Tuning Spark Advance w/out a working Knock Sensor?

Is it possible to tune for Spark advance without a working Knock Sensor? For about 2 years now I have faced an issue with my knock sensor. It will not go away, or fix itself. I have used race gas, same issue. I have lowered spark advance down to 15degrees, same issue. I would like to find a way to keep my knock sensor out of the loop, but still tune so that I do not have too much or too little spark advance.

I am trying to figure out where I go next with the car, but I need this issue figured out before anything else really. I will be buying a wideband O2 for the AF ratio tuning.

Any helpers?

App... 97ss 383-D1-M6 & a bunch of mods. I use LT1_edit version 2.2. My OBD2 program flash has zeroed out the knock sensor input and triggers. It works for me. I do not retard ignition timing, but, reley on air temp IC and cooling system mods to prevent detonation. I can alter timing by use of a new flash, or, in cab manual timing advance with an MSD unit. B.

So I guess to clarify, how does everyone arrive at their "final spark advance" for their "good tunes" without a knock sensor. Is it simply a guess? Do they do dyno runs and increase timing until there is no more gains? Do they do ryno runs until they LOSE hp/tq? These are the only two things I have read so far that seem reasonable.

I want to get my timing ON for now so I can run the nitrous. I may also upgrade the heads, solid roller the cam, and retune it myself. Either way I need to figure out a system for setting the timing.

I might also go turbo... still the dream in my head.

I'd fix the knock sensor issue lol... there's millions of cars out there that don't have knock sensor issues so don't tell me it can't be fixed.

Have you done anything to the motor to make it louder (i.e. valvetrain, something ratteling) in such a way as to make it hear false knock?

It can't be fixed.

When I say I have chased this problem for two years I am not kidding. I have bought a second PCM, second Knock Sensor, LT1 KM, moved spark plug wires to avoid that wire, I mean everything I could possibly think of that MIGHT be somewhat related. If you do not believe me, look up my name and look at all the posts I have made in the last two years to TRY and rack peoples brains. It has been asked for the last two years... if you want to revisit it, please do so... but I am not optimistic. Nothing has changed in the last two years. Still every mod the same, I havent done anything but tighten the motor mounts and exhaust bolts. I even had a shop in houston re-adjust the roller rockers to make SURE it wasn't that... and it wasn't.

Max timing occurs around max cylinder pressure which can be measured on a dyno as torque. You have a window where more timing gives negligible gains. Stay within this window. Most people add timing until they have knock which could be 10 degrees outside of the max cylinder pressure window. That's a good way to ruin your motor but hey, plenty have done it, its just not how I would:no:

Josh,
thank you very much for the useful info. Sounds like I need to get on a dyno and figure out where my timing should be that way.

So exactly how much consistant knock retard were you getting?

What i've heard is, adding timing will start making big power gains for each degree as you get close to the limit... after that, not so much. Power will drop with pre-detonation, as thats not producing as much power as when it's not knocking.
Maybe you could dyno it to max power then back off a degree or 2 to be safe.

As for tuning out knock at various points along the torque curve... it's a guessing game at best I would suppose. Kind of a scary way of tuning lol.

the knock was 5 degrees at idle, 5-7 degrees at every RPM with load, and it dropped to 0 for some reason when foot was taken off the gas... I have wracked my brain too much over this issue, I am over it. I have no knock sensor.

Well, I admit it has been a while since I have been on this forum often, but if my memory serves me correctly... the computer diagnostics page is not the place to go for answers :(

...the computer diagnostics page is not the place to go for answers :(

Sorry but you said so yourself, the issue is not fixable. I bet it would continue even if you traded the car lol :D

The knock sensor is simply a piezoelectric microphone that's sensitive to the sound of pinging. If you were getting consistent knock, and unscrewed the sensor and taped it to a rubber hose or something "quiet", and the knock retard stopped, then you Know there is a sound from the engine that's causing it. If the KR continued (even if the sensor was unplugged altogether), I expect it would have to be the PCM. (the threads of the sensor might need to be electrically grounded for this test to work)

Also i've heard there are 2 different impedences of sensor available, are you sure you had the correct one?

I run mine w/o a knock sensor. You advance timing until the power drops off and then back out a couple of degrees.

Rich

It can't be fixed.

When I say I have chased this problem for two years I am not kidding.

My comment has 0 to do with your question, but have to vent...

A certain guy at work would say "what do you expect? All that stuff you did to it?".. well that guy got fired and today was his last day.. so... My point? I dunno really.

But really that's what he would say if I told him I was having this problem, and that would also be his solution! hahha.

Max timing occurs around max cylinder pressure which can be measured on a dyno as torque. You have a window where more timing gives negligible gains. Stay within this window. Most people add timing until they have knock which could be 10 degrees outside of the max cylinder pressure window.


