alternator pulley and tach question

[cshade]

I've changed out my alternator with a HD model (160 amp) and it came with a small pulley installed. (needed to use a slightly shorter serpentine belt.) The result is the alt spins faster than it is calibrated for. The tach reads 400 rpm higher at idle and around 1500 rpm higher at high rpm!!!

I've driven it around since the change, and I don't notice a difference in operation, i was worried about a rev limiter cutting in early, but thats not an issue.


Does this affect the tranny shift points or injector timing or anything like that? What does the 6.5 computer use rpms for?

[a5150nut]

Run back to where you got your alternator and get the pulley off your old alt. The Alt. is your tack sending unit. And YES everything will be effected by the faulty RPM reading.

[More Power]

I've changed out my alternator with a HD model (160 amp) and it came with a small pulley installed. (needed to use a slightly shorter serpentine belt.) The result is the alt spins faster than it is calibrated for. The tach reads 400 rpm higher at idle and around 1500 rpm higher at high rpm!!!

I've driven it around since the change, and I don't notice a difference in operation, i was worried about a rev limiter cutting in early, but thats not an issue.


Does this affect the tranny shift points or injector timing or anything like that? What does the 6.5 computer use rpms for?

Tach accuracy is the big thing with a smaller pulley - and possibly shorter alternator life. I think the PCM gets engine speed from the CKP (crankshaft position sensor) and possibly the DS4's Optical Encoder Sensor. So yes, get your old pulley back if you can....

Jim