5th Gen Subaru Impreza Forum banner

1 - 20 of 39 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter #1
Havent posted in a while but I want to alert everyone of a possible problem with the new Imprezas. Heads up.This could be a pretty long read.

I have a 2017 Impreza Sport with the 5 speed manual transmission. It has 17000 miles on it currently.

About 2 weeks ago while driving with my radio off, I noticed a metallic rattle coming from the engine bay. I havent really noticed this before as I always drive with my radio blasting,but 2 weeks ago I drove with my radio off and noticed the strange sound. I took it in for my 3rd service and oil change and consulted with them about the rattling noise coming from the engine. Me and the Subaru technician took it for a test drive and I demonstrated to him the problem. This rattling noise mostly happens when the car is under load at low speeds , for example if Im trying to accelerate on 2nd gear under 20mph. The technician immediately recognized the problem and told me it was pre-ignition or spark knock or engine knock and asked me what gas I use for the car. I told him I use 87 octane Costco gas. He advised me that they got a bulletin from Subaru letting them know that Costco gas might cause knocking on the cars. He basically told me to use a higher quality gas and the problem should go away. So having only about 2 bars left of gas I decided to get some Chevron gas and I filled it with 91 octane Chevron gas. The problem DID go away. I tried recreating the problem and couldnt recreate it. So I thought to myself, is Costco gas really that terrible that it would cause my engine to knock? Then I thought about it, I did put 91 octane for the problem to go away, but the recommended octane for the impreza is only 87, so it shouldnt cause any problem to put 87 octane.

So for my next experiment, after I go through the 91 octane Chevron gas, I will get a couple gallons of 87 octane Chevron gas and see if the engine will knock. If it does then theres definitely a problem/ something wrong with the car if I put the recommended octane gas and the engine starts knocking.

I will update in about 1 week when I use up the 91 octane gas and put in 87 again.

Until then observe your cars too. If you have a manual transmission try recreating my problem and see if your engine will knock with 87 octane. Just put it in a higher gear 2nd or 3rd or 4th under 20mph and try accelerating and see if your engine will knock. If you have a CVT version im not really sure how you can try recreating the problem, maybe try shifting to a higher gear on slow speeds or uphill roads to try and put the engine under load and accelerating.
 

·
Registered
Joined
·
366 Posts
Occasional, light pinging is not bad. (An engine is most efficient and makes the most power when running right on the edge of knocking)


All Subaru engines have a "knock sensor" which is supposed to detect this condition. The computer uses input from the "knock sensor" to retard ignition timing to protect the engine from internal damage (hole in piston...etc) The computer is constantly looking for signal from the "knock sensor" and retarding the timing in an attempt to keep the engine on the edge of optimum operation.

Also, with a manual xMission, the DRIVER is in control of the engine-loading. It is never a good idea to heavily load (lug) an engine at lower RPMs. This is a good way to damage your engine. If you need to accellerate...dont lug the engine... DOWNSHIFT.

Perhaps your best recourse may be to change gasoline brands... preferably to NONethanol.... and refine your shifting-habits with manual xMission.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #3
Occasional, light pinging is not bad. (An engine is most efficient and makes the most power when running right on the edge of knocking)


All Subaru engines have a "knock sensor" which is supposed to detect this condition. The computer uses input from the "knock sensor" to retard ignition timing to protect the engine from internal damage (hole in piston...etc) The computer is constantly looking for signal from the "knock sensor" and retarding the timing in an attempt to keep the engine on the edge of optimum operation.

Also, with a manual xMission, the DRIVER is in control of the engine-loading. It is never a good idea to heavily load (lug) an engine at lower RPMs. This is a good way to damage your engine. If you need to accellerate...dont lug the engine... DOWNSHIFT.

Perhaps your best recourse may be to change gasoline brands... preferably to NONethanol.... and refine your shifting-habits with manual xMission.
Yes Ill definitely try changing brands. Ill try couple of gallons of Chevron, and I heard Shell is the best so ill try that too. Also for my car its not really occasional, it happens so often that I thought there was literally something lose or cracked in the engine. It also happens when just crawling through traffic and going slow/ stop and go situations , especially in uphill situations or when cruising at highway speeds even when cruise control is trying to accelerate :surprise: but ill def try refining my shifts.
 

·
Registered
Joined
·
366 Posts
It is possible to connect laptop (or smartphone) with the right software to your OBDII connector under the dashboard. Then configure it to 'monitor' things like (RPM, LOAD, KNOCK-SENSOR, TIMING.... etc)

Then , you simply drive around for a few minutes as the data is logged (captured). Then, the data can be reviewed and graphed. A COMPETENT mechanic can interpret the results to determine if things are working properly.

