Why is a tune required with header/hi-flow cat installation?

[strych9]

First, some caveats: I already know that more power potential can be extracted by performing a tune. However, I have no desire to void my warranty. I am interesting in gaining more of the exhaust sound I want, with no loss from stock performance. A gain of course is ideal, but not a deal breaker. A loss is not acceptable. What I specifically want to know are two things:

1. Will headers and high-flow cats cause a CEL without a tune?
2. Will any performance be lost without a tune?

Explain. Thanks!

[Higgs Boson]

Awesome.

If you want to modify your car, you need to tune it to do it RIGHT. Everything else doesn't even matter. A car runs correctly at a certain AFR depending on cruise vs WOT, etc and without a tune you alter that mixture balance. Will your car "run" without a tune? Sure. Will it be right? No. If you are installing long tube headers you NEED a tune. If you are installing shorties, you can drive it without it but it will be off.

If you don't want to mess with your warranty, paint your center console yellow. Put on a bumper sticker. Swap out your grill.

[strych9]

Originally Posted by Higgs Boson

Awesome.

If you want to modify your car, you need to tune it to do it RIGHT. Everything else doesn't even matter. A car runs correctly at a certain AFR depending on cruise vs WOT, etc and without a tune you alter that mixture balance. Will your car "run" without a tune? Sure. Will it be right? No. If you are installing long tube headers you NEED a tune. If you are installing shorties, you can drive it without it but it will be off.

If you don't want to mess with your warranty, paint your center console yellow. Put on a bumper sticker. Swap out your grill.

Maybe I should elaborate further. I know all about theory, AFR, mixtures, and balance. I'm no noob to modding and racing cars. I think cosmetic mods are a waste of money.

However, I modded late model Mustangs. I had great success with bolt-on mods without having to chip, or tune. Ford's PCMs allowed a lot of leeway as if they expected you to add headers, CAI, etc. The factory-programmed PCM did just fine and the AFM was perfect without a tune. Also, Ford didn't automatically void your warranty with these mods.

I don't know enough about these GM ECMs. I'm trying to educate myself on why you say I NEED a tune with long tubes. You didn't elaborate, but it would be appreciated if you would.

[Higgs Boson]

If you want your AFRs to be right, if you don't want CELs, if you want to know that your car is running correctly, not just might be running sort of right then you need a tune. Mustang included.

There is nothing special about different ECMs. Just more processing power and better logic so they can do the job better.

Long tubes alter the flow quite a bit and also relocate the O2 sensors. If you want them to read/switch/operate properly, you will also want to alter your closed loop tables. Your Ford ECM may not have even had these tables available so there would be no need to tune them. :-) Late model, to me, means anything after 1980 so....if it had a PCM I would assume you mean newer than 1990 or so....

[strych9]

Originally Posted by Higgs Boson

If you want your AFRs to be right, if you don't want CELs, if you want to know that your car is running correctly, not just might be running sort of right then you need a tune. Mustang included.

There is nothing special about different ECMs. Just more processing power and better logic so they can do the job better.

Long tubes alter the flow quite a bit and also relocate the O2 sensors. If you want them to read/switch/operate properly, you will also want to alter your closed loop tables. Your Ford ECM may not have even had these tables available so there would be no need to tune them. :-) Late model, to me, means anything after 1980 so....if it had a PCM I would assume you mean newer than 1990 or so....

This makes sense! Thanks for the clarification.

[bucketobolts]

High flow cats cause CEL because they are not working as GM designed. So why waste the money.

[Higgs Boson]

Originally Posted by bucketobolts

High flow cats cause CEL because they are not working as GM designed. So why waste the money.

some people think the money is for the 15 whp gain and the CEL is just an annoying side effect easily remedied. personally, I don't want a loud car, CEL are easy enough to disable.

[2SS45th]

I've been driving my LTs with cats without a tune for almost a month. Haven't had any issues, no indication that I am running rich or lean. The CEL isn't that annoying, it's just an amber light, it doesn't yell at me or anything.

[gb2ss]

Installed ARH LT & hiflow cats about 3weeks ago,I know I will get better gain with tune, but have not done so yet and do not have CEL on.

[bucketobolts]

Originally Posted by Higgs Boson

some people think the money is for the 15 whp gain and the CEL is just an annoying side effect easily remedied. personally, I don't want a loud car, CEL are easy enough to disable.

So your trying to say high flow cats will make 15hp more than offroads?

[jeepguy_1980]

If LTs affect the AFR and cause the car not to run properly, why is it that GM doesn't void the warranty for headers, but they do void it for the tune, which is supposed to restore the AFR?

[Higgs Boson]

Originally Posted by jeepguy_1980

If LTs affect the AFR and cause the car not to run properly, why is it that GM doesn't void the warranty for headers, but they do void it for the tune, which is supposed to restore the AFR?

what makes you think GM won't deny a warranty claim if you have long tube headers on your car? because you read that on the internet?

if you have an engine problem and roll in with long tubes, 9 out of 10 times you are going to be SOL. granted, you can get an attorney and fight, but it will cost you more than the repair.

the fact is, warranty and mods are dealt with on a case by case basis and the outcome will vary based on the people involved.

a tune will void your warranty outright because, one, it is stated as such in literature and, two, because you can do a lot of harm with a tune if you do not know what you are doing. you can remove rev limiters, lean it out to the point of melting, i don't know, use your imagination, you can change everything about the car with a tune. GM doesn't know if you only removed a speed limiter or leaned it out like crazy. All they know is that it is changed. They aren't going to play with the depth of the changes. Sort of like if you steal gum from the gas station or rob a bank, either way you are still a thief.

Even though a tune is not illegal, factories don't like them. They are the one paying the warranty bill so they are the ones who get to say what they will pay for.

[jeepguy_1980]

Originally Posted by Higgs Boson

what makes you think GM won't deny a warranty claim if you have long tube headers on your car? because you read that on the internet?

That was sort of my point.

[2SS45th]

Dealers don't pay for the warranty work, they could care less. As long as when they send the PCM history to GM and it's clean, they don't care. Talked to the service manager, general manager, and mechanic. As long as the tune is not on the PCM, they won't do anything. Headers run better with a tune, but it isn't necessary.