spark knock at low load

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Gear Head
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Joined: Sun Jun 03, 2018 1:11 pm

spark knock at low load

Post by rmmg1967 » Sun Jun 03, 2018 1:18 pm

Hello all,

I have a project car running with tweecer. Not driveable but I can start and run in driveway. Car starts and idles fine. Wide band shows good AFR. Here is the problem. When I blip the throttle of course the rpm increases quickly then settles at about 1100rpm for about 4 seconds then finally returns to idle rpm of 800rpm. During the 4 sec duration at 1100rpm I can hear spark knock. Load is about .19 at that point. I have a loaded three files. I removed about 10 total degrees of timing by changing
“spark adder for closed throttle” from 5 to 0 degrees and changing “spark adder for neutral” from 5 to 0 degrees. File 001 is the base tune, file 002 is with 5 deg removed, file 003 is with 10 deg removed. File003 is labeled no knock but actually i can hear it slightly, just barely.

I looked at the data in excel and I noticed the timing peaking for the 4 seconds. I also notice my tune has this scaler “spark and fuel lugging time limit” equal to 4 seconds. Is this scalar and the knock duration related, they both match. Look at the file, the timing advances during this 4 sec period so I think it is related.

I looked at all the spark tables and I cant figure out which table the eec is working from during this 4 sec period. By looking at tables, at no time should timing exceed 30deg but in the file001 it reads 40deg then of course file003 it is 30 deg since I already removed 10 deg from the scalars.

This motor ran fine in an 1989 LX for two years. At that time it had stock intake and 19lb/hr inj and stock MAF with stock tune A9L. It did not have any spark knock at anytime.

Now that I installed the powertrain into my project car i upgraded to 24lb/hr inj, cobra intakes and new MAF. File001 is the tune I got from mike glover. File002, file003 I made those changes to reduce the total spark myself.

Any help would be appreciated. My car is not driveable yet but just wanted some insight to the problem. oh yeah, i live in detroit michigan and i only use rec gas, with stabil added. This was same as when engine was in the LX, ran rec gas with stabil added.

Here is car as it is today:
1989 302 block
Underdrive pullies
5sp word class T5
B303 cam
1.7 roller rockers
FMS GT40 turbo swirl heads
24lb/hr inj
73mm C&L MAF
Cobra upper and lower intake, both extude honed
65mm TB
Kcode hipo exh manifolds
2.25 dia dual exhaust with xpipe and magna flow’s
Wide band
Two motorcraft stock hegos.
190LPH fuel pump, -6an lines
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Location: Newmarket, ON

Re: spark knock at low load

Post by skunk » Sun Jun 03, 2018 5:19 pm

I assume your using CalEdit? Does it have a compare option? If yes compare your tune to a stock A9L since you said it ran fine on the stock code....look and see whats changed. If all you did was an intake and injectors there should be very little difference other than injector parameters and whatever you decided to use for a Maf Transfer.

How is when it gets warm (180-200* ECT)? Its very difficult to tune a cold engine and your last log was just starting to break 150*.

Post your findings since most members wont be able to look at the Tweecer tune file if you decide to post it.

Good Luck
1987 Turbocoupe.
A3M1/A9L, BE/EA, Tweecer RT.
306,Single Turbo, Ported E7's, Ported Stock Intake, 42lb Matched Green Tops, PMAS 3" Blow-Thru Protube (42# supercharger calibrated),T5z, 3.73 gears
..... Nothin Fancy.......Just something to keep me from the honey-do list.........

Gear Head
Posts: 2
Joined: Sun Jun 03, 2018 1:11 pm

Re: spark knock at low load

Post by rmmg1967 » Mon Jun 04, 2018 9:41 am

Hello John,

thanks for the advice. Yes i used cal edit. I purchased tweecer and base tune from mike glover. Mike did the tune. I did pull the stock cal a9L and i have done the compare. There are many changes besides for inj and MAF. I will try to make the compare in an csv format and post it so everyone can look at it.

I will also try to get log file when ECT is in the range you suggested. I have repeated this event at those ECTs and i can say i dont hear the knock but i never took the log.

I will take a log soon but now my car is in the paint shop getting some touch up work done so once i have it back, i will take log.

Mike also owes me a 2nd tune but first i have to take some drive logs. My car is not drivable at this point.

Right now it has no interior but it has complete wiring installed, powertrain, fuel system, brakes, suspension, tail lamps, all glass and is freshly painted. Basically i , just have to install trim, headlights, and interior.

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