Sbeghan
Veteran Member
I've got a cable in the mail and poor judgement so I'll be attempting to flash my ECU soon. In preparation I have been looking at an ECU dump and the maps in it trying to understand it. I'm starting this thread so that you can share in my stupidity. Obviously this is for the 1.9L ALH engine, and 02-03s can be flashed via a cable. I grabbed the ECU off of the internets (www.chiptuning.org, stock ECU forum) - when I get my cable I'll dump my ECU and compare it for any discrepancies.
If you want to do some reading here's a previous similar thread http://forums.tdiclub.com/showthread.php?t=279207
a primer on the maps
https://sites.google.com/site/vagecumap/diesel-engine-control
Vag EDC15P Suite (similar to WinOLS but for TDIs specifically)
http://trionic.mobixs.eu/
And I'll post a link to an ECU dump later - for some reason I can't seem to upload zips right now.
So the ECU uses tables called maps to look at the state of the engine and then vary a couple things. Primarily: Fuel quantity (controlled by the fuel pump voltage map, more correctly thought of as length of injection event), fuel timing (how many degrees BTDC or ATDC does the injection start), Boost pressure. It can also sense the fuel quantity, fuel timing, boost pressure, mass air flow, coolant fuel and air temperatures, engine rpm, pedal position, etc.
I'm probably at best, half correct about these things, and mostly wrong. Please correct me (as that's the whole point of this thread).
I believe that the first thing the ECU does is look at the driver's wish map, aka, the go pedal.
Looking at this we can see that it tends to max out quantity of fuel injected at around 50 mg (I'll note that the maps don't actually say 50mg, they say a number and vagsuite translates that to 50mg, but since its calibrated for PD engines sometimes their translations may be off). Note that the map is nonlinear with respect to rpms. This lets you apply a light throttle and the engine will naturally stabilize at some RPM range (as at higher rpms it won't fuel). It also shows that above 5000 RPM it really pulls back on the fueling.
If I were to increase available boost I'd want to go into this map and increase the values so that I could achieve higher fueling.
There is also a related map called inverse driver wish, which is used by the cruise control. As I understand it the cruise control will inject whatever quantity of fuel is needed to maintain a particular speed, and based on the rpms and quantity injected it will move the pedal to show what the throttle position is. Not so important to mess with, but I could play some funny jokes on people by having their pedal go up and down randomly.
So the engine knows how much fuel it wants (max), it also needs to know how much air is available.
Air has a density of about 1.225 g/L at STP. The engine has a displacement of 1.9L or ~.475L per cylinder. So at STP we get 581mg of air available. This can be less with a restricted intake or if you are at high altitudes and there is less air pressure, but in general this is always the floor value of how much air is available. The engine will fuel up to the available limit of air. How does it decide this? With the smoke limiter map.
I also calculated the fuel air ratio in the smoke limiter
I've heard that stoich is optimal (14.6-14.7), but with a diesel you may want to lean it up a bit to reduce smoke (its really hard to burn that last bit when the oxygen is also almost at 0), something like 17-18 as a fuel air ratio. However, the apparent ratios here are much higher across the majority of the map. 20-24 seems to be the going rate. Also, as I understand it, you can decrease the FAR at higher boost pressures - at a 17:1 ratio at no boost you'll have some oxygen left over, but at full stock boost a 17:1 ratio will have twice as much oxygen (and due to the temperature, probably more than twice the partial pressure), so you could conceivably have a lower ratio and still achieve a smokeless burn. The other thing is that having a high ratio requires the use of excess boost which lowers the engine efficiency by creating drag with the turbo.
Can I lower the fuel air ratios across the board and increase my fuel economy?
The other thing that I am concerned about on this map is the max air quantity plateaus at 850mg - at 1.95 bar boost and assuming cool air and perfect air flow you'll have 1158mg of air. Increasing the available boost will increase this even more. Won't the smoke limiter interfere with proper fueling? Heck, If you look at the driver wish 40-50mg fuel is the max in that and I don't see where on the smoke limiter you can even achieve that.
There is also this map:
I believe that this is another hard limit on the quantity of fuel injected. Look at that, max fueling is 37.5 mg of fuel. I think that the torque limiter only pertains to the driver's wish and not to things like the idle fuel (since it clearly asks for fuel in those maps at 0-500 rpm, which is needed to start the engine). Together with the torque and smoke limiter we see that fuel is limited to 37-40 mg and the driver's wish has an effectively flat zone where it can be asking for 40-50 mg and not getting it. BORING. I'll have to do something about that.
There are a couple maps that control fueling behind the scenes. We'll start with the N146 Pump voltage map.
Once injection has started it will continue for a particular time determined by the pump voltage map. From what I understand voltage is applied to a solenoid in the pump to determine how long the injection event lasts. More voltage, longer injection, thus, more fuel. I do not know if this is linear, or what factors affect it (ex, fuel temp, engine speed).
