Crusader 8.1L with erratic VDO Tachometers

[AyeCandy]

Does anyone have any experience in diagnosing erratic tachometer readings (jumping needle when idling or at speed)? The problem is intermittant. I have checked ground wires and connections going to the tachs but have found no connections issues. Sometimes 1 tach is fine and the other is jumping all over and sometimes both tachs are jumping around at the same time. Other times when the engines are started, both tachs are accurate. My Fox Marine Gateway indicates both engines are synced and running at constant RPMs. Both tachs were sent to Lauderdale Tachometer a few years ago and they could not find any problem with them (VDO). It acts like there is electrical interference or a connection issue as to the cause. Any suggestions?

 

[makomark]

Some of the MEFI-4 ECUs have had issues with the tach driver circuit in the past...most usually fail yielding no signal to the tach.

for the stock setup, you can clean and reseat the connectors (pins/sockets) for the tach circuit to see if it helps. Sometimes a dedicated ground wire, fromt he tach back to the engine helps. Always a good idea to verify the tachs work using a stand alone tach tester if available...(they are just pulse generators with fixed functionality). You can also measure the TACH signal from the ECU to see what is provided...A last resort is to send the ECU to a repair shop.

Some just use the digital displays and save the expense of trying to salvage the stock setup....I know of two operators that opt'ed for a mod to 'bypass' the tach driver inside the ECU...