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I have a 72 Chevy truck,with 77 350 HEI. After having problems my timeing,I discoverd my tach was reading 2000 rpm at 55 mph.It did read 3000! AT 70 I only read about 2300,used to be about 3500.I replaced the tach.Same thing.I rebuilt the dist.Same thing.Can anybody help????
Alternator is new.I read 13 volts on my gage.But I did notice when cranking it drops to about 8.I did a load check on the battery and it also checked good.
The battery was checked with a hand held load tester,and my meter shows the same as my gage.
I was afraid you would say that!
did you just put a new tach in? the reason i ask is that if you put an aftermarket tach in, autometer for sure, has three(if i remember right) small wires in the back that you have to cut for the number of cylinders you have. this happened to me about eight years ago, it turned out the tach thought i had a six cylinder, after i cut to of the three wires it was fine.
dont know if this helps or is relevant to you, just takin a stab at it
I'ts a cheap sunpro super tach II column mount with switch on back for cylinder set. To be sure that I didn't have 2 bad tacks I hooked up my automotive digital meter with tack and showed the same RPM.