[Viper]

Hey guys, Im not sure if all dont... some of the top end ones might but how come most aftermarket ecu's dont seem to use knock sensors to detect detonation and take measures to reduce it if detected? Only reason I can think of is that a knock sensor has to be calibrated for each engine and its not an easy job?

[niterida]

Don't know the answer but I certainly wouldn't buy one if it didn't have knock sensor capability.

[dattoman]

If you keep your air fuel ratio right it shouldn't knock
Maybe new cars run extra lean so thats why they have them
Whereas "built" cars fun fatter

[76lxhatch]

Yes its difficult to match the sensing circuitry to individual engines so that the right frequencies are ignored or listened for, so not likely to happen in a universal kit. The sensor itself is basically a microphone, and a filter is required to make some semblance of sense of the noise.

Also however useful it is to have a fast responding ignition retard, it still only happens after knock is detected, i.e. detonation has already occurred. Your tune shouldn't cause detonation full stop, if it does then the knock sensor is a band aid solution at best.

Not all factory ECMs use knock sensors, I think I even read somewhere that they are becoming less common in newer cars (could be wrong).

[Viper]

Thats True 76lx, but what about if you get a bad batch of fuel with low octane? even with a spot on tune its going to detonate and with no knock sensor to help things out.

[76lxhatch]

If you're living that close to the edge you make sure that you don't get crap fuel! It may even be a case of drain it and throw it away.

Remember that maximum torque isn't necessarily achieved with maximum advance on the ignition timing, and if you drive under varying conditions then a spot on tune is one that caters for said conditions with a safety margin. If you're racing and want every last horsepower then you control the conditions very tightly and accept that you might cause some damage if something goes wrong - you certainly don't want the ECU retarding the timing at an inconvenient moment because it may or may not have heard a noise that resembles detonation (false knock can become more common with a performance engine too).

[BIGCAV]

isnt it also the difference between open loop and closed loop ecu's?

msot factory units being closed loop can read the sensors and adjust everything on the fly and can modify what ever is needed

and aftermarkets are open loop meaning the maps and everything are set and it wont learn and modify it self to compensate for a knock like a factory unit



only what iv always thought, not saying its correct but thats my thoughts

[mumstaxi]

Knock sensors generally dont react fast enough for performace applications ,they are usually only used to monitor the vicinity of one cylinder, and wont necessarily "hear" the cylinders further away from the sensor, so inevitably a car with a perfectly working anti-knock system can still detonate anyway !



MT

This post has been edited by mumstaxi: 29 July 2010 - 10:29 AM

[76lxhatch]

BIGCAV, on 29 July 2010 - 11:25 AM, said:

isnt it also the difference between open loop and closed loop ecu's?

msot factory units being closed loop can read the sensors and adjust everything on the fly and can modify what ever is needed

Open loop and closed loop refers to oxygen sensors and fuel delivery only. In closed loop mode the ECU delivers fuel based on the oxygen sensor reading and ignores the open loop fuel table(s). Narrowband oxygen sensors don't give a lot of info, but with the right algorithm you can get quite accurate stoich A/F readings, and even infer relatively accurate A/F ratios either side.

On the other hand although a knock sensor can be used to retard ignition timing when it becomes excessive it is still quite crude, and there is no information as to when the timing should be advanced - settings from the tune are still required.

[Litre8]

The ability of the sensor to differentiate between true knock and piston/valve gear/gear drive may also question its benefit on a 'built' engine that may have a 'mechanical/solid' cam, forged pistons etc.

[Gunmetal LH]

Here we go- MY 2c. My apologies for being so long!

This may be useless info to most but might explain why I THINK some aftermarket ECU's don't have a knock sensor- they just don't have the 'on the fly' adjustability of a factory ECU to 'set itself' for economy.

The parameters can be varied WAY more but not adapted while in normal operation. I mean once the tuning laptop or whatever is disconnected. A good tuner will anticipate engine conditions and what you specifically want. A factory ECU has to accommodate ANY TYPE of driver...

A 1000hp skyline will be s#!t to drive 'nicely' unless it has multiple base maps to choose from.

A VN ECU has around 21 things you can look at being monitored, total, and 4 things you can adjust- useless for making power though.

A VY ECU has 4 PAGES of 50+ things for the engine alone aswell as a few more pages to do with trans, abs etc.

The ECU uses the oxygen sensor to monitor the fuel ratio and the knock sensor to pull back timing to avoid potential damage.

