timing retardation and sensors.

steptoe · Post by **steptoe** » Mon Mar 14, 2011 7:37 pm

it seems knock sensor is used to tune engine.

it does with my EA82T 3 plug ECU system. Hooked up timing light to watch timing retardabout 10 degrees when engine block got a tap from a tool, timnig slowly came back as no more knocks came along

YouTube · Post by **El_Freddo** » Mon Mar 14, 2011 7:45 pm

hit up Rockauto.com to get part numbers if you don't order through them. Search amazon etc with the part number to shop around for the best deal.

This is how I got my cambelt kit for the EJ at about half price of one over here, including postage! 5 days later it was in my hands and about half an hour after that my engine was running again! Crazy world we live in.

I thought the knock sensor being used to continuously tune the engine was common knowledge?

Cheers

Bennie

Gannon · Post by **Gannon** » Mon Mar 14, 2011 8:08 pm

I bought an AFR sensor from this mob, they were good to deal with and it was half the genuine price

This should suit your car
www.cyberspaceautoparts.com.au/Subaru-Knock-Sensor

$140

Post by **Alex** » Tue Mar 15, 2011 12:23 pm

El_Freddo wrote: I thought the knock sensor being used to continuously tune the engine was common knowledge?

i didnt know that haha! learn something new everyday!

alex

RSR 555 · Post by **RSR 555** » Tue Mar 15, 2011 2:39 pm

It doesn't "tune" the engine.. it just retards timing when it sensors pre detonation (pinging) to stop the engne melting pistons or damaging big end bearings

YouTube · Post by **El_Freddo** » Tue Mar 15, 2011 8:15 pm

RSR 555 wrote:It doesn't "tune" the engine.. it just retards timing when it sensors pre detonation (pinging) to stop the engne melting pistons or damaging big end bearings

But isn't changing the timing a form of tuning?? I also thought that when detonation was detected under load that the fueling increased... But I could be so wrong on this!

Cheers

Bennie

Gannon · Post by **Gannon** » Tue Mar 15, 2011 9:10 pm

El_Freddo wrote:But isn't changing the timing a form of tuning??

Well i suppose yes. But i wouldnt call it tuning.

The ECU has a timing target for each RPM x Engine Load, based on a software map. (so say for example, at 3000 RPM and 70% load gives 18 deg BTDC) It then takes this target and adds or subtracts the IAT value depending on the intake air temperature (so if 35 deg air gives a subtraction of 2 deg, the timing is now 16 deg BTDC) . This is the ignition timing that is sent to the coils.
If the knock sensor detects pinging, the ECU may subtract 2 deg, then over a period of a few seconds, it slowly returns it to the original value. If knocking reoccurs a few times in a short amount of time, it will wait longer before returning to the original timing value.

If you put 91RON fuel in an engine designed for 98, the ECU will throw a check engine light because the timing it has to reduce it to is below its allowed value.

If the engine was designed for 91RON fuel, it will only ever run enough timing for 91 fuel, even if you run 98 through it. If it did increase the timing on its own, this would be an example of self tuning.

Please note that the above values are examples only

I also thought that when detonation was detected under load that the fueling increased... But I could be so wrong on this!

Im sorry Bennie, but the knock sensor has nothing to do with fuelling.

YouTube · Post by **El_Freddo** » Wed Mar 16, 2011 5:48 pm

Suparoo wrote: Im sorry Bennie, but the knock sensor has nothing to do with fuelling.

Really? I thought the ECU used the knock sensor to also work out the leanest "healthy" fuel ratio that does not cause pinging.

Your above post was an interesting read!

Cheers

Bennie

Post by **Alex** » Wed Mar 16, 2011 5:57 pm

is it co-incidence im having abit of pinging at the moment?

well its gone now..

alex

Gannon · Post by **Gannon** » Wed Mar 16, 2011 6:35 pm

El_Freddo wrote: I thought the ECU used the knock sensor to also work out the leanest "healthy" fuel ratio that does not cause pinging.

Nah the knock sensor is only used for correcting ignition timing, the oxygen sensor takes care of closed loop fuel control. Open loop fuel control is controlled directly by the fuel map (a combination of RPM x engine load) with slight variations for engine coolant temperature, cold start ect.