I have a 2005 Baja with the normally aspirated 2.5 engine and 33k miles.

 

Since about 13k miles, the engine knocks and pings when using 87 aki gas. If I run 91 aki gas it is fine, HOWEVER, I am not running 91 in a engine that should run on 87. My new 454 and 350 Chevys run fine on 87...I guess their anti-knock sensors actually work, or they have lower compression ratios.

 

Anyway, I have had the car back to the dealer twice and they say there is nothing wrong with it. I have also tried several different gas stations, doesn't seem to make a difference.

 

Question - I am due for a spark plug change. Would changing to a different heat range of spark plug help the problem?

 

thanks

i doubt new plugs will help.

 

are you sure it's recommended to use 87? i figure it is, just checking. it's not a turbo 2.5?

 

some states have different regulations for gas in the winter to reduce pollution, might have better luck in the summer if VA does the same.

[...]Since about 13k miles, the engine knocks and pings when using 87 aki gas. If I run 91 aki gas it is fine, HOWEVER, I am not running 91 in a engine that should run on 87. My new 454 and 350 Chevys run fine on 87...I guess their anti-knock sensors actually work, or they have lower compression ratios.[...]

As you probably know, "Knocks and pings" is a farly general description (are we talking "detonation", or preignition"?), and can have several causes. If the problem came on suddenly at 13k miles, then you need to investigate what changed mechanically/electronically at that mileage.

 

An excessively lean air/fuel mixture can cause knock, and could come on gradually if one or more of the engine management systems has become contaminated. The knock could even relate to something such as carbon in the combustion chambers. Carbon buildup can cause "knocks" in two ways. The first is that it can increase the effective compression ratio, and retarding of the timing through knock-sensor data can help. However, a second and probably more likely possibility is that carbon will cause combustion chamber "hot spots", where the glowing carbon prematurely ignites the mixture. Retarding ignition timing doesn't tend to make a difference if that's happening, so even a properly-functioning knock sensor won't help.

 

If the dealer has verified that engine timing, mixture, running temperature, EGR, etc. are okay, and you're using the correct grade of fuel, then maybe something as simple as a can of combustion chamber cleaner might help. Admittedly, at 13,000 miles carbon isn't usually a problem, but certain conditions can cause it even at low mileage.

 

A bit more info as to when the knocking occurs (engine hot/cold, accelerating/cruising, level/uphill, etc.) might permit better advice.

are you sure it's recommended to use 87? i figure it is, just checking. it's not a turbo 2.5?

 

manual says 87

 

normally aspirated

 

I bought a non-turbo specifically so I did not have to run 91.

 

some states have different regulations for gas in the winter to reduce pollution, might have better luck in the summer if VA does the same.

 

does that same thing, Summer or Winter

As you probably know, "Knocks and pings" is a farly general description (are we talking "detonation", or preignition"?), and can have several causes. If the problem came on suddenly at 13k miles, then you need to investigate what changed mechanically/electronically at that mileage.

 

Well I will use the term "knock", because gasoline is rated as "AKI", or "Anti Knock Index" and the engine has a "knock sensor"

 

If the dealer has verified that engine timing, mixture, running temperature, EGR, etc. are okay, and you're using the correct grade of fuel, then maybe something as simple as a can of combustion chamber cleaner might help. Admittedly, at 13,000 miles carbon isn't usually a problem, but certain conditions can cause it even at low mileage.

 

I tried the combustion chamber cleaner once, a long time back, didn't help. I like you, didn't really expect it to, as at that low of mileage I assumed no buildup of carbon deposits.

 

A bit more info as to when the knocking occurs (engine hot/cold, accelerating/cruising, level/uphill, etc.) might permit better advice.

 

It happens any old time. Winter/Summer, night/day, hills/no hills, cruising along with just me in the car and no cargo. It seems to just knock sometimes, other times it does not knock. No pattern I can come up with.

2 possibilities come to mind:

Lean mixture-problem with O2 sensor.

Defective anti-knock sensor.

Possibly both.

Vacum leak would be a possibility in older cars but the O2 sensor should compensate for.

 

Can you take the car to a dealer that treats the customers better than that (I know, hard to find)? You also have SOA and lemon law as possible resources.

2 possibilities come to mind:

Lean mixture-problem with O2 sensor.

Defective anti-knock sensor.

Possibly both.

Vacum leak would be a possibility in older cars but the O2 sensor should compensate for.

 

Can you take the car to a dealer that treats the customers better than that (I know, hard to find)? You also have SOA and lemon law as possible resources.

 

thanks FJ for the tips.

 

yes, gonna take it to a different dealer. Will report back when/if I get it fixed.

I'm not disputing the 87 listed in the manual - but NA engines often have higher 'native' CRs than turbo cars.

 

I might be tempted to buy gas at a higher end station and perform an ECU reset and monitor a coupla tanks. Wouldn't hurt to use some Techron or seafoam either. If you're up to the task, examining the plugs might tell you if carbon could be an issue.

 

I dunno

 

Carl

Have you tried a better brand of regular gas to see if it goes away?

 

nipper

Have you tried a better brand of regular gas to see if it goes away?

 

nipper

Well, I have 2 Chevys and 1 Honda that run fine on the same gas that I use in the Subaru. I shouldn't have to take special measures for the Subaru, unless that is the Subaru is an inferior vehicle. If that is the case I will get rid of it.

 

But to answer your question, I have tried other brands of 87 and it didn't help. The only thing that helped was running 91.

Knock sensor codes are common with Subarus and we change quite a few knock sensors. It wouldn't surprise me if yours is NG.

Knock sensor codes are common with Subarus and we change quite a few knock sensors. It wouldn't surprise me if yours is NG.

 

He didn't mention a CEL or likely someone would have suggested the knock sensor. Plus - it may very well be that, if the sensor were bad, the ECU would default to the safest timing map. I dunno. Anyone actually confirm 87 RON is proper for that vehicle?

 

Carl

He didn't mention a CEL or likely someone would have suggested the knock sensor. Plus - it may very well be that, if the sensor were bad, the ECU would default to the safest timing map. I dunno. Anyone actually confirm 87 RON is proper for that vehicle?

 

Carl

 

No CELs have ever come on, and the dealer has never seen any bad codes or whatever.

 

As drxflyboy said, I hope it is just a defective knock sensor. I think whether the dealer I take it to actually hears the knocking or not, I will insist they change the knock sensor.

No CELs have ever come on, and the dealer has never seen any bad codes or whatever.

 

As drxflyboy said, I hope it is just a defective knock sensor. I think whether the dealer I take it to actually hears the knocking or not, I will insist they change the knock sensor.

 

according to;

http://www.cars101.com/subaru/baja/baja2005.html

 

89 octane is recommended. Likely your manual say that but that 87 can be used. I dunno

 

Carl

I've heard a lot of newer cars pinging as they drive past. Camry's, Accord's etc. Cars use 87 octane as the minimum recommended octane level. Under most conditions the engine will run fine on 87. But there are times when it still might ping a little. (I'm not suggesting that everyone use 93, that's only of benefit to cars designed to use 93)

 

And if you've run a couple of tanks of bad gas, you shouldt use Seafoam or Techron fuel system cleaner. Bad gas can have lasting effects.