With 500 EFI's, both tachs have started to waver and float when engine speed is constant. Gaffrigs in a 1999 382 Formula.

Any ideas as to why? Ways to fix?

Thanks.

Mine did the same thing last yr. I was ready to buy a new tach. With the advise of a OSO member, I removed the wires on the back of the tach, cleaned them and reinstalled making sure they were tight. Fixed with absolute no more bounce or off wall readings. Maybe you could get as lucky.

Mine sank right to the bottom when they fell in

Sorry had to

On my old truck and boat when the tach starts bouncing when it should be steady it has been arcing under the dist cap or some plug wires touching something and grounding out. Not enough for the engine to run bad just enough to fool the tach. I have noticed that if the wires are the culprit the bounce will be more noticable during periods of high humidity such as in rain or fog.

Maybe its time for a tune up? If you do replace the wires make sure you route them in the same places so that they come into contact with as little as possible. On my boat the previous owner replaced the plug wires right before I bought the boat. It ran fine but I noticed the tach bounce a couple of months later. The guy just ran the plug wires in a hap-hazzard fashion with all of them touching each other. I seperated the wires and the tach bounce quit.

Ron

Remove the tachs. If you can get the "guts" out of the housing then do so. Take a Q-tip and put contact cleaner on the selector switch (for 4-6-8-outboard selection) then move it back and forth a bunch of times.

When done, dry the contacts off and spray CRC on the contacts and put the switch in the proper position. Won't hurt at this point to spray a little red battery terminal wax on the switch.

Put her back together and rock on.

IF you CAN't get the housing apart and get the guts out, then spray a little WD40 around the hole the selector sticks out of )or look for a drain hole closeby to spray it into). Then do the back and forth thing with the selector.

Of all the floating tachs I've seen, if you can get to the contacts for that selector, then you've got the problem licked.