1997 5.7 LX knock sensor

[AKJohne]

Recently rebuilt the heads due to a tuliped intake valve, all back together and was verifying the knock sensor was functioning. Used a timing light and had the motor warm and running at ~ 1800 RPMS on the muffs. One guy watching the light and tapped on the block, sure enough you could see it retard the spark and noticed a RPM drop. Waited a minute or so for it to return to normal RPM and it did not, once I dropped the throttle back to idle and repeated above same thing.

My question how long does the system keep the timing retarded? Or does one have to return to idle?

 

[achris]

..My question how long does the system keep the timing retarded? Or does one have to return to idle?

I've never thought of the question, and I don't think you'll find an answer. That information will be buried deep inside the coding in the ignition module. The only people who could tell you are the Merc engineers who wrote the code, and I strongly suspect it'll be 'proprietary information' that you 'don't need to know'...

 

[AKJohne]

I've never thought of the question, and I don't think you'll find an answer. That information will be buried deep inside the coding in the ignition module. The only people who could tell you are the Merc engineers who wrote the code, and I strongly suspect it'll be 'proprietary information' that you 'don't need to know'...

Thanks Chris,
I suspected there was no simple easy answer, I was hoping someone on here had already done this. Next time I have the boat in the water and have the right conditions I will duplicate my experiment. My friend that helped today used his scope to capture the voltage drop when we tapped the sensor (motor off). .16 millisecond's was the length of time the voltage dropped form 8.44 to 7.3, you would never see it without the right tool and someone that knows how to use it.
Because of my failed intake valve I wanted to know this system worked.
I have had several local shops diss the TBV ignition system, one told me they never advance enough to see good performance, the other said the knock sensor system doesn't work. These guys are supposed to be "pros", they are sharp and have been helpful, however I suspect they never really bothered to understand the system and would just plug in a aftermarket ignition and set it a 34 degrees BTDC.
I have since come under the impression its a great system, until you have to buy parts, or replace the cap due to how quickly they corrode up, makes me want to plug the cap vent, but am sure that is there for a reason...

Hopefully I will have answer before winter, which comes early around here.

 

[achris]

IIRC, you're in Alaska, yes?

 

[AKJohne]

IIRC, you're in Alaska, yes?

Yes sir

 

[Scott06]

Thanks Chris,
I suspected there was no simple easy answer, I was hoping someone on here had already done this. Next time I have the boat in the water and have the right conditions I will duplicate my experiment. My friend that helped today used his scope to capture the voltage drop when we tapped the sensor (motor off). .16 millisecond's was the length of time the voltage dropped form 8.44 to 7.3, you would never see it without the right tool and someone that knows how to use it.
Because of my failed intake valve I wanted to know this system worked.
I have had several local shops diss the TBV ignition system, one told me they never advance enough to see good performance, the other said the knock sensor system doesn't work. These guys are supposed to be "pros", they are sharp and have been helpful, however I suspect they never really bothered to understand the system and would just plug in a aftermarket ignition and set it a 34 degrees BTDC.
I have since come under the impression its a great system, until you have to buy parts, or replace the cap due to how quickly they corrode up, makes me want to plug the cap vent, but am sure that is there for a reason...

Hopefully I will have answer before winter, which comes early around here.

Yes the TBV gets a bad wrap due to the cost of the ignition module. When I repowered from a 4.3 to 5.0 i bought 2 used modules on ebay and sold the 4.3 one for like $200 each. I put a search in on the module when they pop up for a decent price I bought a spare