Timing Is Retarding During Acceleration
Thread Starter
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
Timing Is Retarding During Acceleration
Based on the assumption that ecm forced retard is bad the following graph doesn't look good:
Any ideas what the problem could be?
Any ideas what the problem could be?
Last edited by Lemme; Sep 17, 2010 at 10:35 PM.
Advanced
Joined: Jun 2009
Posts: 90
Likes: 0
From: St. Louis Missouri
I'd take some advance out until the retard goes away.
I'm guessing you didn't get any knock counts?
Are you using or do you have a "Spark Advance PE Mode" or are you doing all of the advance in the main spark advance table?
If you have values in the "spark advance PE mode" take those values down a couple of degrees. It's a small table.
I'm guessing you didn't get any knock counts?
Are you using or do you have a "Spark Advance PE Mode" or are you doing all of the advance in the main spark advance table?
If you have values in the "spark advance PE mode" take those values down a couple of degrees. It's a small table.
Burning Brakes
Joined: May 1999
Posts: 760
Likes: 1
From: Greenwich, CT
Modern engines use an acoustic transducer(s) to listen for sounds/frequencies
that characterize spark-knock in the engine. The presence of those sounds/
frequencies cause the ECM to temporarily pull programmed timing out of the
spark map.
The logic is not difficult to follow. If the ECM pulls out spark and the sounds
go away, then the source involved spark-knock. If it pulls spark and the sounds
DON'T go away, it didn't. The idea is to attempt to prevent engine damage
caused by knock.
There is a brief but interesting discussion of spark timing here:
http://www.streetrodstuff.com/Articl...tion/index.php
IIRC, the author was a GM engineer involved in testing the Northstar engine.
That was GM's DOHC V8 high-end production unit evolved from the original
ZR-1 Lotus design.
Regarding your question, try reducing the spark map at the WOT rpms you plotted.
If the knock-counts go away, you found the source of the problem. The new spark
map may not be optimized for power output, but at least it won't try to beat the
mechanical bits to death...
Good luck.
that characterize spark-knock in the engine. The presence of those sounds/
frequencies cause the ECM to temporarily pull programmed timing out of the
spark map.
The logic is not difficult to follow. If the ECM pulls out spark and the sounds
go away, then the source involved spark-knock. If it pulls spark and the sounds
DON'T go away, it didn't. The idea is to attempt to prevent engine damage
caused by knock.
There is a brief but interesting discussion of spark timing here:
http://www.streetrodstuff.com/Articl...tion/index.php
IIRC, the author was a GM engineer involved in testing the Northstar engine.
That was GM's DOHC V8 high-end production unit evolved from the original
ZR-1 Lotus design.
Regarding your question, try reducing the spark map at the WOT rpms you plotted.
If the knock-counts go away, you found the source of the problem. The new spark
map may not be optimized for power output, but at least it won't try to beat the
mechanical bits to death...
Good luck.
Thread Starter
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
I'd take some advance out until the retard goes away.
I'm guessing you didn't get any knock counts?
Are you using or do you have a "Spark Advance PE Mode" or are you doing all of the advance in the main spark advance table?
If you have values in the "spark advance PE mode" take those values down a couple of degrees. It's a small table.
I'm guessing you didn't get any knock counts?
Are you using or do you have a "Spark Advance PE Mode" or are you doing all of the advance in the main spark advance table?
If you have values in the "spark advance PE mode" take those values down a couple of degrees. It's a small table.
Last edited by Lemme; Sep 17, 2010 at 10:36 PM.
Thread Starter
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
Modern engines use an acoustic transducer(s) to listen for sounds/frequencies
that characterize spark-knock in the engine. The presence of those sounds/
frequencies cause the ECM to temporarily pull programmed timing out of the
spark map.
The logic is not difficult to follow. If the ECM pulls out spark and the sounds
go away, then the source involved spark-knock. If it pulls spark and the sounds
DON'T go away, it didn't. The idea is to attempt to prevent engine damage
caused by knock.
