Knock with Super Retarded Timing
#1
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For some reason, I keep getting knock, even with ridiculously retarded timing. It always happens in the 3k-4k RPM region. Once out of there, the KnockSense goes quiet and stays that way all the way up to redline.
KnocksenseMS is tuned to just go off from noise at ~7k RPM steady cruise.
Datalog is attached at the bottowm, but here is a picture of a pull:
knock_log.jpg?t=1235092551
I checked my base timing, and verified the crank pulley is properly aligned to TDC by sticking a long stick down CYL1. I'm not sure if it might be a rich misfire (would that even set off the knock sensor?). I gapped my plugs (BKR6E's) down to .025 to .028" with no help. I'm also running ~97octane fuel blend, and ambient temps are the mid-30's.
Verifying the cam timing is next on my list, but before doing that I wanted to consult you guys in case I'm being stupid and missing something.
KnocksenseMS is tuned to just go off from noise at ~7k RPM steady cruise.
Datalog is attached at the bottowm, but here is a picture of a pull:
knock_log.jpg?t=1235092551
I checked my base timing, and verified the crank pulley is properly aligned to TDC by sticking a long stick down CYL1. I'm not sure if it might be a rich misfire (would that even set off the knock sensor?). I gapped my plugs (BKR6E's) down to .025 to .028" with no help. I'm also running ~97octane fuel blend, and ambient temps are the mid-30's.
Verifying the cam timing is next on my list, but before doing that I wanted to consult you guys in case I'm being stupid and missing something.
#4
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Yeah, it's stupid low, like my tuning skills. I had it at ~20-13 deg @ 120kpa-170 kpa (respectively) when I started tuning this issue, but while gradually retarding timing in this area, there's no improvement. The car will hesitate a little in the RPM range, and once over 4k it smooths out and just pulls.
Damn good thing this isn't my day job...
Damn good thing this isn't my day job...
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Pull your cat out of the car and see if it gets better. Exhaust restrictions drive EGTs up and cause knock. Excessive retard caused by the knock sensor going off will then drive the EGTs up even further, etc.
Check your timing belt as well. My car ran smooth with the intake cam retarded two teeth. Made buckets of power up top, no power down low, detonated everywhere.
My spark map used to look like yours, 5-6 degrees of timing in boost everywhere. Fixing the timing belt and ditching the cat let me jump up to 12-13 in boost, 15 at redline.
Check your timing belt as well. My car ran smooth with the intake cam retarded two teeth. Made buckets of power up top, no power down low, detonated everywhere.
My spark map used to look like yours, 5-6 degrees of timing in boost everywhere. Fixing the timing belt and ditching the cat let me jump up to 12-13 in boost, 15 at redline.
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DSCF3048.jpg?t=1235112791
Exhaust cam is good @ TDC:
DSCF3050.jpg?t=1235112808
Intake is retarded. Camera angle's bad; it's worse than the pic shows:
DSCF3051.jpg?t=1235112841
Fixed the issue w/o too much trouble. Removed the water pump pulley, upper plastic front cover and intermediate plastic front cover to get access to timing belt tensioner. Put a zip tie on the exhaust cam to make sure it doesn't slip:
DSCF3052.jpg?t=1235112868
then loosened the tensioner to adjust the intake cam.
Had to re-tension the belt, too, as it was a bit beyond the upper limit of tension spec.
The more I work on this car, the more janky mistakes I find from the original owner...
So very
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Thank you Savington, for the good suggestion.
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Sav knows all about shitty cam timing and detonation. When I bought my 99' I knew something wasn't quite right. I did all the maintenance and then when I decided to to a TB I checked, and sure enough, exhaust cam was a tooth advanced. Fixed it and it helped power, but after pulling the head from poping a head gasket (100 shot at idle FTL...), all the exhaust valves leak a spec. Advanced exhaust cam timing = higher valve stem temps = worn valve seats and faces. :( Gonna rebuild it this summer when I do the most badass miata head and block port you bitches have ever seen. (yeah, I said port the block...)
#12
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So I drove my car around today with ~3-4 deg extra spark in the 3k-4k region and OMG the difference in low & mid RPM torque is amazing
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2 degrees is crazy low. With the TB corrected, and your base timing reset, you should be able to run at least 12 degrees at 13psi. Glad you found the issue.
My car was pretty shitty with the intake retarded 2 teeth, though. I dynoed 219/201tq with a boost peak of 14+psi. 14+psi and only 200tq = failz.
My car was pretty shitty with the intake retarded 2 teeth, though. I dynoed 219/201tq with a boost peak of 14+psi. 14+psi and only 200tq = failz.
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