Motronic - long, & not for the uninitiated.

[Robin-535im]

For those interested in the pedantic details of the Motronic, I think I have it all figured out. For those who know where I'm wrong... please enlighten me! For those of you who don't care, this will be really boring.

Here goes: The main purpose of the Motronic (aka DME, ECU) is to make the car run at the 14.7:1 air:fuel ratio that is the accepted best point for a balance of power, emissions and fuel economy. It does this by setting the spark advance timing and the fuel injector pulse duration.

There are several operating modes including startup, warm running, WOT; the last two being those of most interest to us.

Warm running: Engine RPM and air flow are used to look up the correct timing advance and fuel pulse duration for that run point. The computer looks first at the ECU maps (the thing chip tuners modify) and adds to that an offset value for the pulse duration that is learned over time by the history of O2 corrections made in the past. This is the "learning" that our cars do: as we drive down the road, the O2 circuit is constantly trying to make the car run at 14.7:1 air:fuel ratio. It reads the exhaust gas, and modifies the injector pulse duration to reach that ratio. It gradually builds a map of adjustment values for each RPM/Air Flow operating point and adds that to the map that chip tuners program as the starting point, and twiddles it continuously to make the right output ratio.

So reprogramming the fuel map and adding a larger FPR should have no persistant effect to performance in the warm-running condition. All you can do is increase the timing advance as much as you can before it pre-detonates, and let the Motronic stabilize the fuel pulse duration to make the exhaust hit 14.7:1. Note: if in fact your engine needs more gas than can be delivered in the max pulse duration, a larger FPR will overcome that and let you have more fuel, but only up to the point where it again reaches equilibrium. This is most likely to happen at high speeds, where both load and RPM are maxed out and the time available in the cycle for injecting fuel is less than the pulse duration required. Just adding a larger FPR will make the car run rich for the first 10 minutes or so, until the car adapts, and then you're back at 14.7:1, in the warm-running mode.

This is why chips take a while to fully set up. When you first put it in you have to unplug the DME from the car, which erases the learned fuel-pulse-duration-offset map. Your timing is now advanced, but the fuel map is not stabilized at the best setting for 14.7:1 operation - it's just whatever was programmed by the chip tuner. As you drive around town (heavy footed now because it's so much more fun that way) the computer watches all the corrections it has to make at all the RPM/Air Flow operating points and stores that away, averaging them over time. Gradually, this learned fuel duration offset map stabilizes, and it acts as a feed-forward command (any controls engineers out there?) to the engine, so that instead of having to read the O2 signal and correct after the fact, it anticipates the correct pulse duration and uses that as a starting point. The O2 signal is still used to fine tune the pulse duration, and if anything changes in the system, the car will adapt to it over time to within reasonable limits.

Wide Open Throttle (WOT): In this case, the O2 signal is ignored. The engine RPM is used to determine the pulse duration and timing advance. There is no learning... the chip map is it. Here's where the fuel map programming matters too, because what you program is what you get. In this case, a perfect chip would have both timing advance and fuel map programmed for your particular car and you can choose to run at a different air/fuel ratio, such as 13.5:1 which is close to the "maximum power" point. But to get it to run there, you have to read the exhaust gas for all the operating points, and manually tune the pulse duration as well as the timing to make the WOT map just right.

Conclusions? Well...
1) To really tune your car right you need to read the exhaust gas and optimize the WOT map fuel pulse duration.
2) Those of us who drive at 6000 RPM a few times a day will probably benefit from a larger FPR, but you need to look at the exhaust to know for sure.
3) I have too much time on my hands.
4) The learning feature of our cars means all we can really change is the timing advance in the warm-running mode, the rest will adapt.

[632 Regal]

Very good write up, I followed it and even understand it!!

[gale]

Thanks for sharing your insights Robin. Along those lines, I'm still not clear whether the DME & TCU (automatic) are very tightly integrated on engines that have the EML throttles. Know anything about them? My interest is I'd love to do an m70 conversion with a manual trans but don't know what intricacies are involved, I know it's been done but largely with 850 parts. Wouldn't want to get 90% into one only to have it go into permanant limp mode.

Mine is a plain bread & butter m30 with the conventional mechanical direct cable throttle so had no issues with it.

[BennyM]

.

[George M]

yup...nice summary Robin. You hit 6K RPM a few times a day? Wow!
:-)

[DanDombrowski]

It probably is pretty integrated, but I'm not sure about the BMWs, I'm basing my assumption on working with our Jeep which, when the tranny output sensor went bad, made the engine have some wacky throttle patterns, and that has an EML if I'm not mistaken.

Thanks for sharing your insights Robin. Along those lines, I'm still not clear whether the DME & TCU (automatic) are very tightly integrated on engines that have the EML throttles. Know anything about them? My interest is I'd love to do an m70 conversion with a manual trans but don't know what intricacies are involved, I know it's been done but largely with 850 parts. Wouldn't want to get 90% into one only to have it go into permanant limp mode.