There is a brief but interesting discussion of spark timing here:
http://www.streetrodstuff.com/Articl...tion/index.php
IIRC, the author was a GM engineer involved in testing the Northstar engine.
That was GM's DOHC V8 high-end production unit evolved from the original
ZR-1 Lotus design.
Regarding your question, try reducing the spark map at the WOT rpms you plotted.
If the knock-counts go away, you found the source of the problem. The new spark
map may not be optimized for power output, but at least it won't try to beat the
mechanical bits to death...
Good luck.
that characterize spark-knock in the engine. The presence of those sounds/
frequencies cause the ECM to temporarily pull programmed timing out of the
spark map.
The logic is not difficult to follow. If the ECM pulls out spark and the sounds
go away, then the source involved spark-knock. If it pulls spark and the sounds
DON'T go away, it didn't. The idea is to attempt to prevent engine damage
caused by knock.
There is a brief but interesting discussion of spark timing here:
http://www.streetrodstuff.com/Articl...tion/index.php
IIRC, the author was a GM engineer involved in testing the Northstar engine.
That was GM's DOHC V8 high-end production unit evolved from the original
ZR-1 Lotus design.
Regarding your question, try reducing the spark map at the WOT rpms you plotted.
If the knock-counts go away, you found the source of the problem. The new spark
map may not be optimized for power output, but at least it won't try to beat the
mechanical bits to death...
Good luck.
Thread Starter
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
In the graph above it can be seen that around 3000 rpm the timing is suddenly advance by about 10 degrees causing the knocking to start. The table I think that is doing this is the "Power Enrichment Mode Spark Advance Table"
Should I just drop the figure from 9 to 5 for 3200 rpm?
Should I just drop the figure from 9 to 5 for 3200 rpm?
Thread Starter
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
I backed off the timing in the PE spark advance mode table and the results seem pretty good (as far as getting rid of the knock anyway)
Started knocking right at the end of the run as the advance crept up. Must be another table to back off a bit then!
Started knocking right at the end of the run as the advance crept up. Must be another table to back off a bit then!
Last edited by Lemme; Sep 18, 2010 at 01:32 AM.
Advanced
Joined: Jun 2009
Posts: 90
Likes: 0
From: St. Louis Missouri
There's a table called AFR% PE RPM or something like that that has two columns RPM and % I would raise those numbers to see if it helps
Or, for an easier test. Reduce the injector size ( forcing the computer to provide more fuel all the time. If your knock counts go down it was probably because you where too lean at WOT (PE Mode)
I think you are too lean once you hit PE Mode
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Thread Starter
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
My understanding is that as a rough test during WOT if the O2 mV are high (>800mV) then its not lean. The following graph seems to show that enough fuel is being injected:
Last edited by Lemme; Sep 18, 2010 at 05:35 PM.
Thread Starter
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
[QUOTE=bcollid;1575359751]
There's a table called AFR% PE RPM or something like that that has two columns RPM and % I would raise those numbers to see if it helps /QUOTE]
Is this the table?
Some numbers are negative!
PS: Graph originally inserted was not from arap bin.
There's a table called AFR% PE RPM or something like that that has two columns RPM and % I would raise those numbers to see if it helps /QUOTE]
Is this the table?
Some numbers are negative!
PS: Graph originally inserted was not from arap bin.
Last edited by Lemme; Sep 18, 2010 at 09:18 PM.
Thread Starter
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
So what you mean here is to trick the ecm into thinking smaller injectors are installed by changing the size in the tuning table.
Advanced
Joined: Jun 2009
Posts: 90
Likes: 0
From: St. Louis Missouri
[QUOTE=Lemme;1575359906]
Yes - This is the table.
I might move the whole table up to small positive numbers tike 3,4 or 5.
I don't think you can trust the narrow band o2 readling. It is looking for 14.7 AFR
You might also look at a small table called Accell enricment versus change in load, I think it has 4 or 5 values in it.
I might move the whole table up to small positive numbers tike 3,4 or 5.
