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C4C5 specialist! and other experts please advise!


Well-known member
Nov 28, 2001
Northern NJ
I am of the belief that the 2003 Corvettes have a updated program that protects the cats in a four step manner ..based partially off increased air flow sensed by the maf..

I have been told my increased air flow due to my aftermarket intake..is by tech II scanning tool at 7%..

I am of the belief that the new programing begins to effect the fuel enrichment program after 8%..increase..

Am I good to go?

Also should I avoid a pcm update at my next visit to a dealership on my 2001 Z because the new 2003 program entails this four set protocol..instead of the one step used in 2000 Corvettes.

Would a pcm update on a 2001 Z generally done by a dealer encompass a programing change like this that is in effect for the 2003's and late 2002's?

Or would the fact I have a 2001 Z make the changes to the 2003 Vette safety protocol be a non factor even during reprograming during normal dealer visits?..

All I can say is man! I am glad I never pulled that maf screen! Blockage can sometimes be a good thing..

Besides my ride...just curious..if an a tech II scan device says..I've got a 7 % increase in air flow.. My question is: could effectively a 2001 zo6 or regular C5 4 inch maf effectively be used to control the increase in air flow below the threashold where new cat protection protocols kick in?

Is the screen worth..a 1% reduction in air flow?

That would be a kicker wouldn' t it..Go just up to 8%...get 20ponies..

Go to or over 8% and gain almost no horsepower all b/c of programing to save the almighty emissions devices we all loath..

Thanks in advance for your response.



Technical Advisor
May 29, 2001
New Haven, Ct. USA
Nope, but someday.
HI there,
Algorithms, or programs for the PCM in 01 vs 03 are substantially different.
Now, based on Lamba airflow within the engine, there are many different ways of looking at the programs within the PCM.
Does this affect fuel trims so widely that the PCM cannot compensate for this increase in airflow??????
Normally, NO, the PCM will be able to compensate for this, without any further issues.
Please remember, that the converter life is constantly being monitored by the rear o2 sensors, located behind the converters. The difference in voltages between the front sensors, and the rears will indicate to the PCM, that they are ok, and are functioning normally.
Also, the PCM will monitor the fuel trim tables, which are constantly changing due to driving styles, and demand.
Normally, I have seen cold air inductions never cause a problem, unless they are misinstalled. When they are not correctly clamped to the MAF, they set a P0171 and a P0174 codes. Why??
Due to air entering the engine that is NOT being measured by the MAF sensor.
Is the program for the 03 different from the 01?? Absolutely.
Can you install the program for the 03 into the 01?? No.
Are you ok, John?? Yes.
Updating a program is a normal upgrade to the engine management system. Do NOT be afraid to have this done, as it will only keep you c5 running at its absolute best.
Besttoall, c4c5:hb


Well-known member
Nov 28, 2001
Northern NJ

Cool answer and thank you.

I just heard the programing on the 2003 cars runs a different protocol that allows the a/f mixtures to change in 4 steps once airflow goes up 8%..its that manner in which the cats are protected because when the extra fuel goes in..it causes the temperatures to skyrocket creating a concern for the cats..

So they dump fuel into the mixture to cool the combustion to keep cats safe..

Weird stuff ..certainly more involved then I understand but it leads me to believe..maintaining airflow increases below 8% is essential for air intake mods..on late 2002's and 2003 corvettes..

So why all the talk of combustion temperature controls in the pcm ?????

Just cause we love these cars and when and if we do even basic mods we should try and be aware of affecting changing parameters from GM.

To modify with basic simple devices and stay within GM's parameters is a smart and easy way to grab 15 to 20 hp..

Loose that balance and the results go in the crapper!

The information..although not totally understood..is a concept that allows balance and results..

Always balance is the key to success..even in modding cars!

Just shooting the breeze on this great forum!

Thanks for the new slot " Z06 Mods!"

Btw..I am so happy with the basic mods.. I have..the end result 10 to 15% increase in power is all I could ever ask for...(for now anyway! ;) Isn't that always the way though?

A buddy of mine just did a 3:42 gearset and 3500 yank convertor on his 2000 C5..and at exactly the 150 mile mark..he quickly rolled up upon a new Ferrari..

Door handle to door handle..even match..

Shocked the ferrari driver to say the very least..

Mods are fun when chosen carefully..(imho)

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