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70Barracuda

Data Logging Knock Sensor Volts

Can anyone explain what one learns by logging knock sensor 1 and 2 volts.  I have noticed that these pids tend to be logged and that when I got a custom tune it was requested that they be logged.

 

When I looked at a recent log I made at the track for instance I see that min values for Sensor 1 and 2 were 239 and 229  while there max values during the log were 2695 for 1 and 4946 for 2.  So I'm just wondering what this tells me and/or what can be learned from this.

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What you're logging is mV, or millivolts. So your max values are divided by 1000 (2.6 and 4.9 volts)

 

Your tuner will cross that data with misfire events and total spark advance to determine if ST knock is indeed detonation or just engine/trans noise, or other noises causing false knock, such as bangs, clunks, and so on.

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What you're logging is mV, or millivolts. So your max values are divided by 1000 (2.6 and 4.9 volts)

 

Your tuner will cross that data with misfire events and total spark advance to determine if ST knock is indeed detonation or just engine/trans noise, or other noises causing false knock, such as bangs, clunks, and so on.

 

Ok that makes sense, but then my next question would be can I tell anything from the disparity between the two sensors?  In other words does the difference in readings mean that one bank is possibly getting knock readings while the other is not or at least not as much.  Which might indicate an outside source for the knock on that bank (picking up a noise of some kind), since I would think that knock readings caused by detonation should be found on both banks.  Or would I be reading too much into that data? 

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TF got it spot on.  Your second question can be either.  You can have instances, although I'd say rare, where an injector begins to fail and sprays less fuel than the others and you'll get knock in one cylinder or something a long those lines.  I've seen this twice. 

 

Unless it's occurring at a rate high enough to consistently see STKR I wouldn't be overly concerned.  When Mike was dialing in the timing on my car he got it where he was comfortable on 93 octane.  Then had me run the 93 tune with race gas to compare the race gas 109 octane log to the pump gas 93 octane log.  That told us if any knock was real or false and he then fine tuned the knock sensors according to the car's harmonics, engine noise, blower noise, etc to get it dialed in perfectly.  Mike has mine setup to just show a hint of STKR (.5 deg) here or there to let us know the knock sensors are doing their job and listening.  I've hit seams in the road that jar the car while doing data logs and the knock sensors spike and I get 2 or 3 deg of STKR immediately so I know they're working proper.

 

At the track I data log every pass and keep a close eye on the knock sensor mVs as a lot of the nannies are turned off on the race tune for 109 fuel.  Timing is ramped up for the fuel and the timing pulls at higher IATs and higher ECTs, etc.  If I see a pattern where both sensors are peaking above 4000 mVs, and this is usually at the top of the RPM range if it occurs, I'll dial back the timing in my race tune .5 to 1 degree to keep things safer for the conditions.  This is largely dependent on ambient temp and if I'm having to lap the car several times in a row, etc.

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Good info guys.  What started my research on this was my seeing STKR around 5 degrees (plus or minus a bit) on my data logs with Diablo's 91 and 93 tune.  I continued seeing this even when I added some race fuel, so I began to suspect that the knock was caused by some noise or rattle.  However, after I got an email tune (93 octane custom tune) my data log only shows one very short spike of 2 degrees STKR during a quartermile run at the track. Then I made a run with a straight Diablo 93 octane tune and was back to getting around 5 degrees STKR and even 1 degree LTKR.  This tends to lead me to believe that all the STKR I was getting with the straight canned tunes were not probably caused just by something rattling around otherwise my email tune wouldn't have basically eliminated the STKR. 

 

After reading your explanation I'm thinking that the custom tune has probably eliminated the problem and that the one short spike may have been caused by some brief noise or rattle as the rest of the run appeared trouble free.  In the past I had good luck advancing my timing with my R/T but because of all the STKR I've been seeing on my 392 SRT I haven't felt that I've really gotten any benefit by doing so.  Now with a custom tune eliminating STKR I'm thinking I should be able to advance the timing a few degrees and maybe pick up a bit more in the quarter.

 

Question:  I believe I read somewhere that the degrees of STKR is the amount of timing being pulled, in other words if you see 5 degrees STKR the computer is pulling that much timing.  Is my understanding of that correct or am I off base?  And if you see LTKR it is the computer basically pulling a degree on a long term basis?

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Couple things.  The custom tune "may" have the knock sensors de-sensitized such that the STKR does not occur.  On supercharged cars desensitizing the knock sensors a bit is a common practice.  Not sure how often that has to be done on a NA car.

 

You are correct.  If you see 5° of STKR then 5° of timing is being pulled at that moment.  LTKR means the base timing table has had a degree removed from it at that particular point in time as the PCM has seen enough STKR in that area over time that it's predicting it happening again without actually seeing it occur. 

 

If you were seeing 5° of STKR with race fuel in a NA car on a 93 canned tune I would almost guarantee something was banging around under the car or the knock sensor covers were loose.

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If you were seeing 5° of STKR with race fuel in a NA car on a 93 canned tune I would almost guarantee something was banging around under the car or the knock sensor covers were loose.

 

Guess I need to investigate further then, I continued to have STKR even when mixing a 50/50 split with 104 octane with 93 pump gas and on another occasion I ran almost straight 98 Sunoco unleaded (ethanol free) and got knock.

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