I don't think you can trust the narrow band o2 readling. It is looking for 14.7 AFR
You might also look at a small table called Accell enricment versus change in load, I think it has 4 or 5 values in it.
Advanced
Joined: Jun 2009
Posts: 90
Likes: 0
From: St. Louis Missouri
I'm no expert here, but I spent the last year or so working with TunerPro on my 1989 corvette.
Burning Brakes
Joined: May 1999
Posts: 760
Likes: 1
From: Greenwich, CT
Regarding fuel, on N.American cars GM typically ran the WOT AFR up to some
huge number like 10:1. The reason was to "quench" the catalytic converters
on rapid change in air-flow, preventing the cats from melting themselves -
and the vehicle. Fuel was added in different tables, owing to the limitations
of the 8-bit ECMs of the day, and the weirdness of Assembly programming...
Later engines use temperature sensing elements to gage cat temperatures directly,
and so can be less generous with fuel flow. But that is NOT the case for the C4s.
I don't know for a fact if export C4 units carried catalytic converters or not
(with their need for unleaded fuel). However if you use a US bin for engine
control, you have the fueling curves that include the "quench" feature. Thus
unless an injector fails entirely you are very unlikely to EVER manage a lean
WOT fuel condition.
The O2 sensor on the C4 is a narrow-band device, and can ONLY measure AFRs as
above or below 14.7:1. Trying to infer anything else from one is pure superstition.
Note further on the old C4s the O2 sensor only sees HALF the engine. It has no
idea what the other half is doing at any time.
Adding fuel at WOT is a generally a waste of time, but if you want to experiment
with it you must invest in 'wide band' sensors, also known as Nernst cells. The
details of one, and some simple data logging gear, are shown on my old C4
web page - look in my sig to see if it's still around.
Don't forget of course that 'knock sensors' react to any loud, unhappy sound from the
engine - including failing bearings, loose brackets, broken mounts, and the like. Best
to track down the real problem rather than speculate.
Have fun.
huge number like 10:1. The reason was to "quench" the catalytic converters
on rapid change in air-flow, preventing the cats from melting themselves -
and the vehicle. Fuel was added in different tables, owing to the limitations
of the 8-bit ECMs of the day, and the weirdness of Assembly programming...
Later engines use temperature sensing elements to gage cat temperatures directly,
and so can be less generous with fuel flow. But that is NOT the case for the C4s.
I don't know for a fact if export C4 units carried catalytic converters or not
(with their need for unleaded fuel). However if you use a US bin for engine
control, you have the fueling curves that include the "quench" feature. Thus
unless an injector fails entirely you are very unlikely to EVER manage a lean
WOT fuel condition.
The O2 sensor on the C4 is a narrow-band device, and can ONLY measure AFRs as
above or below 14.7:1. Trying to infer anything else from one is pure superstition.
Note further on the old C4s the O2 sensor only sees HALF the engine. It has no
idea what the other half is doing at any time.
Adding fuel at WOT is a generally a waste of time, but if you want to experiment
with it you must invest in 'wide band' sensors, also known as Nernst cells. The
details of one, and some simple data logging gear, are shown on my old C4
web page - look in my sig to see if it's still around.
Don't forget of course that 'knock sensors' react to any loud, unhappy sound from the
engine - including failing bearings, loose brackets, broken mounts, and the like. Best
to track down the real problem rather than speculate.
Have fun.
Thread Starter
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
Regarding fuel, on N.American cars GM typically ran the WOT AFR up to some
huge number like 10:1. The reason was to "quench" the catalytic converters
on rapid change in air-flow, preventing the cats from melting themselves -
and the vehicle. Fuel was added in different tables, owing to the limitations
of the 8-bit ECMs of the day, and the weirdness of Assembly programming...
Later engines use temperature sensing elements to gage cat temperatures directly,
and so can be less generous with fuel flow. But that is NOT the case for the C4s.
I don't know for a fact if export C4 units carried catalytic converters or not
(with their need for unleaded fuel). However if you use a US bin for engine
control, you have the fueling curves that include the "quench" feature. Thus
unless an injector fails entirely you are very unlikely to EVER manage a lean
WOT fuel condition.
