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FA20DIT Wastegate Issues

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I've been tuning a friends 2017 WRX with the FA20DIT and have been having a hell of a time getting the boost control to behave.

It overboosts even on the stock tune. It seems to be a mechanical problem with the wastegate itself because even when I lock the WGDC to 4% the boost pressure overshoots and oscillates.

I've verified no boost leaks and the restrictor pills are all in the right spots.

I'm planning on bench testing the actuator to see if its sticky, but I just wanted to see if anyone else has had this issue before.



Here's me trying to hit a higher boost target and you can see how the WGDC has a very slow and delayed response on the boost pressure causing it to oscillate up and down


First thing I notice is your DAM (Dynamic Advance Multiplier) is not 1.00. I dunno if it's a cause or a consequence of your problem thought! Can you post your log file?


Hey Frank,

I'll upload a log when I get home. But the DAM drops were a consequence of some light knock that was occuring and I don't think it's related.

The boost issue is unaffected by the DAM value as I've seen it do it when the DAM was at 1 right after an ECU flash where it told the DAM to initialize at 1.

But I'll send over a log anyway because WHO KNOWS haha.


Here's the log.

Car is stock besides an AEM intake that I've been working on scaling properly.

The tune for this log was just a stock tune with MAF compensation and WGDC clamped at 4%. I did this by setting the whole Low and High WG tables to 4%

Also if you notice halfway through the log I changed the target boost pressure to be higher than I was hitting to insure the WGDC stayed at 4%.

Attached Files
  • 2017-WRX-Stock-tune-+-Intake-MAF-Scaling.csv
  • Attachments may only be downloaded by paid Gold members. Read more about becoming a Gold member here.

I checked your log and I noticed that your ignition timing is getting into negative number when it overshoot. I can't remember if that value is before or after all the correction in the ECU, but sometimes an overly retarded ignition timing makes it harder to control boost. Also, you do have some knock feedback and correction as well in these area which pulls timing.

Of course, I would suggest to check mechanical problems as you are saying it does the same with the stock tune.

Are you using COBB? If yes, have you checked with an OTS map that are close to your mods?

Honestly I am not very familiar with the DIT engine, so I am just giving generic advice haha!

I appreciate the thoughts! I definitely think its a mechanical thing because of how lazy the wastegate is to react to WGDC changes.

I connected the wastegate direct to the turbo using the factory vacuum line with the restrictor pill. Effectively just blocking off the boost solenoid. At first it seemed ok but there is still some signs of overboosting. I think it is just more subtle because of the lower boost.

wastegate connected directly:


Then I locked the wastegate to some low values and connected it back up:


I also connected a pressure source to the wastegate actuator and it seemed to open and close smoothly. Right now I guess I'm either leaning towards something obstructing the restrictor pill(s) or a faulty solenoid. Gonna swap over some vacuum lines from a working FA20DIT to see if that solves it and then I'm thinking we need to order a new solenoid.

Attached Files
  • FWLR-Stage0-Oct-19-Low-WGDC-Locked-v4.csv
  • Attachments may only be downloaded by paid Gold members. Read more about becoming a Gold member here.

  • FWLR-Stage0-Oct-19-Wastegate-Direct-v5.csv
  • Attachments may only be downloaded by paid Gold members. Read more about becoming a Gold member here.

Swapped the vac lines with a known good car. No difference. Leaning towards either wastegate issue or faulty solenoid.

I took the solenoid off and it was leaking at 0V, I cleaned it and it started to seal up when there was no voltage sent to it. I got the owner to buy a new solenoid, but I'm confident that this is the issue.

Did you solve the problem? Is this with a 3 port ECBS? If so, may need PID adjustments.

It's just the stock 2 port solenoid. I should be getting the new part tomorrow and will know if it solves the problem. The funny thing about the stock boost control strategy is it's not PID, its mostly just P. and I did play with those values but it was overshooting even on the stock tune and the car is stock besides an intake.

Yep. The solenoid was just dirty and not sealing consistently... Weird. Aw well now I can control boost!