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2002 Forester
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Discussion Starter #1
Hello all,

I've been dealing with an incredible racket coming from the engine for over a week now. 2002 Forester L with 150,000 miles. Mobil One 10w30 since new, and driven mild (mostly). Oil level is fine, coolant level is fine with no change.

Problem: On an incline at approximately 50 - 70 mph, the engine begins to rattle as if running lean or at least making a pre-detonation sound. Attempts to maintain the current speed or slightly accelerate brings on an alarming knocking sound. Difficult to pin point, but my guess is that it comes from the passenger side of the engine bay. Sitting behind the wheel when this occurs, so I'm purely guessing at location. I asked my wife to confirm location of sound, and she said it was coming from the back. Hey, it was worth a try :)

I can reduce or eliminate the sound if I let off the gas slightly, but I experimented today by shifting out of Drive and in to 2. I wasn't trying to increase speed, but rather the goal was to see if the change in rpm would affect the knock/banging sound.

More background info: Check Engine light has been on for months and was only the P0420 code. I checked the codes again a few minutes ago, and now it reports P0420, P0442, and P0456. The last 2 codes deal with an EVAP leak, which is new and I'm not sure when they started, since I left the CEL illuminated all this time. I read related posts and assume a pressure leak somewhere, but I'm more concerned with possible causes for the engine noise. Except for this severe knocking, the vehicle has been running strong and smooth.

Thanks for any suggestions and even wild guesses! I'm at a loss for this one.
John
 

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03X MT
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846 Posts
I doubt you will have much luck solving any engine performance issues until parts are replaced to clear codes. I'm assuming the ECU is adjusting the mixture based on the information it is receiving from various sensors.
 

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2016 Forester Limited CVT
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92 Posts
Just a stretch here.....but have you replace your timing belt yet? I had an old corolla that did the same thing you Forester is doing (knock on incline, or heavy gas at high speed), and it turned out to be the timing belt. It had stretched so much that the timing got thrown off causing the knock/ping.

Again, just a stretch....
 

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2002 Forester
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Discussion Starter #4
I cleared the codes last night and drove in this morning. Approx 50 mile commute mixed between back roads and 30 minutes of highway. I left the code reader plugged in and set it to the monitor position. All systems reported Good except for two, which indicated INC for incomplete. The directions for the code reader indicate that it will change after a sufficient amount of time has passed. I'm not sure what that means, since the commute takes an hour.

Except for some valve train noise cruising at about 75 mph, everything was very smooth and quiet. At least it was that way until I reached the bridge close to work. As soon as I got to about 50 mph on the incline side, the loud knocking started again, and I backed off slightly from the gas to try to stop the noise. It worked, but it also means that I can only maintain about 45 mph until I reach the top of the bridge. RPM is about 3000 when the noise starts, but I've tried shifting down in the past in order to elevate the rpm with the hopes that ... not sure what I was hoping.

As of right now, there are no diagnostic codes, and the on board system is reporting overall Good status. Any further thoughts?

Thanks for the quick reply!
 

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2002 Forester
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12 Posts
Discussion Starter #5
I didn't even think about the timing belt. My wife had it changed while I was overseas. I suppose it was at the 120,000 mile mark, but I know it was long enough ago. I do recall hearing the rattle sound at about 80mph last summer when I got home, but this new banging sound is very recent. I'll have to look in to sight holes or other means to verify that the belt and pulleys are alligned properly. Thanks for the suggestion!
 

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13 Forester XT 4EAT
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The inc means that you have not completed that part of the drive cycle yet in your sensor reporting. You could drive 1000 miles and if you don't satisfy that circumstance, you won't have info on that test. Your car obviously has an issue, why don't you get it fixed? I wouldn't just clear codes because they are there until you've addressed the issue.

The other thing, at least in NYS, you won't pass inspection if either the light is on, or you have 3 or more INC on your reading when they hook it up.
 

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2002 Forester
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Discussion Starter #7
Thanks for the info about the INC on the code reader. As far as why I don't just get it fixed, that is the goal of asking for help on diagnosing the problem that causes the sound from the engine on incline/load.

After reading the codes last night, I looked up each code and checked this forum to gather a concensus of possible fixes. The P0420 is reported as typically being the rear O2 sensor rather than the actual code meaning for a failing catalytic converter. In my case, the front cat is starting to rust out and a faint exhaust leak is starting. So the front and rear cat assy has been ordered. The other two codes (P0442 and P0456) are for an EVAP system leak (small and very small). After looking at this forum, I saw several mentions to the gas cap. I removed the cap and saw rust was starting to form right where the cap meets the filler neck. I cleaned up the metal and put a thin coat of POR-15 on it. The cap went back on this morning and so far so good. There were other areas mentioned to keep an eye on, but the filler was obvious and easily fixed.

My concern is that the diagnostics aren't throwing any codes for predetonation or even misfires. I'm pretty sure that a misfire is not what is happening here. I experienced that right at 30,000 miles and an old timer a the Subaru dealer told me to either bring it in or simply yank out the Champion plugs and put something decent in there. The dealership route would replace the coil pack, plugs, wires, and whatever else they felt was necessary. Warranty had just expired, so I tried the plugs. Problem was fixed.

