friend's subaru problems

[Robert2468]

good friend does not know about cars. she has a 2021 Forrester, she got new, has 35,000 miles. dashboard lit up. dealer says there is carbon on some valve, causing misfire cylinder 3. she faithfully changed synthetic oil at the dealer. he asked about gas. she gets I think Costco gas. car is at dealer to fix.

dumb questions:

1. did she do something to cause this, or is this engine design?

2. I told her I use top tier gas, regular grade, I have two acura RDX cars. would that help?

3. I DO like Hondas and Toyotas for longevity. i told her to think about getting a honda or toyota.

would love any and all ideas.

best,
bob

 

[rijndael]

Dirty valves are a common problem with GDI engines that don't also have port injectors, like a Toyota D-4S system.

In many cars, it can happen regardless of oil and gas choices.

 

[D60]

Apparently the '21 is DI (I had to look it up as I try not to follow URaBus)

35k seems early, are others experiencing this on these models?

But OP, NO she did NOT do anything wrong (except maybe buying DI which 99% of consumers don't understand). Any modern vehicle should be fine at 35k with semi-regular oil changes and basic pump gas (obviously high performance/high compression/forced induction perhaps excepted)

 

[Urshurak776]

35K should still be under warranty. I thought those had 5 year 60K? Even with DI issues, that’s super early for that to happen. I question the diagnosis to be honest.

 

[Rebound]

good friend does not know about cars. she has a 2021 Forrester, she got new, has 35,000 miles. dashboard lit up. dealer says there is carbon on some valve, causing misfire cylinder 3. she faithfully changed synthetic oil at the dealer. he asked about gas. she gets I think Costco gas. car is at dealer to fix.

dumb questions:

1. did she do something to cause this, or is this engine design?

2. I told her I use top tier gas, regular grade, I have two acura RDX cars. would that help?

3. I DO like Hondas and Toyotas for longevity. i told her to think about getting a honda or toyota.

would love any and all ideas.

best,
bob

35,000 miles is awfully low mileage for carbon buildup to impact performance. As far as I know, the only way to know that you have carbon buildup is to remove or loosen the intake manifold and visually inspect… and if you’ve done that, you can snap a photo with a borescope and you can scrape off any big chunks.

So unless he showed her a photo of the intake, I think he’s guessing at the cause of her problem. I’d try a second opinion, because many things can cause misfires. Carbon buildup will usually cause misfires and hesitation on a cold engine first, while a bad ignition coil or connection could more likely show up as a problem when accelerating to get onto a highway. Or there could be a vacuum leak. There are lights on the dash, so a diagnostic code readout can help a technician determine the cause.

Because her engine is direct injection, gasoline does not flow over the valves to wash off carbon build up. Top tier gas may still help lessen this because it’s caused by the exhaust gas which enters your intake via the EGR. Top tier does NOT mean higher octane. It means Shell, Exxon or Chevron, for the most part. Any octane. Subarus don’t need high octane gas. I’d also replace the PCV valve at 35,000 because they’re cheap and easy to replace on a Subaru.

 

[SC Maintenance]

Dirty valves. Is walnut shell blast not covered under warranty?

Next time I would pull and record the codes.

 

[Donald]

Is the dealer going to fix under warranty or are they saying it's gas or oil related? I think running top tier gas is good idea for all cars.

Would a run on Techron help here?

 

[JohnnyG]

The OP said "some valve", so it might be the EGR, if there is one.

 

[Nukeman7]

good friend does not know about cars. she has a 2021 Forrester, she got new, has 35,000 miles. dashboard lit up. dealer says there is carbon on some valve, causing misfire cylinder 3. she faithfully changed synthetic oil at the dealer. he asked about gas. she gets I think Costco gas. car is at dealer to fix.

dumb questions:

2. I told her I use top tier gas, regular grade, I have two acura RDX cars. would that help?

best,
bob

Is the dealer going to fix under warranty or are they saying it's gas or oil related? I think running top tier gas is good idea for all cars.

Would a run on Techron help here?

COSTCO gas is Top Tier certified. In fact, it contains the 2nd highest amount of detergents of the Top Tier rated fuels. Shell Nitro is #1 per their advertisement that it contains 6 times the EPA detergent minimum standard, while COSTCO is close behind at 5 times the EPA minimum.

 

[Donald]

COSTCO gas is Top Tier certified. In fact, it contains the 2nd highest amount of detergents of the Top Tier rated fuels. Shell Nitro is #1 per their advertisement that it contains 6 times the EPA detergent minimum standard, while COSTCO is close behind at 5 times the EPA minimum.

Well there are a lot more ExxonMobil stations than Costco stores with gas stations. I try and fill up on my round of errands rather than drive some place to fill up.

The pickup only gets ExxonMobil diesel as it's a branded diesel rather than whatever diesel is available to be sent to gas stations.

 

[Trav]

35K is a little early for carbon deposit on intake valves built up enough to cause a misfire. it could be the EGR but these were recalled in 2019 for bad ignition coils. It has been my experience that because a new model has not been recalled that the problem is not guaranteed to be repaired or doesnt still exist.
There is no reason to not to believe them (well there is) but get a second opinion. I have had people bring their car to me that were told they needed a new engine for a boat load of $$$ claiming the timing chain had jumped. A 2 min test with a coil tester exposed a bad #1 ignition coil.

 

[D60]

35K is a little early for carbon deposit on intake valves built up enough to cause a misfire. it could be the EGR but these were recalled in 2019 for bad ignition coils. It has been my experience that because a new model has not been recalled that the problem is not guaranteed to be repaired or doesnt still exist.
There is no reason to not to believe them (well there is) but get a second opinion. I have had people bring their car to me that were told they needed a new engine for a boat load of $$$ claiming the timing chain had jumped. A 2 min test with a coil tester exposed a bad #1 ignition coil.

Would they likely determine this from relative compression or leakdown or something else?

Either way I'd want to see documentation or proof of some test before the valvetrain is blamed.

 

[Rand]

I think its likely a wallet fleecing. DI Valve issues at 35000 miles unheard of on modern DI.

next thing will be the $2400 list of recommended services.

Personal Thoughts: if its under warranty Subaru should cover the valve cleaning anyway IMO.

 

[Exhaustgases]

This is a free fix! Do not get roped into paying for it.
I think all newer vehicles are on an 8 year Federal emissions warranty. That means anything that happens to it that causes bad emissions is a free fix. And a miss fire caused by anything is defiantly an emissions related problem.

Research this.

And don't sign anything that requires payment. Its on them subydo. You don't pay for parts, you don't pay for labor.

And also isn't it still on warranty? Like someone else mentioned?