Travis S

Hi everyone,

Had my 05 on the Dyno a couple weeks ago. Tuner says that the knock sensor started pulling the timing back around 5500 and up. At least I think that's what he said. Doesn't mean much to me He said he did not want to dumb the knock down without knowing why it was doing it. Did not have time to figure out what was going on at that time. Going to take the car back but was wanting to become more educated prior to that. Does anyone have a clue what he is talking about? Any ideas what it could be? The car is an 05 vert with 75,000 miles on it. Cold air intake, Long Tube Headers, High Flow Cats, Borla Atak Exhaust, Fast 102 Intake, Holly Fuel Rails, Ported throttle Body, MSD Coils with Coil Power Upgrade Harness, MSD wires and a tune. I have done everything my self but the tune. When it comes to the computer and sensors I'm lost. As always your information is really appreciated.

Thank you
Travis

RussM05

Sounds like its too lean. The tuner should not be changing the knock sensors too much. They are there to protect the motor so they may be doing their job.

Make sure the tuner is using a good wide band O2 sensor to monitor Air Fuel ratio. If its never had a tune, your mods have increased the amount of air going into the cylinder, so the VE table needs to be calibrated as well as the MAF. This is basic tuning which if your tuner doesn't understand, then you need to go to a different tuner.

Travis S

Thank you for your input. Maybe I should take it somewhere else and see if they come up with the same result. I remember him asking what fuel I run, He thought it might have had bad gas. I run Chevron super. Don't think it had bad gas.

CMY SIX

but if it's 91 octane, I was just told by my VERY GOOD tuner. that he could pull anymore timing then he had already, that the motor "didn't like it" he thought maybe my piston tops had heavy carbon deposits, I'm thinking about buying a bore scope to take a look, before I pull the heads to "wash" the piston tops, I'll be interested to every body's thoughts on this, my mods are similar to yours, did you really need the "extra harness" for the MSD coils? which ones? street fire?

Travis S

They are the Pro Power. I don't know if I needed the harness or not. I installed because I read that the coils can draw power away from other components and our cars are already voltage sensitive. My tuner has a pretty good reputation in our area so I believe it is something with the car.

CMY SIX

I bought the harness too, but I'm going to run it for awhile and see what happens, I went with MSD's street fire

RussM05

The stock coils are fine. I've witness MSD coil failures and the owner went back to stock coils. His car made ~850 rwhp with stock coils and no misfires. Save you money.

schpenxel

Knock sensors aren't in %. They pull timing in degrees. They are basically little microphones on the side of the engine that are sensitive to the sound/frequency that "knock" produces. How the computer interprets their signal is pretty complicated, but basically if their signal gets over a certain voltage (i.e. there is over a certain amount of noise at that frequency) then the computer will assume there is knock and will reduce ignition timing to get rid of it / save the engine from damage.

Sometimes longtubes can add enough noise near the sensors to set them off when there actually isn't any knock

Sometimes it's actually too much timing, causing knock

Sometimes it's running too lean, causing knock

Tuner needs to spend some time figuring it out

Could add a can of Torco octane booster to a 1/4 tank or so to really bump up the octane in the tank and see if the knock goes away. If it does, it's probably real. If it doesn't, possible it isn't

Here is a really good video on what knock is and is caused by:

Travis S

Hey Carson,

I was hoping you would chime in. That was a good video to explain knocking to a guy like me that does not know much about the inside of the engine. It also makes me more confident in my tuner, He wants the car back on the dyno with a mix of pump and race gas to see if the knock goes away. Now I understand why. Thank you as always.

Unrelated note. I got my Monster LT1 clutch installed. Haven't really been able to drive the car much yet because of weather, but when I have it feels great. Thanks for pointing me in that direction.

schpenxel

Yeah, throwing in some race gas is a good idea to see if the knock is real or not.

Good to hear on the clutch--I really, really hate recommending clutches but I've been happy with mine too.