Mine is a plain bread & butter m30 with the conventional mechanical direct cable throttle so had no issues with it.

[DanDombrowski]

This adaptation is what allows most people to run a low boost turbo setup without extensive computer modifications, as the car adapts to the extra air. Been meaning to try it on my Volvo as many people have done for under $300, but I'll be damned if every time I try I keep getting calls asking why I'm not at work. They want me to go EVERY Monday through Friday? Geez!

Where did you find information that the computer ignores the O2 readout at WOT? As I understand it from riding in cars w/ A/F meters, thats the only time that you can actually read the gauge accurately, as at partial throttle it jumps all over the place. Not saying that the ECM doesn't ignore it, just wondering where you read that.

Now, let me know when you find some way to plug into these cars ECMs and get diagnostic data on a PC. I've been doing that alot at work lately, and you can get some pretty in depth info from newer cars.

Good luck

For those interested in the pedantic details of the Motronic, I think I have it all figured out. For those who know where I'm wrong... please enlighten me! For those of you who don't care, this will be really boring.

Here goes: The main purpose of the Motronic (aka DME, ECU) is to make the car run at the 14.7:1 air:fuel ratio that is the accepted best point for a balance of power, emissions and fuel economy. It does this by setting the spark advance timing and the fuel injector pulse duration.

There are several operating modes including startup, warm running, WOT; the last two being those of most interest to us.

Warm running: Engine RPM and air flow are used to look up the correct timing advance and fuel pulse duration for that run point. The computer looks first at the ECU maps (the thing chip tuners modify) and adds to that an offset value for the pulse duration that is learned over time by the history of O2 corrections made in the past. This is the "learning" that our cars do: as we drive down the road, the O2 circuit is constantly trying to make the car run at 14.7:1 air:fuel ratio. It reads the exhaust gas, and modifies the injector pulse duration to reach that ratio. It gradually builds a map of adjustment values for each RPM/Air Flow operating point and adds that to the map that chip tuners program as the starting point, and twiddles it continuously to make the right output ratio.

So reprogramming the fuel map and adding a larger FPR should have no persistant effect to performance in the warm-running condition. All you can do is increase the timing advance as much as you can before it pre-detonates, and let the Motronic stabilize the fuel pulse duration to make the exhaust hit 14.7:1. Note: if in fact your engine needs more gas than can be delivered in the max pulse duration, a larger FPR will overcome that and let you have more fuel, but only up to the point where it again reaches equilibrium. This is most likely to happen at high speeds, where both load and RPM are maxed out and the time available in the cycle for injecting fuel is less than the pulse duration required. Just adding a larger FPR will make the car run rich for the first 10 minutes or so, until the car adapts, and then you're back at 14.7:1, in the warm-running mode.

This is why chips take a while to fully set up. When you first put it in you have to unplug the DME from the car, which erases the learned fuel-pulse-duration-offset map. Your timing is now advanced, but the fuel map is not stabilized at the best setting for 14.7:1 operation - it's just whatever was programmed by the chip tuner. As you drive around town (heavy footed now because it's so much more fun that way) the computer watches all the corrections it has to make at all the RPM/Air Flow operating points and stores that away, averaging them over time. Gradually, this learned fuel duration offset map stabilizes, and it acts as a feed-forward command (any controls engineers out there?) to the engine, so that instead of having to read the O2 signal and correct after the fact, it anticipates the correct pulse duration and uses that as a starting point. The O2 signal is still used to fine tune the pulse duration, and if anything changes in the system, the car will adapt to it over time to within reasonable limits.

Wide Open Throttle (WOT): In this case, the O2 signal is ignored. The engine RPM is used to determine the pulse duration and timing advance. There is no learning... the chip map is it. Here's where the fuel map programming matters too, because what you program is what you get. In this case, a perfect chip would have both timing advance and fuel map programmed for your particular car and you can choose to run at a different air/fuel ratio, such as 13.5:1 which is close to the "maximum power" point. But to get it to run there, you have to read the exhaust gas for all the operating points, and manually tune the pulse duration as well as the timing to make the WOT map just right.

Conclusions? Well...
1) To really tune your car right you need to read the exhaust gas and optimize the WOT map fuel pulse duration.
2) Those of us who drive at 6000 RPM a few times a day will probably benefit from a larger FPR, but you need to look at the exhaust to know for sure.
3) I have too much time on my hands.
4) The learning feature of our cars means all we can really change is the timing advance in the warm-running mode, the rest will adapt.

