T-leg Piggyback ECU R&D

93forestpearl · Post by **93forestpearl** » Tue Apr 12, 2005 5:59 pm

Just wondering exactly how it will be metering fuel because I'm going to the JY next week to get the rest of the stuff I need to make that motor go in my car. Will I even need the stock MAF? Or will it be MAP based. Can we scale in a larger MAF? Wideband or no?

I'm just trying to figure out exactly what I'll need to get this thing to jive.

Or is it too early to tell? I was just heading out to the JY and if I didn't have to buy the intake and MAF that would be nice.

free5ty1e · Post by **free5ty1e** » Sat Apr 16, 2005 1:59 pm

Hey everyone,

Been out of town for a few days looking at Nevada property. I should be in Florida a month or two longer than previously anticipated, so I'll have more time to work on this project.

93forestpearl - you'll need a MAF for the initial product, and for now the stock one will do. For a larger range sensor I'd need the transfer function of it, or a conversion table, to implement into the software (if you wanted airflow to be converted and displayed properly). Should be no need for a larger MAF with this method anyway - the adjustments in the RPM vs MAP trim table will allow you to fool the ECU into thinking there is a certain amount of airflow at any given time, which will directly affect the injectors' duty cycles. You will need the MAP and MAF sensors for this piggyback to work.

Until I get my hands on a wideband O2 sensor and have a chance to experiment with it, the piggyback will just be for standard sensors. But once I get to playing with one, I can almost guarantee that I will write an auto-tuning feature...

While you're at the JY - you might want to grab any turbo or N/A ECUs and wiring connectors you see. With those, a quick-install adapter can be made for the LegaCU.

-K- · Post by **-K-** » Sat Apr 16, 2005 6:23 pm

Well the stock MAF will still run out of sensor range. So I'm going to be building a insert to lower the amount of air getting to the sensor wire. I'll post a thread on this plan when figure it out. If you want one to play with let me know.

If you are going to put an auto-tune in I'd like to see it use a wbO2 input.

Also if I can't get my SAFC II to work and you think you could get some info out of it I might send it your way. It has a lot of different stock MAF's transfers built in. I can tell it what sensor is being used on the car and what sensor's output I want to go to the ECU. It doesn't have the USDM Legacy but it has a ton of Jap cars.

free5ty1e · Post by **free5ty1e** » Sat Apr 16, 2005 6:35 pm

Yes, the stock MAF will only read what, 200 g/s? But it actually won't matter for the purposes of this product, since the stock ECU knows the stock MAF range and that's what we're faking. It doesn't actually have to read the higher airflow values properly, it only has to know the RPM and MAP readings to determine how to trim (or what to output) for the faked MAF reading for the ECU to interpret into injector control.

I'd be interested to see what you come up with, however... I will have a garage shortly to play in and will be doing all sorts of experiments anyway.

And of course, auto tune must use a wideband O2 - we'll need the accuracy for the minute adjustments this thing'd make.

-K- · Post by **-K-** » Sun Apr 17, 2005 3:37 am

Sounds good, can't wait till I can get my hands on one.

Did you ever think of mapping the MAF, MAP, RPM, and TPS then use the MAP, RPM, and TPS to make up the correct MAF output without a MAF at all?

azn2nr · Post by **azn2nr** » Sun Apr 17, 2005 4:58 am

now that would be cool if we could just produce the signals without the maf being there elimiating it completly.

ohh the possibilites

free5ty1e · Post by **free5ty1e** » Sun Apr 17, 2005 3:12 pm

That's definately possible... not a bad idea. Vikash - any input on this? Hmm.....

For now I'll use the MAF but future revisions may include an option to eliminate it altogether.

Our stock MAP sensors have a range of -280mmHg to 1720mmHg, which is roughly 33.25psi max... should be enough range to do that... (or did I convert wrong?)

vrg3 · Post by **vrg3** » Sun Apr 17, 2005 5:33 pm

I think we might have already mentioned that idea... maybe even in this thread.

But basically, if you can precisely measure intake air temperature, manifold absolute pressure, and engine speed, you can determine airflow for any particular engine. That's what speed density engine management does -- it has a volumetric efficiency table that tells it how much air flows at any given engine speed and MAP, and corrects the density based on IAT and barometric pressure. This VE table does need to be changed whenever anything that affects volumetric efficiency is changed, so it's dependent on modifications.

I think the stock sensor's upper limit is more like 15 or 16 psi.

93forestpearl · Post by **93forestpearl** » Sun Apr 17, 2005 8:34 pm

Is there a way to find out a MAF's transfer function, or can that only be done on a flowbench? There has to be people that know them for larger MAFs being used like one from a cobra or 300zx and such.
Will removing the airbox be ok with this setup? Since I plan on building a rotated mount and doing some fmic plumbing this summer, I'd like to just run some pipe to the fenderwell.

I wonder which air metering method is more accurate. It sounds to me that using the MAP to sense air is quite a bit more complicated than just metering it with a MAF. How would you know what the the VE is with any given modification? I haven't taken fluids yet, but all the changes in directions, volumes, splitting, textures, etc. throughout an engine make me picture long and painful calculations to figure it out. I would hope there's a different way to figure it out.

Will we be able tell the LegaCU how big our injectors are? or is there or is that something we have to deal with?

Aside from that, all I can say is damn, the internet was the best thing to happen to gear heads

vrg3 · Post by **vrg3** » Sun Apr 17, 2005 9:25 pm

You wouldn't know a priori what the VE table's values are. You don't usually calculate it; you guess at it and then observe what happens to the engine when you run with those parameters.

