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Original owner, 1983 P'up LS (diesel)
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szac said:
As DSUZU predicted the tach was off ~1000 revs.
Tons of respect for Dennis, but I'm not so sure the tach could have been off by "1000 revs". I think it depends on the RPM -- because it's probably off by a percentage. For example, at an actual 1.000, the V6 tach would indicate 667 RPM (although it obviously doesn't have that level of precision).

Now, whether the potentiometer adjustment can correct that, I wouldn't know. I did the same tach swap on my Amigo, but I did my adjustment by guesstimate. I adjusted it at idle so that the tach indicated the expected idle RPM. But when I revved the engine, the tach always seemed off (low). I never bothered to check it, though.

You may want to compare it at different RPMs if you're concerned about accuracy.

Jack
 

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Registered
Original owner, 1983 P'up LS (diesel)
Joined
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2,782 Posts
szac said:
JoeIsuzu said:
szac said:
As DSUZU predicted the tach was off ~1000 revs.
Tons of respect for Dennis, but I'm not so sure the tach could have been off by "1000 revs". I think it depends on the RPM -- because it's probably off by a percentage. For example, at an actual 1.000, the V6 tach would indicate 667 RPM (although it obviously doesn't have that level of precision).

Now, whether the potentiometer adjustment can correct that, I wouldn't know. I did the same tach swap on my Amigo, but I did my adjustment by guesstimate. I adjusted it at idle so that the tach indicated the expected idle RPM. But when I revved the engine, the tach always seemed off (low). I never bothered to check it, though.

You may want to compare it at different RPMs if you're concerned about accuracy.

Jack
I'm not too concerned about the accuracy. The "~1000 revs" number was verified when I had the calibration tach up to 3k. The cluster tach read 2k. I held it at 2500 revs on the calibration tach and then adjusted the pot until they match. After that the two tachs were synced as I revved the motor. The truck idles at about 1100 on start, then slows to a light 1000 once warm.

My primary goal was to replace the janky a-pillar gauges that came with the truck with OEM gauges. I'm going to keep the mechanical oil pressure gauge installed and compare with OEM gauge once I install the sender. Hopefully they're close :D
That matches my formula exactly -- the cluster tach indicated 2/3 the actual RPM. And after you synced them, they stayed in sync as you revved the motor. That's good to know.

Jack
 
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