OVERDRIVE SWITCH DOES NOTHING

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Director

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Joined
Feb 28, 2012
Posts
119
Location
Indianapolis, IN
Until today, when you turned OD off, the engine started whining and gained about a thousand RPM. Worked fine yesterday, but today while on I-65 in TN and KY, nothing happens, I just loose speed unless I floor it like I am going to pass someone.
Fuse ? Ideas ?
 
I can think of two possibilities, Since you said you loose speed, it appears it is working, but it is also possible it was not in overdrive when you turned it off.

On level land try it at like 50-60 MPH note the tac readings (not just the speedomerter, As I recall tac should read around 20,000 RPM when you are doing 60 if your rig is like mine

Turn off the OD it goes up to around 25 or 30 KRPM.

Note also that I may be off by a power of 10 on the engine speed.
 
It also will not drop to a lower gear if the speed is too high. In other words, if a downshift from overdrive would cause the engine to over-rev, the transmission simply refuses to do it. Depending on which engine and transmission you have (Ford 6.8L V10, GM 8.1L V8, 5 speed Allison or 4 or 5 speed Ford), you may stay in OD somewhere up around 65-70 mph.
 
As I recall tac should read around 20,000 RPM when you are doing 60 if your rig is like mine

Methinks you got an extra zero, John (I don't think your tach reads the turbocharger RPM). My Cat engine is redlined at 1800, and cruises about 1400-1500 RPM in the 60-65 range.
 
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