mercruiser 3.0 to 5.0 engine swap TACHOMETER issues

[buckinrut85]

Ok... i upgraded a 3.0 mercruiser to a 5.0 mercruiser on an 17ft 1985 Four Winns Horizon. I just made the swap myself and yes i did upgrade the outdrive also. boat runs GREAT. (the gear RATIO IS RITE)... the tachometer works but its not RITE... its saying it idles at around 1500-2000. and at WOT its buried. why? all my other gauges work... properly. Sense it was hooked a 4cyl engine Does it need to be calibrated for an 8cyl engine? Just the RPM gauge is my only issue. ANY IDEAS?

 

[fishrdan]

Re: mercruiser 3.0 to 5.0 engine swap TACHOMETER issues

Does it need to be calibrated for an 8cyl engine?

Yes, well kind of. Look at the back side of the tach for a rotary switch labeled 4-6-8, set it to 8 for your new engine.

 

[zx9rstv]

Re: mercruiser 3.0 to 5.0 engine swap TACHOMETER issues

as stated above, should be a dial to change the tach calibration to 8 cylinders. There might also be pulses . if it's in pulses then you'll want to select for 4 pulses.
also once you have changed the selection for cylinders. You might need to fine tune the calibration by a small Phillips screw in the back as well. This is for fine tuning only. It will not help if the tach cylinder selection is not changed to the proper selection. To fine tune you will need a separate rpm meter to hook up to the ignition.

 

[buckinrut85]

Re: mercruiser 3.0 to 5.0 engine swap TACHOMETER issues

thanks guys. i knew it would be an easy fix. just didnt know where to look. much obliged

 

[Nldp]

Re: mercruiser 3.0 to 5.0 engine swap TACHOMETER issues

I'm very interested in the swap you did . Any details like how did you mount the engine ? The inline mounted front to back I thought . I have a 1984 190 with a 3.0 but want some more performance boat is perfect so buying new not an option . Thanks mark