S52 OBDI chips - including large MAF + injector tunes

[e30 gangsta]

matt > all

[matt]

Sooooo... who wants a chip for Christmas? :mrgreen:

[matt]

No, we use analog datalogging also. The data the the OBDI DME can stream isn't in a format the MXL recognizes anyway.

[lateapex31]

Wow, what a discussion, very informative.

Hey Matt, you don't by chance have the OBDI DME data stream definitions for AIM MXL, do you? I would love to free up some analog sensor inputs :)

[WillisE30]

That makes sense. Thank you for correcting my misperception.

[techno550]

No one is disputing that with you. However, the DME is running off those tables you mentioned (timing and fuel delivery) and the MAF at WOT to determine how much fuel to deliver.

WOT falls under open loop opperation, in other words(I know you know but others reading this might not) the DME is NOT considering the O2 senors, ECT, fuel trims or any of the other emmissions related stuff. Fuel trims don't apply when the vehicle is in open loop.

What point would a fuel trim have if it weren't global?

The DME doesn't use O2 feedback in open loop mode (such as is the condition under WOT), but it does use the fuel trims.

The ECU's part throttle tables are populated with what are basically "target AFR values". The WOT tables are likewise populated. The difference between the values in the PT table and the WOT table is the difference in AFR that is to be seen between PT and WOT.
The part throttle tables are generally populated with values that should hit stoich. When that mark is missed, the O2 sensor detects this and the ECU applies a trim value to compensate. Eventually the trim value is *right* and the target value is hit... that trim value is then applied to all tables, including WOT.

If the fuel values were off by a full point, such as a full point lean, at cruise, then they would also probably be about a full point leaner than intended at WOT. if we corrected the PT tables and not the WOT tables, WOT would still be a full point off. That is why fuel trims are global.

[matt]

No one is disputing that with you. However, the DME is running off those tables you mentioned (timing and fuel delivery) and the MAF at WOT to determine how much fuel to deliver.

WOT falls under open loop opperation, in other words(I know you know but others reading this might not) the DME is NOT considering the O2 senors, ECT, fuel trims or any of the other emmissions related stuff. Fuel trims don't apply when the vehicle is in open loop.

False! Fuel trims ALWAYS apply. The motor is not READING the O2 sensors, but it is using information gathered from the O2 sensors at other times and integrated into the adaptation/trim value.

Now, why it calculates the trims at part throttle. The AFR target everywhere between idle and 90% throttle is stoich. A narrowband O2 sensor reads very accurately only right at stoich. Basically, the ECU looks for stoich at part throttle, if it sees rich there, it decides that something is making the MAF read high or some other issue is going on... it removes fuel globally. Any issue that richens the mix at part throttle will apply at full throttle also. And the same thing applies to a lean mixture, but usually the cause of this is an intake leak. Same result, more fuel is added to idle/PT/WOT via a correction factor.

[WillisE30]

Power numbers are affected by AFR. AFR (even at WOT) is affected by adaptations inside the ECU.

No one is disputing that with you. However, the DME is running off those tables you mentioned (timing and fuel delivery) and the MAF at WOT to determine how much fuel to deliver.

WOT falls under open loop opperation, in other words(I know you know but others reading this might not) the DME is NOT considering the O2 senors, ECT, fuel trims or any of the other emmissions related stuff. Fuel trims don't apply when the vehicle is in open loop.

[techno550]

Power numbers will vary with AFR. A simple swap of a chip (and thus zeroed fuel trims) on the dyno will screw with the results. The ecu uses relative target values. i.e. WOT is a set amount richer than part throttle, as specified by the difference in the values between the WOT tables and the PT tables. More importantly, an incorrect WOT AFR could be lean, and lean with well tuned *agressive* spark tables would cause knock. That knock would be detected by the knock sensors, and the ECU would then pull timing. No more knock, but no more power either. "If it were richer and didn't knock, it would have had another 15 degrees of timing in it, and made X more hp" is not an easy thing to account for on the dyno.

These motors *can* run relatively lean at WOT and make reasonable power... IF the timing is still conservative. The factory software likes to sit in the 14's... right around stoich... until 4500 rpm or so, then starts to taper rich from there. My *race* chips start at 12.8 and stay at 12.8, about 2 full AFR points richer from 1k to 4500, and 1 full AFR point richer from 4500 to 6k, than stock. You have a lot more flexibility with the timing in cases like that.

[matt]

Fuel trims have next to nothing to do with the power you'll make at WOT. I'll be happy to dig up my motronic training manuals tomorrow and post excerpts if you'd like.

Power numbers are affected by AFR. AFR (even at WOT) is affected by adaptations inside the ECU.

Under WOT DME will default to tables for timing and fuel based off of load/airflow, lots of fuel injection systems calculate load based off airflow.

