samh_08

What is the deal with the tach signal on these engines? I have all autometer gauges, all work but the tach so far. First I need to see if the signal is even present in the wire, so how and what am I looking to see in the test?

Autometer says I need part number 9117 which means I have to cut and splice into my coil power supplies..Obviously this is my last resort. I would like to know what everyone did in order to get their tach working properly. BTW I also have EFIlive if that helps matters.

Let me know, thanks.
Sam

V8Rumble

iTrader: (9)

This is a pretty common question in this forum, if you search for

in this forum, you should find several threads with the answer.

rockytopper

Not sure which engine or harness you are refering too but the ls1 engines have a single tach wire and to run the autometer tach you have to switch it to 4 cyl setting. To my knowledge the resistor is needed if you want to stop the low rpm 600-1000 needle flutter. Mine flutters a little at idle but I'm ok with it. Works fine for normal operation.

samh_08

So if my tach is currently on 8 cyl setting, it should read half as much, right? Are there any calibrations I can change of something with EFIlive?

rockytopper

Sorry I can't answer that I am tuner illiterate. My autometer tach has a switch on the back of it to change from 4, 6, or 8 cyl.

Stu Cool

iTrader: (13)

Yes, you should be able to change it with EFI live. Speartech changed mine so that it works with my Sun Tach in the 8 cylinder setting. Don't ask me how though.

Pat

samh_08

That assumes I even have a tach signal in the first place correct? Anyone know how to test this and what I should see?

726.0chevelle

iTrader: (17)

i just cranked my car for the first time today and no tach for me and oil pressure guage not working either. is there a port on these motors to put your own oil pressure sending unit

Stu Cool

iTrader: (13)

If you have room you can pull the oil sending unit at the back of the intake manifold and replace it with your own sender. You will probably need a metric to SAE adapter, The ECU does not use an oil pressure signal, it is only for the gauge. Other folks have drilled and tapped the fitting down near the oil filter.

Pat

726.0chevelle

iTrader: (17)

what threads are the hole behind the intake

samh_08

...not to be an *** but you should probably make a different thread for your questions unrelated to the tach. I have yet to get my ?'s answered

dhutton

iTrader: (1)

Easiest way is to look with an oscilloscope. You should see a square wave with 5 volt (or 12 volt) amplitude. Stock ECM's are roughly 50 Hz or so at idle.

If you don't have a scope, you should measure something with an AC voltmeter if the signal is there. I'm guessing 3 to 5 volts AC.

Don

samh_08

I wouldnt have a scope readily available but I do have a hertz scale on my multimeter. Would that give me an accurate reading? Just to make sure, I would connect one lead of my meter to the tach signal wire and the other lead to ground?

dhutton

iTrader: (1)

Yes, that should work for the frequency. It should be quite accurate and the frequency will vary as you vary the engine speed. Exact frequency is not critical. Using your multimeter set to AC volts you should also see the 3 to 5 volts or so.

Don

samh_08

I have no signal on the white wire (RPM out) from the PCM. Could I possibly use the Camshaft position sensor or something like that. I assume the PCM uses the cam sensor for RPM, right? Let me know ASAP, Thanks!

dhutton

iTrader: (1)

Why don't you try the 680 ohm pullup resistor from the tach wire to switched +12 first? It might help you. You can check for the signal the same way once you add the pullup.

Other than that I would probably go with the Autometer 9117.

Don

NHRAMAN

iTrader: (1)

Mine flutters at idle also--doesn't read right,until about 1200rpm or so..then it is fine..mine is also 7 years old..5". YOU GOTTA run it in 4cyl mode for some reason.

samh_08

Just an FYI for everyone. I did the 680 pull up resistor and it works perfectly! I went in EFIlive and changed my tach signal parameters to what I needed for an 8 cyl. So no you do not have to change your tach to run in 4 cyl mode if you have tuning software to change the signal.