I think max cylinder pressure occurs during spark knock.

Actually, yup, more spark knock = more cylinder pressure.

I agree with "add timing until torque begins to fall off then back up a couple degrees" since cylinder pressure can continue to increase as detonation begins to occur and is the reason for things like a broken ring land, blown head gasket, shattered piston, broken rod/crank/block (not nessessarily in that order).

What you want is max sustained cylinder pressure to occur on the piston down stroke, not on the up stroke, there's a fine line there.

My comment has 0 to do with your question, but have to vent...

A certain guy at work would say "what do you expect? All that stuff you did to it?".. well that guy got fired and today was his last day.. so... My point? I dunno really.

But really that's what he would say if I told him I was having this problem, and that would also be his solution! hahha.

This reply made about as much sense as tiits on a log.

Good discussion here. I will be using the try and max tq without going too far tactic once I get the new heads on the car.

Thanks a bunch guys... I feel like I need a knock sensor when I spray the nitrous, but if I get the timing/tune right... I will be safe. Just scary.

tiits on a log.

The only thing that makes less sense than your statement is my statement in my first reply. :lol:

I think max cylinder pressure occurs during spark knock.

Actually, yup, more spark knock = more cylinder pressure.

I agree with "add timing until torque begins to fall off then back up a couple degrees" since cylinder pressure can continue to increase as detonation begins to occur and is the reason for things like a broken ring land, blown head gasket, shattered piston, broken rod/crank/block (not nessessarily in that order).

What you want is max sustained cylinder pressure to occur on the piston down stroke, not on the up stroke, there's a fine line there.

Agreed:yes:

Max power is produced when peak cylinder pressure (from controlled combustion) occurs about 15 degrees ATDC.

Rich

Max power is produced when peak cylinder pressure (from controlled combustion) occurs about 15 degrees ATDC.

What exactly do you mean by this? Sorry I do not follow.

What exactly do you mean by this? Sorry I do not follow.

He means the gas/fuel charge takes awhile to burn and expand, if you watch the crank rotation and piston travel you will quickly realize ignition must occur BTC so by the time the piston starts the down stroke there's enough pressure to make the power stroke (BTC = before top dead center, dead center means piston top dead center when the crank is straight up and the piston has reached absolute top dead center). Ignition of the fuel charge has to occur before TDC so the flame front has enough time to spead and fully combust as the piston is starting the down stroke, this takes time, usually 20-40 degrees of the crankshaft rotation.

So, if all pressure (the big explosion) was to occur before or at Top Dead Center then power is severly reduced/wasted and maybe some broken ring lands, piston, head gasket as the result.

When the piston is beginning it's down stroke is when the exploding gas has a way to make the most power, too early and you begin to lose power due to the disadvantage in leverage, earlier than that you make spark knock. Reaching peak pressure too late and your piston is too far down and the expanding gas dont have as much as an affect, so you again lose power.

Controlled combustion means having control of when and how fast (predictable) the entire combustion event happens. When control is lost then as a result is usually pre-ignition which in severe cases creates audible spark knock.

Pre-ignition (spark knock) occurs for two reasons, 1 = because the fuel is acting like a deisel and igniting all by itself from the heat and compression inside the combustion chamber, and 2 = because since the fuel charge is already soooo hot when the spark plug sets it off it all ignites instantly rather than the normal slower flame front that the PCM is used too. Leaner mixture burns faster and more fierce, richer mixuture burns slower and more controlled, this is why you enrich WOT.

He means the gas/fuel charge takes awhile to burn and expand, if you watch the crank rotation and piston travel you will quickly realize ignition must occur BTC so by the time the piston starts the down stroke there's enough pressure to make the power stroke (BTC = before top dead center, dead center means piston top dead center when the crank is straight up and the piston has reached absolute top dead center). Ignition of the fuel charge has to occur before TDC so the flame front has enough time to spead and fully combust as the piston is starting the down stroke, this takes time, usually 20-40 degrees of the crankshaft rotation.

So, if all pressure (the big explosion) was to occur before or at Top Dead Center then power is severly reduced/wasted and maybe some broken ring lands, piston, head gasket as the result.

When the piston is beginning it's down stroke is when the exploding gas has a way to make the most power, too early and you begin to lose power due to the disadvantage in leverage, earlier than that you make spark knock. Reaching peak pressure too late and your piston is too far down and the expanding gas dont have as much as an affect, so you again lose power.

Controlled combustion means having control of when and how fast (predictable) the entire combustion event happens. When control is lost then as a result is usually pre-ignition which in severe cases creates audible spark knock.

