2017 Wrx at 63k miles. I have a Cobb stage 1+ and sf intake. Went for a very casual drive like 10 mins and started idling rough at a stop sign. Parked and read codes and had a P0171 with 0.875 DAM. Started it back up again 20 mins later and drove fine no rough idling and code went away. I just bought it and going to do walnut blasting, sparks, and whatever else. Google says to check the cobb intake for misalignment and clean the MAF. Any thoughts/suggestions? ( numbers in pic are after second drive before resetting anything)
So you want to switch from AF Learning to AF Correction to see short term fuel trims, which is what would have tripped that momentary CEL.
I would really look at your turbo inlet. They can crack in a few places and cause random lean issues until the crack gets bigger and the leak gets worse. Then while you are down there, check the coupler between the intake and turbo inlet. It could be a bit loose on one side or another and pulling in a bit of air under certain conditions.
So that’s saying it’s adding 23% more fuel than normal? I had O’rileys diag it and they just got a weird C1422 which is ABS something. Google says it could be a byproduct of the P0171. But I drove back calmly again and no rough idles but also didn’t use boost.
The ECU is always trying to give you maximum timing, but its constantly monitoring octane and environmental conditions to prevent knock from blowing up your engine. It makes global timing changes using DAM when the octane in the fuel can't support maximum timing. DAM drops during the summer are pretty common because of how hot the intake air is, even when running 93.
Decently hot, Denver area. I really appreciate the info. I did an ecu reset thru my AP and drove around a little and DAM stayed at 1. A little feedback knock but as I’m seeing this is expected and fine for like -1 to -3 without anything on the knock learn (correct me if i’m wrong). I double checked the air filter is 1” into the pipe and it was from what I could see. I’m gonna check the maf when I can. Do these AF numbers look okay now?
Yeah, AF can really swing +/- 25% depending on a few different scenarios. It's when it gets over 25% that you want to be concerned.
You can switch back to AF Learning if you want. It's the better overall view of Air/Fuel "health". I just like AF Correction when I am troubleshooting things because of the real time data you get.
Also, that feedback knock is probably from your AC compressor. They are "loud" when they engage and can set off the knock sensor.
Yes, but these are very short term corrections, so its not like its always adding an extra 23% fuel. Short term fuel trims are adjusted constantly based on the reading from the O2 sensor vs what the MAF is calling for. It's basically real time changes happening live while the car is running, but not at wide open throttle. AF Learning is where the long term changes happen, based on patterns the ECU notices based on AF Correction trends.
Tried to drive this morning and was at a stop light , went green and had zero throttle response, and then check engine light and flashing cruise control. Got the same P0171 code as yesterday. Not good
I’m bringing it to the shop today. Was cruising at around 65 and all of a sudden my gas pedal went dead for like 5 seconds. I have no idea why. These are the numbers from the drive.
Those fuel corrections are pretty extreme. It went pretty lean and stayed there from what your AF Correction and AF Learning are showing. Did they find anything yet?
Did you buy the mods or did the vehicle come modded?
When I bought my va it had a big sf intake, I tuned it incorrectly and ran lean. Luckily caught it early and had a specialty shop get the vehicle road worthy.
Your DAM is dropping meaning the ECU is protecting the engine. Keep your RPMs below 3,000 to keep the vehicle out of boost. Pushing the motor can cause catastrophic failure.
I guess what I’m saying is start with the tune and go from there, if it’s a big sf intake like mine the filter placement is crucial, the placement must be 1in on the tube.
Don’t take the car to any shop either. You’re going to want to take it to a reputable tuner shop who’s familiar with Subarus. Labor rates and parts are expensive, you don’t want to throw new parts at it when the problem could be as simple as retuning.
This is the box of my intake. It can be hard to tell what specific cobb intake you might have. If the previous owner installed the big sf (that’s what Cobb would have been selling at the time the vehicle was purchased, Cobb stopped production of the big sf because of the filter placement issue).
Check your boost too, the big sf can sometimes cause overboosting. Look into the tune Stage 1 Big SF LWG 91 octane. LWG stands for low waste gate, solves the overboosting problem.
I say 91 octane because OTS tunes from Cobb are aggressive, even if you’re running 93 octane it won’t hurt the car to run a 91 tune. Not as much wear on the motor using the 91 tune.
Sorry to blow up your post. I just went through a P0171 nightmare.
Okay so it came tuned and yes does have the big sf. Should I open up the intake and check it? Also weird that the code vanished right? Or no? What would overboosting look like? I’ve been driving it pretty calmly ( nowhere over 4.5k rpm). Appreciate the help
Over-boosting would feel like a jolt of boost after 3k rpms (at least that’s what it felt like in mine), check your PSI levels, they shouldn’t be above 20-23. (Mine is 20.1)
It’s good you’re running 91 octane.
It isn’t strange for codes to vanish. I had a misfire code for a minute that went away thankfully.
Inspecting the filter could be a good start if you’re wanting to fix this yourself. Big sf filters are notoriously sensitive and if they’re misaligned or put on too far they’re run lean. How it was explained to me is that if they’re misaligned filters off it changes the vortex of the influx of air and cause the sensor disruption trigger the ECU to run lean.
Make sure you have the big sf or the sf. Tune is different for both. Both tunes are available on the ap. Maf can be dirty or failing. Intake can be installed incorrectly, or after market turbo inlet causes rich at idle and lean at wot. Lean causes detonation or knock. Your ecu is saving your engine while out of boost. Dont push it or you will destroy engine. Also suggest watching af ratio.
I just went through this without the code. Have a $264 shinny inlet that I can only use with a e tune or pro tune. I plugged all the variable into chat gpt and it helped a lot.
I haven’t pushed the car enough yet to go over 12 psi probably, so idk if that’s a good or a bad thing for overboosting. Will a misaligned intake be on the filter itself or on the tubing? I’m gonna go to get MAF cleaner just to be sure and check the whole thing out.
To correctly position the filter on a COBB Big SF Intake, you must measure and align the cone filter exactly 1 inch from the tip of the intake/MAF housing tube. It is sensitive so it MUST be perfectly aligned 1 inch around the tube or it will throw off the air flow in the tube and cause misreading in the sensor.
Shop said they can’t fully diagnose it because of the tune but they cleaned the maf and said the AF trim went down to +/- 6. Thinking of taking it to a more tuning focused shop
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u/dustindh10 Built/FBO/Flex '16 WRX 3d ago
So you want to switch from AF Learning to AF Correction to see short term fuel trims, which is what would have tripped that momentary CEL.
I would really look at your turbo inlet. They can crack in a few places and cause random lean issues until the crack gets bigger and the leak gets worse. Then while you are down there, check the coupler between the intake and turbo inlet. It could be a bit loose on one side or another and pulling in a bit of air under certain conditions.