I had some VERY strange knock occurences last night ...

I knew that the cooler weather was causing a little knock, but nothing bad. So, I grabbed my laptop while I was going out to dial it out. I turned down the requested load by about 12% and richened the mix by ~.2 (I'd been running 11.8:1) before heading out. 3rd gear pull was dead on ... a couple 1 counts for a few cells. Then a 4th gear pull up a slight incline ... 16 counts and it was audible in the vehicle.

It's the first time I'd ever heard knock in the Evo ... I've felt it, but never heard it. The ECU pulled back about 4* but the octane flag only dropped to 99.xx%. So, I got to my destination and pulled down the boost even more and double checked the fuel. Fuel was good around 11.5:1 and timing had already been pulled as a general safety measure so I left it.

I made 4 more pulls before going home. 1 3rd gear that was dead on, one 4th gear with 0 knock, a short 5th and 6th to check with increased engine load, and another 4th with a 3 count around 5200.

I'm assuming bad gas was the cause of this. I just emptied my catch can (compressor water separator) on the PCV side last weekend.

What do you guys think?

 

just sounds like you're tuned to the ragged edge.. that'll get you clean runs and some freaks like that.

I tune it to where I can hot lap it and not get significant knock, so in the real world this gives me a little cushion.

I prefer to be very consistent then to have a car that can make a slightly higher HP glory run.

 

I tune the same way Chris. Until the weather got cool I was running completely knock free. When it got cooler I started to see a few knock counts here and there so I pulled out timing where it needed it. This 16 count come out of nowhere. I don't understand why it was only on that one pull ... it's was definitely real knock.

 

I hate anomalies like that. On strange stuff like that it can be sooo many things that it can be a nightmare to track down. It could be a chip of metal that SOMEHOW got sucked into the combustion chamber and was glowing so hot that it caused the high knock count before eventually passing through to the exhaust. Could be the bad gas but thats usually far more consistent than just one hard pull. It could also be a sensor glitch too.

I have learned to tune on the conservative side for daily driving to minimize these fluke issues whenever possible. Has anyone else noticed that their first hard pull generally gets some knock? I assume its from some carbon build up or something because after that first burst of full boost pressure, the knock never continues. Now I floor it to about 5K before I record my pulls which solved my issue, just wondered if anyone else gets that.

 

often the ECU will add fuel/reduce timing on subseqent runs in the areas where knock was encountered on the first run.

 

you're not alone that's for sure... I had a customer the other day that did 5 back to back runs

run 1 - 0 knock
run 2 - 0
run 3 - 10 count
run 4 - 0 knock
run 5 - 0 count

typically if you have a run with mild knock the other runs will show signs of having a problem in the same area by having some 1-3 counts etc... but not this one, it was just out of nowhere. The customer felt the timing pull but nothing auidible to my knowledge.

I've asked the customer to repeat the logs to see if we can catch it doing that again but thus far it has not come back so it's unclear if it was real knock or not. So what about you.. did you see any indication of knock in that same area in other runs?

 

Previous logs showed no knock in that area. Most of the knock I encountered after the weather change was down low where the boost was coming in earlier.

I actually turned down the boost by about 2 psi and richened the fuel and the knock just showed up. I got a 3 count in the same area on the pulls afterwards with even less boost and a richer mix.

What's strange is that I had been running a very aggressive tune without knock before the cooler weather. I was even at the track last weekend and didn't get knock in the same area on the 4 runs I logged. I backed off for safety and get crazy detonation on a calmer tune.

 

cold weather doesn't automatically mean it's safer, sometimes right the opposite, lots of people have to pull timing or richen it up...sometimes it's just to much power for pump gas.

 

I never said cold weather was safer ...

I had been running at 11.8:1 and it became obvious that wasn't going to work over the winter. It's just odd that I encountered such a problem while de-tuning the fuel and boost.

You're right .. some times it is just too much for pump.

 

instead of pulling timing or adding fuel where you see the knocks during cold wheater. Why dont you just increase your temperature correction table (20 Celcius and below) by about 3-4 points. that way you arent decreasing performance during warm.
this worked for me.

 

Getting back to page 1 or 2 about spark plugs, I had appreciable success in eliminating intermittent cases of mild to moderate knock by going to non-projected plugs. BR8ES plugs worked the best, but I needed the DSM ignition conversion (AEM) to make them last. BR7ES plugs work nearly as well and last just as long as projected 7s on the stock EVO coils. Theory would have you believe that you end up with reduced timing advance due to the plug being further from the piston, but in practice I was unable to find measurable evidence of this. I always ended up tuning back to the same timing I would typically run on regular plugs. I think the EVO combustion chambers are fast enough that the difference is small in the grand scheme of things.

I'm just getting into tuning on the stock ECU now, but I expect I will get the same results from the NP plugs. Might be worth a shot if you're struggling with intermittent knock issues on a reasonable tune, and it's an inexpensive test to carry out.

 

Thanks for chiming in Kev! Didn't to expect to see you in tbis forum seeing as you're the DSMlink evo guy lol. I might try out the BR7's and see how things go (can't hurt really).

P.S. Use those revolvers and sell me those 280's damnit!

Jamie

 

[OT Digression]I've been an "AEM guy" for the last year, and got it to run better than a 2g ECU and no worse than the stock ECU (better in many cases). This stock ECU tuning stuff is cumbersome compared to the other two options, but I'm gonna give it the old college try. The Revolvers and just about everything else I had on the car has been sold. The 280s just lingered for some reason, and I'm too lazy to pull them out now. [/OT Digression]

The BR7s should do well for you. I'm switching back to them this week as well, since the DSM ignition conversion came off the car with the AEM. I don't think I'll ever go back to projected tip plugs after what I've seen over the last two years. I've got BR8s in the RWD, but may try BR9s when we start to get our money's worth out of the 42R. Run the coldest plug you can get away with, IMO.

 

I'll give this a try ... it honestly makes the most sense. My question is what is being skewed to compensate for the temperature? Knowing what this table actually does will help us all in tuning for weather changes.

 

I used some BR7EIX plugs, lowered 1*/200-240 load from 6k rpm up and knock is gone. I may get 1-2 count upwards of 7.2krpm sometimes.