Pre-ignition (spark knock) occurs for two reasons, 1 = because the fuel is acting like a deisel and igniting all by itself from the heat and compression inside the combustion chamber, and 2 = because since the fuel charge is already soooo hot when the spark plug sets it off it all ignites instantly rather than the normal slower flame front that the PCM is used too. Leaner mixture burns faster and more fierce, richer mixuture burns slower and more controlled, this is why you enrich WOT.

Well said!

Rich

Well said!

Rich

Thanks Rich though you probably originally posted all that at one time or another.

Thanks Rich though you probably originally posted all that at one time or another.


Yeah, it's interesting how much optimum advance differs between different head designs, even sticking with 2V OHV designs. The worst of the common engines is a high compression BBC. These typically need 40-42 degrees of advance. This is due the inefficient chambers as a consequence of the need for big domes (see pic). I have seen blown small block Chevys with dished pistons needing ~24 degrees, quite a difference.

http://www.jepistons.com/cat/je/auto/chevy_bb/img/111596.jpg

As engine revs go up, you would expect that more and more advance would be needed to produce peak cylinder pressure at the desired point of crank rotation. But as the revs go up, combustion becomes more and more efficient due to better mixing/atomizing of the intake charge (a function of increased turbulence). So many engines end up with a fairly "flat" timing curve from the midrange on up. Interesting stuff.

Rich

Yeah, it's interesting how much optimum advance differs between different head designs, even sticking with 2V OHV designs. The worst of the common engines is a high compression BBC. These typically need 40-42 degrees of advance. This is due the inefficient chambers as a consequence of the need for big domes (see pic). I have seen blown small block Chevys with dished pistons needing ~24 degrees, quite a difference.

http://www.jepistons.com/cat/je/auto/chevy_bb/img/111596.jpg

As engine revs go up, you would expect that more and more advance would be needed to produce peak cylinder pressure at the desired point of crank rotation. But as the revs go up, combustion becomes more and more efficient due to better mixing/atomizing of the intake charge (a function of increased turbulence). So many engines end up with a fairly "flat" timing curve from the midrange on up. Interesting stuff.

Rich

That is crazy, so would you say the most inefficient of the big domes must be the king of domes.. HEMI?.. If you also made it High compression? Stock it's sporting 2 plugs per cylinder like some Fords did on the Ranger motors back in the day. I know 4v shape is same as "HEMI" but what are your thoughts? I know GM stuck with 2v on the LS motors and are making killer mpg + power, lots has to do with weight and RPM but still it's a good combination I think partly due to combustion chamber design.

The (original) Hemi has a very different combustion space shape than a typical BBC. It is crescent shaped with a centrally located plug. The BBC with a big dome has the plug off to one side and the dome breaks up the combustion space and is in the way of the flame front. Looking at the picture of a Chevy piston I posted, keep in mind that the plug is lovated over on the right side where there is that little notch for plug clearance. In any case though, the Hemi design was all about airflow!

Hemi piston

http://www.campbellenterprises.com/pistons/diamond-pistons/diamond-piston-mopar-hemi.jpg

Rich

Thanks a bunch for the lesson guys. I now have a better understanding of what is going on. I love it when good posts like this get the juices flowing.

A good cooling system helps. ~20% of combustion energy converted to torque, 60% discharged to exhaust, 20% removed by the cooling media. Charge preignition is caused by pressure and heat. I modified my WP and cooling system to Evans poly-glycol. Reduces or eliminates critical media (water-glycol mix) boiling common in FI applications. B.

Is it possible to tune for Spark advance without a working Knock Sensor? For about 2 years now I have faced an issue with my knock sensor. It will not go away, or fix itself. I have used race gas, same issue. I have lowered spark advance down to 15degrees, same issue. I would like to find a way to keep my knock sensor out of the loop, but still tune so that I do not have too much or too little spark advance.

I am trying to figure out where I go next with the car, but I need this issue figured out before anything else really. I will be buying a wideband O2 for the AF ratio tuning.

Any helpers?

Could you find a wireing diagram for the knock sencer...and possibly rewire it? all the way up to the PCM.

What about getting a lt4 KM, or use someone elses really fast to see if it does help?

I have used 4 different LTx KMs, so that isnt it. I may one day just go re-wire it real quick and see what that does, not a bad idea. I have the block ready to be 100% pulled right now, just debating if it is worth it or not....

Just turn it off. It isn't needed with a proper tune.

Rich

I have used 4 different LTx KMs, so that isnt it. I may one day just go re-wire it real quick and see what that does, not a bad idea. I have the block ready to be 100% pulled right now, just debating if it is worth it or not....You didn't install the sensors with teflon tape did ya? Tape shouldn't be used on a sensor that has to complete a path to ground. Sometimes it doesn't