Tach vrs. True RPM
02-29-2004, 04:18 AM
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Tach vrs. True RPM
Picked up my new used '91 last night and noticed something odd.
The tach reads kinda high. Like around 5k at 60 mph.
By ear, I can 'hear' that the engine is running around 3000 (all the equipment and tire size, etc is the same as my previous '91), so I know it's not engine/tranny related. The clutch is not slipping, but I'm wondering what could cause the tach to be so 'off'. Gear tooth?
And, will the high read on the tach effect how the computer is reading the rest of the data input??
I will be puting it on a timing light very soon, but I'm in the middle of a 6 day tour of duty right now, so it will have to wait. Just curious...
Thanks,
The tach reads kinda high. Like around 5k at 60 mph.
By ear, I can 'hear' that the engine is running around 3000 (all the equipment and tire size, etc is the same as my previous '91), so I know it's not engine/tranny related. The clutch is not slipping, but I'm wondering what could cause the tach to be so 'off'. Gear tooth?
And, will the high read on the tach effect how the computer is reading the rest of the data input??
I will be puting it on a timing light very soon, but I'm in the middle of a 6 day tour of duty right now, so it will have to wait. Just curious...
Thanks,
02-29-2004, 04:30 AM
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Originally Posted by Blair
Picked up my new used '91 last night and noticed something odd.
The tach reads kinda high. Like around 5k at 60 mph.
By ear, I can 'hear' that the engine is running around 3000 (all the equipment and tire size, etc is the same as my previous '91), so I know it's not engine/tranny related. The clutch is not slipping, but I'm wondering what could cause the tach to be so 'off'. Gear tooth?
And, will the high read on the tach effect how the computer is reading the rest of the data input??
I will be puting it on a timing light very soon, but I'm in the middle of a 6 day tour of duty right now, so it will have to wait. Just curious...
Thanks,
The tach reads kinda high. Like around 5k at 60 mph.
By ear, I can 'hear' that the engine is running around 3000 (all the equipment and tire size, etc is the same as my previous '91), so I know it's not engine/tranny related. The clutch is not slipping, but I'm wondering what could cause the tach to be so 'off'. Gear tooth?
And, will the high read on the tach effect how the computer is reading the rest of the data input??
I will be puting it on a timing light very soon, but I'm in the middle of a 6 day tour of duty right now, so it will have to wait. Just curious...
Thanks,
02-29-2004, 08:16 AM
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Originally Posted by MTL_4runner
I believe the tach is electrical (someone please correct me if I am wrong). Might need to get measurements on the tachs input to verify if it is the guage or the input causing all the probs.
The Toyota tachometer accepts a pulsed ignition signal from the coil. This signal is converted into a proportional DC signal that drives an analog current meter in the dash to display engine rpm. Its reading can be scaled to correctly display the correct engine rpm by adding a calibrated resistive shunt to the meter input.
source: http://www.tamor.org/techreports/toy...od/default.htm
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