tach question

[dzbowtie]

just installed an auto gage 2301 in my 70 c10 with hei. the tach is set to read 8 cyl. the wires are connected properly, with the ground attached to the bottom of the metal dash (is this a bad location?) when the truck is in park, the tach seems to read correctly, idles approx 500, and when i hit the accelerator, the tach will raise to over 4000 as expected. however, when the truck is in gear, the tach will raise up to around 2500, but seems to slow down, topping out around 32-3400, when it should read 4000+. what would cause this to only occur when driving, as opposed to in park? the tach is mounted at a slightly upward angle (nothing drastic), surely this would not effect operations? this is not the first tach that has done this, which makes me believe that i did something incorrectly (power to key on source, green to hei port), or there could be some issue while the truck is driving. any advise would be greatly appreciated. could there be too many grounds in one location?

[Mrturner1]

Does the truck pull pretty hard and smooth all the way up through the rpm range when at wide open throttle or does is slow down around 3400 and stop pulling as fast?

[dzbowtie]

the truck spins up faster at lower rpms and does seems to slow down higher in the range. ive had the same 350 in a camaro with factory tach spin up to 3500-4000 (cam float approx 6200) with no problems (th350 with 3.42). this is now in a c10 with 3.73. i would think that it would still spin to that rpm level (no engine problems) just quicker due to the gear ratio. and since another tach did the same thing, im wondering if there is some sort of interferance or wiring issue. highly doubt the tach is an issue. i had an old sun tach read properly, but it fell apart from age, so i used an equus before the auto gage and both are having the similar reading...

[dzbowtie]

the only thing I noticed that I did differently after removing the old tach (which read properly) was after running the new wires to the distributor (both power and tach wires), I taped them together to give then a cleaner look from the firewall to the distributor. could this touching of the wires cause some sort of interference?

[1quik70]

Double check the ground and that you have the wire plugged into the right spot on the distributor. Make sure your power is a clean feed from a keyed source.

[dzbowtie]

i checked the ground and it seems good. i checked the power to the tach and with key on, it shows 12v. the power wire to the tach is sharing the same key-on source on the fuse block with another power source going to a water temp gauge. that gauge has always worked properly. also, the other morning i was heading to work and the needle seemed to read correctly as i was pulling a hill (approx 3800 with no trouble). then it just kicked back down to just over 2000 and went back to the same behavior of not wanting to pull much over 3000 when im turning rpms. i checked the power wire to the distributor and its connected properly. i removed the tach wire from the distributor and replaced the female connector with a new one, then reconnected it. hopefully this incorrect reading will go away.