crewchef

iTrader: (6)

Has anyone used HPT to get their tach signal right on the 3rd Gen stock tach?

There are two settings, Tach Output - Resolution High and Resolution Low. I have both set to 4 now but tach is still off. Originally thought it was just stock tach being a little off (about 300 at idle) but I've noticed as RPM goes up the difference grows larger. If anyone has this working correctly please let me know what settings you used.

I thought about just trying different numbers but wasn't sure if I used something way off if it could damage the tach.

Thanks!

Wnts2Go10O

iTrader: (12)

its because the ls1 signal is a 4 cylinder signal. your tach is reading half.

super_kev

iTrader: (5)

Check out the tach signal conversion unit from Dakota Digital.

crewchef

iTrader: (6)

Thanks for the responses. I know the LS1 signal is normally a 4cyl signal and my tach needs 8cyl signal. HP Tuners gives you the ability to change the PCM output going to the tach to be what you want it to be. I changed mine to what I thought was 8cyl, 4/4 as described but it's still off.

Does anyone know what these two fields should be set to for the right tach signal on the 3rd Gen?

YsoFast

I thought it could be fixed by changing some software settings too. Let me dig up the info I have and I will let you know. I know for a fact the speed can be recalibrated this way but I am 80% sure the tach can be too.

crewchef

iTrader: (6)

YsoFast, thanks. I've got the speedometer dead on. I changed the tach to the 4/4 setting thinking that was correct for 8cyl and it seems close but not dead on. About 300/400 off at idle but the difference keeps going up as RPM increases. I know the stock tach is not that accurate but if that was the only problem then it should be off 300/400 all the time. Right now it looks like it's XX% off which makes me believe I've got it set wrong. I could probably just play around with the numbers to find it but thought I would check to see if someone else had already figured it out.

MrDude_1

iTrader: (4)

your stock tach is probly just off... like 90% of all 3rdgen tachs, as they age, they go farther and farther off..

crewchef

iTrader: (6)

MrDude, I'll buy into the fact that the tach is a little off but it was pretty darn close to right just before we pulled the L98. That and the fact that the difference keeps increasing as the RPMs go up make me believe I've not got the settings correct.

A stock 98 LS1 has tach output set to 6/6 (4cyl ?) in the fields I described. I changed to 4/4 thinking that was correct for the 3rdGen tach. Maybe I should try 3/3? I don't know just trying to science this out.

MrDude_1

iTrader: (4)

oh, you're looking for the settings.. gotcha.
i thought you were saying you wanted to mess with the settings to compensate for its drift.. my mistake.


i have notes somewhere on it.. but for the life of me, i cant find them at the moment.
i got them off here and hptuners forum... and they were copied off the EFI live forum.. its just a formula used in the PCM for tach output based on the crank position sensor reluctor wheel...

crewchef

iTrader: (6)

If you can locate them I would appreciate it. I went back and did another search on the EFILive, HPTuners forums and here too with no luck. I've found where the question was asked a couple of times but no good response other than "Dakota Digital" fix.

I'm going to send an email to support too and see if they can steer me in the right direction.

crewchef

iTrader: (6)

Got it, almost dead on now. For anyone else that might run into this later the settings should be 3/3 in HPT.

With those settings the tach is within 100 RPM of the HPT read out from idle on up.

Wnts2Go10O

iTrader: (12)

his post should be added to the FAQ sticky

MrDude_1

iTrader: (4)

i need to find that info i had earlier and post it up in here... i showed the formula for it so you could do any setting you needed.