Codes 74 & 78?

[Rob Mac]

Hi People
I am getting codes 74 & 78.Cant figure what they are. I have 94 Silverado 6.5 turbo diesel. Have just had a new Fuel Injection Pump installed,any ideas?

[Robyn]

74 is the transmission input speed sensor
78 is the wastegate solenoid. The wastegate solenoid is mounted on the drivers side valve cover at the rear of the engine. It has a wire harness pluging into it as well as a vacuum harness.. One vacuum line goes to the pump the other goes to the waste gate on the turbo. These solenoids go away from time to time
The speeds sensor is inside the tranny. Check all the electrical connections to be sure they are good and tight first.
let us know
Robyn

[Warren96]

If you had someone working on it they may have broken a rubber vacum line in the turbo vacum circuit.They get brittle,with age and heat.And like Robin said the wastegate goes bad.Try new vacum hoses first,they are cheap!