High rpm (Page 1/2) TXGOOD JUL 28, 12:42 PM My car shows idling at about 1700 and when on the highway at about 4500 at 65 or so MPH. I have tried a couple of different tachs with the same result. I bought a hand held tach and when the car reads 1700 idle the handheld shows about 1000 I raised the RPM up to about 3500 according to the car and the handheld showed 2600. I think it goes up a couple hundred from there as the engine spins faster which would make the 4500 at 65 is probably more like 3200-3300 which I think is more accurate for a TH125 and V6. Any ideas? What sends the info to the tach as what RPM to display? Thanks Gall757 JUL 28, 02:42 PM Fiero tachs tend to read high when they fail. I think a resistor goes bad, or some other component. They can be rebuilt by forum member J Gunsett. TXGOOD JUL 28, 02:50 PM I have tried three different tachs including one redone by who you mentioned so it must be something else feeding the tach the wrong info. Gall757 JUL 28, 03:42 PM hmmm. Have you tried removing the tach filter? TXGOOD JUL 28, 05:45 PM quote Originally posted by Gall757: hmmm. Have you tried removing the tach filter? No, I haven`t tried that yet. I will see what it does. TXGOOD JUL 28, 06:49 PM When I disconnected the tach filter the tach would not work at all. It`s one of those "can" type that has a separate ground wire. I may order the stock looking one from Rodney Dickman. tshark JUL 28, 09:05 PM Bypass the tach, first. See if that changes anything. Understand that the final drive ratio on the V6/TH125 is different by year. Mine ran 3500 RPM at 75 MPH. Where are you connecting the handheld tach. Between a spark plug? Is this a recent thing? Gall757 JUL 28, 09:09 PM quote Originally posted by tshark: Bypass the tach, first. do you mean 'bypass the tach filter"? If the filter is disconnected, the tach will not work. fieroguru JUL 28, 09:58 PM quote Originally posted by Gall757: do you mean 'bypass the tach filter"? If the filter is disconnected, the tach will not work. I have never retained the tach filter on any swap and it isn't used on the 4cyl cars either. Its purpose is to help soften some very minor tach needle puslation. Remove it, jumper the two two wires and see for yourself. TXGOOD JUL 28, 10:14 PM quote Originally posted by tshark: Bypass the tach, first. See if that changes anything. Understand that the final drive ratio on the V6/TH125 is different by year. Mine ran 3500 RPM at 75 MPH. Where are you connecting the handheld tach. Between a spark plug? Is this a recent thing? The handheld uses a 1/2" reflective strip that you stick to the harmonic balancer and the meter reads off of that.