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Join Date: Dec 2009
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Tach has tanked

Greetings All!
This is my first post, would like any help with my puzzle. After changing plugs, cap and rotor I hooked up timing light, fired her up, tach had failed. I've since replaced coil, delay relay, had (Bosch) DC box checked, it's OK. Wiring on tach gauge in place. Tach has tanked. For any and all help, thanks! been stumped for days. Thanks for your attention.
'87 930 stock.
Old 12-29-2009, 02:29 PM
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Check on the left hand side of the engine bay near the CDI box. There's a round connector with a black wire/purple tracer that may have come loose or disconnected.

Old 12-29-2009, 04:22 PM
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A930Rocket

I went to garage and checked for black and or purple wire at connectors, not found, the only wire not red or red striped appears tonight to be dark green red striped. I will removed the IC and DCI box and check more throughly tomorrow in the light of day. Thanks for your help and reply.
Old 12-29-2009, 05:48 PM
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If you remove the 6 pin plastic plug in the bottom of the permatune CDI, then carefully pull back the rubber boot to see the wires you will see the skinny black and purple tach signal wire 930rocket is talking about.
I think it's on one corner of the plug.
It may go through that thin seperate section of the wire harness with a plug at the bottom of the picture.

Make sure all 6 spade terminals are locked into the plastic plug and they are all pushing onto the male spade terminals on the CDI box when you push the plug into place.
They are old and the locking pins on the side of the female spade termainals in the plug can be bent by now.
Old 12-29-2009, 06:10 PM
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JFairman
The second time tonight someone held up the light. won't wait until tomorrow
33 degrees F and going down. Thanks A930Rocket and JFairman headed for the garage.

Last edited by flashdash; 12-29-2009 at 10:38 PM..
Old 12-29-2009, 08:48 PM
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My TACH IS BACK checked wiring into CDI box all good. Checked again small plug on thin harness to DCI. MY TACH IS BACK!!!!!!! seems my plug can close and needle not inter receptacle that's the plug I use to set frequency valve, is that the wrong plug to set ( CO ) frequency valve dwell of 45-48 deg? Thanks help is a Balm!
Old 12-30-2009, 11:06 AM
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You check the frequency valve's dwell at the rubber socket that looks just like one of the round relay rubber sockets, but it is mounted sideways on the side of the rear relay console to the left of the CDI and to the left of the large rear window defroster relay.
Old 12-30-2009, 11:35 AM
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JFairman,

this is the socket that I understand is used to set idle speed bridging test jack from ports B to C. my question now is, how then is this socket used to set frequency valve? thanks in advance.

Last edited by flashdash; 12-30-2009 at 02:04 PM..
Old 12-30-2009, 01:49 PM
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You can't "set" the frequency valve, that is set with firmware or some analog program similar to that in the K-jetronic lambda ECU under the driver seat.

If the frequency or duty cycle reading is incorrect it means you have to replace the oxygen sensor to make it right.

You could replace the lambda ECU with a modern frequency valve controller but thats a whole different thing that 911st is experienced with.
Old 12-30-2009, 02:48 PM
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JFairman
Thanks for the positive steering. I will have the AFR's checked and corrected. Timing, idle check OK. Because of the Revs. and the grip I find on this forum, opened my r/deck and jumped in. The water's fine!
Old 12-30-2009, 09:58 PM
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