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Tachometer going crazy

G

gorros

New member
"I have a boat equipped with t

"I have a boat equipped with two 4.3 MPI. The tachometer on one engine is jumping all around the place 300-4000 RPM without any change in actual engine speed. Also, that engine seem to get too much gas (smoke quite bad at idle speed).
No specific reading (using a smartcraft reading tool) is showing.
Any sugestion?
I hope anyone have an idea"
 
"The tach most likely needs re

"The tach most likely needs replaced. But, first disconnect it (gray wire) at the neg. side of the coil to see if your engine runs better. If it improves then replace the tach."
 
"I'm not too experienced w

"I'm not too experienced with engines, and I dont really understand how the tachometer itself could affect the engine performance. Isn't the tacometer just receiving a signal, and if the tachometer is broken it doesnt show it properly, or is there some kind of response that the engine use?"
 
"All that I know is a tachomet

"All that I know is a tachometer receives a pulse signal from the neg. side of the coil and the tach's circuitry converts the signal into a continuous voltage that moves the needle. If the tach's circuitry fouls up, it can kill the ignition signal to the coil."
 
if the tachometer has an elect

if the tachometer has an electrical short and can short out the coil.
 
"Well, disconnected the tachom

"Well, disconnected the tachometer, but problem still remain. Smoke a lot (seem to get way too much gas)."
 
Put in another tach for the ta

Put in another tach for the tach problem. One or more of the fuel injectors may have dirty spray nozzles and are squirting fuel into the cylinders and the fuel is not atomizing for a clean burn. Pull the spark plugs and note which ones are blackened; they are the cylinders w/the problem injectors.

The injectors may just require "hot" cleaning whereby a technician attaches a canister of cleaner/gas mixture to the fuel rails and runs the engine to clean them.
 
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