Power FC Knock

[RHDskyline]

So driving home last night on the highway for about a half an hour going about 90-100 km/h (cause the weather was ****), the car was fine.

Once i get into town, slowing down. a light on my dash starts blinking red.

I tried to find what the light was but it looked like

a tube with lines about above it.


I feel bad cause i can't describe it. it was on the right side of the dash, next to the tachometer.

When i looked at the power FC commander, the Knock meter was way higher than it usually is.

Now im trying to put 2 and 2 together, and say that my engine is forming a knock.

but after driving the car nice again in town. the light never came on and the knock meter went down.


any insight or help would be greatly appreciated.

Thanks

[GT-RJules]

i've had no experience with the powerFC, but lots of things can cause the "cat light" to come on.

cat is plugged, loose sensors, loose manifold, or exhaust is not secure. most of that stuff is easy to diagnose, hopefully that can help you narrow it down.

[SRC]

The PFC uses that light as a warning for when knock readings go over 60 i think it is?

[GTR-Dad]

The warning level defaults to 60, but is user adjustable. If knock above the threshold was indicated on the commander that's what the CEL was alerting you to.

What were you doing when the light came on?

If you were not loading the engine heavily it's unlikely that knock would exceed 60 (assuming that's what it's programed to alert at). If you were going hard, you may have had some bad fuel, but it sounds like you were seeing this on deceleration.

Knock sensors are just microphones tuned to report intensity of a particular frequency. Noises other than 'knock' can trigger them. Check for exhaust components that could rattle against something etc.

Dan

[RHDskyline]

Hey. Thanks for th help guys

The light did come on while just driving normally around town

the previous owner told me that the power fc was tuned to have that light come when the car is being pushed to hard. Which has happened to me before. But once I lay off. The light goes off

This time was different because it was flashing and the knock meter went up

but the light went off now and everything is back to normal

I don't have a cat in my exhaust so it's not that

What is the warning light? What does it come on for in a stock skyline ?

[GTR-Dad]

The OEM purpose is to tell you when your cat is too hot.

The PFC uses it to tell you when your knock, injector duty cycle, or airflow meter are at alarm levels.

Dan

[Skym]

Also stock ECU uses the cat light as a engine check light. I know this, because diagnostic screw on side of stock ECU wasn't set properly on my car and cat light kept lighting up and turning off when car hit bump in road (switching between diagnostic mode, run mode).

I think knock count can be seen on PowerFC hand controller.

If knock count is high, sometimes failing coilpack can cause it to happen or like mentioned above, something loose on anything connected to engine. Just tapping knock sensor can make knock count rise.

[RHDskyline]

I don't think its anything to do with the coilpacks cause they are new.

I think the problem was the knock, but it hasn't occured yet

[Skym]

You'll probably need to datalog the movements of cursor on ignition map via Apexi tuning software, as too advanced ignition timing for fuel used can cause knock. If ignition timing is safe, you shouldn't encounter knock, even with bad batch of fuel.

[GTR-Dad]

You'll probably need to datalog the movements of cursor on ignition map via Apexi tuning software, as too advanced ignition timing for fuel used can cause knock. If ignition timing is safe, you shouldn't encounter knock, even with bad batch of fuel.

Logging is required to really know what's going on, but I'd argue that when you tune to a particular fuel, you should 'expect' that octane and flame speed at the minimum will be consistent.

If you get bad fuel or a tank full of 'regular' because buddy made a mistake filling the 'premium' tank at the gas station, you should expect knock if you load the engine hard. Tuning 'safely' enough to run on the wrong or bad fuel leaves a lot on the table.

As mentioned earlier, the PFC does NOT retard timing or add fuel to manage measured knock events like the OEM and some other stand alones do (if the knock sensors are working). That is up to you.

Cheers,
Dan

[Skym]

I've experimented with stock ignition timing and octane rating in the past. Stock ECU is said to be tuned to run on 100 octane fuel in Japan. But I noticed can take lower octane gas. I can go as low as 95 octane (old verion of premium that was supposed to be 96 octane but was actually 95 octane) before engine showed signs of knocking under acceleration. Fuel octane can go as low as 91 octane where I live (regular). On 98 octane, no problems. The biggest difference I noticed was engine felt smoother on higher octane gas (98 octane). A sign that engine is tuned properly.

I noticed some tuners achieve max power engine can produce and back off a couple of degrees to account for bad fuel and sacrifice hp. Some pull more ignition timing to sacrifice more hp. But gives a bigger margin incase engine encounters a bad batch of fuel.