The DME does not "default" to anything. At idle, part throttle, and wide open throttle, it is reading the fuel tables we tell it to read, calculating required fuel based on mass air flow, then applying a correction factor that it calculates itself at part throttle.

but saying that power numbers will be is misleading.

I don't appreciate that. Hundreds of hours figuring out the ECU's programming, thousands of dollars spent on dyno tuning, and hundreds of thousands of miles of road testing disagree with your assertion also.

[WillisE30]

Fuel trims have next to nothing to do with the power you'll make at WOT. I'll be happy to dig up my motronic training manuals tomorrow and post excerpts if you'd like. Under WOT DME will default to tables for timing and fuel based off of load/airflow, lots of fuel injection systems calculate load based off airflow.

In other words if you're looking at straight horsepower numbers on a dyno swapping chips will give you a better comparison than you're claiming. I'll be the first to grant you that things like idle and part throttle drivability will be effected, but saying that power numbers will be is misleading.

[matt]

It takes a good while. Usually comparisons are done with ~6 dyno pulls. Not nearly enough. A half hour on the street should be plenty.

Besides, there is more power to be had in the ignition tables of the chip than the fuel tables.

I agree with that, but the AFR is critical also.

Sure the AFR might not be ideal, but it almost never is.

Actually, it almost always is, in a properly functioning system. I've attached a screenshot of a datalog on the TRM stage 1 turbo prototype. Running a TRM chip and 30lb injectors with a stock MAF on a 413.

[BimmerToad]

I don't really understand what you're saying here. The person burning the chip (hopefully) decides what the target AFR is. At full throttle, that's rich of stoich 99 times out of 100.

When you first mentioned target AFR, I thought you were implying there was a target AFR value of a WOT closed loop system. Now that I realize that you mentioned target AFR with respect to the chip tuner, so now we're on the same page. Sorry for the confusion.

Anyway, that quote doesn't exactly apply to the Bosch systems we use. There may be some systems that ignore the MAF because of resonances or other issues at WOT, but not ours. The MAF is NEVER disregarded.

My bad, totally forgot about the MAF.

Back to comparing chips, assuming a well functioning clean fuel system, would it take that long for the fuel trims to get a ball park figure prior to a dyno run? Sure the AFR might not be ideal, but it almost never is. Besides, there is more power to be had in the ignition tables of the chip than the fuel tables.

[matt]

Was that really necessary? Sorry man, but you're coming off like a total douche

Well... sorry about that. I am trying to lead you toward the answer rather than just spitting it out.

AFR targets at WOT are determined by the tuner burning the chip, not some target AFR ratio.

I don't really understand what you're saying here. The person burning the chip (hopefully) decides what the target AFR is. At full throttle, that's rich of stoich 99 times out of 100.

Anyway, that quote doesn't exactly apply to the Bosch systems we use. There may be some systems that ignore the MAF because of resonances or other issues at WOT, but not ours. The MAF is NEVER disregarded.

Now, why it calculates the trims at part throttle. The AFR target everywhere between idle and 90% throttle is stoich. A narrowband O2 sensor reads very accurately only right at stoich. Basically, the ECU looks for stoich at part throttle, if it sees rich there, it decides that something is making the MAF read high or some other issue is going on... it removes fuel globally. Any issue that richens the mix at part throttle will apply at full throttle also. And the same thing applies to a lean mixture, but usually the cause of this is an intake leak. Same result, more fuel is added to idle/PT/WOT via a correction factor.

The OBD1 system we're talking about does not use the oxygen sensor under WOT.

That's sort of true, but doesn't tell the whole story. Hopefully, I made it clearer above.

[BimmerToad]

Fuel trims are calculated at part throttle and applied globally.

The ECU can read and react to all of its sensors very quickly even at max engine speed.

I understand that fuel trims would be applied globally, to account for a fowling fuel filter or changes in injector performance. Sensors are read at max engine speed, but not all sensors governing emissions at WOT.

AFR targets at WOT are determined by the tuner burning the chip, not some target AFR ratio. The OBD1 system we're talking about does not use the oxygen sensor under WOT.

Taken from a chapter about European engine control systems (Bosch) Hatch & King, Computerized Engine Controls, 2003

During wide-open throttle operation, the control unit commands a fixed enriched air/fuel mixture. To avoid fuel quantity miscalculations from airflow sensor fluctuations, at this speed the fuel quantity is calculated based on engine speed

I know future European emission regulations may call for closed loop WOT throttle systems, but our mid-90s OBD1 Bosch systems aren't that advanced. If they were, then there would be a much lower gain in power from aftermarket chips, since the WOT tune would have an ideal AFR for torque, and timing could probably be set a bit more aggressive.

There is a really simple reason for this, not hard to deduce...

Was that really necessary? Sorry man, but you're coming off like a total douche