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86' 951...Does anyone know where you can easily access the wire that feeds the tachometer? In searching through old threads, it looks like one of the wires down by the DME under the passenger side dash feeds the tach, but the descriptions of the harnesses and color of the wire don't seem to match what I have. Below are some pics of the wiring I have...
Also, once I find the wire, does anyone know what signal actually drives the tachometer? Is it a pulsing 12V or maybe a pulsing ground?
yep, just did this this weekend, it is DME 21. It is a thick green shielded wire. Close to the plug, it is narrower and still green before the shielding starts. I fed my wire through the rubber boot for the plug, and soldered on to the narrower bit right by the plug. My AVCR now shows a clean rpm signal that is spot on.
I don't know what type of signal it is.
Six, thanks for that link. I read through the thread and it looks like a pulsed ground signal is needed at pin 21 of the DME connector. I gave this a quick try (just quickly tapping a ground wire to pin 21), but couldn't get the tach to even bounce. Any idea if I can get to the 12V or ground pins for the tach without pulling out the gauge cluster? I'm thinking maybe I don't have those connections without having the DME/KLR actuall installed...
SCEV..
The green/black wire within the red 4 term plug (its in one of your pics) is the signal to the tach from the DME.
This ground signal comes out of term 21 on the DME's 35 term connector along with another green wire. The other green wire goes to the KLR and the green/black wire connects to term 2 on the red 4 term plug. The other half of the black/green wire goes from the red connector to term 3 on the flat 'B' connection behind the gauge cluster driving the tach.
SCEV..
The green/black wire within the red 4 term plug (its in one of your pics) is the signal to the tach from the DME.
This ground signal comes out of term 21 on the DME's 35 term connector along with another green wire. The other green wire goes to the KLR and the green/black wire connects to term 2 on the red 4 term plug. The other half of the black/green wire goes from the red connector to term 3 on the flat 'B' connection behind the gauge cluster driving the tach.
I think I somewhat followed all that...but bottom line is the green/black wire in one of the two 4-pin red connectors goes directly back to the tachometer. I'll test both tonight to see if I can get the tach to bounce.
Out of curiosity, what do these two red 4-pin connectors plug into? I should have taken more pictures when I took everything apart...
One side of the connector is part of the dash harness going to the cluster and the other side comes from the engine harness and goes to the DME. The tach needs to have power for it to bounce -- so you should hook everything up to test and simply pull the green/black wire out of the cluster side of that red connector. You can get some bounce by just tapping that wire to ground -- or see the video about dragging the wire across grounded bolt threads. Tounce will be erratic, but it will confirm if the tach is alive anyway, assuming that's your goal.
Perhaps some backstory would help...I've converted my 951 to electric drive, so the DME/KLR will never be going back in . What I'm trying to do is drive the tachometer from my electric motor. I think I can create a pulsing ground, just needed to know where to connect it.
I was hoping 12V and ground would already be sent to the tach just from turning the key. Are you saying these connections are in the red 4-pin connector as well, and if not hooked up there would be no 12V/ground sent to the tach?
Success! I turned on the car and quickly touched ground to the green/black wires in the two red 4-pin connectors, and when I did this to the female connector, I got movement on the tach needle!
Next I tried the bolt trick to create a quicker pulse, and got the needle to easily jump up to the 3000 RPM range.
Finally, I used one of the outputs from my controller (EVnetics Soliton 1) to turn my 4ppt signal I get from my motor to a 2ppt signal which the Porsche wants (I only know it's 2ppt from trial and error...tried 4ppt first and the tach was showing twice as much as it should) and it worked beautifully the first time! Well, it seems to be about 100 RPMs off, but I can live with that.
Well now there's something you don't see everyday! Very impressive effort there! How does it feel on the road?
With a 4 cylinders, 4-stroke motor, the tach is looking for two pulses per revolution -- or 2ppt in Soliton-speak. If you can, try setting the pulse to 12 volts if you haven't already. Even though the speedo and tach work off the falling edge of a square pulse, I've noticed the speedometer "seems" to be more accurate with a pulse that starts at 12 and drops to zero, though that could be my imagination. If that doesn't work, and you want to dial in the RPMs with accuracy, the speedometer calibrator project linked below would work equally well with the tach (though you'd want to change the input conditioning a little).
Well now there's something you don't see everyday! Very impressive effort there! How does it feel on the road?
With a 4 cylinders, 4-stroke motor, the tach is looking for two pulses per revolution -- or 2ppt in Soliton-speak. If you can, try setting the pulse to 12 volts if you haven't already. Even though the speedo and tach work off the falling edge of a square pulse, I've noticed the speedometer "seems" to be more accurate with a pulse that starts at 12 and drops to zero, though that could be my imagination. If that doesn't work, and you want to dial in the RPMs with accuracy, the speedometer calibrator project linked below would work equally well with the tach (though you'd want to change the input conditioning a little).
It drives pretty good, just got it on the road a couple weeks ago, so still working out the kinks. One major project I know I need to tackle is upgrading the rear suspension. It's sagging pretty bad, 24.5" from ground to highest point on fender...front is 25.5" and has 1" lowering springs installed! I don't know much about torsion bars though.
Thanks for the link to the speedometer calibration, think I might need to do that too. If you notice in the video I posted, my speedometer needle rests way below 0, so it is way off, like 15 mph below where it's supposed to be. I need to take it out and see its its constantly off or a percentage.
You well know the problem for energy. Lead acid is 2+ the weight of Lion.
How much weight do you have in batteries?
The easy solution for the rear is to install coil over shocks to have an adjustable way to level the car.
I am guessing 25-30 mile range, between charges. I was considering a small Honda genset ~1KW for off site recharge, with 1-2 gal of gas. If you are not in a hurry.
The good news is there are charging stations in public places today.
I'm using Lithium Ion batteries, 60 of the CALB CA series 100AH cells. In the trunk I've got 48 cells at 7.5lbs each, so 360lbs total. Plus the charger at 14lbs brings my total to 374lbs in the trunk. I did remove the gas tank, spare tire and jack, so that should offset it some.
I'm hoping to get around 60 miles per charge using 80% of the battery capacity. 60 cells x 3.2V x 100AH (cells are actually 115AH+) gives me a 19.2kW pack. If my car comes in close to 250 watts/mile (probably ambitious) that's 76.8 miles using all 100AH, or 61.44 milesusing only 80AH.
I didn't realize you could add coilovers to the rear, thought it was just torsion bars...I'll have to look into that!
02-23-2015, 05:59 PM
Tachometer Signal
. What I'm trying to do is drive the tachometer from my electric motor. I think I can create a pulsing ground, just needed to know where to connect it. 
