Tach

[ls1typhoon]

Dave,
My stock Ty tach has never worked with the ls1 engine... I've been tracking down the wiring and I belive I've found the wires.
Is there a way to find out? For sure.
Can I feed some signal to the tach for test?

The input to the tachometer is a white wire that is part of the dash harness. It comes into a 10-pin connector that is near the original ECM. This connector was between the Inst Panel harness, and the engine/ECM harness. I forget if it's pin C or H, but it's in the center of one of the rows. LS ECM's have a tachometer output. Also a white wire, IIRC.

Because the Ty tach is configured for a 6 cyl engine, and the LS is an 8, the tach will read 25% high. The easiest way around this is to get a Dakota Digital signal conditioner. I have used them on other projects for just this purpose. About $80.

I don't know of an easy way to 'test' the tach input wire.

Dave

Anyone know how to test if the tach is actually working
Before I spend $$$ for the converter.

Eddy

 

[DaveP]

Re: Tach

Anyone know how to test if the tach is actually working
Before I spend $$$ for the converter.

Find the wires and hook it up. If it reads 25% high, it's working correctly; buy the converter.

 

[Norm]

Re: Tach

You won't need a convertor, you can change the settings in the ecm .

 

[eviltwin]

Re: Tach

You won't need a convertor, you can change the settings in the ecm .

X2. And LS1s put out a 4 cylinder tach signal from the factory

 

[ls1typhoon]

Re: Tach

Yes, I know about the LS1 4 cyl output and the Ty's 6 cyl tach... The problem is, my tach does not move at all. It's either not connected or the tach is broken. I've found this connector beneath the glove box:

I'm pretty sure the white wire is the tach signal. As you can see, the cable is plugged in so, unless the wire doesn't make it over to the instrument panel, the tach should at least move, right? Also, when I connect OdbWiz to the ODB2 connector, I do get a tachometer reading but I believe this derived from something else...

I guess if I connect say a voltmeter to the white wire maybe I'll see a pulsing voltage?

Thanks,
Eddy

 

[ls1typhoon]

Re: Tach

X2. And LS1s put out a 4 cylinder tach signal from the factory

I noticed on your previous posts about hooking up the tach (http://www.syty.net/forums/showthread.php?t=65822) you spliced into the white wire. Does this mean there is a separate red wire, not in this harness, that actually goes to the tach?

Also, you said I could just program the ECM for the LS1 to output a 6 cylinder pulse... What program or device do you use to program the ECM? I use ODBWiz on my PC which doesn't have that capability...
thanks,
Eddy

 

[fivetodrive]

Re: Tach

I may have a 4 cylinder tach laying around. I wonder if that would work?

 

[ls1typhoon]

Re: Tach

OK, I got the tach working... But, it was not straight forward. First, I verified that the tach wire was connected to the PCU blue connector pin 35 - which is correct for a 97 corvette ls1. Then I checked the voltage from that pin and there wasn't much there. According to Summit/Autometer, there should be around 3 vdc - more when rpms are higher. Then I checked to make sure the PCU was the correct series number - it was. Summit/Autometer recomended a 10k resistor connected to +5vdc (Pull-up resistor) attached to the tach signal wire. I did this and the voltage increased but no change when rpms are increased. So, next an Autometer 9117 adapter was recommended. This adapter connects in the engine compartment between +5vdc for both banks of the ls1 coils (ie no PCU involved). And the output goes to the tach.
Finally, the tach works! I had to get another tach since the output is an 8 cylinder, 4 pulse/cycle signal. Otherwise, I could have gotten the Dakota adapter, but I really didn't want 2 different adapters just to keep using the Typhoon tach. I had a pillar post space available so I just got a 2 1/16 mini tach from Autometer.

Whew! What a hassle!
Eddy