If your Impreza is as bad as you suggest, I would expect the DEALERSHIP to capture the data and send to Subaru for evaluation.
 

·
Registered
Joined
·
88 Posts
I notice I tend to get the same noise out of mine when it's that time of the month and money is tight I run 87. I usually fill with 93 and when it comes that time I'll switch cars for the week :laugh:
 

·
Registered
Joined
·
9 Posts
I have 2017 Impreza with CVT and I usually fill Costco 87 gas. I can say that I heard the same knocking noise when I drove at 20-25 mph and the RPM was low. If I downshifted at that moment I can say that I was in 3rd (virtual) gear.

Recently I filled 87 gas from Valero and not sure but it looks like I no longer hear the knocking.

I’ll do my experiment next time too and fill the Costco’s 91 gas to see if there is a difference.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
9 Posts
So I used a tank of Costco’s 91 gas and the car didn’t make “knocking” sounds luckily.


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
16 Posts
Discussion Starter #8
Sorry guys Ive been really busy and forgot to update this post. Long story short engine still knocks on load with 87 octane even with diff brands of gas like Chevron and Shell. Took it back to the dealer and they assured me it was normal and part of Subaru's emissions control and they haven't seen any engine get damaged by this problem. I'm not really trusting this statement so I've just been filling my car with 91 octane.
 

·
Registered
Joined
·
106 Posts
That sounds asinine of them to say that pinging with the recommended octane of gas is normal. It shouldn't even ping with 85 since the computer should recognize it with the knock sensors and retard the timing to prevent it...
 

·
Registered
Joined
·
13 Posts
Having the same issue still, about to fill car with 91 octane and try the same based on dealer recommendation
 

·
Banned
Joined
·
417 Posts
That sounds asinine of them to say that pinging with the recommended octane of gas is normal. It shouldn't even ping with 85 since the computer should recognize it with the knock sensors and retard the timing to prevent it...
Oh it will... but it takes a while to learn. Meanwhile, you’ll have detonation. AFTER it learns you’ll have less power and worse gas mileage.

People forget ECU learning is just for “the time being”, meaning, as soon as you drive on level low-load roads it then learns THAT and re-learns that set of circumstances. Then you’re back to square one when you either drive differently, hills are involved, the temperature changes, the gas you just got isn’t up to its rated octane... and so on.


The US has significantly worse gas than, say, Japan. Theirs is of higher quality and is tightly regulated. Ours is the opposite.

There was a saying I learned long ago to take to heart: You have to be smarter than the equipment you operate. It’s served me well.

Just because The Man says something does not make it so... whomever that “official” voice is.

Not that many years ago Subaru “speced” the turbo cars for conventional dino oil. After enough engines blew, and more years passed with engine failures, they accepted the common sense reality and changed their turbo motor’s specs to synthetic. People listen to The Word too much.

There are more examples, but they’re just more of the same.

I listen to my own experience and that of others. Bureaucracy is always out of touch with reality.



Use the gasoline that works best... regardless. For me, that’s always been at least one grade higher than speced.

You spend enough time analyzing ECU data and you will, too.
 

·
Registered
Joined
·
16 Posts
Mine started knocking under load like when driving from a stop. This happened right after my first service from the dealer.
I have the 18' model. Dealer recommended using higher fuel grade which does eliminate the symptoms. But the car didn't knock on recommended fuel before the service.

Here's a Link to the knocking video from my car that I uploaded to YouTube
 

·
Registered
Joined
·
13 Posts
Mine started knocking under load like when driving from a stop. This happened right after my first service from the dealer.
I have the 18' model. Dealer recommended using higher fuel grade which does eliminate the symptoms. But the car didn't knock on recommended fuel before the service.

Here's a Link to the knocking video from my car that I uploaded to YouTube
Strange. Did they give you any explanation? For me it was said to be carbon build up - could be due to a lot of the city driving I do but I still get a lot of longer trips in on the weekend. I’ve only gotten through a tank and a half of shell 91 octane but the sound has not improved from what I can tell. Might try higher octane. Then back to dealer as required in the notes by my last service.
 

