Pulley Ratio for Alternator - pulsed tach signal.

[wicked6]

So, I have this quandary -



Anyone got a spare crank pulley they can verify the diameter of for this thread. . ?? I measured (in the truck), about 6. 75 inches. . If so, the pulley ratio should be 3:1, (6. 75 to 2. 25 inches) which would mean I should calibrate my VDO electronic tach with 3 pulses per revolution, correct. . ???



Linc

 

[wicked6]

Welp. . Cal'd the tach according to the instructions, and no luck... I also noticed my voltage did not come up to 14 V like it did earlier. . AGGH!!!



I will probably yank the alternator & have it bench tested to see if it's on the fritz, (160k miles) and have the tach lead tested as well. .



More beer. .



Linc

 

[wicked6]

all this discovery... !! OK - poking around a bit more through the archives netted some better guidance - the Nippondenso alternators are supposed to generate 6 AC pulses / revolution, which means my ASSumption of 3 pulses per engine revolution lacked. . well... a critical multiplier. .



. . should be 18 pulses / crank revolution from the alternator... I will give this a shot & report back...



Linc

 

[wicked6]

bingo! 18 pulses per engine revolution is the magic number. Now it looks like I have a dying alternator - signal dies out after about 20 seconds... !! ugh!



Linc

 

[wicked6]

oops. . UNbingo... . alternator rebuilder says 3 pulses / alternator revolution, so 9 is the magic ##. . Ugh. . will try again... .



Oh yeah - the alternator had 160k miles on it, brushes still had ~50% left, rear bearing was drying out, front bearing was still good... no noise... .





Linc

 

[Steve Graham]

So, I have this quandary -



Anyone got a spare crank pulley they can verify the diameter of for this thread. . ?? I measured (in the truck), about 6. 75 inches. . If so, the pulley ratio should be 3:1, (6. 75 to 2. 25 inches) which would mean I should calibrate my VDO electronic tach with 3 pulses per revolution, correct. . ???



Linc

Cummins list the Damper at 174mm or 6. 80 inches.