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Old 08-08-2001, 04:24 PM
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sixto sixto is offline
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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