Hi guys and gals.

 

I have a 2005 Impreza GX with an EJ20. It has been pinging when the revs are in the 1,000 - 2,500 RPM range. Even on very light load, i have run multiple cans of upper engine cleaner through it. Tried different fuel. Its been doing it for quite a while now. Premium fuel does help with the noise, but its still there.

 

I hooked up a timing light on number 1 and the timing is weird. The timing jumps back 15 odd degrees randomly, multiple times every second. It doesn't hold in the same point as you would expect it to do if it was firing at the right time. I suspect this is the cause of my engine ping. I have used two different types of light, both show the same thing.

 

I 'tested' the knock sensor by using the timing light and watching where it was, then lightly tapping the knock sensor bolt, the timing rolls back then slowly returns back to normal. I figured this means the sensor is ok.

 

The only other thing i can think of is the cam angle sensor or crank angle sensor. Is there a way to tell if they are ok? or would they cause this erratic timing retardation at random times?

I'd be tempted to say knock sensor, but I'd hook up a scanner and watch the timing advance compared with knock sensor inputs while driving.

 

Have you tried fuel system cleaners or a new fuel filter yet?

Thanks for the idea. I have been using scantool, not sure it gives me any details on knock sensor inputs. It does show timing advance though.

 

Its something for me to check out though. See if the advance changes when the knock occurs at a set throttle.

 

I have run fuel system cleaner through it a few times, the fuel filter was changed not that long ago too.

Does this engine have AVCS? I think that started in 05 but im not sure id the Impreza got it. I imagine it would give a code if the valve control was hanging up, but the solenoids are known to plug up with sludgy oil and cause problems.

 

Another though could be a vacuum leak, or sticky tumble valves (if they had those in 05, again I'm not too sure what year those started). The Australian market cars might not have any of this stuff either I don't know.

I don't think it has an AVCS, not that i could find at least.

 

Where should i look for a tumble valve?

More specifically, Tumble Generator Valve. It's a set of valves on each intake port mounted between the intake manifold and cylinder head that close when the engine is cold. The purpose is to accelerate air flow just before entering the cylinders which helps the fuel mixture vaporize more readily. Its aimed solely at emissions reduction during warmup. They are supposed to open up as the engine warms up to operating temp. Thing is, they change airflow characteristics, so if/when they get gummed up and stuck they will alter the way air enters the cylinder when warm as well. I don't know if that would cause pinging though.

 

Pretty easy to identify, they are enclosed in a separate housing right at the base of the intake manifold.

Which brings up the idea of a vacuum leak again, as these provide an extra gasket surface which can fail and leak air into the manifold. Even small amounts can have a detrimental leaning effect on the fuel mixture, especially if it occurs on only one cylinder.

Out of curiosity, what does the MAP reading say with the engine at idle? Also, how many miles are on this engine? Aauto or manual transmission? Does it have an EGR valve?

I don't believe it has a tumble generator valve, the plenum joins straight to the head.

 

I will have to look tonight to see if it has an EGR valve or not, from memory i don't remember seeing one, but i will have to look to be sure.

 

It has about 191,000k's on the clock. It is an auto, it is an ex rep car, so its done quite a few k's in a short time.

 

I had never owned a subaru before this and had no idea that you were meant to use upper engine cleaner every service. I serviced it about 3 times and never knew to use it. I have since run quite a bit of engine cleaner through it as i wasn't sure if it was carbon build up or not. I have even taken it for a nice long drive up a mountain and highway to try and get it hot in an effort to burn any carbon it may have built up.

 

I will have to look at the MAP value tonight. The advance when i tested it last night at idle was 7 degrees and jumped to 10, then 7 (it was a bit erratic) but at that time i don't know if it was at full operating temperature. When driving, not revving too high hit about 48. Any idea of what the advance should be at set RPM levels?

 

I really appreciate the time you are taking to help me with this. I also know how hard it is to diagnose without having something in front of you.

I've just assumed this whole time that this is a non-turbo engine is that correct?

 

I've seen up to 42 degrees of timing advance while driving my 96 Ej22, so 48 is probably in the ballpark for that engine. The USDM cars never got the high compression engines that they used in other markets. Engine tuning can vary quite a bit.

 

I don't think most people use engine cleaners that often. A clean engine runs better though.

You are right, its a non turbo EJ20. Still waiting to go home and check the MAP settings, only a few more hours!

I got a few screen shots. It doesn't seem to show the MAP settings.

 

At idle i get:

Throttle position: 9.4%

Engine RPM: 662

load 1.6%

Advance 10degrees, this does jump back to 7 every so often, not stable

Inlet manifold pressure: 26KPA

Air flow rate: 1.81 g/s

Intake air temp 58c

Coolant temp 93c

 

In gear, with my foot on the brake i can get it to ping.

Throttle 17.6%

RPM 1725

Load 16.1%

Timing advance: 23 degrees

Intake manifold pressure 65kpa

air flow 16.17 g/s

 

The weird thing is, if i put my foot down harder to get higher revs, the ping stops and the timing advance drops to about 15 degrees. I thought with higher revs, the timing would also advance....

The ping stops because the knock sensor is picking it up and retarding the timing. The amount of advance varies depending on engine rpm as well, so I'd this is happening at 1000 rpm the timing may be normal. But it should advance smoothly as engine speed increases, then generally reach a peak in the mid rpm range.

 

Manifold pressure. Thats the MAP reading I was asking about. It looks like your intake vacuum is too low. Seems to me that it should be around 55-65 kPa at idle, but I'll have to check on that.