So I've been reading in the tuning forums about how people experience high RPM Knock Retard with stock or lightly modded motors N/A.
I was thinking about testing the knock sensor to see if it is maybe
to sensitive i started to research the idea a little and i came across this write up on Engine Knock, its a good read, but my question is , has anyone tried hooking their 2.4 twin cam or other jbody motor knock sensor to a switch or adding a shim to the sensor to reduce sensitivity? Im looking for any gain possible.
Here is the excerpt from the article that i found interesting :
Tuning A Knock Sensor Equipped Engine
When trying to get maximum drag strip performance out of a feed-back timing control engine, you might want to disconnect the knock sensor. The sensor is designed to listen for vibration, and it does a very good job. Anything that can cause a harmonic might be picked up by the sensor and be interpreted as detonation. The major problem with that lies in what is called the hysteresis of knock. Once knock starts, you need to pull out more timing than would originally be needed for knock to ever occur. For example, if your Z28 makes maximum torque and doesn't detonate at 38° advance and you advance the timing to 39° and detonation occurs, the knock sensor may have to pull the timing out to 30° to stop the knock. There goes the timing and there goes your ET and mph. Also, at WOT the engine might knock, just for a millisecond, and bingo, there goes the timing. If you have an exhaust that shifts slightly during hard acceleration and vibrates, say goodbye to advance again.
The cure is to run good unleaded fuel; around 100 octane works best with today's performance cars. And you should also disconnect the knock sensor. It's funny how racers will spend thousands of dollars to modify their engines and be too cheap to put good fuel in when they race.
Most new GM vehicles use the knock sensor during the first few seconds of operating to test the knock control system. If it doesn't get a signal back from the sensor, it will send a knock control trouble code and illuminate the Service Engine Soon light. So if this knock sensor trick works for you, just splice a toggle switch into the knock sensor wire and open the switch before you make your run.
This trick is usually good for 0.1-0.2 seconds and 1-2 mph.
Here is the link for this article:
Here
GM High Performance MAG also did an article on this a few months back, for mildly modded engines they also reccomended disconnecting the knock sensor as they are way too sensitive in stock form. I tested this out in an 01 Auto Z24 but have'nt been able to get back to back results (had issues both days)
_______________________
** Flat Broke Racing Inc.**
Be careful with this one, make sure you have no knock what so ever, or you may blow a motor when disco'ng the sensor.
If your sure your not detonating, then it shouldnt hurt.
But if you do detonate, its all over.
Quote:
Be careful with this one, make sure you have no knock what so ever, or you may blow a motor when disco'ng the sensor.
If your sure your not detonating, then it shouldnt hurt.
But if you do detonate, its all over.
Yeah you're completely right about that one thats why i think when i test it out im going to run 93 octane. Hopefully there wont be any knock
Also, could anyone tell me the location of the knock sensor on a 1999 2.4?
Or you can buy HPT and desensitize it the right way.
I used to race cars, now I race myself.
5K PB: 24:50
10K PB: 54:26
Quote:
Most new GM vehicles use the knock sensor during the first few seconds of operating to test the knock control system. If it doesn't get a signal back from the sensor, it will send a knock control trouble code and illuminate the Service Engine Soon light. So if this knock sensor trick works for you, just splice a toggle switch into the knock sensor wire and open the switch before you make your run.
This is where I have a problem. I have a knock control problem with my 3400 swap. I will tell you, firsthand, that the above listed modification will only make your car slower. WAY slower. When the ECU does a test and finds that there is no knock sensor present, it will try to safegaurd itself by pulling the maximum ammount of timing that it is programmed to pull. You cant just simply unhook it, or put it on a switch for a quick disconnect option, without losing a lot of timing.
In my scenerio the KS wire is hooked to a 10k ohm resistor, and then grounded. This way the ECU believes that the knock sensor is present, but no knock is detected.
