Adavncing Ignition Timing

[LegacyT]

I was wodering if I removed the knock sensor and reset the ECU would the engine advance the timing and hold it there, continuously? Then I'd just have to be careful and use my ear to tell me I need better fuel, lower boost etc. Will this work to advance the timing??

Thanks,
Mark

[entirelyturbo]

The ECU would know if knock sensor is missing by burnin' up your dash with a CEL. Whether you reset it or not. Even if that doesn't bother you, I would assume that the ECU just reverts to a timing setting that is acceptable in most situations. But I'll let vrg3 or morgie or someone more attuned to our ECU's confirm that one.

What there's been so much of on eBay with the $5 mods for 20HP is putting a transistor in the intake air temp sensor fooling the ECU into thinking it's getting cold air, advancing timing. However, our cars don't have IAT's so that won't work either.

So if you want to advance ignition timing without a ECU reprogramming or piggyback chip you're SOL if you ask me

[morgie]

I remember someone did that simple trick :

When he replaced the knock sensor, he bought a Rubber bushing that goes on the valve-cover bolts, and put it under the knock sensor. That way the sensor would be less sensitive, and the ecu wouldn't raise you a CEL indicating that the knock sensor is not there.

[vrg3]

If you just removed the knock sensor entirely, the computer would notice and maintain fairly retarded timing at all times to be safe.

If you unmounted it from the engine and wrapped it up in foam or something, so the ECU wouldn't know, you could get around that, but I'd strongly recommend you not do that. It could be dangerous.

Our ECUs are fairly smart. Its behavior is not well documented, and the following may not apply to all Subaru ECUs, but anyway... The ECU doesn't use a fixed timing map. It has a map based on engine speed, boost, etc, but supplements it with active readings from the knock sensor. It occasionally tries advancing timing a bit and sees what feedback it gets from the sensors. If everything seems to run fine, and it gets better power it'll keep the timing advanced. If not, it won't.

There's more to it, though. There's supposedly some kind of crank acceleration limiter built into the ECU as well, which tries to ensure the structural safety of all the rotating components by retarding timing if necessary. The Torque Chip II ( http://www.torquechip.com/ ) is supposed to be able to work around this.

In short, you can't trick the ECU into doing exactly what you want in this regard, and certainly unplugging the knock sensor won't do it.

I second subyluvr2212's statement. You'd need to reprogram the ECU or use a piggyback device like an S-ITC or whatever in order to advance your timing. And don't be fooled by all the stuff on eBay. Intake Air Temperature sensors do more than control timing on many cars, and in any case advanced timing on its own isn't always a good thing.

[LegacyT]

could a circuit be fabbed up or something like such to replace the knock sensor? From what I hear these engines run with the timing pulled way back, and the ECU never seems to advance it substantially.

Mark,

[vrg3]

What would said circuit do?

Our engines run pretty well with the timing as it is... Advancing timing doesn't always make more power, and when you're under boost you really do need timing to be fairly retarded.

[Legacy777]

I've played around with pretty much all the knock sensor mods/tweaks there is out there. resistor mod to dampen the signal, rubber/fiber bushing to dampen the signal. All the results were sporadic and inconsistant. In all cases I ended up reverting back to the stock setup.

Regardless of what is said about our knock sensors being overactive, etc. I haven't necessarily seen this from viewing knock sensor reading from the select monitor. I have seen it pull timing a few degrees, but it was under a certain load/rpm, etc. This is why the knock sensor is important to be there. Your engine does not operate statically. It is a dynamic system with ever-changing surroundings, loads, etc.

As vrg3 mentioned.....our ecu's are pretty damn smart. Every time I dig into things I learn something new, which in most cases is something completely new or in other instances contradicts some of the common info out there.

The only thing I suggest you do with the knock sensor if you haven't already done so, is get the updated one. It's like 40-60 bucks.

[-K-]

I know I could get more power with timing. My ECU is still running at safe timing for a non intercooled engine, with the cold air mine is getting even under boost I could advance the timing and be safe.

[ciper]

But the ECU starts at an agressive level and pulls timing back based on feedback from the knock sensor. The knock it detects isnt audible, though I guess it could get false positives...

[-K-]

But how much does it start at? And does it pull some timing under boost just to be safe? What about at WOT? If I new all that I'd be happy.

[ciper]

I think WOT works by interpolation, it decides on the trend from the other RPM and decides on a level, along with fuel correction. So even though its closed loop mode I dont think it is static maps (more like static maps with a modifier).

Does that sound right?

[vrg3]

From what I understand, it's more like semi-dynamic maps. There's a map, and it's continuously refined. The knock sensor is always closing the feedback loop.

I'm not saying you're wrong, -K-, but your ECU should be running with more advanced timing than a nonintercooled setup. There is a limit to how advanced it can allow the timing to get, but it should still learn that it can advance.

[-K-]

Cool, I still don't know how much "play" it built into the maps though it's good to have safe settings for now.