Abnormal Timing Values
Thread Starter
Staging Lane
Joined: Aug 2002
Posts: 55
Likes: 0
From: Plano, Texas
Abnormal Timing Values Does anyone have knowledge of why timing values would negative in this case? This was accompanied by Grams/Cylinder values < .08. It's as if the PCM doesn't know what timing value to use (also saw low timing numbers, < 8, in our 2002 Z06 measurements, both with VRam, and also when Grams/Cylinder < .08).
In the high octane timing table, you will see negative values in the 400 RPM column at higher Grams/Cylinder values.
Mods:
2000 Corvette A4 w/3.42 Diff
VaraRam, no MAF screen, Z06 intake manifold, SVO 30# Injectors, Belanger headers, Corsa
LS1Edit tuning to injector flow rate, PE vs RPM, Fuel Air Multiplier, small timing bump, differential size, and shift firmness & mapping.
Measurements done with EASE (so no garbage - and saw the same results over a few runs) and recorded RPM values were normal.
Observation:
Very brief (a few rows) of negative timing values between first & second gear shifts and second & third gear shifts. Car sounds like it is back firing / misfiring and stumbles ever so slightly. I also noticed that calculated Grams/Cylinder falls below the lower limit (.08) of the timing table.
To see a negative value, the RPM signal would have to be momentarily unavailable to the PCM, but didn't see variations in EASE.
Background:
LS1 timing table (high & low octane) cell value is determined by RPM and Grams/Cylinder (calculated airflow volume through the cylinder). The high octane table contains negative timing values in the 400 RPM column and in rows above .44 Grams/Cylinder.
A bad timing value, must be caused by one of those two inputs (assuming the computer is functioning properly).
Grams/Cylinder = 15 * MAF Rate / RPM
MAF Rate is a derived value in Grams/Second, based on MAF Frequency.
MAF Frequency is a measured value in Hertz (Hz).
LS1 MAF table assigns a MAF Rate value to a MAF Frequency value (table not altered).
If the MAF is sending an incorrect frequency signal, then all the subsequent values will be off. If the signal is high, derived MAF Rate will be high, which will cause a higher Grams/Cylinder value. Relationships appears to be linear, so the reverse is true. If the MAF frequency is erratic, without the presence of the screen, then the rest would fluctuate, but not enough to explain the timing results.
In the high octane timing table, you will see negative values in the 400 RPM column at higher Grams/Cylinder values.
Mods:
2000 Corvette A4 w/3.42 Diff
VaraRam, no MAF screen, Z06 intake manifold, SVO 30# Injectors, Belanger headers, Corsa
LS1Edit tuning to injector flow rate, PE vs RPM, Fuel Air Multiplier, small timing bump, differential size, and shift firmness & mapping.
Measurements done with EASE (so no garbage - and saw the same results over a few runs) and recorded RPM values were normal.
Observation:
Very brief (a few rows) of negative timing values between first & second gear shifts and second & third gear shifts. Car sounds like it is back firing / misfiring and stumbles ever so slightly. I also noticed that calculated Grams/Cylinder falls below the lower limit (.08) of the timing table.
To see a negative value, the RPM signal would have to be momentarily unavailable to the PCM, but didn't see variations in EASE.
Background:
LS1 timing table (high & low octane) cell value is determined by RPM and Grams/Cylinder (calculated airflow volume through the cylinder). The high octane table contains negative timing values in the 400 RPM column and in rows above .44 Grams/Cylinder.
A bad timing value, must be caused by one of those two inputs (assuming the computer is functioning properly).
Grams/Cylinder = 15 * MAF Rate / RPM
MAF Rate is a derived value in Grams/Second, based on MAF Frequency.
MAF Frequency is a measured value in Hertz (Hz).
LS1 MAF table assigns a MAF Rate value to a MAF Frequency value (table not altered).
If the MAF is sending an incorrect frequency signal, then all the subsequent values will be off. If the signal is high, derived MAF Rate will be high, which will cause a higher Grams/Cylinder value. Relationships appears to be linear, so the reverse is true. If the MAF frequency is erratic, without the presence of the screen, then the rest would fluctuate, but not enough to explain the timing results.
Thread Starter
Staging Lane
Joined: Aug 2002
Posts: 55
Likes: 0
From: Plano, Texas
Here is a screen shot (couldn't fit all) of the high octane table from the stock 2000 Corvette A4 file. Check the bottom left corner.
http://home.comcast.net/~al4.hanna/2000c5a4highoct.jpg
http://home.comcast.net/~al4.hanna/2000c5a4highoct.jpg