I know the Holden ECU's have a knock sensor there as part of the economy settings 'at cruise' so it can keep on leaning out until there is a problem then it richens it until the knock goes away.

eg. The VN V6 ECU's have a feature which leans out the fuel between a certain rev range and above a certain speed. When cruising above 80kmh and the engine is between 1500 & 3000 rpm for over a few (can't remember) minutes, it will decrease the fuel ratio by .1 every minute until the engine goes outside of the 1500-3000 rpm range or a knock is detected.

The knock sensor will be monitored all the time so the engine can have as much advance as it can all the time- more economical and better power...

On the VN V6 there are (apparently) 4 fuel maps the engine will use depending on throttle position vs load (vac) vs speed etc. The ECU then 'trims' the fuel ratio's for either better power or economy depending on what it's doing. You've heard of 'resetting the ECU' and then thrashing the crap out of the car and it will have better power- that's basically resetting the 'long term fuel trim'.
If you always drive your car like a granny and occasionally thrash it, then the memory will know it's an 'unusual' condition and it will not accommodate for it.

A test (if your engine isn't a noisy bastard like mine) is the get a hammer and just lightly tap the block somewhere and you'll hear the revs drop a little.

You may have to tap it quickly several times so the ECU doesn't dismiss it as an odd knock but an actual problem.


mumstaxi: "Knock sensors generally dont react fast enough for performace applications ,they are usually only used to monitor the vicinity of one cylinder, and wont necessarily "hear" the cylinders further away from the sensor, so inevitably a car with a perfectly working anti-knock system can still detonate anyway !"

A knock sensor will pick up everything no worries. With my VN V6's noisy timing chain, it's enough to retard itself.

I use '95' fuel or better because when it's stinking hot with '91' fuel, it will 'knock like a bastard' and the computer will not be able to reduce the timing enough to prevent it.

Take onto account the engine air intake temp being significantly increased by a stinking hot engine and radiator and '98' will still knock like crazy if you really load up the engine.


If anyone has knowledge contrary to any of this- don't hold back...

[Viper]

Cheers guys, has answered my question I think. all seems reasonable.

[76lxhatch]

If your 1000hp Skyline engine is capable of running nicely with the hardware it has, a properly tuned and able computerised EFI system will allow it to run nicely at all times. Multiple maps are for changed conditions - e.g. if you turn up the boost or change the fuel.

I've been playing around with VN/VP/VR ECUs of late and the following is based on what I know to date, I'm no expert (yet!)

Even the VN ECUs with their original programs are relatively flexible (certainly more than 4 adjustments) in comparison to quite a few aftermarket systems, primarily because they don't have be set up for ease of installation/conversion. There is essentially only one fuel map, but there are many adjustment tables for different conditions such as temperature etc - each one will add or remove to base figure as necessary. An aftermarket setup doesn't necessarily need to compete with a complex factory system, it may well be good enough to be reasonably priced, easy to install, and an improvement over carbed vehicles. VR ECMs introduced a whole swag of new features like lean cruise, decel fuel cut off and many more adjustments.

The functionality you speak of with running the engine lean (lean cruise) was introduced from VR onward, but it doesn't do it blindly - basically a set of target A/F ratios are kept in a table, and assuming the base fuel (VE) table is correctly populated with the values required to get 14.7:1 (stoich) A/F, then its simple maths to alter to suit any ratio. Lean cruise seems to go up to around 17:1, but only at low loads and high speeds. It does not use the knock sensor to do this, although given that there are a large number of alterations for different conditions to both fuel and spark, it can still be handy for those fringe areas of operation. Note that there are settings for maximum possible spark advance and retard which will be honoured at all times.

The long term fuel trim (BLM) is indeed reset with the ECU reset, but if you are having issues with this then you need to look at your oxygen sensor(s). I'm pretty sure the trim is primarily calculated from the oxygen sensor reading, and you have to remember that these sensors are consumable items, they should be replaced just like spark plugs, and are prone to damage in certain conditions. Thrashing the car after a reset won't achieve much because the learned adjustments are relative to RPM and MAP/load so it will simply fill the BLM table on an ongoing basis as each area of operation is reached.

The knock filter board varies between engines, always try to use one designed for your specific engine as it will result in less false positives. V8 (HSV) and V6 in particular I've read are quite different in terms of sound frequencies. False positives are the main issue, as you noted the program will count knocks and only take action once the count reaches a set figure to avoid false positives, but its really only a last ditch failsafe rather than an ongoing engine management parameter.

Using a good knock sensor while tuning may well be of benefit in saving your engine as a one-off, but if its regularly triggered (legitimately) then your engine will eventually sustain damage. If you are experiencing bad detonation under any conditions, something is not right and the knock sensor will not fix it.

