good position on the "Economy" gauge/meter on the dash.
But occasionally, the meter goes almost to full
RED position (for a mile or two) then jumps back
into the white zone.

What functions/parameters from the engine feed the
computation to operate this "Economy" meter/gauge?

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Old 08-07-2001, 08:42 PM
J.HIDALGO's Avatar
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Join Date: Jul 1999
Location: Jax, FL
Posts: 1,785
Everytime you accelerate the economy needle should go to the red. Basically, as you "exercise" the engine, it produces more vacuum therefore, needle goes to the right/red...
If this happens during normal cruising speed (no sudden acceleration) then, that is another story.
'86 300E
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Old 08-07-2001, 08:57 PM
Posts: n/a
It must be 'another story'. It happens after
a hard deceleration, then the needle 'jumps'
back to left/white and there is a noticible increase in power at same time. Yes, it happens
with no varying the accelerator, level ground.

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Old 08-08-2001, 04:24 PM
sixto's Avatar
smoke gets in your eyes
Join Date: Jun 2000
Location: SF Bay Area
Posts: 18,745
Actually, the left/white zone is more vacuum and the right/red zone is less vacuum. The higher the vacuum while cruising, the higher the mpg.

I believe the economy gauge reads manifold vacuum directly, as in there's a vacuum hose that tees off the vacuum hose going to the transmission modulator.

A really uneducated guess would be that a solenoid or switching valve stays open too long then closes.

The manual talks about checking the vacuum hose for oil (that shouldn't be there). Could be that you have a leaking transmission modulator or something like that causing the faulty economy gauge readings.

91 300SE
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Old 08-08-2001, 06:50 PM
J.HIDALGO's Avatar
Registered User
Join Date: Jul 1999
Location: Jax, FL
Posts: 1,785
Ooops! I had it backwards. The principle is the same, though. You probably have a vacuum leak somewhere...
Thanks Sixto!
'86 300E
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