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Knock correction causing stuttering

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19K views 51 replies 10 participants last post by  ImprezaSport_17  
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#1 ·
I have a 2019 Impreza with manual trans.

I've been chasing down a slight stutter during both cruise and acceleration for quite some time. Previously thought it was misfire so I took it to the dealership and they couldn't find anything but gave me a tsb that they said pertained to my issue(tsb had nothing to do with it). Issue was still there though. Irritated and determined, I bought a launch scan tool(I had worked at dealerships/shops for a while so I am fairly mechanically inclined).

I had been checking different things until I came across knock correction. For the last 3 months I've been monitoring knock correction with other things to find a correlation/cause. The stutter I'm feeling is the knock correction pulling timing. I don't feel it until it hits -3 to -7 degrees retard, which happens atleast a few times a drive, but I can't seem to find any other readings that correspond with that other than it happens around 2300 RPM when I'm cruising at 55MPH.

In the time I was working on cars, I didn't deal a whole lot with timing so this is a somewhat new thing for me. Looking for any direction I can be pointed to look or anyone else that's had a similar issue.

It is under warranty and I am going to be talking to them about it but I drive 1 hour to work and another hour back home 5 days a week. I don't always feel it and am already guessing they're not going to find anything on their 10 min drive around the block so I want to try and narrow this down as much as possible for them.
 
#2 ·
Others in the forum have noted that running higher-octane fuel can improve things. Especially in hot ambient temperatures which will make lesser fuels knock the engine.

However, at this point, you are only assuming that the knock-sensor is causing the "stuttering". You have not mentioned anything conclusive.

As an experiment, you can try a tankfull of higher-octane fuel. This should reduce or eliminate knocking so the sensor is no longer impacting things. You can still monitor to make sure the sensor is not activating.

The goal of this experiment would be to determine if the "stuttering" goes away during this time.
 
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#3 ·
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I've ran 91 or 93 for the last 3 months exclusively, the knock sensor isnt detecting anything, only knock correction. Nothing has been an assumption as I have 3 months of recorded live data showing that my knock correction is pulling the timing.

I was just on another thread that went on for about 3 years of people with 2017-2019 having this issue and one of the last posts of the thread talked about doing an idle relearn procedure with positive results. Going to try that this weekend.
 
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#7 · (Edited)
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I've gone done the same road with my 18 5mt car. Here is an image of one of many data recordings. The upper right box is actual ignition timing. Lower right is knock signal, upper left is engine rpm and lower left is throttle plate opening angle. You can see the ECM pulling/retarding ignition timing without a knock signal, sometimes as far as -20 degrees. I spent many hours reviewing data, and the best I can tell is the mapping for emissions is what does it. The problem did seem to get slightly better after the first ignition coil recall. I haven't gotten the latest one done yet. I've mostly given up on the issue, except for keeping an eye on this forum for updates, and I upshift around 4k rpm now instead of 3k. I know this isn't the best example of what the timing is doing, but it was the first recording I looked at. I drove myself (and my wife) crazy trying to figure this out.
 
#10 ·
Automotive electronics in the last 25 years or so have become so invasive that actually chasing-down an issue like yours takes a lot of time and expensive equipment. Now that you've uncovered the 'problem', what can you do about it? Completely reprogram the ECU? Slap in an illegal ECU, and risk a failed inspection and federal fines? Find some 'work-around' which may or may not either work or even be legal? Fine-tuning engines today is just about impossible; it's better to just adjust your driving technique to work with your engine's shortcomings.

I really don't like how my CVT goes too quickly into a too-high gear, and how reluctant it is to shift down in anything short of nearly flooring the gas. As a result, I tend to corner with greater throttle than I'm used to, just to keep the transmission in a more drivable range. I also often use the shift-paddles as an over-ride even in normal traffic. Work with what you've got...
 
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#12 ·
Day 2 after the idle relearn procedure. It's still showing knock correction but not nearly to the frequency or degree it was before. The most it's shown is -2.3 degrees (I could physically feel it around -4 degrees and up). Its usually staying around -.6 to -1 degree and that was onlyhand full of times in the 120 miles I've driven since yesterday morning. Still curious as to why it's trying to correct a knock that isn't there. Going to see if I can talk to the tech instead of the service writer this weekend during my oil change to pick their brain a bit.
 
