I believe I found my hesition, I was watching my spark advance and knock detected, and knock retard data with my snap on scanner.
I found that from a stop if I punch it the timing goes from 19*@idle spark advance to 0* spark advance and approx. 6* knock retard, as it nears 3000rpm knock retard goes to 0* and spark advance increases.

I found a link reguarding desensitizing the knock sensor by installing a couple resistors. I could only find a resistor that was 4.7k so I installed it as a bypass of the knock sensor (testing only) and there is no more knock retard but the spark advance drops to approx. 2* when I floor it from a stop and then increases at a pcm given rate. The hesition is alot less drastic and the car feels smoother/more responsive.

Is it possible to retain more base pcm timing with this or any mod?
Would I need a reprogram to achieve this?

I would like to retain as much base timing when I floor it and advance from there.
e.g.- 92 camaro sbc base timing(dist.) 14* btc + pcm timing advance


thx

 

Only way to advance the timing that I am aware of is with software like tunercat or LT1edit... there may be a timing controller with a spark advance dial out there but tuning would be far cheaper.

 

ttt

 

I am not really sure exactly what you are asking. But after trying a bunch of things to cure "false knock" I turned off knock retard (in the program) years ago and never looked back.

Rich

 

Are you sure it reads 2-deg under those conditions? I have looked at an awful lot of data logs, and never seen anything below maybe 18-deg.

How did you "bypass" the knock sensor? If you put the voltage in the circuit out of range (1.5-3.5V) you would get a code for the knock sensor and the PCM would default to a table of knock retard vs. various operating parameters, and you wold see almost continuous retard, up to 15-deg at times. An 18-deg advance pulled off the PCM's timing table, minus 15-deg of retard would put you suspicioulsy close to the 2-deg number you see. But you say you have no knock retard showing with that circuit?????

And just to clarify... there is no "base + adv." in the PCM tables.... there is a specific spark advance value programmed into a table with a grid of cells defined by engine load (MAP) on one axis and RPM on the other.

 

Before:
At idle the spark advance was 19* I go WOT and it drops to 0-2* spark advance and 6* knock retard. slowly the spark advance increases and retard lowers as rpms increase till I hit 2500-3000 rpm's @36-38* advance.

After:
Now at idle its reads 19* spark advance, I go WOT and the timing drops down to 2 degrees of spark advance with no retard, then it will slowly increase advance till gets to 2.5k-3k.(approx 36-38*)

The bypass was based of a thread I found reguarding desensatizing the knock sensor. I didn't have the resistors needed at the time. Here's the link:
http://www.charm.net/~mchaney/knock.gif
I took the reading of 3900 ohm's at the sensor added the R1 resistor value (975 ohm's)= 4875ohm's. I had a 4700 ohm resistor on hand so I then connected it to the knock sensor connector then to ground. (hence the bypass) I have no idea why spark advance drops from 19* at idle to 2* at WOT and bilds from there.
I know there isn't really a base timimg with these cars. I was interested if it were possible to have/set the timing map to go no lower than 14* from idle to WOT. Like older distributor cars where there was a base timing manually set and advance was subject to the pcm tables.

 

ttt-Injuneer

 

ok so I got the knock sensor mod done I go for a test drive and make 4 WOT passes all 4 left 60ft worth of rubber stripes on the asphalt. get back the shop clean up and head home, on the way home I tried making a couple WOT passes and its back to normal ...hesitates off the line.

WTF, this thing should s*hit and get.

anyone else have any ideas?????

 

I have the "less than 4,000rpm" stock timing table in my online scanner writeup.... scroll down about 3/4 of the way to the bottom:

http://members.aol.com/InjuneerZZ/ScanMast.htm

As you can see, the lowest value programmed into the table is 8-dg. Assuming you were at 1,000rpm when you floored it, you should see 9deg of advance. If you are getting a few deg of knock retard, it is possible to see what you are getting.

From the numbers you are quoting, seems like there is a lot of knock retard AT TIMES. Could be an intermittent wiring problem with the sensor, although you should be getting a DTC 43 code for the KS. Are you getting a code?

How was the coolant temp on the 4 pulls that laid rubber, vs. your later attempts when power was down?

How are you getting the advance and retard numbers? Do you have a data log that I could look at?

 

but there doesnt appear to be any kncok retard just spark advance drops to 0-2*. there are no codes, and to coolant temp was within 20* between the two runs. I use my snap-on scanner which has data log but I need to find the software for my computer. However there is somthing I want to try ,the four good pulls were just before I needed to turn on my head lights. I have under drive pulleys and at idle with the lights on plus fan on ,system voltage is at 10.9 volts.