E40 ecm tach output reading off

[andrew69_04]

Im stumped. I've been searching for hours, and i've made about 15 different changes with my tune and nothing makes a bit of difference. I put an LS2 out of a 2006 GTO into a 1979 camaro. The ecm is an E40. 24x reluctor. the factory dash tach is for a V8. I had no tach movement when run off the tach output wire at the beginning so we had to use a pull up resistor ( i've tried, 300, 600, 4700, 10,000 ohm) and its the same no matter what. My RPM's are reading exactally half of what my VCM scanner is showing. I have tried changing the Hi/LO res from 2 all the way to 15, and its the same every time. I've done this several times with LS1 swaps and it works like a charm, this time it acts like my changes don't have any effect.

All the search info i could find was on the E38 ecm, not the E40. can anyone please help??

[andrew69_04]

From everything i have read, changing the values both to 3 should give me my 4 PPR that i need for the V8 tach. i have been making the changes and just writing the cal. do i need to do a write entire to get the actual signal to change?

[Eaglegoat]

Make the settings stock. Set your dash tach or signal box to 4 cylinder.

[andrew69_04]

I was trying to do this without buying a signal box, but it appears that's the direction we are going to have to go

[AustinH]

Did you ever get this issue solved?

I am running into the same issue with a 06 GTO Ls2 and an Autometer Gauge. The gauge can be adjusted using dopswitches between 1/2/3/4 pulses per rev. The gauge gets a strong signal (not improved with a pull-up) but no settings match up to the PCM output. I set about to adjust it with HPTuners but I dont see any response from ResolutionH/L changes. Stumped at this point, until I can get a scope on the signal.

[schpenxel]

What's it showing vs. reality?

What pull up resistor values you have tried?

Is it ever right? i.e. wrong at low RPM's and closer at higher RPM's or anything like that?

[AustinH]

Hi,

Here are a few samples:
Tach (analog) / VCM
500 / 820
1000 / 1600
2000 / 3150

Tach is set to 2 pulse per rev. Currently the tune is set for Frequency, 7/7 but there is no change in tach output with different high/low values. I have also tried crank and serial but thouse cause the tach to stop working. I am using a 1k pull up, but the signal was strong without it (and the same value) so I dont think it was required, still in the car though. My next step is to borrow a scope and try to see exactly what the tach output is.

[schpenxel]

So pretty much low by factor of 1.6 everywhere. At least it's consistent I suppose.

You may have answered this already but where are you getting the tach signal from? I used one of the coil wires + a 1K pull up resistor earlier on a shift light and it worked (E40 also).

[AustinH]

Hey Guys,

I am still struggling with this issue, its the last thing to wrap up on my swap. I am using teh factory ECM output, pin 48. The signal is strong but i cant get it to line up right with my autometer tach, the signal does NOT respond to reprogramming with HP Tuners. I tried wiring into a coil signal wire but that didnt work either.

Im about to give up and go with a autometer tach adatper but I was really hoping to not do this.

-Austin