kkingcqe
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It appears that I finally have a resolution. Check engine light reading P0171 had, within the past month or so, become very consistent about every 25 miles. I recently replaced a cracked PCV hose and bought a pressure gauge to check fuel pump pressure. No difference. Finally asked at a pay forum that features certified mechanics because I had run out of things to try. He suggested that the next step was to check or replace MAF sensor. Although the OBD Auto Doctor software that I also recently purchased showed acceptable MAF readings at idle he said that I should replace it anyway. It appears that the MAF sensor was the problem. No check engine light, no knocking. Still idles rather roughly for a modern engine, but I've put up with that for 5 years so I guess it's okay. Thought you might like to know. Thanks for the help! --Ken
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Just a short follow-up. Changed the oil right after valve cover gasket replacement. After 1500 miles I am pleased to report the oil level reads slightly over full, just as it did when freshly changed. Pretty amazing for an engine with 237k on the clock. I've noticed that some days the ping is almost nonexistent and other days it sounds like a diesel. Also some days gas mileage is spectacular, occasionally achieving 30 mpg on my journey home, and other days it's closer to 25. In either case operation is very smooth. Lastly, it looks like the inefficient catalyst CEL is here to stay. Perhaps the bargain Pace Setter catalytic converter is not such a bargain. --Ken
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An oil analysis does make sense. I never had one done but talked extensively with someone at a local lab about doing this on Amtrak's road fleet when I worked there. We never followed through because the Director of Equipment did not believe it was cost effective. In this case it just might yield definitive answer as to whether it's time to start looking for another car. I ordered the Blackstone collection kit.
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The Subaru service manual does address rod bearing knocking so it is a known problem. Bearings have a different sound, they are consistent, and they don't go away at higher speeds but do change with engine RPM. Now that I cannot blame EGR I almost have to stay with the carbon. Blaming dislodging carbon on my newly acquired P0420 code.
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4AT automatic. We'll,cleaning out the EGR system had no effect. Changed plugs tonight in case I was mistaken but ones I took out were identical. Ping does not happen when engine is cold.
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That is an interesting thought Tex. I am so glad that I brought this problem here. You especially have come up with the best ideas. And I keep hoping that the solution lies somewhere other than piston rings.
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They do have a massive exhaust passage compared to those tiny tubes used on early systems. When I bought the car it had two issues that were confounding each other so no one was figuring out the problem. One was the EGR valve that was so full of carbon that it would not close. Add a MAF sensor that was off but not setting a check engine code. It made for poor driveability and no one was quite sure what to do. Those two corrections took a pig of a car and made it the pleasure to drive I always knew it could be.
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Thanks GD. I appreciate you talking through this. Here is what I am thinking. Purpose of the EGR system is to cool combustion slightly. Since all of the timing and blending and ratio stuff is interconnected, taking away that cooling effect could cause an increase in combustion temperature and... bingo! If, as I think it should, the ECU ignores the knock sensor at low RPM and load conditions that would further explain why there is no automatic correction happening until the engine speeds up. You are 100% correct about when the EGR is functioning. I did not know before but I have been looking into this over the past few days. EGR is closed at idle and WOT. All the rest of the time it is passing a small amount of exhaust gas and the system is tuned to allow for it. Only piece that is missing is the P0401 error code. If I had that I would be certain. Anyway, I flushed the EGR system last night so I am sure there is a good flow and we'll see how she sounds today. As I mentioned, the car's performance is exceptionally smooth with better than expected fuel mileage. Only the pinging sound is at issue.
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I am battling a check engine light but it is for the front cat. As a result of trying to clean carbon out of the cylinders I may have clogged my new catalytic converter. I'm looking at the EGR system because it does have a certain logic that it may be the issue. Yesterday there was a little pinging occasionally but nothing like Friday night when it was embarrassing to drive. I had done a little cleaning of the EGR ports over the weekend so I did some more last night. This afternoon I should have the opportunity to leave the windows down to listen for the ping echoing from roadside objects. Thanks Tex for the tip on the PCV valve. The shop manual never even mentions it. I replace it last night, but the original one still rattles. Yes I could tell that I was the first one to remove it in over 200,000 miles.
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My first cars were built in the 1960s. Lots of carbon buildup from carbureted induction systems. You'll have to take my word that the noise is the same but not occurring at the same time. I've been looking for a solution for this for some time and she's been through several oil changes during. Mechanical knocking noises tend to have a more solid sound, if you know what I mean. That and they get worse or at least speed up at higher revs. Got a couple of things to check when I get home tonight. I appreciate your input (and everyone else's) because one of these ideas is going to be the right one.
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There is some heat shield rattle from the rear converter. Sometimes it happens at the same time and the sound is a little different from the ping. The mechanic put in $600 worth of parts on the timing belt change which I believe included tensioner(s). The sound really isn't a knock although I tend to think of it that way, but I have heard bad rod bearings or collapsed hydraulic lifters and this definitely is not it. I even had a mechanic at Meineke comment about how smoothly and quietly the car idles. On occasion it does idle roughly but there is no rapping noise although it does tend to vibrate stuff in the door pockets. My guess is that is the EGR not quite snapping shut. PCV valve? Far as I have been able to determine there is no PCV valve, but there is no problem with oil control. The oil consumption is very low, in my opinion. I don't expect to have to put any oil in between changes now that the leak is fixed. There was a lot of clean metal when I took a look at the pistons yesterday. More than I expected. I'm still planning on messing with the EGR when I get home tonight.
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I've always said that engine ping is akin to marbles in a coffee can. Subaru manual talks about a wrist pin issue that would happen under similar conditions but the description of the sound is different. It is actually a knocking sound like you might hear with a bad bearing. I'm thinking that timing correction is probably not mapped in the computer for these RPM/load conditions. What I am saying is that the ECU ignores pinging sounds at this RPM and load. That's what I am thinking. Wish it would set a CEL, but the computer is happy. Once I push heavier on the throttle the sound disappears. Whether it is gone or just masked by engine noise I don't know. As I recall, when my big American V-8 engines pinged there was no mistaking the sound. It was louder than the engine roar.
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I'm wondering the source of the oil consumption figure since Subaru of America has been saying that ~1000 miles to a quart is okay even for a new engine. My question for GD is have you seen this same problem and can directly attribute it to the carbon and rings? My car runs great and if you never put the windows down you would never know there was a problem. The ping or clatter is not under heavy load. It is with minimal throttle pressure and load, like when I am driving to attain maximum fuel economy. Subaru repair manual does not acknowledge this as a condition that can happen. I appreciate the passion and certainty that several folks have related in their postings. But I have owned Subarus for almost 20 years and have literally spent thousands of dollars fixing things that weren't bad. Would seem reasonable to offer anyone who is sure of their solution to this problem that I'll pay twice if your solution actually fixes the problem. You pay for the fix if it doesn't. Made that same offer to the Subaru dealer in Lansing, MI about 15 years ago on the check engine light of my '96 and he would not take the bet. I don't think I will be able to record the sound. My smart phone does not deal with sound very well and honestly I have no idea how to get a file from the phone to somewhere you can access it.
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Put in factory spec NGKs last change. Sunoco 93 has no effect. Might be worth changing the plugs.
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Scoped cylinders almost no carbon. Oil burning is about 2000 miles to a quart.