Cloud9...68

Hello,

I apologize in advance if this is a stupid question, or if it's been covered in another thread, but I'm very new at this, and want to make sure I understand correctly what I need to do. I finally decided to go with an Aim EVO4S/GS Dash/SmartyCam HD system for my track-focused 1992 Porsche 968, and have been chipping away at the installation over the past few months, in between getting the car driveable again (long story). The most challenging aspect was connecting my home-made steering angle sensor, which required removal of my intake manifold to gain sufficient access to the steering shaft, but I've finally gotten it connected.

I thought I was in the home stretch, but then realized I still need to get the rpm signal to the EVO4S. I assume I have to tap into the DME's wiring to achieve this, so I checked the DME pin diagram in the manual, and Pin 6 labeled as "speed signal at rev counter." But in the description of how to troubleshoot a fault code, it says to place the leads of an oscilloscope to pins 49 and 48 of the disconnected DME control plug. Could somebody confirm which pin or pins to use? The patch cable that came with the Aim package has three wires, labeled "RPM 150-450V" (I assume they mean 1.5 - 4.5V), "OUTDIGIT1"(which matches the description of pin #5 of the RPM connector in the EVO4S pinout diagram), and ground.

Also, as I recall, the connector to the DME uses a large ribbon cable, as opposed (not surprisingly) to individual wires. How exactly would I go about physically tapping into a wire that is inside a ribbon cable? Or am I interpreting this whole thing incorrectly? Thanks.

ProCoach

The square wave, 12V on-off tachometer signal to the dash cluster is what you want. That pin 6 sounds familiar (have done this on other 968's some time ago) and the correct lead in the RPM harness is the only RPM input on the EVO4S, 150V-450V RPM.

The 150V-450V nomenclature is to indicate that you could connect it to the low side of the coil, but that's a last resort!

Make sure you tell the EVO4S configuration that you're connecting to a 4-cylinder car by selecting the RPM multiplier /2

The output signal is a trigger for a variety of externally driven accessories ranging from shift lights to cooling fans and pumps (with the requisite relay to limit draw) depending on what you're measuring (what sensors you have) or any channel you select.

Good luck and have fun! The EVO4S is a great unit and very flexible, powerful and more than sufficient for almost everyone.

Cloud9...68

Thanks, Peter. So from your recollection, I'd have to tap into the wire going to Pin 6, which the shop manual refers to as "speed signal at rev counter". So I would connect the gray wire labeled "RPM 150-450V" to the wire coming out of Pin 6, the black ground wire to ground, and leave the blue "OUTDIGIT1" wire unconnected?

If that's all correct, it takes care of the "what", but I could still use some guidance on the "how" - as in, how do I tap into a wire that's contained within a ribbon cable? Should I try to find the wire at the dash cluster? If so, any tips on how to identify it? Although, I have my EVO4S mounted literally two feet from the DME, so it would be nice if I could do my tapping at the DME, vs. wrestling with the under-dash wiring. Thanks.

ProCoach

Yep, this is correct.

No recent experience on connecting to the DME, although I would look at the cluster end.

linzman

I had a shift light that was wired to the coil. I got rid of the shift light and used that wire when I did mine. Works well. Peter is right, don't forget to set for 4 cyl or your RPMs will read be double.

Matt Romanowski

It's been a while since I've been behind a 968 dash. I'd look to the back of the tach for the feed there. I won't be able to get to my wiring diagrams until later next week.

Cloud9...68

Well, not having much luck. I took off the DME connector, and its wires don't go into a ribbon connector as I had remembered, just into a large bundle of individual wires. Unfortunately and astoundingly, none of the wiring diagrams in the manual have a diagram of the DME! So, I have no idea which of the 48 wires coming out of the DME connector goes to pin 6.

As far as the instrument cluster, that is an option, and I have removed it, but I remember it being a pretty difficult and delicate operation, and one not without risk. So, my best option may be the coil. Am I the only one who has ever struggled with this? I'm sure most Porsches of a similar vintage to mine are wired similarly. How did you guys get the rpm signal from your cars to your DA units? I'll also post this question on the 968 and 944 forums. Thanks.

linzman

You can also access the tach wire from under the dashboard without taking out the whole instrument panel, but in my caged track car, and me being 6'8", the thought of lying upside down on my race seat (never mind having to climb back out from that position ) to find the wire was much less appealing than using the wire off the coil.

Cloud9...68

I hear you. I'm a long way from 6'8", but I got under the dash this afternoon, and have no idea which wire I would have to tap into, and even if I did, I'm not sure how I would get the necessary tools onto it - it's a very tight and uncomfortable squeeze under there! Sigh... may have to go the coil route. I'm glad it worked well for you - hopefully it will for me as well. Is the connection as simple as connecting the patch cable's gray RPM wire to the "+" terminal on the coil, and the black ground wire to the "-" terminal, or should this wire be connected to a chassis ground? And I assume the OUTDIGIT1 wire still remains unconnected, correct? Thanks.

linzman

I have an Evo 4, not the new S, but here is only a single wire coming from the coil. Don't have access to the car now, but if I recall correctly, none of the other wires were connected to anything, just the one labeled RPM

ProCoach

NO!

The RPM lead goes to the "-" terminal, the signal terminal. The ground lead from the harness goes to chassis ground. The OUTDIGIT1 wire remains unconnected. The "+" on the coil is merely battery voltage whenever the switch is on. No signal present there.

I would MUCH rather see you go to the DME tach signal, but that's me.

Cloud9...68

Peter,

Thanks for the clarification. If I could get my eyes on a wiring diagram for the DME, I'd gladly tap into the wire coming from Pin 6, if for no other reason than that the DME is SO CLOSE to where I've mounted by EVO4S, which means not having to fish yet another wire through the already-very-crowded wiring harness boot at the firewall. I've posted the request for a DME wiring diagram on several forums, but no luck yet, but it is Sunday evening of a holiday weekend. Access at the tach is awful, so at this point, that's my least favorite option, but that could change with a clever tip from someone who has done this before.

Linzman,

I see you have a 968. Do you race it, or just use it for track days like me?