Focus Fanatics Forum banner

aftermarket tach reading wrong

608 Views 5 Replies 4 Participants Last post by  cruzstyle
I have a pretty weird issue here, i have installed the a tach from auto meter using a ford racing tach adaptor. now the damn thing is accurate up to like 4500 after that it is way of, but the time that i'm at 7k on the stock tach it's at 10k. any comments
1 - 6 of 6 Posts

· Registered
128 Posts
teddy2heavy said:
that is how mine is we have it set on 8 not 4
Do not confuse the two. PPR is not the same as "8 cylinder".

In a conventional 8-cylinder engine, the #1 spark plug fires once every two revolutions. Since there are 8 cylinders, there are 4 spark plug firings per revolution. Therefore, at the coil, there are 4 PPR (Pulses per Revolution)

Similarly, a 6-cylinder has 3 PPR and a 4-cylinder has 2 PPR and a 10-cylinder has 5PPR and so on.

Now, with a crank position sensor, the sensor picks up the 36minus1 teeth on the trigger wheel and sends the signal to the ECU What the Ford Tach Adapter does is divides this signal by 9 to get 4PPR. Regardless of whether it is a 4, 6, 8, or 10 cylinder engine.

So, if you have a conventional style tach, yes it needs to be set to "8-cylinder"; but if it is a newer digital style tach it needs to be set to 4 PPR.
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.