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#13 ·
Update: First 2 days were good, after that it's back to how it was before. Hitting -7 degrees and just as often. Talked to the service advisor and hes herd of the issue. Checked my oil level which was good and I told him Ive used premium fuel exclusively for the last 3 months. Going to schedule an appointment with their master tech and see what happens from there. If they can't fix it I'm just going to drive it until something actually gives. I am already on track to have this paid off before the warranty is up so I can either trade it in or sell it.
 
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#14 ·
Hey guys, Marty1 here from the Crosstrek forum. SOA has finally come out with a TSB (09-77-21) to address this issue. Below is the first page. In a few weeks the link to the entire TSB will show up under "Manufacturer Communications" for the Impreza and Trek on the NHTSA site.

Image
 
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#17 ·
I wish they would fix the jerkiness in the CVT that my 18 Legacy doesn't have. It is much worse with the AC on but is noticeable without also. Things like moving at slower speeds or sometimes even when going faster around 50 and hitting the gas it will jerk but like I said much worse with the AC on.
 
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#20 ·
Glad that it's finally being addressed. Never thought it was an issue before until y'all mentioned it.
 
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#21 ·
I first felt it at about 19k miles. Bought it with 8k. Thought I got a bad batch of gas at first but with 30k miles on it now and a scanner with live data to pinpoint what I was feeling, that obviously wasn't the case. I'm still going to trade it in simply because even though they have a fix for the issue, that's not to say it hasn't caused excess wear with the timing being pulled as sporadically and as often as it has. I drive an hour one way to work and it does it atleast every 5 minutes.
 
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#27 ·
Dealer said they are going to charge me for this cause I'm out of warranty and it's only an elective TSB. What the heck
 
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#29 ·
I contacted them via the main site a couple days ago but no reply yet
 
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#30 ·
I thought about taking mine in to get it done but I'm trading it in early next week for a 2021 wrx. I'd have to take off work to go in and have it done and I've left early to take it in and have it looked at/talk to them about the issue more times than I can count.
 
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#34 ·
I’m probably gonna pay for it too. Need all the power I can get
 
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#38 ·
They told me if you're over 3 yr or 36k mi then they charge an hour labor for it.
 
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#40 ·
So..update. I got tsb 09-77-21 done. It cost me $70. I have roughly 100 miles since. My scanner has shown no large changes in timing advance other than going about 5 degrees negative for a split second when the ac kicks on at idle.
The low to mid rpm range has been much much more responsive and consistent. Another nice plus is that my mpg are up by about 3. I recommend getting it done even if you are out of bumper to bumper warranty and have to pay for it.
 
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#41 ·
Thanks for the update. Looking forward to being rid of this issue.
 
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#42 ·
Well SOA finally got back to me via email saying the dealer was right about not taking care of it under warranty (just passed 36k mi), but they were going to give me a $150 Parts and Service coupon to go towards the ECM update.
 
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#43 ·
So does that mean that because you are just outside of warranty they were ok to charge you or that even if you were under the factory warranty they would still charge you?
 
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#44 ·
SOA response “Typically, the ECM programming would be covered under the factory warranty of 3 years or 36,000 miles and being you are beyond that this would not be a matter for warranty. Although there is a Technical Service bulletin, it is simply a guideline for the repair process of the ECM. This is not a warranty extension or guarantee that the repairs will be covered.”
 
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#46 ·
What the f? diagnostic for what? My dealer is charging me 1/2 hour for labor cause it's a damn flash. They're also the ones that told me to contact SOA to see if they would give me a service voucher lol
 
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#48 ·
Got the tsb done this past Saturday. Put 300 miles since then and feels like it pulls more consistently now but still evaluating. Gonna be driving another few hundred miles today in Texas heat so let’s see.
 
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#50 ·
I wish they made it a recall. Why create a new ECU update if they don't consider it an issue?

So I put another 300 miles on it yesterday. Engine definitely feels more consistent. It's not going to blow your mind, but anything helps.
 
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