[rodomo]

Litre8, on 29 July 2010 - 01:44 PM, said:

The ability of the sensor to differentiate between true knock and piston/valve gear/gear drive may also question its benefit on a 'built' engine that may have a 'mechanical/solid' cam, forged pistons etc.

That's what my engine builder mate said when I was on the phone to him tonight.
"Built" engines were more likely to have aggressive cams with little or no quietening ramps and the knock sensor can't tell the difference between detonation and mechanical rattle.

Gunmetal LH:
"A knock sensor will pick up everything no worries. With my VN V6's noisy timing chain, it's enough to retard itself."

This post has been edited by rodomo: 29 July 2010 - 10:56 PM

[ls2lxhatch]

Corvettes Win 2001 LeMans with Bosch Closed-Loop Knock Control

[76lxhatch]

That's interesting, pity they didn't give any detail on the outcome (other than winning) - I would be curious to know if they avoided damage altogether or just held it off long enough to run the engines strong to the finish.

[Gunmetal LH]

76lxhatch- What I mean when I mentioned-

"A VN ECU has around 21 things you can look at being monitored, total, and 4 things you can adjust- useless for making power though.

A VY ECU has 4 PAGES of 50+ things for the engine alone aswell as a few more pages to do with trans, abs etc."


I was referring to what you can look at with Holden's Tech1 or Tech2 diagnostic plug in computers. Not adjust fuel maps etc. only look at the engine's sensors and inputs. Should've added that. Sorry.


There are many ways to 'open' and adjust the computer's parameters using a laptop and cable/s. Look on evilbay and you should find connectors on there.



You said: "...Lean cruise seems to go up to around 17:1, but only at low loads and high speeds. It does not use the knock sensor to do this..." & " it can still be handy for those fringe areas of operation."

Yep. The knock sensor will be monitored as a limiting factor so it doesn't go stupidly lean and start to wreck itself. On a stinking hot day the engine may ping before it reaches the 18:1(?? read that somewhere) limit.

Changing the revs outside of the set range (lift off or floor it) will turn off the lean cruise mode.



I wasn't aware it was on VR's onwards. I have a VR memcal which alot of people say to put in as it will be better but I never bothered. As s#!t as my VN is, it's pretty good as-is.



ls2lxhatch- Interesting read. I understand that as a way to retard individual cylinder timing if detonation is detected, to suppliment base/ECU adjusted timing. I'm wondering if the LeMans Corvette ECU has no knock sensor beforehand?

[ls2lxhatch]

The factory 2000-2001 Corvette ECU has knock sensors but I have no idea what was used on the LeMans cars.

According to the article knock sensor input is even more valuable on a race engine. Therefore cost and complexity would be the most likely reason why some aftermarket ECU's do not have knock sensor input.

[76lxhatch]

Gunmetal LH, on 31 July 2010 - 12:54 AM, said:

I was referring to what you can look at with Holden's Tech1 or Tech2 diagnostic plug in computers. Not adjust fuel maps etc. only look at the engine's sensors and inputs.

Ah, that makes sense. I don't have any of those tools, just working directly with the calibration settings using the laptop because its a lot cheaper!

Gunmetal LH, on 31 July 2010 - 12:54 AM, said:

The knock sensor will be monitored as a limiting factor so it doesn't go stupidly lean and start to wreck itself. On a stinking hot day the engine may ping before it reaches the 18:1(?? read that somewhere) limit.

In the VR V6 manual tune I started with (its a lot more modified now) the max is 17:1 in lean cruise mode, from memory the 18:1 you're talking about is the threshold when you start getting error codes for running too lean. With all my logging to date I haven't found any knock in lean cruise at these A/F ratios, what detonation I have encountered has been under high load low rpm acceleration (as you would expect) where the target is more like 13:1 to 14.7:1 (and the actual was pretty close according to the wideband) - I decided to tune for 91 so some parts of the ignition timing map I copied from the SV3800 tune were a bit excessive.

Gunmetal LH, on 31 July 2010 - 12:54 AM, said:

ls2lxhatch- Interesting read. I understand that as a way to retard individual cylinder timing if detonation is detected, to suppliment base/ECU adjusted timing. I'm wondering if the LeMans Corvette ECU has no knock sensor beforehand?

One would assume that the knock sensor(s)/filter(s) would need to be as accurate as possible, so they would likely be matched to both the ECU and painstakingly tested against the engine itself. Would be very difficult to get per cylinder readings though wouldn't it...?

[ls2lxhatch]

I guess that if you know which cylinder just fired and the knock sensor is triggered, then per cylinder readings is the relatively easy part.

You would however need an ECU that can maintain a retard table for each cylinder.