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Tuning for Parts

Q What should I know before I start?

If you already have a good tune, then you have traded some safety for power. Switching any part could potentially erase your safety margin, so before you start, you could increase that safety margin. For example:

  • Cut all of your timing advance in half, or even set it to zero, or subtract 4 degrees everywhere. Do this to the dynamic advance table (aka knock correction advance) or the base timing table, but not both. When you’re done, you can but the original values back. I prefer to do this with the advance table rather than the base table, because the advance table’s non-zero values are where the engine is most susceptible to knock.
  • Multiply your MAF scaling by 1.1, above 50 g/s, so that you get 10% more fuel when you’re in boost. Force the ECU to run open-loop, or keep a close eye on your AF Learning, just to be sure that the ECU doesn’t learn to undo your change.
  • Set your Maximum WGDC to zero, so that you’re left with only whatever amount of boost your wastegate spring provides.

When you get the new part dialed in, you can start un-doing the change that you made, but do it in 3 or 4 steps, and log a few pulls each time, to make sure the motor is running like it should.

Q What do I need to tune for my new intake?

The ECU has a big table (the “MAF Sensor Scaling” table) that tells it how many grams of air per second it’s inhaling, according to the voltage it sees from the MAF sensor. The MAF sensor can read differently if it’s placed inside a different-sized tube, or in a different location relative to any bends in the tube, etc. So, if you change your intake, your MAF table will probably need some adjustment.

If it’s an intake that lots of other people have, you may be able to come up with a good table based on others’ MAF scaling tables. That approach worked for me, but I have to admit there was some luck involved. Three other people already had my same intake, and their MAF tables were pretty similar. I basically just averaged them out, and ended up with AFRs only off by about 1% at full throttle (verified with a wideband). See the warning at the end of this page, though.

For a new intake, “you need a tune” really just means changing that one table. Doing it right takes some time (unless you can just copy a known-good table for your particular intake), but it’s nothing like doing a whole tune from scratch.

One thing about intakes - if the aftermarket intake is fairly similar to the stock unit, the car can learn to adjust to it to some extent. It can learn very well for idle and cruise, but I suggest staying out of boost until/unless you can verify that it hasn’t thrown off your AFRs much.

This will not change the amount of power your car makes. If your MAF or injectors were limiting factors for your current tune, then you will probably want do need some Tuning For Power after you get the MAF scaling dialed in.

Q How do I tune for my new intake?

Watch this space.

Q What do I need to tune for my new injectors?

For new injectors, you need to adjust the values in the ECU that tell it how much they flow (scaling) and how many milliseconds elapse between sending power to the injector and actually squirting fuel (latency). This can be done fairly quickly but you will need a wideband O2 sensor to confirm your AFRs at high flow rates.

This will not change the amount of power your car makes. If your injector capacity was the limiting factor of your current tune, then you will probably want do need some Tuning For Power after you get the latency and flow rates dialed in.

Q How do I tune for my new injectors?

If the manufacturer provided latency and flow scaling figures, you should probably start with those. But note that for ID 1000, it’s pretty widely agreed that the scaling should be around 900 rather than the provided spec (not sure why - opinions differ).

Or, if you can find open-source tunes that use your injectors, consider starting with those. Better yet, look at a few tunes and average them. If you can find a tune that uses your same injectors and intake, borrow the MAF scaling as well. Inaccuracies in one will often be compensated in the other, deliberately or otherwise.

Whichever settings you start with, consider them a starting point only. You’ll need to log and adjust, because reality isn’t always as predictable as it should be.

Tweaking the scaling will probably get you pretty close for much of the flow range. You can get close just by entering the scaling number in, but I highly recommend using a wideband to verify the results. However, even after doing this, idle and low throttle are likely to be off a bit.

Tweaking the latency will get the low end dialed in. This post has some information about latency adjustment.

It’s hard to say whether you’ll need to tweak the fuel table or not. In theory, you shouldn’t have to. In practice however, some injectors have nonlinear quirks that require adding or removing fuel in certain regions of the fuel table in order to maintain the desired AFR. Mine certainly did, and LittleBlueGT found the same thing with one set of injectors that he tried. The only way to find out if this is necessary is to log AFR with a wideband - preferably before as well as after the swap, since there’s no guarantee that the AFRs you see in the fuel table are really the AFRs you get, even before the swap. They’re probably close, but if you don’t measure, you don’t know.

Q What do I need to tune for my new FMIC?

Probably nothing, unless you also changed your intake. A FMIC is less restrictive than a TMIC, so it will flow more air, but the MAF sensor will be telling the ECU about the airflow, so that’s not something you need to tune. A FMIC will cool the air more effectively, but that only makes your existing tune safer.

You should verify your AFRs and boost levels after the FMIC install, but that’s just to make sure you don’t have any new leaks as a result of the FMIC install process. If it was installed properly, with no leaks, you’re set.

You might want to revise your tune to get more power now that you have a FMIC, but that’s what the Tuning For Power page is all about.

Q What do I need to tune for my new exhaust?

Reduced backpressure = more boost from the turbo = you need to tweak your boost control. In particular, you’ll need to adjust your wastegate duty cycle (WGDC) tables to prevent over-boosting.

Exhaust upgrades are the sort of thing that people do because it allows for significantly more power, which means revising boost, timing and usually fueling. That’s real tuning, it takes time and effort. That’s the sort of thing that tuners can justify asking $hundreds for. And that’s the sort of thing that the Tuning For Power page is all about.

Q Can I use these values I found on the internet?

Maybe. Maybe not. Be careful.

When I got my Perrin 816s (fuel injectors), I searched around and found a few examples from the same injectors, and they varied a lot. They couldn’t all be correct. I tried some, but I ended up starting over from scratch.

The problem is that it’s fairly common for people to run a MAF scaling that’s off by 10%, and compensate for that by running injector scalings that are off by 10% to get the right air-fuel ratio. Or, they just accept the fact that the AFRs in their fueling table will be 10% off from the true AFRs, and they adjust the fueling table to compensate (for example, calling for 10.2 AFR in the fueling table in order to get a consistent 11.0 reading from the wideband).

There’s nothing particularly wrong with that, by the way. It’s common because it works. If the actual AFRs are where they should be, then so be it. It just makes it hard to share individual aspects of the tune when everything needs to be counter-balanced to get the right numbers in the end.

Unless you have reason to believe that the person offering you a MAF scale or injector settings has also dialed in their injector settings and MAF scale correctly (i.e. the part they’re not sharing with you is also accurate), and the values in their fueling table actually match the values they see on their wideband O2 meter, then you should be very suspicious. Compare the values to what other people with similar mods are using. If they all agree, then you can probably trust the numbers you’ve been given. If they vary widely, then you’re on your own.


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Page last modified on February 24, 2019, at 11:04 AM
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