On this map I notice a couple things. At 0 requested fuel it still applies voltage to the map from 1260 to 210 RPM. This I think is what helps maintain idle, starts the engine (gives fuel at low RPM from the starter), and creates the soft stop in RPMs when you push the clutch in (notice how the RPMs quickly drop to 1200 rpm and then they settle into 900 rpm softly?). 0 rpms gives 0 fuel, of course.
I see that at moderate fueling requests (from >0 to 20 mg) the voltage decreases with increasing RPMs or stays pretty flat. I am wondering if increasing the RPMs increases the pressure in the fuel pump thus needing less voltage or time open for an equivalent injection of fuel. Above 20mg requested fuel the opposite holds true, holding the injection event open longer at higher RPMs.
Does anyone know why this is?
Next up are the start of injection maps. I have a slew of these that I can see ranging from -20C to 86C. There only really appear to be two of them - a cold and hot one. This should be read as when the injection starts BTDC. Negative numbers indicate ATDC requests.
Hot Timing
Cold Timing
At 4C and below the cold map is used. There is a transitory map at 10C and 20C, and a hot map that is used at 35C and above.
Notice that as RPMs go up and in general, as fueling goes up the SOI goes up (more advanced). There are two reasons for this that I understand. For a given quantity of fuel you must have a given time period for injection and you want to balance the injection around TDC, so for higher RPMs you need to advance the start of injection because by the time you finish injecting the same quantity of fuel you will be further past TDC into the power stroke. Similar to this, for more fuel, you need to lengthen the injection event, both advancing the start of injection, and by lengthening the injection period, retarding the end of injection.
With a cold engine you want to advance timing to give the fuel more time to burn. With a hot engine you can retard the timing because the fuel burns more easily and you want to have most of the burn around TDC or just after it.
Some questions I have about the map are: what's with the bump in timing at 1491 RPM when cold? In fact, why are these maps so darn bumpy?
Also, why is the SOI after TDC in the normal driving regime on a hot engine (1500-2500 RPM, 0-20 mg/stroke)? Is this for efficiency or emissions?
The last fueling map I'll bring up is the Start Injection Quantity map.
When you're starting the engine this is how much fuel is injected at a given RPM and temperature of the engine. I've heard that on some maps on a hot engine it requests 0 fuel, leading to hot starting problems. Its otherwise not that interesting.
Continuing on... Boost! There is a map, the Boost Target Map
For a given RPM and *requested* fueling the ECU will look at this map and say "I want this much boost!" (If it wants 25mg @ 2500 rpm but is making 1000 mbar of pressure it will request 1500mbar and inject less according to the smoke limiter map).
---continued---
If you want to do some reading here's a previous similar thread http://forums.tdiclub.com/showthread.php?t=279207
a primer on the maps
https://sites.google.com/site/vagecumap/diesel-engine-control
Vag EDC15P Suite (similar to WinOLS but for TDIs specifically)
http://trionic.mobixs.eu/
And I'll post a link to an ECU dump later - for some reason I can't seem to upload zips right now.
So the ECU uses tables called maps to look at the state of the engine and then vary a couple things. Primarily: Fuel quantity (controlled by the fuel pump voltage map, more correctly thought of as length of injection event), fuel timing (how many degrees BTDC or ATDC does the injection start), Boost pressure. It can also sense the fuel quantity, fuel timing, boost pressure, mass air flow, coolant fuel and air temperatures, engine rpm, pedal position, etc.
I'm probably at best, half correct about these things, and mostly wrong. Please correct me (as that's the whole point of this thread).
I believe that the first thing the ECU does is look at the driver's wish map, aka, the go pedal.
Looking at this we can see that it tends to max out quantity of fuel injected at around 50 mg (I'll note that the maps don't actually say 50mg, they say a number and vagsuite translates that to 50mg, but since its calibrated for PD engines sometimes their translations may be off). Note that the map is nonlinear with respect to rpms. This lets you apply a light throttle and the engine will naturally stabilize at some RPM range (as at higher rpms it won't fuel). It also shows that above 5000 RPM it really pulls back on the fueling.
If I were to increase available boost I'd want to go into this map and increase the values so that I could achieve higher fueling.
There is also a related map called inverse driver wish, which is used by the cruise control. As I understand it the cruise control will inject whatever quantity of fuel is needed to maintain a particular speed, and based on the rpms and quantity injected it will move the pedal to show what the throttle position is. Not so important to mess with, but I could play some funny jokes on people by having their pedal go up and down randomly.
So the engine knows how much fuel it wants (max), it also needs to know how much air is available.
Air has a density of about 1.225 g/L at STP. The engine has a displacement of 1.9L or ~.475L per cylinder. So at STP we get 581mg of air available. This can be less with a restricted intake or if you are at high altitudes and there is less air pressure, but in general this is always the floor value of how much air is available. The engine will fuel up to the available limit of air. How does it decide this? With the smoke limiter map.
