219 replies to this topic

[Adam]

This thread has turned to awesomeness!!!

[tmh983]

how did you go setting up the triggering on the megasquirt to read the subaru crank and cam pulse patterns?

Get the closed loop idle working asap, it will make it heaps better.
Also, i'd be thinking of putting the IAT sensor after the intercooler. Especially as how heat-soak prone the subaru top mounts are. You could probably just carefully drill a hole in the outlet tank and just screw it straight in. Is it just a generic GM sensor you are using?

[acres]

I added a 2.2k and 12k resistor inline within the patch harness for both sensors. This reduces the current draw to aid in "ghosting" of the signal and also produces a voltage drop down to about 15% of the sensor output to prevent false triggers from noise. It has perfect sync up until 3000rpm before a few false triggers kick in so I am going replace the 12k resistors with 36k resistors and see if that helps as it should reduce the voltage down to about 4.5%.

Initially I thought thats where the IAT sensor should go too but then I realised you only need to measure the temp of the air pre turbo. Once it's compressed it doesn't matter how hot the air gets, the mass of air won't change. If you are measuring the air post turbo you will be measuring extra heat from compression,etc and the ecu will compensate by removing fuel as it assumes there is less air entering the engine. This would also be compounded once sensor heatsoak sets in too. The last thing you want with a hot charge is to be pulling fuel too.
The sensor is a GM open element type. I could of just used a spare coolant sensor I had laying around but apparently these have a much slower reaction time to temp changes as they are closed element.

[tmh983]

hmm, yes its a bit of a tricky situation with the iat sensor with speed density tuning of turbo cars. I think thats why most manufactures use maf instead of map.
The problem with putting it pre intercooler is when the intercooler gets heat soaked, the total mass flow at a given manifold pressure will be reduced, but the ecu won't compensate because its basically reading ambient temp. and it will run rich as until the cooler outlet temp comes down. This isn't so much of a problem for front mount cars.
Also, the mass of air after the turbo most definately depends on the temperature. If the cooler outlet temp is at 30deg @ 200kPa (for example), there will be 13% more total mass flow than if the cooler is heat soaked at 60deg @ the same 200kPa boost pressure. This means the ecu needs to command 13% less fuel to maintain the same air fuel ratio. In your case, with the iat pre-cooler, your 11.5:1 afr tune becomes 10.2:1 and you will be blowing black smoke everywhere.

If it was me, I would put it post cooler and make sure the ecu temp correction map is spot on, and also the calibration of the sensor obviously needs to be perfect. If you get those 2 things right, you can go ahead and tune the engine with worrying at all about iat correction. But don't forget, if you tune it all now, and later change the position of the sensor, you will have to go through and retune the whole thing.

[acres]

See now you have me thinking too hard about this again All of what you just said was my original train of thought too but then I changed my mind and decided that placing it on the manifold would cause lean running while manifold, sensor and I/C heatsoak had set in. I think I may have neglected the fact though that boost is taken from the manifold (ie. map sensor) and not from the compressor.
Or maybe it was the calculation that the code uses.
I may have to re-think this again.

[tmh983]

haha, yeah it can be a bit brain melting sometimes. Its probably worth talking to a 'professional' tuner about the location of the iat.
I made a lot of mistakes when i first started messing with tuning engines, i could have saved myself a lot of hassle if i'd just had a good chat to someone who really knew what was what. (I blew up a brand new built sr20 by accident... ouch $$$)

Does the triggereing circuit use any sort of zero crossing detection? what about low pass filters? if you upload a circuit diagram of the trigger inputs, i can probably help design a better circuit for you I don't spose megasquirt lets you take traces of the input signal? upload that also if you can.

[TSG]

This thread has turned to awesomeness!!!

This thread hurts my brain. And I am a pretty techy person I wish I had the room/money to play with cars properly.

[Shadoxity]

hmm, yes its a bit of a tricky situation with the iat sensor with speed density tuning of turbo cars. I think thats why most manufactures use maf instead of map.
The problem with putting it pre intercooler is when the intercooler gets heat soaked, the total mass flow at a given manifold pressure will be reduced, but the ecu won't compensate because its basically reading ambient temp. and it will run rich as until the cooler outlet temp comes down. This isn't so much of a problem for front mount cars.
Also, the mass of air after the turbo most definately depends on the temperature. If the cooler outlet temp is at 30deg @ 200kPa (for example), there will be 13% more total mass flow than if the cooler is heat soaked at 60deg @ the same 200kPa boost pressure. This means the ecu needs to command 13% less fuel to maintain the same air fuel ratio. In your case, with the iat pre-cooler, your 11.5:1 afr tune becomes 10.2:1 and you will be blowing black smoke everywhere.

