Conventional Tach on LS2

[Critter]

Originally Posted by 1972K20

Critter, when the computer is flashed, who would you recommend to have it done correctly?

Me!

[mooseknuckles]

I have an autometer elec tach and it's reading about 1000rpm too low....psi harness.

[Billett]

Bringing up a slightly old thread. Can't seem to get my autometer tach to read right. Ive tried connecting the signal in all 4 modes my tach is capable of and it doesnt want to read at all. It just sits at about 3k and if i really get into it it will go up to 4k or so. Ive tried the 1/4w 680 ohm resistor mod from the lt1 site but that didnt change anything either. The pcm is a 2003 and hasn't been tuned at all yet. Should the tuner be able to change the output in the pcm to fix the signal to the tach and get it working, or should I keep trying to fix it before bringing it over there?

[Billett]

Called the shop and they told me they can't change it in the tune. I've heard from others that you can, specifically for EFI live, but I have no personal experience. Called automated and they told me that about once a day they get a call from someone who tried the pull up. Circuit with a 680ohm resistor and that it is just too little resistance. They suggested a 10k or 5k ohm resistor instead. They said 1/2 watt, but I have a 1/4 in my hand so I'll try that first and let you guys know whether it works. Going to email the lt1tech site as well so they can let everyone know that 680 ohm may not work for everyone.

[Critter]

Originally Posted by Billett

Called automated and they told me that about once a day they get a call from someone who tried the pull up.

Please elaborate on this. They get a call from someone who tried to pull up and...??? it didn't work, or it fried the ecu, or what? I use EfiLive for all of mine and so far they work great, maybe I have just been that lucky for the last couple years. That usually isn't the case for me though.

EDIT: Just realized I may be an idiot. I have been talking about GenIII ecms this whole time. I guess the troubles yall are having are with the actual GenIV computers?'

Sorry if I have polluted this thread with useless information.

[Billett]

No the problem is my phone keeps auto correcting things I don't mean. I am talking about a gen III pcm. 680 is too little resistance according to autometer. They suggest trying higher resistances. It did not work for me with 1/4 watt resistors. I did not try 1/2 watt. Next step might have to be autometer 9117, the box that pulls signal from the coil feed.

[Critter]

Interesting.

You said, "Can't seem to get my autometer tach to read right. Ive tried connecting the signal in all 4 modes my tach is capable of and it doesnt want to read at all. It just sits at about 3k and if i really get into it it will go up to 4k or so."

Like I said I have never used a resistor of any type. I just tell the ecm to pull up the signal for the tach and then I adjust the parameters so it is accurate (this is actually a little complicated and if it isn't right the tach will basically not work). I test them all before I send them out and they have all worked. These have all been LS1B ecms using EFILive to flash that I am thinking of. What are the tuners using to flash the ecm? HPTuners?

[Billett]

Hasn't been tuned yet and I don't know what software they use. The 3-4k signal was with the 680 ohm resistor installed. Once I took that out and tried the 10k resistor the needle dropped back down to 0 and hasn't moved since.

[Critter]

UPDATE from my end. I have since run into a few GenIII pcms that need the resitor, so far here is the general pattern I have seen.

DBC computers pull up just fine and do not need a resitor

DBW computer need the risistor EVEN THOUGH EFI LIVE GIVES YOU THE "PULLUP" OPTION IN THE TUNE SOFTWARE.

I am assuming this carries over into the GenIV ecms beings they are all DBW. At the time I first posted my comments I had done a few dozen harnesses but all but 2 were DBC. The couple of DBW I had done for whatever reason the guys never got around to hooking up a tach. I had set them all to pull up the tach signal assuming they worked like all the other genIII ecms I had done/tested. I have since discovered the errors of my ways.

I apologize to anyone I might have misled with my previous comments.