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Tach does not work correctly after 8.1L swap
Hello all,
I completed an 8.1L swap last year in a 70’s GM truck using a MEFI-4 ECM. Never got that damn thing tuned right so I just replaced the MEFI-4 system with a P59 PCM (basically a stock Silverado PCM with a custom tune) using a Howell Engine Development 8.1L harness. The truck runs 100% better but my tachometer now reads like half what it should.
I did a search and found a few hits but most seem to be that the tach reads high until an adapter is used or use a 4 cyl tach. I noticed those threads were a few years old. My tach reads low.
Anybody have any insight how to make this tach read properly or what tach should be purchased? I am currently using an older Sunpro mini tach. I don't have a problem getting a new tach, just not sure what I need.
Thank you
1968 GMC C1500, 396, TH400
1972 Chevrolet C20 Beater, TBI 5.7L, 700R4
1978 Chevrolet K-quazi-20, 8.1L, SM465, NP205
8.1L Swap
2001 Chevrolet K2500HD, Ext Cab, SWB, 8.1L, ZF 6 speed
2004 Chevrolet Tahoe Z71
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