[Hector]

the EAT chip, optimum performance will not be achieved right away until a "learning curve" has been established. ...and I thought all this was just a crap shoot :o)

[MarkD]

Hi Robin,
what you posted is basically correct but there is still more that could be added. (such as timing CORRECTION MAPS that retard timing based on IAT and coolant temperature)

Also, the WOT maps are trimmed based on the value that the software sees it has to trim the Part Throttle (PT maps) by. Part Throttle mode is what you call "warm running". The DME switches between PT and WOT mode by looking at for the WOT switch on the TPS to close. This usually happens at around 75% of the gas pedal depression.

Since the software trims the WOT fuel maps, increasing fuel pressure or using bigger injectors does not work as well as could be expected, unless you adjust the WOT fuel maps in the chip to supply more fuel also.


Mark

For those interested in the pedantic details of the Motronic, I think I have it all figured out. For those who know where I'm wrong... please enlighten me! For those of you who don't care, this will be really boring.

Here goes: The main purpose of the Motronic (aka DME, ECU) is to make the car run at the 14.7:1 air:fuel ratio that is the accepted best point for a balance of power, emissions and fuel economy. It does this by setting the spark advance timing and the fuel injector pulse duration.

There are several operating modes including startup, warm running, WOT; the last two being those of most interest to us.

Warm running: Engine RPM and air flow are used to look up the correct timing advance and fuel pulse duration for that run point. The computer looks first at the ECU maps (the thing chip tuners modify) and adds to that an offset value for the pulse duration that is learned over time by the history of O2 corrections made in the past. This is the "learning" that our cars do: as we drive down the road, the O2 circuit is constantly trying to make the car run at 14.7:1 air:fuel ratio. It reads the exhaust gas, and modifies the injector pulse duration to reach that ratio. It gradually builds a map of adjustment values for each RPM/Air Flow operating point and adds that to the map that chip tuners program as the starting point, and twiddles it continuously to make the right output ratio.

So reprogramming the fuel map and adding a larger FPR should have no persistant effect to performance in the warm-running condition. All you can do is increase the timing advance as much as you can before it pre-detonates, and let the Motronic stabilize the fuel pulse duration to make the exhaust hit 14.7:1. Note: if in fact your engine needs more gas than can be delivered in the max pulse duration, a larger FPR will overcome that and let you have more fuel, but only up to the point where it again reaches equilibrium. This is most likely to happen at high speeds, where both load and RPM are maxed out and the time available in the cycle for injecting fuel is less than the pulse duration required. Just adding a larger FPR will make the car run rich for the first 10 minutes or so, until the car adapts, and then you're back at 14.7:1, in the warm-running mode.

This is why chips take a while to fully set up. When you first put it in you have to unplug the DME from the car, which erases the learned fuel-pulse-duration-offset map. Your timing is now advanced, but the fuel map is not stabilized at the best setting for 14.7:1 operation - it's just whatever was programmed by the chip tuner. As you drive around town (heavy footed now because it's so much more fun that way) the computer watches all the corrections it has to make at all the RPM/Air Flow operating points and stores that away, averaging them over time. Gradually, this learned fuel duration offset map stabilizes, and it acts as a feed-forward command (any controls engineers out there?) to the engine, so that instead of having to read the O2 signal and correct after the fact, it anticipates the correct pulse duration and uses that as a starting point. The O2 signal is still used to fine tune the pulse duration, and if anything changes in the system, the car will adapt to it over time to within reasonable limits.

Wide Open Throttle (WOT): In this case, the O2 signal is ignored. The engine RPM is used to determine the pulse duration and timing advance. There is no learning... the chip map is it. Here's where the fuel map programming matters too, because what you program is what you get. In this case, a perfect chip would have both timing advance and fuel map programmed for your particular car and you can choose to run at a different air/fuel ratio, such as 13.5:1 which is close to the "maximum power" point. But to get it to run there, you have to read the exhaust gas for all the operating points, and manually tune the pulse duration as well as the timing to make the WOT map just right.

Conclusions? Well...
1) To really tune your car right you need to read the exhaust gas and optimize the WOT map fuel pulse duration.
2) Those of us who drive at 6000 RPM a few times a day will probably benefit from a larger FPR, but you need to look at the exhaust to know for sure.
3) I have too much time on my hands.
4) The learning feature of our cars means all we can really change is the timing advance in the warm-running mode, the rest will adapt.

[winfred]

they wouldn't put numbers that high on the tach if they didn't want you to go there i make it a point to air em out a few times a day if for no other reason if i need to stomp on some unsuspecting fartcan honda it doesn't belch out that nasty cloud of soot that accumulats, now on diesels i love that cloud, it's fun to fart all over some ******* that riding your bumper if i didn't have too many car projects allready id take on the 524td that's at the shop 5 speed it, intercool it, add a egt gauge, and start turning up the injection pump and wastegate

You hit 6K RPM a few times a day?