The O2 sensor on the C4 is a narrow-band device, and can ONLY measure AFRs as
above or below 14.7:1. Trying to infer anything else from one is pure superstition.
Note further on the old C4s the O2 sensor only sees HALF the engine. It has no
idea what the other half is doing at any time.
Adding fuel at WOT is a generally a waste of time, but if you want to experiment
with it you must invest in 'wide band' sensors, also known as Nernst cells. The
details of one, and some simple data logging gear, are shown on my old C4
web page - look in my sig to see if it's still around.
Don't forget of course that 'knock sensors' react to any loud, unhappy sound from the
engine - including failing bearings, loose brackets, broken mounts, and the like. Best
to track down the real problem rather than speculate.
Have fun.
huge number like 10:1. The reason was to "quench" the catalytic converters
on rapid change in air-flow, preventing the cats from melting themselves -
and the vehicle. Fuel was added in different tables, owing to the limitations
of the 8-bit ECMs of the day, and the weirdness of Assembly programming...
Later engines use temperature sensing elements to gage cat temperatures directly,
and so can be less generous with fuel flow. But that is NOT the case for the C4s.
I don't know for a fact if export C4 units carried catalytic converters or not
(with their need for unleaded fuel). However if you use a US bin for engine
control, you have the fueling curves that include the "quench" feature. Thus
unless an injector fails entirely you are very unlikely to EVER manage a lean
WOT fuel condition.
The O2 sensor on the C4 is a narrow-band device, and can ONLY measure AFRs as
above or below 14.7:1. Trying to infer anything else from one is pure superstition.
Note further on the old C4s the O2 sensor only sees HALF the engine. It has no
idea what the other half is doing at any time.
Adding fuel at WOT is a generally a waste of time, but if you want to experiment
with it you must invest in 'wide band' sensors, also known as Nernst cells. The
details of one, and some simple data logging gear, are shown on my old C4
web page - look in my sig to see if it's still around.
Don't forget of course that 'knock sensors' react to any loud, unhappy sound from the
engine - including failing bearings, loose brackets, broken mounts, and the like. Best
to track down the real problem rather than speculate.
Have fun.
As I start to mod this motor and start pushing out more horsepower to achieve some respectable 1/4 mile times it seems that the wideband sensor has to be the way to go.
My c4 came to Australia via Japan complete with the original precats and main cat. The precats had temp sensors installed by the Japanese wired to a light on the dash to illuminate if the cats reached a certain temperature. My exhaust now only has a main cat (AIR and EGR systems removed). I have just put on some LT tri-Y headers with 3 inch Y pipe (in place of stock manifolds, no pre-cats and standard pipe) but haven't been able to see any acceleration improvement yet from them. Seems to be a bit more air flow through the MAF than before but doesn't seem to translate at the lower rpms (up to 4500) into more torque.
Thanks for the heads up.
Last edited by Lemme; Sep 18, 2010 at 06:41 PM.
Thread Starter
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
Advanced
Joined: Jun 2009
Posts: 90
Likes: 0
From: St. Louis Missouri
Regarding fuel, on N.American cars GM typically ran the WOT AFR up to some
huge number like 10:1. The reason was to "quench" the catalytic converters
on rapid change in air-flow, preventing the cats from melting themselves -
and the vehicle. Fuel was added in different tables, owing to the limitations
of the 8-bit ECMs of the day, and the weirdness of Assembly programming...
Later engines use temperature sensing elements to gage cat temperatures directly,
and so can be less generous with fuel flow. But that is NOT the case for the C4s.
I don't know for a fact if export C4 units carried catalytic converters or not
(with their need for unleaded fuel). However if you use a US bin for engine
control, you have the fueling curves that include the "quench" feature. Thus
unless an injector fails entirely you are very unlikely to EVER manage a lean
WOT fuel condition.
The O2 sensor on the C4 is a narrow-band device, and can ONLY measure AFRs as
above or below 14.7:1. Trying to infer anything else from one is pure superstition.
