Tach does not work correctly after 8.1L swap

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12-21-2009, 04:15 PM
DirtyLarry

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
12-21-2009, 10:13 PM
RedHeartbeat

If you have access to tuning software like HPTUNER you can get the signal count output modified. If not then you can contact BakerElectronix.com for one of their adjustable tach signal modules. I'm sure he's still in business though I haven't had to buy anything from him in years.
12-22-2009, 10:57 AM
DirtyLarry

Quote:

Originally Posted by RedHeartbeat

If you have access to tuning software like HPTUNER you can get the signal count output modified. If not then you can contact BakerElectronix.com for one of their adjustable tach signal modules. I'm sure he's still in business though I haven't had to buy anything from him in years.

Thanks!

I ordered a MDS Tach Driver kit 8913 last night so I’ll see how well this works once it gets here.
12-22-2009, 04:24 PM
oleshifty

i believe these motors use a 4cyl tach setting....(atleast when adding an aftermarket tach) Not sure if that'll help at all...
12-22-2009, 06:29 PM
DirtyLarry

Quote:

Originally Posted by oleshifty

i believe these motors use a 4cyl tach setting....(atleast when adding an aftermarket tach) Not sure if that'll help at all...

Yeah, that is what I read. I have a SunPro mini tach but it doesn’t have any switches that I can find to adjust it to a 4 cyl mode. If it did that would save me a big hassle.

Actually, I am not impressed with the way the MSD kit interrupts a coil signal. That just makes me nervous so I would much rather swap a tach than hack open a perfectly good coil harness and cut into it.

If anybody has any tach recommendations I am certainly open to that. BTW, I called SunPro and they wanted to sell me an adapter that is even more hocky than the MSD dealeo.
12-22-2009, 08:40 PM
Frenchy

If it were me I'd just buy a new tach.
12-22-2009, 09:56 PM
DirtyLarry

Quote:

Originally Posted by sleeper1500

If it were me I'd just buy a new tach.

Well, I am a dumbass. I went to SunPro’s website and pulled down the PDF instructions for the Mini tach II. Mine is much older but it did indeed have a cylinder setting on the back behind that I could not see until I removed it from the base. Flip the switch to 4 cyl and it works fine. So, never mind me….
06-14-2024, 07:39 AM
MeganN012

The tachometer in my car doesn't work correctly, leaving me in the dark about engine RPMs. It's akin to missing out on an air fryer sale—frustrating and disappointing. Without accurate RPM readings, gauging engine performance feels like gambling blindfolded. Just as an air fryer sale promises healthier cooking at a bargain, a functional tachometer ensures smooth driving and timely gear shifts. Its malfunction is like passing up on a golden opportunity. Addressing this issue promptly is crucial, akin to seizing the last air fryer on sale—a chance not to be missed for both efficiency and peace of mind on the road.