I agree with the HPTuners thing. The factory ECM will pull timing at some real inconvenient times for your 1/4 mile times. The guys with HPTuners would probably recognize this as something referred to as 'Torque Mgmt". Basically it's the programming that GM has for the powertrain that helps keep it from damaging itself. Such as pulling timing at a shiftpoint so it doesnt have full power when it selects the next gear. Simply getting rid of TQ mgmt should decrease your 1/4 time. The KS + Reistor + ground thingy is kind of a last resort type of deal. HPT would be, like mentined, the correct way of doing it.
Torque Management (TM) and Knock retard (KR) are two very differnt things. TM is programmed into the PCM to protect the tranny. It is enabled from the torque reading at the torque converter. It will do everything from pulling timing to shutting off all injectors depending on what mode of TM you are in. As you can see this could be very bad for a modded engine but that is a whole other topic.
Knock Retard (KR) will only pull timing to correct the situation and it is used to protect the engine when knock is detected. Depending on how much knock you are getting will determine how much timing it pulls to keep the engine running in a safe state. Sure before OBD2 came along the knock systems were pretty unrealiable and people would do things to get around it (unplugging them, washers, etc). Now a days though with OBD2 the knock systems actually work really really well at detecting knock, the only thing is they are very agressive in controling it once it "hears: it. There is also a table in the PCM called Knock revoery rate, basicly it is a table to tell the PCM how to recover from knock once it detects it. On the 3800 it is set to .8 degrees per second. What that means is if your seeing knock the PCM will retard timing till the knock is gone and will only add back .8 of a degree of timing per second till it reaches the timing it was at before it detected knock as long as no more knock is detected. For example if you see 15 degrees of KR then it will take almost 19 seconds till you return to your full timing. As you can see once it does detect it it will have a huge impact on the performance of the car, but it will also keep it safe. There is other things you have to consider too, like burst knock and false knock. Burst knock is when you first floor it, your injectors are actually going to be behind the incoming air and you will run lean for a split second intill the injectors catch up. This will be seen in a scan as KR as soon as you floor it but it should return to 0 almost instantly. This can be corrected in the AE fuel tables, no big deal. False knock is something that a lot of people confuse for real knock. Well what is false knock? Lets say that your down pipe is hitting against the underside of the car, well if it's bad enough the knock sensors will pick that up as knock and pull the timing as needed. When I get home I can get some screen shots from my tuning program to show you some of the tables I am talking about. IMO leave your knock sensors alone, they are there to protect your engine and unless you really know how your engine is working inside you are running a big risk. Remember it only takes .3ms to blow up.
Quoth the Raven 'Nevermore
raven@accesswave.ca
Raven Autosports
55 McQuade Lake Cres,
Halifax, Nova Scotia, Canada
(902) 850-3330
10.82@132
Well i have the best of both world my car has a short so one day the knock sensor works and the other day the knock sensor doesnt work. And I know that i should really fix that problem I kinda like the way it runs
[IMG]http://memimage.cardomain.net/member_images/10/web/2422000-2422999/2422466_1.jpg[IMG]
Quote:
Torque Management (TM) and Knock retard (KR) are two very differnt things. TM is programmed into the PCM to protect the tranny. It is enabled from the torque reading at the torque converter. It will do everything from pulling timing to shutting off all injectors depending on what mode of TM you are in. As you can see this could be very bad for a modded engine but that is a whole other topic.
