# Questions about ecu

**URL:** <https://community.cartalk.com/t/questions-about-ecu/176791>\
**Category:** Maintenance/Repairs\
**Tags:** mustang, ford\
**Created:** [May 14, 2021, 3:19am UTC](https://community.cartalk.com/t/questions-about-ecu/176791 "2021-05-14T03:19:28Z")\
**Posts on this page:** 1\
**Showing post:** 10

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**Author:** ![FoDaddy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/fodaddy/32/717_2.png) [@FoDaddy](https://community.cartalk.com/u/FoDaddy)\
**Post date:** [May 14, 2021, 1:03pm UTC](https://community.cartalk.com/t/questions-about-ecu/176791/10 "2021-05-14T13:03:45Z")

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> [@J162\_165342](#):
>
> When i go into the app it doesn’t give me an option to retune, only switch between 87 and 93 octane tunes.

Possible those are just the canned tunes.

> [@J162\_165342](#):
>
> I’m not sure if the car has a custom tune right now specifically for the mods I listed or if it’s on a preset tune.

Depending on the CAI, it may just have a canned tune just for use in correcting the speedometer for the 3.73 gears. Some CAI’s require a custom tune, some don’t.

> [@J162\_165342](#):
>
> My question is what would happen if i started adding more mods but didn’t retune?

Your car will not run correctly.

> [@J162\_165342](#):
>
> I want to add long tube headers but multiple sources say it’s bad to add mods after a tune and then not retune. Is this true?

Yes

> [@J162\_165342](#):
>
> If so, how do I retune, or do i have to shell out $400 again for a new custom tune?

You shell out the money for a custom tune. You’ll also have to make sure the tuner (outfit/person who writes the tune) you choose works with the tuner (the electronic device) you have. [I put long tubes on my Mustang last year](https://community.cartalk.com/t/long-tube-headers-and-a-dyno-tune/166699). My tuner is a guy that owns a local speed shop, so it was put on the dyno and had a custom tune made for my specific car, which going to yield better results than a canned tune or emailed tune, but at the same time is much more labor intensive and costly.

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