EGR tuning $8D S_AUJP

[34blazer]

The table only goes to 2000 rpm. My question for that part was, what is the rpm limit for the EGR DC? Its not listed in the XDF.

[34blazer]

Scratch that. EGR is functioning properly and my questions have been answered. This morning I observed effects of the EGR and found that it provides no increase in fuel milage. Depending on the duty cycle, the impact negatively affected fuel milage. As soon as DC rose above 30% I noticed an increase in BLM counts. Not satisfied with that observation I toggled EGR on and off while highway mode was active, watching NBO2 readings similtaneously. With EGR DC at or above 30%, the A/F mixture would lean out, ~30-50mV. While it helps with emissions, it doesnt help fuel milage at all, at least in my case. Toggled off, the BLM counts fell back down to where im used to observing them, some cells fell by 6 counts. So I have no use for EGR anymore.

[RobertISaar]

not sure how 8D accounts for it, but you did have spark being added due to EGR active, yes?

i've had good results with EGR enabled on 60V6 applications, after some tweaking of the fueling and spark modifiers for when EGR is active anyways.

[daleulan]

BLM is only giving you the difference between the airflow the ECM thinks is there (after subtracting out the EGR that it thinks is there) compared with what is actually happening on the engine, not the actual fuel economy. I think that generation of ECM had a BPC vs. EGR calibration in there somewhere and any error in that calibration would show up as a BLM shift. There will be an emissions benefit but you should see a slight mileage improvement when looking at the pulse width at the same vehicle speed - you'd need to log injector pulse width, RPM, vehicle speed and integrate pulse width * RPM and compare against miles (or kilometres) driven to get at least a semi-accurate reading. Also EGR is usually set up to allow more advanced ignition timing - maybe 5 to 8 crank degrees - which should help your efficiency numbers. I don't know if I've ever seen a calibrated EGR system make efficiency drop, but certainly if the timing isn't adjusted up that can happen. That being said, with EGR there is a peak efficiency point where you've lowered NOx as much as you can and advanced the timing as much as you can and if you increase the flow rate any more then you get an efficiency drop - if some is good, more is not necessarily better. Just like tequila. It also should help lower the exhaust temperatures at part-throttle.

[34blazer]

I know $42 has a scaler for EGR on/off, iirc $88 uses a modifier table, and $24 as well. There isnt any modifier I could find for spark or fuel in the S_AUJP xdf, and im not capable of finding something like that in the disassembly yet. I will make a note of the items to be logged and will record while on my way home from work. Even $24 has more modifiers that could be used. When I get home ill also look thru other $8D masks to see if there is more available items, if so ill put them in the S_AUJP xdf as long as the locations match up.

[RobertISaar]

That being said, with EGR there is a peak efficiency point where you've lowered NOx as much as you can and advanced the timing as much as you can and if you increase the flow rate any more then you get an efficiency drop - if some is good, more is not necessarily better. Just like tequila. It also should help lower the exhaust temperatures at part-throttle.

IIRC, that threshold is where the amount of exhaust gasses in the chamber make up so much of the air/fuel charge where misfires are inevitable. i would take a guess at saying that a stronger ignition system would allow higher concentrations.

[34blazer]

IIRC, that threshold is where the amount of exhaust gasses in the chamber make up so much of the air/fuel charge where misfires are inevitable. i would take a guess at saying that a stronger ignition system would allow higher concentrations.

well, I just set the DC at 60 in the 50-60 kpa MAP range, and 30-40% in the 40 kpa range, havent noticed a misfire yet. $8D has the DC set at 100% thru most of the range, I dont think the little 660 could handle that LOL.

[34blazer]

I managed to find a PDF copy of the ANHT hac(limited access at work), looks like $8D uses EGR partial pressure to adjust fuel requirments, the equation is there so Ill have to figure out which way to adjust that table so it doesnt skew my BLM counts too much. Not sure on the the spark yet....

[34blazer]

not sure how 8D accounts for it, but you did have spark being added due to EGR active, yes?

i've had good results with EGR enabled on 60V6 applications, after some tweaking of the fueling and spark modifiers for when EGR is active anyways.

can you share your EGR DC table, unless it is untouched from the factory? the 2.8 in the fiero is bone stock, well, with the exception of the ported headers.

[RobertISaar]

wouldn't be of much use to you, i use the 3 tower digital setups, not the EVRV used before them. also comparing iron head 2.8 to aluminum head 3.1 and 3100 is another lopsided comparison.