How can you tell if the PCM is running the low octane program?
03-24-2003, 04:01 PM
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How can you tell if the PCM is running the low octane program? I ran my car at the track Saturday and it was 3 tenths and 3 mph slow. I ran AutoTap and saw 3 to 3.5 degrees of knock retard in 4th gear and sometimes 3rd.
I've heard that excessive knock can cause the PCM to use the "low octane table". If that happens, how can you tell? Is there a register to check with AutoTap? How much would it hurt performance?
Thanks in advance.
I've heard that excessive knock can cause the PCM to use the "low octane table". If that happens, how can you tell? Is there a register to check with AutoTap? How much would it hurt performance?
Thanks in advance.
03-24-2003, 05:21 PM
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Re: How can you tell if the PCM is running the low octane program? If your not seeing around 26-28 degrees of timing during WOT then the PCM has seen enough knock counts to trip the bad gas bit and drop into ther low octane tming table that would be continued to be used until PCM sees at least 20% more fuel has been added since last time the engine was turned off.
Once in low timing table clearly engine no longer can produce the same amount of perfomance as in high octane table and either you have bad gas but most likely require the PCM to be LS1edit tuned for better overall performance.
Once in low timing table clearly engine no longer can produce the same amount of perfomance as in high octane table and either you have bad gas but most likely require the PCM to be LS1edit tuned for better overall performance.
03-29-2003, 03:16 AM
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Re: How can you tell if the PCM is running the low octane program? John, is it true that it switches to the low octane tables when you have less than 5 gallons in the tank?
I never thought this was true, but I have seen a couple of guys state this.
I never thought this was true, but I have seen a couple of guys state this.
03-29-2003, 01:49 PM
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Re: How can you tell if the PCM is running the low octane program? I know for the Corvette, not sure on other models, that when PCM sees less the 1/4 tank to assure car does not run out of gas does function differently.
To be safe if your racing I would maintain over 1/4 tank.
The mistake people do is once they are stuck in low octance table instead of adding fuel they reset the PCM by removing battery which also forces all I/M 240 smog tests back to a incomplete ( failed) state and now PCM has to suck up clock time getting some tests complete again which could take up to 40 valid drive cycles.
So I suggest adding at least 20% more fuel to reset the bad gas bit so high octane table is used again.
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by samuriarte:
<strong> John, is it true that it switches to the low octane tables when you have less than 5 gallons in the tank?
I never thought this was true, but I have seen a couple of guys state this. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">
To be safe if your racing I would maintain over 1/4 tank.
The mistake people do is once they are stuck in low octance table instead of adding fuel they reset the PCM by removing battery which also forces all I/M 240 smog tests back to a incomplete ( failed) state and now PCM has to suck up clock time getting some tests complete again which could take up to 40 valid drive cycles.
So I suggest adding at least 20% more fuel to reset the bad gas bit so high octane table is used again.
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by samuriarte:
<strong> John, is it true that it switches to the low octane tables when you have less than 5 gallons in the tank?
I never thought this was true, but I have seen a couple of guys state this. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">
03-29-2003, 05:40 PM
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Re: How can you tell if the PCM is running the low octane program? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Team ZR-1:
<strong> I know for the Corvette, not sure on other models, that when PCM sees less the 1/4 tank to assure car does not run out of gas does function differently.
To be safe if your racing I would maintain over 1/4 tank.
The mistake people do is once they are stuck in low octance table instead of adding fuel they reset the PCM by removing battery which also forces all I/M 240 smog tests back to a incomplete ( failed) state and now PCM has to suck up clock time getting some tests complete again which could take up to 40 valid drive cycles.
So I suggest adding at least 20% more fuel to reset the bad gas bit so high octane table is used again.
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by samuriarte:
<strong> John, is it true that it switches to the low octane tables when you have less than 5 gallons in the tank?
I never thought this was true, but I have seen a couple of guys state this. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"></strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You know for a fact that the pcm switches to the low octane table when you have 25% or less fuel?
<strong> I know for the Corvette, not sure on other models, that when PCM sees less the 1/4 tank to assure car does not run out of gas does function differently.
To be safe if your racing I would maintain over 1/4 tank.
The mistake people do is once they are stuck in low octance table instead of adding fuel they reset the PCM by removing battery which also forces all I/M 240 smog tests back to a incomplete ( failed) state and now PCM has to suck up clock time getting some tests complete again which could take up to 40 valid drive cycles.
So I suggest adding at least 20% more fuel to reset the bad gas bit so high octane table is used again.
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by samuriarte:
<strong> John, is it true that it switches to the low octane tables when you have less than 5 gallons in the tank?
I never thought this was true, but I have seen a couple of guys state this. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"></strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You know for a fact that the pcm switches to the low octane table when you have 25% or less fuel?
03-30-2003, 10:15 PM
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Re: How can you tell if the PCM is running the low octane program? This is something that has been mis-interpreted. The car does not go to the low octane table when there is less than 5 gallons of gas in car. You have to ADD at least 5 gallons of gas in the car to get you off of the low octane table (hence team ZR-1's 20% more fuel thing).
Somehow somebody interpreted this as you need to have at least 5 gallons of gas in the car.
The timing of your car is not dependant on how much gas is in the car. There are alot of things that effect timing, but fuel level is not one of them.
Somehow somebody interpreted this as you need to have at least 5 gallons of gas in the car.
The timing of your car is not dependant on how much gas is in the car. There are alot of things that effect timing, but fuel level is not one of them.
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03-30-2003, 11:20 PM
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Re: How can you tell if the PCM is running the low octane program? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by NoGo:
<strong> This is something that has been mis-interpreted. The car does not go to the low octane table when there is less than 5 gallons of gas in car. You have to ADD at least 5 gallons of gas in the car to get you off of the low octane table (hence team ZR-1's 20% more fuel thing).
Somehow somebody interpreted this as you need to have at least 5 gallons of gas in the car.
The timing of your car is not dependant on how much gas is in the car. There are alot of things that effect timing, but fuel level is not one of them. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Thanks for the clarification.
<strong> This is something that has been mis-interpreted. The car does not go to the low octane table when there is less than 5 gallons of gas in car. You have to ADD at least 5 gallons of gas in the car to get you off of the low octane table (hence team ZR-1's 20% more fuel thing).
Somehow somebody interpreted this as you need to have at least 5 gallons of gas in the car.
The timing of your car is not dependant on how much gas is in the car. There are alot of things that effect timing, but fuel level is not one of them. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Thanks for the clarification.