Stock R32 GTS-T ECU doesn't pull ignition timing on knock ignition map (disabled by running same figures on both main, knock ignition map). Knock fuel map just adds alot of fuel above 4000rpm when on boost. Factory ignition timing is said to be fairly conservative.

R33, R34 stock GTS ECU does pull ignition timing (to O on some parts of knock ignition map). I gather why R33, R34 GTS ECU's do and R32 GTS ECU doesn't, is due to R33, R34 have a higher compression RB25DET engine.

With a magazine test in Australia using pump gas, then octane booster with PowerFC, the knock count seemed to drop when running more ignition timing than they did on pump gas when running octane booster. But power increased due to running more ignition timing. I think was Martini brand octane booster.

So going by magazine test result's, pulling enough ignition timing should make it safe to run on pump gas, octane booster (without the hp gain on octane booster).

[GTR-Dad]

I thought factory knock maps pulled timing. Interesting to hear the GTS-T doesn't. How do you know? (I know of at least some Mines GTR knock maps that don't pull ignition timing and figured the change was their mod.) Any info on the R32 GTR factory knock maps?

With a magazine test in Australia using pump gas, then octane booster with PowerFC, the knock count seemed drop when running more ignition timing than they did on pump gas when running octane booster. But power increased due to running more ignition timing. I think was Martini brand octane booster.

So going by magazine test result's, pulling enough ignition timing should make it safe to run on pump gas, octane booster (without the hp gain on octane booster).

This is hard to understand....

In general, torque will increase with ignition timing advance, level out, and then start dropping. You want to set timing to mean best torque, the advance where you just get all the avaialable torque increase.

Forced induction engines running the kind of boost modded RB's typically run will typically start knocking before mean best torque, so you need to decide how much ignition advance you want leave as a margin for bad gas, high intake temps, etc vs how much torque you're willing to sacrifice.

Adding octane booster to 'regular' gas will reduce the tendancy to knock, effectively making it more like 'premium'.

Within this framework, you've got something measurable - knock - being evaluated against other variables - octane booster and ignition advance. It would be helpful to describe how the variables were changed, independently, together, how much etc. and the effect each configuration had on knock, the dependent variable.

Thx for sharing! It's great to get good information.

Dan

[NismoS-tune]

I used STP octane booster for 3 years but had heard in was only like .3 more octane. I recall reading a myth or fact arcticle or two about octane boosters not really adding much octane. My cars ran no different (same knock let's say) with or without octane booster. Difference was every gas tank cost $6 more.

[Skym]

I noticed some octane boosters are good and some aren't. Martini seems to be a proven brand.

GTR-Dad, I have Nistune tuning software to tune my car and maps from stock ECU's come with tuning software. I also have stock maps from my car (R32GTS-T). It kind of shocked me that R32 GTS-T ECU didn't pull ignition timing when looking at stock maps from my car. But I thought it might have been due to being a Type-M. But maps from other R32 GTS-T ECU's were the same.

I looked at stock R32 GTR ECU maps and ECU seems to pull ignition timing on knock ignition map by up to 17 degrees max and add fuel throughout fuel knock map, except the highest load cell in the corner of fuel map.

I have the magazine article somewhere and I remember it wasn't for a Skyline, might have been a Silvia / SR20DET. Would be a mission to flick through every magazine to find it, as I have tried to find it in the past. I remember they they were using Martini octane booster and knock count was lower on the higher octane gas, etc.

I know there's a similar online PDF version that I have posted in the past that compares 98 octane pump gas vs Martini octane booster vs Martini race fuel on R33GTR. It goes into more detail on RON increase with octane booster, racefuel and power achieved on Hub Dyno, etc.

Here it is -

http://www.motoractive.com.au/articles/AS_boostjuice_pg114-116_asm41.pdf

Another area they mention is amount of boost affecting burnrate. I was running same amount of boost (only 12psi with bigger turbo) when test I did with low octane gas was done.

I remember high knock count was mentioned in this thread below with PowerFC. And tuner reckons is due to boost spikes on a cold night -

http://www.skylinesaustralia.com/forums/Power-Fc-Knock-Warning-t319627.html

Also someone mentioned some ignition timing changes on ignition map in thread above and by how much to solve the problem.

[GTR-Dad]

^^^Thx!^^^^
Great background.
Dan