Knock Retard (KR) will only pull timing to correct the situation and it is used to protect the engine when knock is detected. Depending on how much knock you are getting will determine how much timing it pulls to keep the engine running in a safe state. Sure before OBD2 came along the knock systems were pretty unrealiable and people would do things to get around it (unplugging them, washers, etc). Now a days though with OBD2 the knock systems actually work really really well at detecting knock, the only thing is they are very agressive in controling it once it "hears: it. There is also a table in the PCM called Knock revoery rate, basicly it is a table to tell the PCM how to recover from knock once it detects it. On the 3800 it is set to .8 degrees per second. What that means is if your seeing knock the PCM will retard timing till the knock is gone and will only add back .8 of a degree of timing per second till it reaches the timing it was at before it detected knock as long as no more knock is detected. For example if you see 15 degrees of KR then it will take almost 19 seconds till you return to your full timing. As you can see once it does detect it it will have a huge impact on the performance of the car, but it will also keep it safe. There is other things you have to consider too, like burst knock and false knock. Burst knock is when you first floor it, your injectors are actually going to be behind the incoming air and you will run lean for a split second intill the injectors catch up. This will be seen in a scan as KR as soon as you floor it but it should return to 0 almost instantly. This can be corrected in the AE fuel tables, no big deal. False knock is something that a lot of people confuse for real knock. Well what is false knock? Lets say that your down pipe is hitting against the underside of the car, well if it's bad enough the knock sensors will pick that up as knock and pull the timing as needed. When I get home I can get some screen shots from my tuning program to show you some of the tables I am talking about. IMO leave your knock sensors alone, they are there to protect your engine and unless you really know how your engine is working inside you are running a big risk. Remember it only takes .3ms to blow up.
Thats interesting, thanks for all the useful info raven
.....now if someone would just give me 450 bucks for hptuners lol
what does everyone think abou the resistor idea? If your confident about your engine, about having a lack of knock i mean, then does the resistor have any negative affect
i read that article too.
But for j's, there Knock Attack in HPT. Its my understanding that with each of knock detected, it uses a value set on the table (called multipliers) and subtracts that valuve from advance *. Its agressive, but with hpt we can make it less agressive so that it doesnt retard soo much.
I may have explained this wrong(or not very well), but i'm sure shifted will explain it better once he reads this post.
However, for J's, theres a maximum amount of Knock retard and with the stock s/c reflash in the Power Enriched Mode its 6 * and 8* in non PE mode. That doesn't seem like too much, does it?
Nate
Evolution of Cavyboy-->C22t--> C24na--->c24s/c
1995 Cavalier W/2k1 Engine
GM S/C 13.940@99.78pmh w/2.068 60ft
SHOoff wrote:Quote:
Most new GM vehicles use the knock sensor during the first few seconds of operating to test the knock control system. If it doesn't get a signal back from the sensor, it will send a knock control trouble code and illuminate the Service Engine Soon light. So if this knock sensor trick works for you, just splice a toggle switch into the knock sensor wire and open the switch before you make your run.
This is where I have a problem. I have a knock control problem with my 3400 swap. I will tell you, firsthand, that the above listed modification will only make your car slower. WAY slower. When the ECU does a test and finds that there is no knock sensor present, it will try to safegaurd itself by pulling the maximum ammount of timing that it is programmed to pull. You cant just simply unhook it, or put it on a switch for a quick disconnect option, without losing a lot of timing.
In my scenerio the KS wire is hooked to a 10k ohm resistor, and then grounded. This way the ECU believes that the knock sensor is present, but no knock is detected.
I agree with the HPTuners thing. The factory ECM will pull timing at some real inconvenient times for your 1/4 mile times. The guys with HPTuners would probably recognize this as something referred to as 'Torque Mgmt". Basically it's the programming that GM has for the powertrain that helps keep it from damaging itself. Such as pulling timing at a shiftpoint so it doesnt have full power when it selects the next gear. Simply getting rid of TQ mgmt should decrease your 1/4 time. The KS + Reistor + ground thingy is kind of a last resort type of deal. HPT would be, like mentined, the correct way of doing it.
actually your wrong on this, in GM ODB2 cars the ECM only does a single test that lasts about 10-15 seconds at initial startup, so you have to start the car and let it run a min, then pull the plug or flick the switch off for the knock sensor. I used to do this all the time before HPT (just had a tech 2) and it never detected anything.
_______________________
** Flat Broke Racing Inc.**
