i have a SAFC and PLX R-500......first i had the SAFC hooked up to pin78 (white wire) add it never displayed anything but 0.....now i have my R-500 hooked up to pin 78 and all it reads is 0....is there something wrong with my knock sensor? if there is wouldn't my ecu throw a code?

please help

 

Very well could be. But are you checking the high points on the AFC and PLX meter? Basically they have a high point stamp becuase they happen so fast that you wouldn't see it just by viewing it most of the time. I should read more than zero though.

 

I thought I heard the knock counts on the S-AFC were worthless anyways. I hope I am wrong.

 

I think i saw the same thing. Maybe DB posted it.

 

can someone explain in detail what kind of readings (voltages) are we getting when the knock occurs ?

 

SAFC Knock Counts aren't totally worthless. The problem is that the counts you see can be engine noise as well. It is a reading from your knock sensor so please take that into consideration becuase if you see some knock above a certian level your ECU is seeing this as well and the stock ecu will use those counts, if those counts are above the ECU's threshold it will pull timing. What happens alot is that the knock sensor readout isn't setup correctly on the SAFC and then you get incorrect readings.

The knock sensor is a 5 volt sensor. 0v min and 5v max. When knock occurs you will ususaly get a spike in the normal voltage or noise trend. Most of the time this spike will be probably 1v over the normal noise trend to be true detonation. You can get these spikes even before you can hear it. To grab this correct you need a system that samples the knock sensor during spark ignition this way you filter out the other background noise. You also need somthing to sample at a very high rate to catch all 4 cylinders (250 samples per second). This is how it is managed using the AEM EMS. The PLX probably has a high reading storage like the SAFC so you can see the max value, this I don't know for sure, but if it does it would be worth it to atleast have some sort of indication.

Somthing is always better than nothing.

 

Wouldnt you want to sample just before the ignition spark? Basically just the last part of the compression stroke should be captured, right?

 

have you try tapping the engine with a wrench to see if you get any reading.

 

No, knock occurs after the spark. At high RPM there's around a 20-30 crank-degree window when knock is a problem. If you have true pre-ignition your engine is probably destroyed already.

Dave H.

 

i know the SAFC knock sensor was not that good and that is why i didn't pay attention to it reading 0.......... but the PLX R-500 ( http://www.plxdevices.com/R-500_productinfo.htm ) has a real knock sensor

"The R-500 is capable of displaying raw knock volts or normalized knock volts giving you a very power tool for maximizing your timing."

 

bump......... anyone else have any ideas? how much is it for a new knock sensor?

 

Mike,

Have you double check the connection to pin 78 and the connection to the knock sensor? I just talked to the PLX engineer and he asked you to plug in a headphone to the stereo jack to listen for any knocks. Please let me know.

Thanks,
Tom
Gruppes
510-783-5300

 

thanks Tom i will try that tonight.........i tryed tapping the engine with a wrench and that didn't work

 

Also, make sure you connect the pink wire to pin 78...not the yellow (output).

Thanks,
Tom
Gruppes
510-783-5300

 

I'm interested in learning these knock issues. Since I installed my HKS 264/272 cams, I've been seeing knock counts up to 40-50. This only happens on warm to hot days. The hotter the day the more knock counts I see on my SAFCII. I see knock counts up to 30-40 on idle at a stop light on a hot day. Now in the morning or cool days/temperature, I get no knock at all. Before the cams, I'd be lucky if I see 10 counts of knock. Can anyone explain this?