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Engine acting strange....tachs not even....

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firepiper

Contributing Member
Don't even know how to explain, Boat has been running great all summer. Last week I noticed the stbd engine having to be given more throttle to stay in synch w port. Set port to 1000 rpm and bring stbd to synch, and it is at 1300 rpm. Cruising speed is even worse. Port @ 2700, stbd @ 3100. So, I checked cap/rotor/wires, timing, did compression check and changed plugs,(all looked fine, and numbers were same as last check, around 150#). Dove under boat and checked hull, clean, shafts/props all fine. Trans fluid good. Fuel h2o separator clean, no h2o. Engines both start fine and idle nice and even. Checked fuel pressure, fine at 42 psi at 3000. What am I missing? Thanks:confused:
 
Interesting. Having similar but diffeent problem with mine: Synchronizer says "PORT SLOW" yet my ear says it's dead on. RPMs via the tachs are the same. If I synch them "correctly" via the synchronizer, my ear says they're a WAY off. Been trying to figure this puzzle out for years!

In your case--assuming your ear says the motors are turning the same rpm--then it's gotta be a bad tach.

Jeff

PS: If anyone has a suggestion for MY problem, I'd appreciate it.
 
erich's suggestion is step one. If problem remains with the engine, check each plug wire - not visually, but electrically. I'd suspect one or more has an internal break.

Jeff - the sync module/amplifiers can be finicky beasts. Pull one tach input and connect it with the other - should be Synced. have also seen a couple where the reading would be off due to a bad ground in one side of the instrument panel wiring - DVM to check for voltage difference between the 'grounds' for each engine at the instrument panel. Last resort is send the module back to the factory...Most are in excess of $100 and they have less than $10 of parts inside - a dual F-V converter, a difference amp, and a display driver...go figure
 
Thank you all.....took advice from a post on another forum. I was told to rap on the tack to see if it is a loose or sticky connection. Sure enough, a good tap with my hand, and tadaa! Thanks again
 
firepiper said:
Thank you all.....took advice from a post on another forum. I was told to rap on the tack to see if it is a loose or sticky connection. Sure enough, a good tap with my hand, and tadaa! Thanks again
Click to expand...

If the problem reappears, there is another "trick" you can try. A lot of the Faria tachs have a switch on the back for selecting 4, 6, or 8 cylinders. Change the setting back and forth through all the settings a few times and then leave it on the proper setting. This may clean the internal contacts and correct the erroneous readings.
 
Treat the patient, not the monitor. In other words don't be misled by all our fancy electronic gadgets, but rely instead on what your own senses tell you is happening. If the gauge reading just doesn't make sense relative to what you are seeing, hearing and feeling, suspect the gauge first.
 
I have never trusted my sync gauge. I use my tachs, hearing, and throttle position. But will try some of these tricks to get it working right.
 
..."I have never trusted my sync gauge."

I used to, but the fool thing has started lying to me (for two years now). My ear says "port slow" by the synch is actually is dead on.

Here's a neat way to get 'em really close: Make a slight turn, one way, then the other. The engine on the inside of the turn will slow a smidgen, where the outside engine will pick up (due to loading). Makes for a very fine rpm 'adjustment' and tells you which throttle to bump after you resume astraight course. It's also a fun thing to do when running a straight (boring) course.

Jeff
 
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