gst

yes, i have searched. Could anyone tell me where the tacho signal wire is? I am connecting a shift light module to my car and need to tab onto that wire. i presume that the signal wire would first go into the DME which will then send signals to the VDO gauge. Should I tab onto that wire before or after the DME? what is the color of that wire?

Thanks in advance for your help.

rattlsnak

What year 993? Difference depending on if its OBDII or not.

gst

my 993 is OBD1, with the round diagnostic port

gst

anybody can assist?

Toga

I hope somebody will! I'll need that signal too, to install correctly my becker navpro.

Lorenfb

On the early 993 with the 55 pin DME, the tach output is pin 6 of the DME.
It's also pin 14 of the diagnostic connector.

TheOtherEric

Interesting. I didn't know you could tap into the diagnostic connector.

For my 1995, I tapped into an RPM signal wire where the thick pack of wires connects to the ECU under the drivers seat. Like Loren said, it's pin 6, which doesn't mean anything to me, except that looking at the electrical schematics in the shop manual, you'll find that pin 6 is Black/Violet. So tap that one. I suppose that this signal will be pulse-width modulated (frequency modulated) since I think it comes straight from the sensor which reads off a gear. The gear has either 58 or 60 teeth; hard to understand the shop manual's description (60 teeth with 2 missing for a reference signal). Your volt meter won't give you anything meaningful if you try to check it since it can't measure frequencies. But I think it's like a 5V signal.

And if you're hooking up a DA system, you should tap the throttle position sensor while you're at it. It's pin 53, which is White/Green. I verified this with a volt meter but I'm not sure of the numbers (0.5 to 4.5 volts, I think).

Both of these taps seemed to work fine when I hooked up my DA system. Somebody had posted these wire colors last year https://rennlist.com/forums/993-forum/140726-wiring-a-data-logger-for-throttle-angle-and-rpm-inputs.html
but the wire colors were not correct for a 1995 (not sure about '96).

Lorenfb

"I suppose that this signal will be pulse-width modulated (frequency modulated) since I think it comes straight from the sensor which reads off a gear."

Actually, the signal is developed internally to DME. It's freq is proportional to
the spark rate, i.e. one pulse per spark.

TheOtherEric

Hmmm. Thanks. Does that explain why my DL1 was showing a 40 Hz signal at idle? I would have expected either 800 Hz (actual engine speed) or perhaps much higher due to the gear teeth, so I was surprised at the 40 Hz signal. When I gassed it up to about 1600 rpm, the signal went to 80 Hz, so that was at least a good thing.

Lorenfb

The following calculations example all:

1. @ 6000 RPMs a six produces a spark every 3.3ms (.0033 seconds)
2. @ 1000 RPMs the period is 20ms or the rate is 50Hz
3. @ 800 RPMs the rate is 800/1000 X 50 = 40 Hz

TheOtherEric

Thanks for the follow up. I have no idea if we're actually helping gst or not, but I'm sure that anyone who tries hooking up a data logger in a 993 will find it useful.

gst

i will be locating the blue/violet wire this weekend for my purpose. 1 further question though, you guys mentioned about the throttle position signal wire, if i am not mistaken, that wire would have nothing to do with the tach signal?

I have considered the DIY in p-car website also. under the OBC retrofit, it appears that there are a few tach signal leads. Is it better to tap into the line going into the DME, ie. pin 6, carrying the "raw" signal??

Help is always around the corner, thanks so much guys

Felix

I'm interested in using a DL1 to read engine temp and intake air temp. From what I can see from the wiring diagrams these sensors provide a variable resistance to ground. I assume the ECU uses a pull-up resistor or something similar to convert this to a voltage which it then uses as an input parameter.

Any ideas how I can use the same sensor to provide a suitable input to the DL1 without confusing the ECU or, worse yet, damaging it?

Lorenfb

"Any ideas how I can use the same sensor to provide a suitable input to the DL1 without confusing the ECU or, worse yet, damaging it?"

Just "read" the voltages with a device that has about 10X the input resistance as the sensors.