Factory EEPROM Tuning Theory

[Def]

I posted this in the Forced Induction forum, but with a whooping 4 views in 24 hours, I figured I'd get more feedback and discussion here. Sorry for the cross-post, but I had no idea that forum was so dead!

I've lately had the urge to clear up a few questions regarding this interesting topic of tuning your factory EEPROM with commonly available burners/emulators and good ole' fashion ingenuity.

Here it goes -

The topic is IGNITION TIMING.

-Background info, most should be intimately familiar with this-

With Hondas, a MAP sensor is available and the ECU uses this as a way to approximate the amount of air entering the engine. When you boost the car, a GM 3 bar MAP sensor can easily tell you what pressure the engine is seeing. This makes it very easy to approximate what an MSD BTM does, i.e. retard the timing a set amount per psi of boost(say 0.5 degrees/psi).

With a Nissan, it uses a MAF sensor that has a hotwire that is cooled by incoming air. More voltage is required to keep the wire hot when more air is moving over it. Using this voltage as an input allows one to accurately meter the air once the voltage versus mass airflow curve is known.

Now onto my question - the factory ECU only sees this representation of the incoming mass airflow which is definitely NOT the same as pressure. So how would one tailor the ignition tables to retard under boost, but give a good amount of advance under vacuum? I'm guessing the ignition tables generally taper off as loads increase but go up slightly as RPMs go up(less time for the burn to start given the same ignition advance since the engine will be rotating - 20 degrees of engine rotation at 1000RPM is six times longer than at 6000RPM).

So am I just thinking about this too much? Would one just program a MAF EEPROM to drop off timing with increasing load in a linear fashion without even thinking about pressure just like one would increase fuel in a linear fashion for increasing loads?

I suppose looking at the pressure of the intake manifold one is just using that as a round about representation of the incoming mass air of the engine, which the MAF is already metering directly. So in reality it probably is the more simplistic and accurate approach without resorting to looking at the inperfect science of measuring engine induction through pressure and RPM and a gross estimate of volumetric efficiency at that RPM.

Maybe I've been spending too much time looking at guys with their Hondata or Ghettodata and being a little jealous.

Hopefully this will get a little enjoyable discussion going, and help me get ready for the time when I start tuning my own Nissan.

[:: orion ::]

You got it...MAF reads mass of air, no pressure.

If you want to add timing retard based on pressure, then you need E-Manage, or something else like that...

JWT has ignition retard built into their ECUs, but it's based on load values - And like the stock ECU, it looks at throttle position and airflow, then determines a loads value, and gives timing based on that.

Easiest way to retad timing is to trick the ECU by unplugging the TPS, setting the base timing back to ~16-17 BTDC, and then plugging the TPS back in. ECU assumes a base of 20 BTDC and goes from there...so your 4 degree retard stays across the board, with no ill side effects or great negative effects on power.

And you can't "flash" a stock ECU, unless you already have a daughter board and an eprom soldered on...like the JWT setup.

Using the distributoto retard base timing will give you a safe ~250rwhp (8-9psi from a T3/T4 on a KA24DE), but after that, you need something more.

MSD BTM does this based on pressure, but you'd still need fuel tuning.

Later - Brian

[ziggy682]

I too, have been thinking about eprom progamming as a means of fuel and ignition management for my KAT. I've been keeping a close eye on http://www.zcontrol.net/ , because he is supposed to be porting this to work with other Nissan ecu's including KA and SR ecu's. By the way, the guy doing zcontrol is the same guy who did ghettodyne for Hondas.

I haven't dug too much into learning about the fuel and ignition maps yet, but I don't think you could really adjust timing directly with boost because of our MAF's. I think you're onto the right idea, with retarding timing as a function of rpm, and air flow.

By the way, there's a forum for eprom tuning that has a 240SX area here http://forum.ztechz.net/.

[huguetpj]

I'm not quite sure if the ECU changes timing according to throttle position, as orion stated, although I'm a bit rusty and need to read all the links and pages I have saved up again (unfortunately their in my home comp).

What I do know is this. The MAF voltage is not linear so it gets transformed into a linear function by the VQ table. This in turn is multiplied (?) by the k value in the ECU. This is why you can't use a 300zx MAF with your stock ECU, both the VQ table and k values are different. So now you have a linear function to give you an air flow value. This is cross referenced in the ignition table with rpm to give you an advance/retard from base timing. So definetely no direct relation to pressure, but through some R&D you could setup a nice ignition table using just MAF vrs rpm readings. For this, though, you would need to exactly now what ignition value the ECU is using... look in http://www.zcontrol.net and you'll find it to be very useful once xtensive comes out with the 240sx program.

By the way, I found one of my links. Take a look at this:

http://cherrypicker.tripod.com....html

It will surely give you plenty of pretty ideas... it gave them to me :pface

[:: orion ::]

I'm not quite sure if the ECU changes timing according to throttle position, as orion stated, although I'm a bit rusty and need to read all the links and pages I have saved up again (unfortunately their in my home comp)...

If I understand it correctly, the ECU uses "load values" vs RPM for the ignition timing maps....

