Electric Speedo Erratic
11-07-2014, 12:01 AM
#1
Electric Speedo Erratic
In my 92 TPI Formula (T56 conversion, originally T5) while warming up in neutral the speedo bounces erratically between 0 and 50 mph. When you start moving it drops to zero then moves normally, steadily. Sometimes once moving at any speed it suddenly drops to zero and the engine goes into limp mode. It can be reset by turning the ignition off, then restarting while still moving; sometimes it starts working again on its own.
I have an SGI5 connected for the T56 and its closest setting still reads approx 3x actual speed. I think this is a separate issue but they may be related. I never owned or drove the car with the T5 in it so I don't know if this condition was pre-existing, or new to the T56/SGI5.
I do know there is a fair amount of electrical noise when the car is running, from the general front-of-console area. If you play with the fan switch while the speedo is bouncing, it seems to affect the bounce pattern.
Not sure which of these items may be related, but thought I'd spill the whole story. I'm not much of an electrical guy so any help would be appreciated.
I have an SGI5 connected for the T56 and its closest setting still reads approx 3x actual speed. I think this is a separate issue but they may be related. I never owned or drove the car with the T5 in it so I don't know if this condition was pre-existing, or new to the T56/SGI5.
I do know there is a fair amount of electrical noise when the car is running, from the general front-of-console area. If you play with the fan switch while the speedo is bouncing, it seems to affect the bounce pattern.
Not sure which of these items may be related, but thought I'd spill the whole story. I'm not much of an electrical guy so any help would be appreciated.
11-16-2014, 08:56 AM
#3
Re: Electric Speedo Erratic
Seems like this is very common with the DD SGI box. I've got a T56 and it's connected to a SGI box then to the factory AND a aftermarket digital speedo. When I start my car the speedo will climb as high as 100MPH and then fall to the 20-30MPH range - while I'm parked in neutral ) . Once I begin to actually drive,... the speedo readout becomes accurate.
I first had the T56 installed with a 350HP carb engine,..... then it was completely disassembled ( every nut/bolt in the car ) and rebuilt as an LT1 with T56. The same speedo fluctuations are present now as when the Carb engine was installed.
IIRC the SGI instructions state that the speedo wires should be tightly "wrapped" or "twisted" together to help overcome this - others have said that an in-line noise filter will help. I twisted the wires some but it didn't help,... I've never tried an inline noise filter.
Might not help - but at least you know it's not just your car acting this way !
I first had the T56 installed with a 350HP carb engine,..... then it was completely disassembled ( every nut/bolt in the car ) and rebuilt as an LT1 with T56. The same speedo fluctuations are present now as when the Carb engine was installed.
IIRC the SGI instructions state that the speedo wires should be tightly "wrapped" or "twisted" together to help overcome this - others have said that an in-line noise filter will help. I twisted the wires some but it didn't help,... I've never tried an inline noise filter.
Might not help - but at least you know it's not just your car acting this way !
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