Note further on the old C4s the O2 sensor only sees HALF the engine. It has no
idea what the other half is doing at any time.
Adding fuel at WOT is a generally a waste of time, but if you want to experiment
with it you must invest in 'wide band' sensors, also known as Nernst cells. The
details of one, and some simple data logging gear, are shown on my old C4
web page - look in my sig to see if it's still around.
Don't forget of course that 'knock sensors' react to any loud, unhappy sound from the
engine - including failing bearings, loose brackets, broken mounts, and the like. Best
to track down the real problem rather than speculate.
Have fun.
huge number like 10:1. The reason was to "quench" the catalytic converters
on rapid change in air-flow, preventing the cats from melting themselves -
and the vehicle. Fuel was added in different tables, owing to the limitations
of the 8-bit ECMs of the day, and the weirdness of Assembly programming...
Later engines use temperature sensing elements to gage cat temperatures directly,
and so can be less generous with fuel flow. But that is NOT the case for the C4s.
I don't know for a fact if export C4 units carried catalytic converters or not
(with their need for unleaded fuel). However if you use a US bin for engine
control, you have the fueling curves that include the "quench" feature. Thus
unless an injector fails entirely you are very unlikely to EVER manage a lean
WOT fuel condition.
The O2 sensor on the C4 is a narrow-band device, and can ONLY measure AFRs as
above or below 14.7:1. Trying to infer anything else from one is pure superstition.
Note further on the old C4s the O2 sensor only sees HALF the engine. It has no
idea what the other half is doing at any time.
Adding fuel at WOT is a generally a waste of time, but if you want to experiment
with it you must invest in 'wide band' sensors, also known as Nernst cells. The
details of one, and some simple data logging gear, are shown on my old C4
web page - look in my sig to see if it's still around.
Don't forget of course that 'knock sensors' react to any loud, unhappy sound from the
engine - including failing bearings, loose brackets, broken mounts, and the like. Best
to track down the real problem rather than speculate.
Have fun.
On the Dyno with a Wideband o2, in forth gear and starting at 2000rpm, when I hit the gas my AFR goes from 15 straight to 10 to 1 and then comes back up to 12.5 to 1.
I have not been able to find a table or anyway to get rid of the quick drop to 10:1 AFR. The dyno shop doesn't have any experience with C4.
Is the quick change to 10 :1 when I punch it a result of this quench factor. If so is there a way to get around it or just leave it there.
The car runs well. The Dyno guy thinks it looks odd. I am happy with everything else about how the car responds.
I have a 1989 C4
Burning Brakes
Joined: May 1999
Posts: 760
Likes: 1
From: Greenwich, CT
Uh, don't look at me. I didn't have an '89. 
That being said:
1. If you still have a cat converter I WOULD NOT want to get rid of the 'quench'
feature. Look back into the archives here and you'll find a number of folks with
mysterious holes burned in the floors of their C4s. The culprit is CO - which results
from a 'lean' combustion event. Cats are sized to handle a very small amount of
CO, which they convert to CO2 in a highly exothermic reaction. Overload the cat
and it can run up past 2,000*F very quickly. Burning down the garage will spoil
your whole day ...
That is the reason for the fat (10:1) AFR numbers, and GM didn't do it just for fun.
2. If the cats are removed you can modulate fuel flow through the tables already
identified, i.e. PE and AE. The 'LV8' terms make them a pain to sort out - but the
Motorola ECMs were never meant for the general public to diddle anyway.
3. Re the other guy's question about 'LV8': In 85-89, GM used a 'load factor' term
to program engine fuel rates. It's basically air flow (from a hot-wire anemometer)
divided by RPM, factored into several tables to simulate engine performance over
the range of speeds and manifold pressures the engine is likely to see. The main
input is the voltage-out MAF meter signal, sent to the 8-bit Motorola A/D converter.