·
Registered
Joined
·
16 Posts
Strange. Did they give you any explanation? For me it was said to be carbon build up - could be due to a lot of the city driving I do but I still get a lot of longer trips in on the weekend. I’ve only gotten through a tank and a half of shell 91 octane but the sound has not improved from what I can tell. Might try higher octane. Then back to dealer as required in the notes by my last service.
The higher octane definitely hides the symptoms for me. But I read somewhere on a Subaru xv forum that it is because of a faulty EGR valve that doesn't seem to throw error codes. I'm taking it in to Subaru today after an angry letter.
I mostly drive it on highways so carbon build shouldn't be a problem for now. Also it only started for me after the first service. Was totally fine before that.
On a side note, I also have a weird continuous crickety/whirring noise in the cabin when coasting (foot off throttle) between 85 to 70 kmph. Noise disappears when I push the throttle. Don't know if it's related

In any case, we shouldn't have to put higher octane fuel when the minimum 91 shouldn't be knocking. I'll update when I get my car back and if they've fixed it
 

·
Registered
Joined
·
16 Posts
Just got back from the dealer. Said they can't do anything about it. Not very reassuring. Next step is to make a warranty claim
 

·
Registered
Joined
·
13 Posts
That’s annoying as all hell. Yea I agree that higher octane masks it slightly. I’ve heard of walnut blasting as an option - cleaning out the carbon build up inside the intake valves. Should be covered under warranty. Even if it can only be heard with radio off it’s still unnerving to have your engine sound like that when the car is so new.
 

·
Registered
Joined
·
13 Posts
That’s annoying as all hell. Yea I agree that higher octane masks it slightly. I’ve heard of walnut blasting as an option - cleaning out the carbon build up inside the intake valves. Should be covered under warranty. Even if it can only be heard with radio off it’s still unnerving to have your engine sound like that when the car is so new.
@Saimsk
 

·
Registered
Joined
·
16 Posts
It's a really stupid response from the dealer, in my opinion. "We can't do anything about it" - it's the last thing anyone wants to hear. I don't mind putting higher octane fuel into it. But if it's any indication that my engine is damaged, then they should be looking into it and fixing it. I've driven my friend's XV(Crosstrek) and outback, both running the minimum fuel requirement and they don't knock. I've also driven another friends Mazda 3, no knocks on minimum fuel. It's just really frustrating that they don't even want to keep the car to run tests.
I'm still in the process of making a warranty claim to either get return the car and get a refund or get another car. I have a suspicion that they've done something stupid during my first service and dont know how to fix it
 

·
Banned
Joined
·
417 Posts
Saimsk, you're just setting yourself up for a long frustrating future... IMHO. When the solution to your stated gripe is so very simple... higher octane. Sometimes it is in one's own best interests to step back and get some perspective.

I already know before I own a vehicle that I'm going to use a higher grade of gasoline than what the "book" says to use. There is more than 60 years of driving behind that decision, most of those years having to do with the performance side of cars of one kind or another. Many cars, many years, and there has never been a car that didn't work best with a higher grade of gasoline. It's fundamental to how engines work.

Manufacturers' "recommended" is rarely the "best." It'll get you by. From the air in your tires to the gas you put in it to the care and maintenance... they give you a baseline of what to do, the MINIMUM you need to do. NOT the best thing you can do.

It's up to you to know the difference.

Maybe what's up with your discontent is something else... like not really liking the car or being sorry you bought it instead of something else you really want. In that case, and it happens all the time, cut the frustration out of your life and attack the real elephant in the room... get rid of the car asap and move on.

I put higher octane in my cars for one simple reason... it allows the engine to work at its best. I know that I've done everything I know to eliminate anything less than my engine's maximum without worry circumstances may combine to hurt it... in other words, suffer detonation or worse. To that same end I make certain it's otherwise taken care of as well, with clean filters and the best oil and all the rest. I wouldn't have decided to own it just to get the least from it. I want ALL my car has to give, for as long as I own it AND to have the most value left when I get rid of it.

No one nor no thing ever does its best or lasts as long by getting minimum care.
 

·
Registered
Joined
·
13 Posts
It's a really stupid response from the dealer, in my opinion. "We can't do anything about it" - it's the last thing anyone wants to hear. I don't mind putting higher octane fuel into it. But if it's any indication that my engine is damaged, then they should be looking into it and fixing it. I've driven my friend's XV(Crosstrek) and outback, both running the minimum fuel requirement and they don't knock. I've also driven another friends Mazda 3, no knocks on minimum fuel. It's just really frustrating that they don't even want to keep the car to run tests.
I'm still in the process of making a warranty claim to either get return the car and get a refund or get another car. I have a suspicion that they've done something stupid during my first service and dont know how to fix it
Agreed. It does depend on the dealer as well. Any knocking on a new car is unnerving. Good thing you are coving your bases - if anything is wrong with the engine you’ve covered yourself by seeing the dealer and keeping notes. Curious to see how the warranty claim goes - let me know how it goes if you wish. Best of luck.
 
1 - 20 of 39 Posts
Top