If it was me, I would put it post cooler and make sure the ecu temp correction map is spot on, and also the calibration of the sensor obviously needs to be perfect. If you get those 2 things right, you can go ahead and tune the engine with worrying at all about iat correction. But don't forget, if you tune it all now, and later change the position of the sensor, you will have to go through and retune the whole thing.

You are very good with your calculations And have some great info.

See now you have me thinking too hard about this again All of what you just said was my original train of thought too but then I changed my mind and decided that placing it on the manifold would cause lean running while manifold, sensor and I/C heatsoak had set in. I think I may have neglected the fact though that boost is taken from the manifold (ie. map sensor) and not from the compressor.
Or maybe it was the calculation that the code uses.
I may have to re-think this again.

Definately put the IAT in the manifold! In the race cars we drilled it out pretty much opposite from where the throttle body sits and mounted it there.
You want the IAT to be picking up the "real world" measurements of what is actually going into the engine. Maf style sensors are pre turbo as they are measuring the air flow to do their calculations.

The megasquirt (without looking about it) i imagine is similar to the Autronic SM4 i had in the race rex, or the motec that my brother in law had.
You want the IAT to be mounted into the intake manifold (hence intake air temp ) As this will allow the ecu to adjust as per the actual engine conditions, not something completely different to what is going into the engine.

This thread hurts my brain. And I am a pretty techy person I wish I had the room/money to play with cars properly.

Hahaha *thumbs up* cars are just a money pit... could just as easily dig a whole and throw my money there....

[acres]

Its probably worth talking to a 'professional' tuner about the location of the iat.

But then you learn nothing Although destroying a built motor would be painful!

Anyway guys after sleeping on it I can't work out why I thought the IAT sensor would be more suitable pre turbo, so thank you for setting me straight on this as I most likely would have just chucked it in after the filter without thinking about it again. I'm thinking the most appropriate place to put it would be just before the throttle body now. Although this wont necessarily give the best indication at idle it should reduce sensor heatsoak substantially (from a hot restart or long idle periods) and give a solid indication of real intake temps while under boost. I think placing it in the manifold will most likely cause a short period of lean running while under throttle after a hot restart or long idle as the sensor will become heatsoaked and unable to cool until the throttle opens and air begins to flow over it. I doubt it will cool at idle as there is minimal airflow, being in a vacuum. Thoughts on this?

That's how the cam/crank signal detection works. An op-amp is activated at the zero crossing point (ac signal rising from negative to positive) giving, in theory, a clear regulated on/off signal signal to the cpu. The circuit is built highly adjustable (since the same circuit is used on many, many different VR, Hall and optical sensors). It contains 2 potentiometers to adjust both the zero crossing point (from zero volts and up) and hysteresis of the signal. I spent a couple of weeks and many, many, many recharges of the battery adjusting these pots trying to clean up the signal but it was impossible to get it perfect. I could get it close but there is a fine line between getting a signal (with noise) and having the trigger or hysteresis too high to operate the op-amp correctly. Adding the resistors to reduce the signal worked perfectly to remove the noise and false triggers. I have attached a diagram of the vr circuit from the manual:



Ignore the top and bottom circuit. There is a jumper placed form Tachselect - VRin & Tsel - VRout. R56 and R52 are the adjustment pots. This circuit is the crank circuit on the main board, the cam circuit is near identical and is found on the expander board.
There is a few software filters in tunerstudio but I haven't bothered using those yet. Going through the megasquirt forums it seems alot of cars need resistors placed before the circuit too but there is no one solution for any particular car. It depends on the sensor itself, the condition of the trigger wheels, the type of trigger wheels, whether the wires are shielded, how much air gap is between the sensor and wheel, etc.
I added another 12k resistor inline last night to the crank circuit as I didn't have anything bigger and haven't had time to go buy more yet. I am yet to test this to see if it improves though. So it is now Sensor - 12k -12k - 2.2k - ecu.

Thanks for the email Leon, I just saw it came through. I'll go check out those defs now.

[Shadoxity]

Put the IAT in the manifold, You will find this will be where most professional shops will install it. Its easy to do as well, drill, insert, be done with it

I found with the SM4 in my MY00 wrx it would get the occasional false reading for cam and crank sensors, didnt seem to affect it to much though.