I also calculated the fuel air ratio in the smoke limiter
I've heard that stoich is optimal (14.6-14.7), but with a diesel you may want to lean it up a bit to reduce smoke (its really hard to burn that last bit when the oxygen is also almost at 0), something like 17-18 as a fuel air ratio. However, the apparent ratios here are much higher across the majority of the map. 20-24 seems to be the going rate. Also, as I understand it, you can decrease the FAR at higher boost pressures - at a 17:1 ratio at no boost you'll have some oxygen left over, but at full stock boost a 17:1 ratio will have twice as much oxygen (and due to the temperature, probably more than twice the partial pressure), so you could conceivably have a lower ratio and still achieve a smokeless burn. The other thing is that having a high ratio requires the use of excess boost which lowers the engine efficiency by creating drag with the turbo.
Can I lower the fuel air ratios across the board and increase my fuel economy?
The other thing that I am concerned about on this map is the max air quantity plateaus at 850mg - at 1.95 bar boost and assuming cool air and perfect air flow you'll have 1158mg of air. Increasing the available boost will increase this even more. Won't the smoke limiter interfere with proper fueling? Heck, If you look at the driver wish 40-50mg fuel is the max in that and I don't see where on the smoke limiter you can even achieve that.
There is also this map:
I believe that this is another hard limit on the quantity of fuel injected. Look at that, max fueling is 37.5 mg of fuel. I think that the torque limiter only pertains to the driver's wish and not to things like the idle fuel (since it clearly asks for fuel in those maps at 0-500 rpm, which is needed to start the engine). Together with the torque and smoke limiter we see that fuel is limited to 37-40 mg and the driver's wish has an effectively flat zone where it can be asking for 40-50 mg and not getting it. BORING. I'll have to do something about that.
There are a couple maps that control fueling behind the scenes. We'll start with the N146 Pump voltage map.
Once injection has started it will continue for a particular time determined by the pump voltage map. From what I understand voltage is applied to a solenoid in the pump to determine how long the injection event lasts. More voltage, longer injection, thus, more fuel. I do not know if this is linear, or what factors affect it (ex, fuel temp, engine speed).
On this map I notice a couple things. At 0 requested fuel it still applies voltage to the map from 1260 to 210 RPM. This I think is what helps maintain idle, starts the engine (gives fuel at low RPM from the starter), and creates the soft stop in RPMs when you push the clutch in (notice how the RPMs quickly drop to 1200 rpm and then they settle into 900 rpm softly?). 0 rpms gives 0 fuel, of course.
I see that at moderate fueling requests (from >0 to 20 mg) the voltage decreases with increasing RPMs or stays pretty flat. I am wondering if increasing the RPMs increases the pressure in the fuel pump thus needing less voltage or time open for an equivalent injection of fuel. Above 20mg requested fuel the opposite holds true, holding the injection event open longer at higher RPMs.
Does anyone know why this is?
Next up are the start of injection maps. I have a slew of these that I can see ranging from -20C to 86C. There only really appear to be two of them - a cold and hot one. This should be read as when the injection starts BTDC. Negative numbers indicate ATDC requests.
Hot Timing
Cold Timing
At 4C and below the cold map is used. There is a transitory map at 10C and 20C, and a hot map that is used at 35C and above.
Notice that as RPMs go up and in general, as fueling goes up the SOI goes up (more advanced). There are two reasons for this that I understand. For a given quantity of fuel you must have a given time period for injection and you want to balance the injection around TDC, so for higher RPMs you need to advance the start of injection because by the time you finish injecting the same quantity of fuel you will be further past TDC into the power stroke. Similar to this, for more fuel, you need to lengthen the injection event, both advancing the start of injection, and by lengthening the injection period, retarding the end of injection.
With a cold engine you want to advance timing to give the fuel more time to burn. With a hot engine you can retard the timing because the fuel burns more easily and you want to have most of the burn around TDC or just after it.
Some questions I have about the map are: what's with the bump in timing at 1491 RPM when cold? In fact, why are these maps so darn bumpy?
Also, why is the SOI after TDC in the normal driving regime on a hot engine (1500-2500 RPM, 0-20 mg/stroke)? Is this for efficiency or emissions?
The last fueling map I'll bring up is the Start Injection Quantity map.
When you're starting the engine this is how much fuel is injected at a given RPM and temperature of the engine. I've heard that on some maps on a hot engine it requests 0 fuel, leading to hot starting problems. Its otherwise not that interesting.
Continuing on... Boost! There is a map, the Boost Target Map
For a given RPM and *requested* fueling the ECU will look at this map and say "I want this much boost!" (If it wants 25mg @ 2500 rpm but is making 1000 mbar of pressure it will request 1500mbar and inject less according to the smoke limiter map).
---continued---
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