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FIX-IT, Technician
Category: Heavy Equipment
Satisfied Customers: 1195
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freightliner..liter..ecm controles the speedometer and the tack

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I have a 1995 fld120 freightliner truck with a 12.7 liter detroit and i want to know if the ecm controles the speedometer and the tack on that truck or that engine ?
Hi there.i can help you with this..ill need your vin and ill let you know..
Customer: replied 7 years ago.
OK sorry it took so long I had to go get it off the truck 1fuydzyb8sh789092
ill check it out,in the mean time,have a look at the back of transmission were the vehicle speed sensor is,,is it 2 or 4 wire..
Customer: replied 7 years ago.
is it by the output shaft
yes sir..
Customer: replied 7 years ago.
OK it is a 4 wire
yes 2 go to the ecm the other 2 go to the speedo as for the tach if you dont see a pick up on the flywheel housing then its ecm controlled..
Customer: replied 7 years ago.
so would that work irradically if the ecm was messed up ? I have had no problem with the engine so far ?
whats acting up tach or speedo?
Customer: replied 7 years ago.
Both the speedometer worked this morning for about 20 miles and the tack lasted about 10 after I cleaned all the ground connections and the tack works most of the time but goes all the way around sometimes and does not work at all sometimes
check the speedo head for power and grd,key on,, 81c and gnd,then check the vss circuts what is the resistance? 117 and 118 circuts,if its around 800 to 1100 ohms your good,,if all checks out,replace the head and let me know. do the same for the tach...power and grd with key on,,what is the resistance down those wires..its possible there is a tach sender on your flywheel housing check 162 and 163 for resistance if shows resistance,,tach head is possible..let me know how you do..also try disconnecting your alternator,they can cause those 2 guages to go crazy...
Customer: replied 7 years ago.
so if the alternator is messed up that could cause the problem ? it doesn't seem right some times
it possible..i've seen the alternator cause a engine miss fire.......amazing !!
FIX-IT and 2 other Heavy Equipment Specialists are ready to help you
Customer: replied 7 years ago.
Thank you
no prolemo