Let me know how you go with the romraider stuff

[Ren-dog]

Holy shit there is some crazy brain melting stuff in here.

Looks awesome! cant wait to see power figures.

[Morgan]

Leon, off topic a little but I met your mate today (James, I think) in the blue Bugeye sedan at Gasweld!

Small world

[Jimbo]

ME.

I thought i put heaps of effort into making the nugget TT work.


I miss it. Woulda had some mad scientist shit going on.

[acres]

Yep, I will make the TT successful, god damn-it! I've got some more ideas brewing for where I want to take it next but I'm not getting ahead of myself yet. One step at a time.

Leon I got those b4 defs working and all is well. A bit disappointing that the maps aren't finished though, some are just incomprehensible and others are just missing. The maps around the sequential system operation are good though. The cranking tables I was looking for aren't there though, probably why you couldn't find them hey.
Did you not get any misfires when the autronic lost sync? Having the cam or crank signal drop out for a tooth or two while running isn't too bad as it will just re-sync instantly but without those resistors it wouldn't get a reliable sync while cranking, which meant no start. Still, would rather no sync errors at all to prevent misfiring, especially under boost and throttle.

Tim just realised I didn't answer your question about the scope, but no it doesn't directly scope the signal. It does however have a tooth logger which could be considered a bit of a crude scope? With the subaru 6/7 pattern it simply places a vertical line on the screen at each trigger event, false or otherwise. It also provides a spreadsheet of the input pin's status for the cam and crank ports at each trigger event. ie. '0' for off '1' for on. It is handy for diagnosing whether the faults are coming from the cam or crank signal.

I was going to build one of these as I don't have a scope but just haven't got round to it yet:



It's a design of a sound scope by one of the developers of the megasquirt code. You use it with some free software found online.

I can post up a screenshot of the tooth logger if you like?

[acres]

I think I fixed this screenshot of the cranking pulsewidths from the previous page. My photobucket settings were on small images.



Bah, nevermind. Still didn't work.

Edited by acres, 25 February 2012 - 12:04 PM.

[Shadoxity]

Holy shit there is some crazy brain melting stuff in here.

Looks awesome! cant wait to see power figures.

Definately! Ill start up a thread when i start modifying my MY02 b4, started with some tuning, but going to make some mods in april. See what i can get out of her with out too much work .
If i can hit over 180kw atw without to much hassle and reducing the VOD (this is the main part im working on currently) then i will be pretty stoked!.

Std these cars are pretty much as fast as a bug eye wrx, and with all the extra luxuries how can people be so critical? I love the mix of power and luxury in the twins. its great.

And much nicer to drive around town than the wrx.

Leon, off topic a little but I met your mate today (James, I think) in the blue Bugeye sedan at Gasweld!

Small world

Oh Jamie? Nice

It is such a small world. Looking forward to another cruise when im back in town sometime!

ME.

I thought i put heaps of effort into making the nugget TT work.
I miss it. Woulda had some mad scientist shit going on

Nice fork

Im keen to see how Acres goes with it.

I think I fixed this screenshot of the cranking pulsewidths from the previous page. My photobucket settings were on small images.



Bah, nevermind. Still didn't work.

I see the tables you are talking about, and i remember them from my STI, but yea, as you said these do not exist in the defs available for the twins.

I would love for someone to do the definitions. Im sure we could get $500 or more raised for someone to do it, but i just dont think anyone will


Acres, I will probably be up near the gold coast in May, If all works out ill get in contact with you around then, might get to check out your car and your progress by then

[acres]

Acres, I will probably be up near the gold coast in May, If all works out ill get in contact with you around then, might get to check out your car and your progress by then

Sounds good. You have my email.

Definitely start a build thread, would be good to see your progress.

[acres]

So, it's been 12 months since an update.
I have been doing some work on this again lately so here is a few images for the manifold I have been working on. It's still only tacked together at this point though so there is still a bit of work to do and once completed I will move on to the dumps, intake pipes, frount mount piping and maybe an intake manifold. Turbo's will both be twist mounted running separate in guard intakes and front mount is vertical dual core. Intake valve and merge for the intakes will be post cooler, immediately before the throttle body.













Thanks
Aaron

[Jimbo]

Mate, nice work. Dumb question, but will it still be sequential?

[acres]

Mate, nice work. Dumb question, but will it still be sequential?

Thanks. Yes will still be sequential, I am relocating the ecv to the dump by way of a butterfly valve.