The net result seems to be a derived sorta-VE table. Those aren't my area of expertise -
but they always struck me as a lo-res kludge - JMO. From 90-93 GM changed to a MAP
based control scheme, with the same style ECM. That was a simpler design (to me),
and some folks worked out ways to improve the control resolution without altering
the hardware.
Starting in '94 GM moved up to 16-bit ECM computing, which afforded way more
processor power - not to mention bigger A/D converters, more memory, and better
electronics overall. There, MAF and MAP control schemes were combined.
The LS1 engines jumped up to another whole level of PCM power and complexity,
with LANs inside the car, and programs that just give me a headache...
Several folks over on the 3rd Gen Prom board have worked out ways to update the C4
control gear to more modern computers - but it's a job for a hobbyist with both good
wiring and computer skills - and an understanding of process control can't hurt, either.
Hope that helps.
That being said:1. If you still have a cat converter I WOULD NOT want to get rid of the 'quench'
feature. Look back into the archives here and you'll find a number of folks with
mysterious holes burned in the floors of their C4s. The culprit is CO - which results
from a 'lean' combustion event. Cats are sized to handle a very small amount of
CO, which they convert to CO2 in a highly exothermic reaction. Overload the cat
and it can run up past 2,000*F very quickly. Burning down the garage will spoil
your whole day ...
That is the reason for the fat (10:1) AFR numbers, and GM didn't do it just for fun.
2. If the cats are removed you can modulate fuel flow through the tables already
identified, i.e. PE and AE. The 'LV8' terms make them a pain to sort out - but the
Motorola ECMs were never meant for the general public to diddle anyway.
3. Re the other guy's question about 'LV8': In 85-89, GM used a 'load factor' term
to program engine fuel rates. It's basically air flow (from a hot-wire anemometer)
divided by RPM, factored into several tables to simulate engine performance over
the range of speeds and manifold pressures the engine is likely to see. The main
input is the voltage-out MAF meter signal, sent to the 8-bit Motorola A/D converter.
The net result seems to be a derived sorta-VE table. Those aren't my area of expertise -
but they always struck me as a lo-res kludge - JMO. From 90-93 GM changed to a MAP
based control scheme, with the same style ECM. That was a simpler design (to me),
and some folks worked out ways to improve the control resolution without altering
the hardware.
Starting in '94 GM moved up to 16-bit ECM computing, which afforded way more
processor power - not to mention bigger A/D converters, more memory, and better
electronics overall. There, MAF and MAP control schemes were combined.
The LS1 engines jumped up to another whole level of PCM power and complexity,
with LANs inside the car, and programs that just give me a headache...
Several folks over on the 3rd Gen Prom board have worked out ways to update the C4
control gear to more modern computers - but it's a job for a hobbyist with both good
wiring and computer skills - and an understanding of process control can't hurt, either.
Hope that helps.
Advanced
Joined: Jun 2009
Posts: 90
Likes: 0
From: St. Louis Missouri
Uh, don't look at me. I didn't have an '89. That being said:
1. If you still have a cat converter I WOULD NOT want to get rid of the 'quench'
feature. Look back into the archives here and you'll find a number of folks with
mysterious holes burned in the floors of their C4s. The culprit is CO - which results
from a 'lean' combustion event. Cats are sized to handle a very small amount of
CO, which they convert to CO2 in a highly exothermic reaction. Overload the cat
and it can run up past 2,000*F very quickly. Burning down the garage will spoil
your whole day ...
That is the reason for the fat (10:1) AFR numbers, and GM didn't do it just for fun.
2. If the cats are removed you can modulate fuel flow through the tables already
identified, i.e. PE and AE. The 'LV8' terms make them a pain to sort out - but the
Motorola ECMs were never meant for the general public to diddle anyway.
3. Re the other guy's question about 'LV8': In 85-89, GM used a 'load factor' term
to program engine fuel rates. It's basically air flow (from a hot-wire anemometer)
divided by RPM, factored into several tables to simulate engine performance over
the range of speeds and manifold pressures the engine is likely to see. The main
input is the voltage-out MAF meter signal, sent to the 8-bit Motorola A/D converter.
