Tuning question?
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Tuning question? Ok I have a tune on my truck from a autocal v3 mail-order tuner,and I've had it for a couple years now ,and I installed long tube headers on my truck recently ,and tuner said to do a data log and send it over and they will send me a updated tune,so I did that and waited a few weeks,then tuner says that the data log looks good there is nothing that he sees that he can change that would be worth for me to pay for???I thought u had to get a new tune after long tube headers because it changes the air and fuel ratio,u could be running lean or rich ?so why would my tuner say this??because it runs worse now with the long tube headers,more sluggish and eating gas lile no other ...should I get a second opinion on my tube?is there anyway this statement is true?
Last edited by LsMike420; Jan 20, 2026 at 06:12 PM.
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Joined: Dec 2017
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From: Bossier City, Louisiana
Hello,
My sense here is that something else is causing your running problems than the addition of a set of headers. For my two LS swapped and header-equipped vehicles, things do run slightly leaner but my fuel injectors have enough extra capacity to cope. I see this coping mechanism at work when I look at the Long Term and Short Term Fuel Trims adding fuel to bring the mixture back towards normal. Sure, I could change the tuning slightly to richen things up but the effects of the headers are small enough that the PCM and the injectors can solve the problem all on their own.
Your tuner person did you a favor. Go back to that guy again when you make a more radical change to your engine and pay him well.
Rick
My sense here is that something else is causing your running problems than the addition of a set of headers. For my two LS swapped and header-equipped vehicles, things do run slightly leaner but my fuel injectors have enough extra capacity to cope. I see this coping mechanism at work when I look at the Long Term and Short Term Fuel Trims adding fuel to bring the mixture back towards normal. Sure, I could change the tuning slightly to richen things up but the effects of the headers are small enough that the PCM and the injectors can solve the problem all on their own.
Your tuner person did you a favor. Go back to that guy again when you make a more radical change to your engine and pay him well.
Rick
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Joined: Jan 2018
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Tuning is complicated. Any time someone makes a generalization - like saying that headers will make the engine run lean - you have to take it with a grain of salt.
If the tune uses speed-density, or if the injectors are already completely maxed out, headers might do that.
If the tune uses a MAF sensor, and the injectors are big enough, headers won't do that. The ECU will see the increased airflow and it will spray an increased amount of fuel - just like before the headers, it simply looks at the airflow and the target AFR, and it tells the injectors to spray whatever amount of fuel is required to hit the target AFR.
If your tuner didn't see anything in the log that indicated a problem, then the tune is probably not the problem. Probably. Diagnostics is hard enough when the car is right there in front of you, it's a lot harder when you have nothing but a log, or nothing but a paragraph. But at this point I'd be looking for other things that might cause it to run poorly.
If the tune uses speed-density, or if the injectors are already completely maxed out, headers might do that.
If the tune uses a MAF sensor, and the injectors are big enough, headers won't do that. The ECU will see the increased airflow and it will spray an increased amount of fuel - just like before the headers, it simply looks at the airflow and the target AFR, and it tells the injectors to spray whatever amount of fuel is required to hit the target AFR.
If your tuner didn't see anything in the log that indicated a problem, then the tune is probably not the problem. Probably. Diagnostics is hard enough when the car is right there in front of you, it's a lot harder when you have nothing but a log, or nothing but a paragraph. But at this point I'd be looking for other things that might cause it to run poorly.