And the load value is determined by throttle position and airflow.

- Brian

[huguetpj]

Maybe I'm understanding it wrong... but here:http://cherrypicker.tripod.com....html

Look for 'Primary Timing Map', third paragraph.

As I said, I may be wrong. I'll find out soon enough. :pface

[Def]

I'm not quite sure if the ECU changes timing according to throttle position, as orion stated, although I'm a bit rusty and need to read all the links and pages I have saved up again (unfortunately their in my home comp).

What I do know is this. The MAF voltage is not linear so it gets transformed into a linear function by the VQ table. This in turn is multiplied (?) by the k value in the ECU. This is why you can't use a 300zx MAF with your stock ECU, both the VQ table and k values are different. So now you have a linear function to give you an air flow value. This is cross referenced in the ignition table with rpm to give you an advance/retard from base timing. So definetely no direct relation to pressure, but through some R&D you could setup a nice ignition table using just MAF vrs rpm readings. For this, though, you would need to exactly now what ignition value the ECU is using... look in http://www.zcontrol.net and you'll find it to be very useful once xtensive comes out with the 240sx program.

By the way, I found one of my links. Take a look at this:

http://cherrypicker.tripod.com....html

It will surely give you plenty of pretty ideas... it gave them to me :pface

Thanks for the zcontrol.net link! That would be super hot to have a program that made poking around in the ECU immeasurably easier. Hopefully it will be done by the time I actually get around to this(good condition S13 KA24DE manual fastbacks are hard to find!).

I already saw that link for tuning the VG20DETT, and it too gave me plenty of ideas.

It also seems that the only "load" an ECU sees is based on the MAF voltage, as I've never heard TPS being referenced when it comes to tuning. I also seem to remember Enthalpy busting someone that showed his "know how" by saying that our ECUs used the TPS input for fuel/timing. When you think about it, some values will never be used on a fuel or timing map(i.e. max MAF voltage at 1000RPM), but they're a safety measure and just easier to put in due to the square dimensions.

Timing *AND* fuel control makes this seem like a really attractive option. Not to mention JWT charges more for their somewhat sloppy tunes(IMO) than BMW tuners do for quality tunes of the much MUCH harder to crack Motronic ECUs my M3 has!

FYI, soldering on a daughterboard and ZIF socket is very common nowadays with just about every ECU out there.

[huguetpj]

FYI, soldering on a daughterboard and ZIF socket is very common nowadays with just about every ECU out there.

It's the desing of the daughterboard that has me a bit confused. But I'm pretty sure once I sit down and look at the original uC/versatile ROM circuit on the motherboard it will be quite simple... specially since the board already has a 40pin connector (used for testing the ECU at the factory).

Right now I just received the PCBs from zcontrol, gonna see if I can solder the components and start playing with the interface... although if my car was running it would be even better

[:: orion ::]

My only comment would be that TPS is directly related to the timing control in that it MUST be unplugged to set the base timing correctly.

Without it plugged in the ECU's feedback and timing control is interupted...

And you guys need to realize that the KA ECU is a little more complicated than the SR or VG ECU...the guy referenced on that page, Ash, was a a local guy, and a good friend of mine. He did the "Zimulator", which was the basis for som eof the other programs...basically allowed you to ROM tune on the fly.

And he couldn't even copy my JWT chip to evaluate it - IIRC, the SR and VG use 256k, 32 pin chips...and the KA uses a 1meg, 40 pin chip that is more expensive and contains more data.

Now, this could be due to the OBD stuff included in S14 ECUs, but nonetheless, throttle position plays a major role in S14 tuning from what I can tell...

As proof, I offer my S14 KA-T dyno with the TPS unplugged - The A/F, that were at ~12.X on the previous pull, stayed at 14 or above, even at WOT...I of course let off at ~3500, but it shows that it's used for fuel tuning somehow, and most likely timing as demonstrated above.

Now, does this hold true for S13s...maybe not.

So, food for thought... - Brian

[Def]

Hrmm.. maybe the ECU calculate a "load" value from a formula involving both the TPS input and MAF voltage. Makes sense and wouldn't be that hard to do.

[huguetpj]

Good point. The TPS needs to be unplug to set base timing. Will have to look into that. But the ztalk program will be very useful in determining this.

By the way, not sure about OBD-II S14s, but at least my 1993 OBD-I KA24DE ECU has a single "versatile rom" chip for ROM. It contains only 256k of ROM, some 16k of RAM (probably not used) and some I/O ports... ohh and a counter.

Now to read the ROM there are 2 ways. You either desolder the "versatile rom" IC and use a universal programmer to do so. Rather $$$ expensive. The other way, using the consult port is to have the ECU dump the contents of the ROM. That way you can have a ROM image to play around.

To tune the ECU you have to solder in a WORKING daughterboard with at least one 256k ROM chip. Then disable the versatile rom IC by removing a superficial jumper on the back of the motherboard. That way the ECU is fooled into reading the ROM contained on the daughterboard through the 40pin connector used for testing at the factory.

This is what JWT does, this is what the Badbiki board does. It ain't that difficult it just takes patience and time. Then tuning... :help