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Where are you attaching the tach? Posted by Ari [Email] ![]() ![]() In Reply to: 8k tach, Green9kAERO, Tue, 18 Apr 2006 10:09:43 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Depending on where you get the signal for the new tach, you may be 'pulling down' the ignition pulse signal. At a minimum, it should be on the original tachometer side of the ignition amplifier, not on the distributor side.
What do you know about this tach? Every electrical device pulls some current from the thing it is sensing. It may be a little, or it may be more than a little. The stock ignition system is designed to provide pulses to the stock tach, and to the ECU, and was sized for that current load. If this tach was designed to work with an ignition that used points, for example, it may put too big a load on the ignition amplifier, and it can't produce pulses with a high enough voltage for the stock ECU to read. So the ECU doesn't know the engine is running, and shuts off the fuel pump. Even if the aftermarket tach was desgined for an electronic ignition system, it still may be too much, when combined with the stock tach AND the ECU for the ignition amp to drive.
Or, the tach is faulty and shorting out the signal.
Last question - why a 8K tach? Saab engines are great, by the four-stroke engines aren't known for high revving. Heck, I can't get my 2-stroke Sonnett much over 7K. Even if you really mod the engine, you'll still only be using a small portion of the tach.
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