Tach issues with a 1986 Turbo

[Rroberts]

IMG_0936.jpeg (3.25 MiB) Viewed 429 times

IMG_0936.jpeg (3.25 MiB) Viewed 429 times

I have recently installed a rebuilt engine in my 1986 944 Turbo and am struggling with the tach.

Initially I did not have the red 4 pin connector connected but saw the post by Shift22. Once I connected this, the boost gauge started working, but the tach was still dead. The rest of the gauges appear to be working fine. I saw the You Tube video by Tom showing how to test your tach with a 9 volt battery and it did bounce as his did in the video. There is voltage at the Green/Black wire coming from the KLR. I did check the resistance between the third pin from the top where the “B” plug connects to the back of the cluster and the tach post at 9:00 on the back of the cluster and it shows a good connection. Any suggestions on where to look next?

Really excited to get this back on the road and any assistance would be greatly appreciated.

Thanks, Randy

[Tom]

Remove the 35-pin connector from the DME and check for continuity between pin 21 in that connector and pin 3 of the cluster's B connector in the cluster. Pin 21 is the ignition pulse, which is carried from the DME to the cluster on the green/black wire. If that signal is not getting to the cluster, check the red square connector and make sure the green/black wire is connected on the engine and cluster sides of that connector. If all that checks out and the tach is still not working, let us know and we can go from there. Since the 9v battery trick worked, it's just a matter of getting power, ground and the pulse to the tach...

[Rroberts]

Thanks Tom for replying so quickly.

I checked and I do have continuity between Pin 21 on the DME harness and Pin 3 on the B gauge cluster connector. The tach should be receiving the signal, How do I verify the ground and power to the tach? I did clean the grounds on the gauge cluster itself along with the two sets of grounds under the drivers side of the dash when I first realized the gauges were not functioning correctly.

Thanks again, Randy.

[Tom]

Thanks Tom for replying so quickly.

I checked and I do have continuity between Pin 21 on the DME harness and Pin 3 on the B gauge cluster connector. The tach should be receiving the signal, How do I verify the ground and power to the tach? I did clean the grounds on the gauge cluster itself along with the two sets of grounds under the drivers side of the dash when I first realized the gauges were not functioning correctly.

Thanks again, Randy.

See picture below. With the cluster plugged in and ignition on, you should see battery voltage at the 2 o-clock post, and you should have continuity to ground on the 12 o'clock post. If you have power and ground on those posts, and the tach bounces around when you tap the 10 o'clock post to ground (as in the 9v battery test), then the tach should work.

It's hard to get behind the cluster when it's all plugged in. You may need to unplug the cluster, attach wires --green , black and red so you know which is which-- to the three posts, and then reinstall the cluster and test the signals on those test wires. Just be very careful with the 12v wire -- if you accidently short it to ground, you'll be changing fuses or worse...

tach-pin-outs.jpg (212.78 KiB) Viewed 404 times

[Rroberts]

Thanks again, Tom

I have the 3 wires attached and will install the cluster again tomorrow. Will be careful with the 12V positive lead and let you know what we find.

Randy

[Rroberts]

Good afternoon, Tom

Wanted to let you know everything is back together and working. Really appreciate your help and really enjoy this forum. Have learned so much by going through the posts and really excited to get the car back on the road.

Thanks, Randy

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[Tom]

Good afternoon, Tom

Wanted to let you know everything is back together and working. Really appreciate your help and really enjoy this forum. Have learned so much by going through the posts and really excited to get the car back on the road.

Thanks, Randyimage.jpg

Awesome -- so what was the issue?

I'm wildly biased, but for 944 tech, I'd argue you can't beat Carpokes right now. Pelican is dying down, RL is less active and lost its once-great way, and Facebook is like trying to get car advice from the Time Square crowd on New Years Eve... I've said this before, but the best way to say thanks is to tell other like-minded Porsche fans about Carpokes!

[Rroberts]

Good evening,

I wish I could tell you why it is working now, but I don't know. I bet I had the cluster out at least 5 times trying to check everything, but the last time I put it in the tach started working. The only changes I made the last time it was out were the three test wires that I added and I had disconnected and re-connected the harness on the DME. I am leaving the three test leads going to the tach, just in case is stops working again. It will be much easier to diagnose then.

Don't worry, I am telling all my friends about Carpokes!