If you go to this thread, you will see Jeanius is having a problem with a dramatic drop in gas mileage.
http://www.f-body.com/forum/showthre...5&page=2&pp=15
He sent me a data log, and it was a very good scan.... 16-18 frames per seconds. 6 minutes long, with idle, part load driving and a couple WOT blasts. Almost everything was "by the book"..... very "normal".
Things that were good:
MAP - high steady vacuum at idle (31-32kPa), very little pressure loss at WOT (99-101kPa on a BAR of 103)
TPS - 0.59V at idle, 4.55V at 100% TPP
IAC - 31-38 counts at idle, increased as high as 82 at cruise
VOLTS - 12.7-13.3V, but an interesting 0.1V jump every time knock counts jumped up, triggering up to 10deg retard
MAF - 7.4gps at idle, 235gps at WOT/5100rpm. There was a weird value in record #2167 indicating 248gps at only 3775rpm, as the throttle was reopening after a shift. Why?????
BLM's - Balanced left to right (but see below)
Pulse Widths - Balanced left to right
Things that were suspect:
BLM's - Pulling fuel in all of the well developed Cells. At idle they were 112/112, indicating its having to pull 12.5% excess fuel to keep it at 14.7:1. This causes problems at WOT, since the PCM ignores negative fuel corrections and holds the BLM"s at 128. Something is causing it to run rich, and the BLM's are having to pull out a lot of fuel to keep it in control.
O2's - At WOT, the passenger side is always a bit richer than the driver's side, even though the BLM's are balanced and the pulse widths are balanced. This may be problem of mismatched O2 sensors, or the sensors not operating at the same temperature.
Coolant Temp - Generally high, at 210-217degF. May be contributing to knock retard
IAT - Generally on the high side at 98-103degF. May be heat soak of the sensor.
Knock Retard - A significant problem. Every time he opens the throttle, there is a small amount of knock retard.... generally less than 1deg. But at WOT, it will start by pulling a degree or two, and suddenly the knock count jumps up, and it pulls anywhere from 5deg-10deg of timing. When the knock count jumps up, the system volts consistantly jump 0.1V. Any thoughts on this one? Not every WOT blast is accompanied by this sudden jump in knock counts/retard.
Offhand, I don't see anything that is causing it to experience a sudden drop in fuel mileage. Most signs are healthy. The things that might need to be looked at:
Why do the BLM's have to pull so much fuel?
Is the coolant temp contributing to knock?
Why the rogue reading on the MAF?
Why is the passenger side richer than the driver's side at WOT?
Why the constant small amounts of knock retard?
Just curious.... is your EGR system still installed and working?
Leaking injectors can cause a couple of the symptoms..... obvioulsy it would hurt gas mileage. And leaking injectors can cause the "less than 128" BLM's because the excess fuel in the exhaust consumes some of the residual O2 in the exhaust, causing the O2 sensors to report a "false" rich condition.
Something I also need help on from a conceptual point of view: What generates "knock counts"? How are knock counts related to knock retard? I have reviewed hundreds data logs, and I have seen increasing knock counts that do not cause knock retard, knock retard when knock counts are not increasing, and just about every other possible combination.
How does the PCM arrive at knock counts? Is it calculated from conditions that are known to promote knock, like certain combinations of MAP, coolant temp, throttle postion, RPM, etc? It does not seem to be related to specific knock sensor activity.
Does anyone know how "knock counts" are determined?
http://www.f-body.com/forum/showthre...5&page=2&pp=15
He sent me a data log, and it was a very good scan.... 16-18 frames per seconds. 6 minutes long, with idle, part load driving and a couple WOT blasts. Almost everything was "by the book"..... very "normal".
Things that were good:
MAP - high steady vacuum at idle (31-32kPa), very little pressure loss at WOT (99-101kPa on a BAR of 103)
TPS - 0.59V at idle, 4.55V at 100% TPP
IAC - 31-38 counts at idle, increased as high as 82 at cruise
VOLTS - 12.7-13.3V, but an interesting 0.1V jump every time knock counts jumped up, triggering up to 10deg retard
MAF - 7.4gps at idle, 235gps at WOT/5100rpm. There was a weird value in record #2167 indicating 248gps at only 3775rpm, as the throttle was reopening after a shift. Why?????
BLM's - Balanced left to right (but see below)
Pulse Widths - Balanced left to right
Things that were suspect:
BLM's - Pulling fuel in all of the well developed Cells. At idle they were 112/112, indicating its having to pull 12.5% excess fuel to keep it at 14.7:1. This causes problems at WOT, since the PCM ignores negative fuel corrections and holds the BLM"s at 128. Something is causing it to run rich, and the BLM's are having to pull out a lot of fuel to keep it in control.
O2's - At WOT, the passenger side is always a bit richer than the driver's side, even though the BLM's are balanced and the pulse widths are balanced. This may be problem of mismatched O2 sensors, or the sensors not operating at the same temperature.
Coolant Temp - Generally high, at 210-217degF. May be contributing to knock retard
IAT - Generally on the high side at 98-103degF. May be heat soak of the sensor.
Knock Retard - A significant problem. Every time he opens the throttle, there is a small amount of knock retard.... generally less than 1deg. But at WOT, it will start by pulling a degree or two, and suddenly the knock count jumps up, and it pulls anywhere from 5deg-10deg of timing. When the knock count jumps up, the system volts consistantly jump 0.1V. Any thoughts on this one? Not every WOT blast is accompanied by this sudden jump in knock counts/retard.
Offhand, I don't see anything that is causing it to experience a sudden drop in fuel mileage. Most signs are healthy. The things that might need to be looked at:
Why do the BLM's have to pull so much fuel?
Is the coolant temp contributing to knock?
Why the rogue reading on the MAF?
Why is the passenger side richer than the driver's side at WOT?
Why the constant small amounts of knock retard?
Just curious.... is your EGR system still installed and working?
Leaking injectors can cause a couple of the symptoms..... obvioulsy it would hurt gas mileage. And leaking injectors can cause the "less than 128" BLM's because the excess fuel in the exhaust consumes some of the residual O2 in the exhaust, causing the O2 sensors to report a "false" rich condition.
Something I also need help on from a conceptual point of view: What generates "knock counts"? How are knock counts related to knock retard? I have reviewed hundreds data logs, and I have seen increasing knock counts that do not cause knock retard, knock retard when knock counts are not increasing, and just about every other possible combination.
How does the PCM arrive at knock counts? Is it calculated from conditions that are known to promote knock, like certain combinations of MAP, coolant temp, throttle postion, RPM, etc? It does not seem to be related to specific knock sensor activity.
Does anyone know how "knock counts" are determined?
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