Megasquirt talk (split from robokills project thread)

[NoHachi]

Okidoki..try and give some answers.:

KrizKH:you are spot on. The way I would set ignition timing for a roadcar would be to just use crappy gas and then tune it to just below the knock threshhold. In my experience, most engines produce peak power at those points anyway..This would be the one point where a bench could give better results..Without the bench I can get it 90% of the way though.

@Zax: U can use a method very similar to what you're doing, but then actually works. U need a knocksensor from another angine. These are piezzo crystal pickups that convert pressure to an electric current. Usually they are a thick round chunky thing with a hole in the middle. Attach the sensor (through the hole in the middle) to the engine using an available bolt. Now run the output of the sensor to a normal jack plug to a laptop..Use the laptop as an amplifier and plug in some headphones...(Offcourse any other amp would work..

@Denmark...I would be cautious of using electronically controlled knock sensors during the tuning fase..they can and often do go wrong..Certainly if you get knock in one of the cylinders furthest away from the pickup. A trained set of ears is still the best way. As a safetyfeature during normal operation, the link performs perfectly.

[Ivan141]

Zax, just do a search on the MSEFI.com forums... I believe there are basic knock sensing setups for megasquirt (called knocksense).
It's a very crude way of detecting knock, but it's better than nothing and you can use it as an input to megasquirt, allowing it to protect the engine when knock is detected. Cant wait till the VEMS guys get the Ion sensing technology figured out, it doesnt get much better than that at the moment (allows complete diagnosis of flamefront propagation, and thus also knock).

[JMR_AW11]

You guys are a little optimistic if you think you can get the MS to run as sweet as a factory ECU.

The last time I looked at the latest MS2 it had 12x12 3D tables.

i.e. 12 rpm mapping points.

The standard Megasquirt has an 8x8 table which means 8 rpm mapping points. 8 rpm tuning points for an engine capable of 8000rpm?

The standard MS can only resolve the fuel into 100 microsecond resolution.
The stock AE86 ECU has 1 microsecond resolution. A hundred times more resolution.

Your 20 year old AE86 ECU has 17 (seventeen) rpm mapping points for the 3D ignition map. That is 17 points from 800rpm to 7200rpm in 400rpm steps. (17 is a lot more than 8 )

The standard MS is toytown technology.

I would guess the MS is designed for bigger lazier engines like in the US.

Not for the 4A-GE. Sure it will work but the 3D maps are too crude IMO.

Also, the factory ECU for the 4A-GE has around 40 (yes forty) lookup tables in it in total for the fuelling and ignition. Some are big maps but most are tiny little correction maps to keep the engine sweet when driving in traffic. All the program code is written to suit the characteristics of the 4A-GE engine.

I don't know how many lookups the MS has for you to play with but I will be very surprised if anyone can get a MS to run as well as a stock ECU.

How are you going to control the ignition timing?

You might be better going for a Unichip on your stock ECU.

[robokill]

JMR_AW11

My engine never ran sweet! so hten why bother with the stock ecu :-)

[Mux213]

Robo, that sais more about your engine then the ecu

I have no idea what is better, only thing I can imagine is that when you change the specs of your engine so much from stock, a stock ECU wont make the right desisions.

From the explination of JMR_AW11 though, I'm wondering if MS is the right choice, but agian, I have no knowladge of these things

[Denmark]

I would also say that it´s really easy to make it drive like the stock ecu,no matter how many "lookup table" the oe one have!

/Skassa

[JMR_AW11]

Denmark Wrote:I would also say that it´s really easy to make it drive like the stock ecu,no matter how many "lookup table" the oe one have!

/Skassa

In that case I am sure there is a (well paid) vacancy awaiting your skills at Denso in Japan!

[JMR_AW11]

Mux213 Wrote:Robo, that sais more about your engine then the ecu

I have no idea what is better, only thing I can imagine is that when you change the specs of your engine so much from stock, a stock ECU wont make the right desisions.

From the explination of JMR_AW11 though, I'm wondering if MS is the right choice, but agian, I have no knowladge of these things

Good points. I would still ask the question about ignition timing.

Can the MS control ignition timing too? I thought it had to be modded to MS2 and you have to fit Ford ignition parts. (this may be old data)

This is why I reckon you would be better off buying a Unichip from Ebay and getting the modified car mapped by a tuner.

The stock (UK) ECUs also feature a failsafe function. Even if the ECU MCU chip fails (unlikely) then the ECU can still keep providing a spark and fuel to keep the engine running. The engine will run badly but it will keep the engine running. This is probably a safety feature as an engine that can suddenly cut out is dangerous.

This is a serious issue and cannot be disregarded. If people do build their own ECUs they should only do it if they are very experienced and can solder with high quality on a proper anti static ESD workstation.

An ECU is subject to years of vibration and temperature changes. The ECU is bolted direct to the chassis on some cars. These two things are the worst things to affect reliability. Any poor soldering or poorly secured components will eventually fail. The factory ECU is meticulously designed to withstand decades of temperature and vibration stress without failing. It may look old fashioned inside but it is very well built.

I work in the electronics industry and I can assure you the easiest way to find a weakness in a circuit board is to put it on a special vibrating platform or to give it thermal shock (by heating it or cooling it in cycles over several days)

If you do go down the MS route then at least go for the MS2 with the bigger tables, but most important of all, make sure it gets built for you by an expert.

[NoHachi]

You are right Skassa..all those maps are excellently suited for the 4A-GE and make cruising/sudden acceleration etc a lot better and combine that with optimal fuel economy...
Sadly though..as soon as you start making significant changes, like for example the cams, most of the maps become useless. Tuning all of these maps takes huge amounts of engine-bench time..more then most people will want to spend..so your best off with a system that suits the amount of tuning you will put into it..The relative simplicty of the MS in those cases is an advantage.

All things put together, an MS is still lightyears ahead of any carb system and those run pretty damn good. Even the older vacuum-advance systems could be tweeked untill they eeked up to 150hp/l out of an engine. So for all out performance, the demands aren't that hard to meet..but For optimal driveability, superb streetmanners and all of that combined with fuel economy and low emissions..for that you'd need a more capable ecu and an army of engineers to tune it.

Luckily I know some of these engineers, so I didn't have to learn stuff by blowing engines up. ;-)

[JMR_AW11]

I've just looked at the MS2 webpage and sure, you can now have ignition timing control.

But is is far cruder than the 20 year old stock ECU.
it's only got 12 mapping points as opposed to 17 on the main ignition map for the stock ECU.

Also the stock ECU has a seperate ignition map for idle/overrun.

MS2 has at least got a coolant ignition correction map. The stock ECU has two.
(one is for overtemperature correction at certain MAP sensor settings)

On top of this there is an ignition timing correction when the TVIS activates on the stock ECU (there is even a delay routine to allow the TVIS to open)

Also, the stock ECU has a clever idle stability routine. When the idle falters, the stock ECU can sense this and it can kick in extra timing advance to bring the idle rpm back up quickly to prevent a stall. There are maps for the attack and decay charateristics of this function and also for how much advance it can add.

If you went for a Unichip you would lose none of these features.