chevy1500z71

ever since i swapped in a manual transmission iv noticed that during a normall acceleration, my motor hits a wall almost right after take off, around 2000rpms. well i finally loged it the other day and it clear that my power loos is coming from 8 degrees of knock retard, now when its doing this, my spark advacne is only around 12 degrees, theres no way its knocking.

i think my problem has to do with how overdriven my supercharger is, during a normal acceleration i will reach near 0 vacuum, maybe even make a pound of boost during a harder acceleration, and it seems like right around 0 is where i loose 8 degrees. i also notice that if im cruising and i lay into the pedal a little, it will retard my timing around 4-5 degrees as the vacuum decreases.

is this some sort of burst knock or is my motor really knocking? when im logging all i can read is "knock retard" i cant tell if its from burst knock, or if it actually from the knock sensor sensing knock. my compression is in the mid-uper 8s, and im running 93 octane fuel. when i run the truck out to wide open at max rpms it doesn't show any signs of knock and will run out to 32 degrees of timing no problem. My first thought was bad gas, but its been like this for months now that iv taken the time to notice it.

another thing i notice is how low my timing tables are, are these numbers the actual value of what my timing is? it seems odd that i cruise around 15 degrees of timing where a car with a mechanical distributor would be near 40 degrees at cruise speed.

uraijit

Yeah, I'd be looking for burst knock, and turning that off.

As far as what your actual timing is at, what is your base (mechanical) timing set to? And does it match what's in your PROM? What's your offset set to? Are you using TunerPro or TunerCat? The two programs handle spark tables differently.

chevy1500z71

initial spark is 0, the ecm is 0 and it is set to 0. the main spark bias is 9, does this nmean 9 degrees is added to the whole table?

when im data loging, my readings are consistent with the table, if it were adding 9 degree, wouldn't i see it?

uraijit

Are you using TunerPro or TunerCat? As I understand it (and my understanding is limited) TunerPro calculates the offset into what's actually in the table, so what you see there, is what you get (minus coolant temp offsets, and whatnot).

So even if you have your spark bias at 9*, it should still calculate your spark tables to what you have them entered in at.

The spark bias, as I understand is just so that the engine is capable of retarding timing to negative numbers, if need be.

I think TunerCat requires you to calculate your timing based off of the bias though. Not 100% on that, as I've never used TC, but that's what I've been told.

Saar

this is only if the person writing the XDF factors this into the equation...

also, the main offset? the ECM takes that out, since it should match the amount of initial advance you have dialed in.

chevy1500z71

i understand that the main bias would be taken away if it were anything above 0, and i think i understand what the 9 degrees is for, so long as your right about it being alreayd figured into the timing table. yes im using tunerpro. when i datalog, i read spark advance reference, this seems to corespond with the table properly minus the reduction or adition of timing for modifiers like coolant temp or spark knock, but it must be correct becasue it reads 22 degrees at idle, which is what i have it set at and theres no way it would idle good at 31 degrees.

my concern is that if i 0 out the maximum knock retard table it will fix my problem of fixing false knock, but my understanding of burst knock is that it would preemptively reduce timing for things like rapid throttle movement, wouldnt i still want features like this? this is why for now i just zerod out burst knock above 80kpa for now untill i know a little ore about it.

another thing i wanted to touch on was timing, how much timing do you guys like to accelerate at? its hard for me to set up a good timing table because i accelerate so low in vacuum that its hard to have much of a curve other then rpm based at the end of the table, right now i accelerate at about 12 degrees, it feels kinda like a dog, shouldn't i be in the mid 20s by 2000 rpms? my cruise is around 20 now, but i dont see why ic ant cruise neer 40 degrees of timing and get better mpg? how do you guys feel about these numbers?

uraijit

That's good to know about the XDF. How does one go about checking to make sure that this is the case?

Also, what I meant was that the "initial advance" is taken into account with the spark table (So that if you were running 6 degrees initial advance, and the computer was set to 6* initial, it will take the value wanted from the table (for example 36*) subtract the 6* of initial advance, and calculate that the ECM needs to add another 30*, to reach the total 36*.

In the process of doing this, though, it adds an extra step.

Tunercat takes the target (36*) and adds the Main Spark Advance Bias, before inputting those numbers into the file (.BIN) that it creates. (On mine that is roughly 10 degrees, (9.84) but we'll round up for simplicity sake.) So in the .bin file, it actually says 46* where you want the end result to be *36.

So when the ECM polls that particular part of the table, it sees 46*. It then subtracts initial 6* of mechanical timing. So it thinks at this point that it needs to add 40*. Then it looks at the Main Spark Advance Bias (10*) and subtracts it, bringing it back up to 30* of electronic advance, for a total of 36* mechanical/electronic advance.

The reason that it does this is because the ECM isn't capable of storing negative values in tables.

ETA: Also, Burst Knock can be useful to some (I'm personally not one who uses it, but some people swear by it). If you think you want to use Burst Knock, come back to it later. Right now, what you want to do is track down what's causing your issues.

Temporarily disable it, and then test to see if the timing still cuts out when you don't want it to... If that fixes the problem, you know where to start working (or just leave it off), and enjoy your ride.

chevy1500z71

what im afraid of is that i could have a knock and i would never hear it over my exhaust, which is why it was comforting to know i have a functioning knock sensor, but if the knock sensor is just getting set off by every little thing then it does me no good, which is what makes me Leary to remove burst knock. that being said, im getting rid of it, i know iv got to, 12 degrees of timign and low compression, theres no way im really knocking.

i was looking over my timing table and i am AMAZED at how crappy it is, its no wonder why iv been getting such poor mpg and my spark plugs never last. my 45mph cruise was around 10 degrees of timing! my acceleration was like 8-12 degrees, sure the motor kicked *** at wide open where i had the timig dialed up to 31 degrees but this motor has alot more potential for part throttle driving. the problem was my boost comes on so quick that im never in the lower part of the table where the timing is at, i needed to basically move the table over towards the upper kpa values i guess would be the best way to describe it. im now going to be accelerating at around 20 degrees and cruise will be up to about 34 degrees, ill see how it goes, ill probably add more timing through the normal acceleration range. im glad i got this figured out.

RBob

iTrader: (1)

Have you checked the spark plugs for signs of detonation? With a boosted engine tuning is critical. The engine can easily knock at a hint of too much chamber pressure at the wrong time.

IIRC, you are using $0D code? If so I haven't seen a burst knock routine in it.

You need to read the plugs to know whether the reported knock is real or false. Then if false find out what is setting off the sensor. It may be that the sensor is too tight. There are ways to de-sensitize it and still allow it to pick up real knock.

RBob.

chevy1500z71

yes, that is the correct code.

i have yet to get a set of plugs to last ore then 4,000 miles. every time i remove them i see no speckles on the strap, is there anything else id be looking for on the plugs that would indicate knock?

i have to admit, iv been known to overtighten things, kind of a bad habit iv developed since iv been wrenching since i was a week little kid, i don't realize how strong i am lol, i keep thinking its going to come loose if i dont lean into it, terrible habit. so ill check into that, i also hear that a knock sensor from a 305 is less sensitive.

overtightening my knocks sensor wouldnt ruin it would it? would loosening it up would do the trick or do i need to replace it now? i read on a corvette foru that guys put teflon tape on the threads to desensify them a bit, im going to try it out, if it continues to have a false knock then ill try the 305 sensor.