Carver 404-Engine Alarm Merc 7.4

[RReardon]

Hi All

The mechanic attached the diagnostic to the engine today and the error was a "knock sensor" being alarmed. As the mechanic explained this, he checked the engines out above 3000 rpm and didn't feel there were any performance deficiencies. He then mentioned that they replaced the sensor, ran the engines above 3000 rpm, and no alarm.

Sounds like a faulty "knock sensor" from what he was saying. Of course in retrospect, I wished I would have asked him what exactly a "knock sensor" is measuring. I am assuming it is measuring knock and vibration of the engine. Probably also asked what conditions cause an engine to knock.

I will find out Friday evening when we head up to beautiful Frankfort, MI if they nailed it.

Thanks again for all the great knowledge.

Rich

[bud37]

Heh there ,good stuff.......the knock sensor does measure engine knock and is designed to signal the edu to retard the timing until the knock goes away...near as I can tell they are running quite a bit of timing in these engines and need to control timing knock if maybe the gas is not up to snuff. The older carbed engines ran a lot less total....safe trip.........

[Viper]

That'll do it. Glad it worked out.

[tomschauer]

Cylinder knock or " detonation" can damage valves pistons etc. that's why the have the sensor. It sounds like you may have just had a bad sensor which is an easy fix.
other causes could be low octane fuel, you should always run at least 89 octane in these roller motors, 91 is better. Stay away from the 86, it will cost you much more in the long run. Water in fuel, bad or old fuel will also trigger the knock sensor and make you motor "stumble" if not alarm.