The net result seems to be a derived sorta-VE table. Those aren't my area of expertise -
but they always struck me as a lo-res kludge - JMO. From 90-93 GM changed to a MAP
based control scheme, with the same style ECM. That was a simpler design (to me),
and some folks worked out ways to improve the control resolution without altering
the hardware.
Starting in '94 GM moved up to 16-bit ECM computing, which afforded way more
processor power - not to mention bigger A/D converters, more memory, and better
electronics overall. There, MAF and MAP control schemes were combined.
The LS1 engines jumped up to another whole level of PCM power and complexity,
with LANs inside the car, and programs that just give me a headache...
Several folks over on the 3rd Gen Prom board have worked out ways to update the C4
control gear to more modern computers - but it's a job for a hobbyist with both good
wiring and computer skills - and an understanding of process control can't hurt, either.
Hope that helps.
That being said:1. If you still have a cat converter I WOULD NOT want to get rid of the 'quench'
feature. Look back into the archives here and you'll find a number of folks with
mysterious holes burned in the floors of their C4s. The culprit is CO - which results
from a 'lean' combustion event. Cats are sized to handle a very small amount of
CO, which they convert to CO2 in a highly exothermic reaction. Overload the cat
and it can run up past 2,000*F very quickly. Burning down the garage will spoil
your whole day ...
That is the reason for the fat (10:1) AFR numbers, and GM didn't do it just for fun.
2. If the cats are removed you can modulate fuel flow through the tables already
identified, i.e. PE and AE. The 'LV8' terms make them a pain to sort out - but the
Motorola ECMs were never meant for the general public to diddle anyway.
3. Re the other guy's question about 'LV8': In 85-89, GM used a 'load factor' term
to program engine fuel rates. It's basically air flow (from a hot-wire anemometer)
divided by RPM, factored into several tables to simulate engine performance over
the range of speeds and manifold pressures the engine is likely to see. The main
input is the voltage-out MAF meter signal, sent to the 8-bit Motorola A/D converter.
The net result seems to be a derived sorta-VE table. Those aren't my area of expertise -
but they always struck me as a lo-res kludge - JMO. From 90-93 GM changed to a MAP
based control scheme, with the same style ECM. That was a simpler design (to me),
and some folks worked out ways to improve the control resolution without altering
the hardware.
Starting in '94 GM moved up to 16-bit ECM computing, which afforded way more
processor power - not to mention bigger A/D converters, more memory, and better
electronics overall. There, MAF and MAP control schemes were combined.
The LS1 engines jumped up to another whole level of PCM power and complexity,
with LANs inside the car, and programs that just give me a headache...
Several folks over on the 3rd Gen Prom board have worked out ways to update the C4
control gear to more modern computers - but it's a job for a hobbyist with both good
wiring and computer skills - and an understanding of process control can't hurt, either.
Hope that helps.
The dyno guy thought it looked odd and I hadn't seen anyone else on the forum talk about this 10:1 AFR on tip in so I figured something was misconfigured on my tune.
Thread Starter
Drifting
Joined: Nov 2009
Posts: 1,341
Likes: 2
From: Perth Western Australia
St. Jude Donor '10
question about 'LV8': In 85-89, GM used a 'load factor' term
to program engine fuel rates. It's basically air flow (from a hot-wire anemometer)
divided by RPM, factored into several tables to simulate engine performance over
the range of speeds and manifold pressures the engine is likely to see. The main
input is the voltage-out MAF meter signal, sent to the 8-bit Motorola A/D converter.
The net result seems to be a derived sorta-VE table.
to program engine fuel rates. It's basically air flow (from a hot-wire anemometer)
divided by RPM, factored into several tables to simulate engine performance over
the range of speeds and manifold pressures the engine is likely to see. The main
input is the voltage-out MAF meter signal, sent to the 8-bit Motorola A/D converter.
The net result seems to be a derived sorta-VE table.
What is the base fuel pulse though that these tables are adding and subtracting fuel to? Is it related to the 10:1 afr quench target?