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
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.
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.
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.
I did jumper the two wires and the tach still did not work. I thought that maybe the wires had been connected backwards because I saw a post where there is an output and an input and on either side of the filter the resistance is not the same but the tach reads the same both ways I connect the wires. I`m not sure how the filter has been wired because like I said it`s the one that has a separate ground wire unlike the stock, which only grounds, I guess through the actual body of the filter. I don`t know if the ground has to play a part in the connection because like I said I used a jumper wire and connected both spades of the stock connector together and the tach still did not move.
If it stopped working, there is likely something not quite right with the wiring. Here is the stock wiring. The jumper needs to go from the coil connection to the tach connection.
Once the tach filter is properly bypassed, if the tach is still reading too high, it is likely a ground issue at/in the instrument cluster. Are there any other strange things happening with the cluster lights?
The tach filter appears to be a simple high frequency filter with the can serving as the ground. Connecting the input and output wires together should send an almost identical signal to the car's tachometer but the signal may contain some higher frequency energy as well. Fieroguru is correct that something may be amiss with the wiring somewhere.
Originally posted by fieroguru: 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.
84-86 L4 Fiero and other HEI cars has the Tach Filter when the car has a tach. DIS engines do not have this.
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Originally posted by Rexgirl: The tach filter appears to be a simple high frequency filter with the can serving as the ground. Connecting the input and output wires together should send an almost identical signal to the car's tachometer but the signal may contain some higher frequency energy as well. Fieroguru is correct that something may be amiss with the wiring somewhere.
Tach filler is RC network/filter that uses a ground to case but that ground is Not a HEI system ground or used by the Tach. It mostly stops High Freq E'noise getting to Tach and other things.
You can bypass this as a test but if the tach or wire to it is bad then HEI will have problems and can kill the coil, ICM and/or even fry off Fuse Link H to the ignition.
Well, since I haven`t been able to get my tach to read right would I have a chance of getting it close to reading right with a variable resistor? Woulld I install it between the tach filter and the coil or after the tach filter going into the wiring harness? Thanks
