I realize that the KNOCK sensor on the PFC means nothing to some people. I watch it when I'm tuning as it will certainly go up if I get near "bad things happening to my engine".

Anyways, my KNOCK reading is usally 0 - 5 at idle and almost always below 50 under WOT.

Tonight after I hard pull, I looked down and saw my KNOCK bar extending across the entire PFC screen!!! I did a quick check on MAX KNOCK, and it read 170!!! I cleared the max's and while cruising in 5th about 3k rpms (80mph) KNOCK was contantly between 140 - 160! When I gave a little gas (not WOT, just maybe 1/4 throttle) KNOCK was back up to 170!

I pulled off the side of the road, let the car cool down a bit, then started it back up. Was getting KNOCK readings in the 40's at idle...I was like aaaa...****, I must have done something bad.

I went and ate dinner, then started the car back up to drive home...KNOCK is back down to normal levels! I tried a short pull and hit max knock of 66. Higher than usual for my car, but nothing that worries me.

Think my knock sensor could have been possessed for a little bit, maybe it's loose or something was rattling around in my engine bay?!?

Anyone else have anything like this happen to them before?

k

 

what are your a/f ratios?

 

ARF's are fine, just finished tuning a few nights ago with a WB. low 11's.

k

 

We need to check to see if the sensor has LOOSEn itself. That could be causing it. As well as a degradation of the wiring. I should have though of this when you had you car up in the air tonight. I was a little pre-occupied...I guess.

 

Hey Kyle, let me just say the exact same thing happened to me this weekend. I was racing one of those new cobras and after I smoked it I looked down at my commander to see that it said a knock value of 155! I about crapped. I took it easy on her and under light throttle the knock value bar was across the screen. I convinced myself and the wife that 5000 more dollars for a new engine wasn't that bad. But the next day it fired right up and ran normal. I think it could be the knock sensor is loose, or maybe one of my plugs is bad. I don't know. Keep us informed of what you find. PS how much is a new race engine,...just in case

 

Mine has been fine since that day. Vaccuum is good, knock readings have been normal...car pulls hard...idle is normal...very weird. I changed plugs and noticed two small chips out of one of the plugs which *could* have caused the knock sensor to be unhappy. ?!?

k

 

saturday night cruising with a pack of wrx's and other talons i pulled second gear kind of hard and then i look at the commander when i pulled over about 1 minute to stop atnd talk my pfc said 163 too...very weird

 

My knock readings go high sometimes also, but I found the cause even before using the DATALOGIT.

Drive train noise when shifting.

 

I see a single high knock value sometimes a couple when shifting. My experience described about was a continous knock reading in the 140 - 160 range during light acceleration and a knock reading of 40 at idle when it is usually 1 - 3.

k

 

I don't know what it is with knock values,but my car is
reading very high #'s also.At full throttle in 2nd or 3rd
it will have readings as high as 189.Does this mean I'm
burning too lean.If so what do I need to do?

 

Thats exactly what I was thinking. I always see my peaks of 80-90 when i shift. Under WOT they are usually <30.

 

Chuck,

What do you think missing 3rd would do to the knock sensor reading?

 

I was having knock values of 62-64 until I pulled the PFC out and cut the 4 wires of the ECU harness as in the instructions. Now my knock values under WOT are 50-53. Does anyone think this is odd??

 

Guess that depends on how are you *ground* it.

K

 

Shifting doesn't do much of a blip to logged knock sensor readings. Missing 3rd doesn't do much to it either. Too bad I didn't have an "in car" camera. It would have recorded me BANGING 3rd in...then banging the top of the gear shift lever. Never use anything other than REDLINE ever again!!!

 

What about a bad tank of gas? When did you fill up last? Just an idea.

Tim

 

Maybe a dumb question but what does each mark stand for when looking at the PFC? The screen cuts it into parts could figure what the intervals were.

 

which screen are you looking at?

 

its the screen that maps it out.

It has the bar that goes from left to right.

Monitor to 1 channel to knock.

 

i don't know what each of them is but if you hit the left key then it will hold the current reading and will give you a numerical value, then press the left key again to release.

 

Here is a lame idea. If your leading and trailing plug wires or coil harness were switched, this would cause high knock levels as the trailing plug/s would fire first.

Have you done any such work lately

 

Consistent negative split would have had a more obvious result: popped engine.

But I wonder what would happen if say a plug wire was loose? Pulling away from the plug? A not-so consistent resistance? Higher RPM it might become more evident. Then disappear the first time you "check" the plugs. Hmm.

 

I think the stock knock sensor is only good for a stock engine. I drove a single turbo that was loud as hell and at idle my knock was over 50. I never went more than 20% throttle and my knock was over 150. The stock sensor isn't accurate so I wouldn't worry if your getting that high of readings just cruising around. Loud exhaust or even a ported engine could set it off

 

Whew! (I think)... Just installed my pfc and during its learning process it went up to 7. Seeing how I thought any detonation was bad I thought something was wrong. Now I see all this is normal and the stock knock isn't reliable!?!?

Either way I guess I am in good company!

 

My knock sensor has been very repeatable and seemingly reliable, my knock under full throttle is usually below 20 with the WI. I have witnessed Chuck's drivetrain noise related knock and it is real, his knock under full throttle behaves just like my car under full throttle so to date the knock sensor has been a valuable tool.

The few times I have seen the knock levels go across the screen and hit near or above 100 were 1) lost fuel delivery at the top end, broken apex seal, and, 2) 1st pull during spool-up, guess the knock was from thermal expansion of the different parts as knock went away on next pull.