NICO · Post by **NICO** » Tue Apr 19, 2005 5:52 am

ok is there a system that wont cost me a lot that i can make work on my legacy turbo? i ant scared to wire the hole thing up what i was thinking take a wrx system and make it work can it be done i am running out of time.

free5ty1e · Post by **free5ty1e** » Wed Apr 20, 2005 1:46 am

Well, the LegaCU is only worked on in my free time right now, but it's coming along. It keeps getting set back by paid work, and issues I have to deal with on my cars. Like right now, I'll be distracted for a bit while I figure out my clutch situation as it has decided to begin slipping... (hint hint)

http://bbs.legacycentral.org/viewtopic.php?t=21168

azn2nr · Post by **azn2nr** » Fri Apr 29, 2005 2:37 am

any updates

93forestpearl · Post by **93forestpearl** » Wed May 18, 2005 8:54 pm

bump

Had an idea, and can't remember if its been covered. Could this unit function as some sort of a security device? As in, enter a code for the car to run or something like that. Not to many people have access to a flatbed.

free5ty1e · Post by **free5ty1e** » Thu May 19, 2005 1:53 am

heh... life's a biatch sometimes - LegaCU has been untouched for a few crazy weeks now, I should once again be heading out to Nevada in the next month or two and then, once settled will again resume work on this. It will be a great piggyback but it might be a bit longer than anticipated...

free5ty1e · Post by **free5ty1e** » Thu May 19, 2005 1:54 am

(oh and hey - thats a great idea. I don't see why not.)

vrg3 · Post by **vrg3** » Thu May 19, 2005 2:06 am

Yeah, life's like that... It's worth waiting for a good thing though.

Yeah, the immobilizer feature is a cool idea. You could have a mode where it allows the car to start but only after several seconds of cranking, and then makes it run rough and then stall out after a short time. The would-be thief might just think the engine's crapping out or something.

free5ty1e · Post by **free5ty1e** » Wed Jun 08, 2005 2:53 pm

OK... I have just shipped the latest iPod one-touch voice recorder unit off to be tested, and have a few days of leeway that I intend to use to get back to work on the LegaCU. Just took down the immobilizer feature in the "to do" section of the code, and am finding all the pieces of the prototype.

I do believe the first thing I'll try to do is digitally control boost with the stock solenoid. I suppose I'll be limited to the amount of pressure the stock MAP sensor can read, pre-FCD of course.

So Vikash - to speed things along here, could you help me think this through? I would read the signal voltage from the MAP sensor, and based on the reading I would either raise a pin to logic high to open the bleed or lower the pin back to ground to close it again... correct? Which wire controls the solenoid, any idea? That should be a relatively quick function to code and test...

vrg3 · Post by **vrg3** » Wed Jun 08, 2005 3:01 pm

I don't think you want to get into closed-loop boost control... What you're suggesting is likely to result in oscillations. You would have to at the very least implement PD control.

What I was suggesting should still be fairly simple, but would require the infrastructure for editing tables:

Read in the tach signal and convert it to a number representing the frequency. Read in the TPS signal. Then use those two to look up a duty cycle in a 2-D table, and drive the wastegate control solenoid at that duty cycle.

http://www.graphics.cornell.edu/~v/ecupins/

The solenoid is powered through the ignition relay, and the ground side of the circuit is switched by the ECU -- it normally goes to the ECU's "Wastegate control" pin. So you'd want to drive it with your own open collector driver.

You'd have to pacify the ECU by connecting the pin to an ignition-switched +12v source through a 200-ohm 1-watt resistor or something.

You could start by setting a constant duty cycle at all sites in the table. The higher the duty cycle, the higher the boost. Then you can start playing with the table to make it bleed more at higher RPMs and higher throttle positions.

The above is exactly how newer Subarus do boost control from the factory.

free5ty1e · Post by **free5ty1e** » Wed Jun 08, 2005 3:08 pm

Thaaats right. I remember that whole plan now - forgive my lack of remembrance, I have been distracted as of late

Thy will be done.

free5ty1e · Post by **free5ty1e** » Wed Jun 08, 2005 4:26 pm

by the by, for my initial prototyping I will not be intercepting signals at the ECU just yet. Do you know which wire is which on the solenoid's connector in the engine compartment? That's where I'll modify for now since it's much more accessable - before I go and mess with the ECU connector.

I'd rather spend the time and make a proper plug-and-play connector from this ECU and harness Jason sent me later when I'm ready.

vrg3 · Post by **vrg3** » Wed Jun 08, 2005 5:51 pm

You could figure it out pretty easily -- just unplug the connector and look for the pin that doesn't have +12v on it. But I would imagine it's the black wire, as the other one is pink/red.

THAWA · Post by **THAWA** » Thu Jun 09, 2005 3:50 am

How close are you to coming to nevada now?

free5ty1e · Post by **free5ty1e** » Thu Jun 09, 2005 2:22 pm

Looks like I actually will be staying in Orlando for at least a few more months before moving out there. The LegaCU ought to be in testing with some Legacy owners before I relocate.

Oh, and the first experiment I will run with the prototype is the closed-loop boost controller, where you just set a display to your desired boost level and it servo-locks the wastegate to achieve that. I keep going over the operation in my head and I've got to see how bad, if at all, this thing oscillates. Then I'll try the table idea. But the closed-loop boost control is a lot less work and much closer to testing, which is what I've been dying to begin doing while I've got half a chance.

Worst case, if the PSoC can handle the closed-loop boost control but nothing else, then I'll put it all on a separate chip. They're only like $4 apiece so its no big deal to add more processing power...

mikec · Post by **mikec** » Thu Jun 09, 2005 3:10 pm

Closed loop adjustable boost control alone would be pretty sweet. Especially for about the same price as a decent store bought MBC.

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T-leg Piggyback ECU R&D