I guess what I'm trying to find out are possible mechanical conditions that aren't detected by the OBD but manifest themselves during very specific driving conditions. As a side, I had my trailer hooked up over the weekend and pulling a small load (about 1000 lbs rolling). From a dead stop and going up a steep incline, I accelerated very easily and never heard the engine sound off key. The RPM got to about 4000 and stayed there in second gear until I reached the top of the hill, at which point it shifted in to 3rd.

Thanks again though for the input.
 

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2017 VW Golf SportWagen 5MT
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Sounds like the engine is knocking under load. Could be:

1) too lean a mixture
2) timing off
3) too much carbon buildup in the combustion chambers/pistons

If you are running on 87 octane (which I'm betting you are), run the tank fairly low, fill up with the highest quality, highest octane gas you can find (Chevron around here) and see if you notice any changes over one tank of gas. This is the cheapest and easiest troubleshooting step I can think of.

Stan
 

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2004 Forester 4EAT
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5,462 Posts
I would guess fuel related. Ignition problems tend to be worse at idle than at speed. (Not always though) Fuel pump, filter, bad injector on pass side... Change filter as a precaution unless yours is in the tank. (Hope it's not, for your sake) Sounds from your description that it's speed related rather than rmp related though. That part has me puzzled? Can you replicate problem at lower speed but same rpm? (downshift, but go slower) Gut feeling says fuel related though.
 

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2002 Forester
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Discussion Starter #11
Glad to hear about the octane. Yes, I have been running 87 since new. Dealer suggested that 87 was optimal for the engine. Anyway, as luck would have it, the tank was very low today. I filled up with 93 before leaving work. After about 1 minute of running, the engine had a huge hesitation and stumble that almost stalled the engine. The engine smoothed out and no codes were thrown. I had the code reader also plugged in to see if any real time reports could be generated. The OBD said nothing.

I drove the vehicle around town for about 15 minutes prior to heading across the bridge. My wife commented how smooth the engine sounded, but she didn't know that I filled with higher octane. I can't say that it ran better or not, but the slight valve clatter that would sometime occur with minor load was not evident. Traffic opened up for a moment and I accelerated to try and duplicate the condition that brings on the heavy knock. It was smooth running for about 15 seconds as it accelerated from about 50 to 60 mph. I ran out of lane, so I had to back off. There's a smaller bridge a little further up the road, and that one I pushed the engine much harder to try to hit the right load. The knock and rattle finally began to occur after about 15 seconds of heavy acceleration. I say heavy, but it's not to the point that the transmission down shifts. The rpm was at about 3500. The knock was there, but it had a different tone. Basically it didn't sound as "destructive", if that makes sense.

The comment about the fuel filter got me thinking. I'm pretty sure I failed to replace that filter... ever. All of the other engine and tranny related filters are clear in my mind, but not the fuel filter. I'll take a look this evening to see if it's mounted in the engine bay or not.

I really appreciate everyone's time on this one. This is the first car that I had to maintain that didn't have a distributor. I feel more comfortable working on a car with multiple distributors, since I can understand the mechanical function. No distributor... time to open up the maintenance book!
 

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sounds to me like you have a slow knock sensor. it should be detecting the knock and retarding the timing to prevent preignition rattle. as for the codes you had stored in the ecu p0420, p0442 and p0456 they would not have affected the drivability of the engine, or caused the knock. i would be looking at the knock sensor more closely as its the only sensor that will prevent the knock. and as long as it is showing some resistance the computor is happy and wont throw a code
 

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2017 VW Golf SportWagen 5MT
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I'd keep filling up with higher octane for a while, if you noticed a positive difference this quickly it can only do good.

These engines have 10:1 compression ratio. I would not dare putting 87 in them, personally. Then again, our fuel here in CA is pretty bad.

Stan
 

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2002 Forester
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Discussion Starter #14
Interesting about the knock sensor. Thanks for that one.

After 100 miles with the 93 octane, I can now hear a definite change in the sound of the engine. There was no faint rattle from the engine at highway speeds, and there was absolutely no heavy knocking going over the bridges this morning!

Unrelated but an update to a previous msg, my code reader no longer shows INC in any of the I/M categories. Recap on that was I cleared the codes from the OBD in the evening. The next day I drove 50 miles, after which there were two categories that weren't reporting a good status but showed INC instead (incomplete). Later that afternoon though I noticed they changed to a Good status. It may have something to do with miles driven and number of engine starts.

One last question for now. I've seen the comment from many posters on this list under other threads regarding the use of Seafoam engine cleaner. What I didn't notice was any follow on regarding potential damage to the cats. In my case I've already order the replacement cat assy, so I'm not concerned about damaging the original ones. Searches for product reviews have mostly links to videos of people pumping out clouds of white smoke from their exhaust with no other info. I'm assuming that Seafoam is similar to running Marvel Mystery oil or transmission fluid through the engine. Any suggestions on the use of this stuff?

Thanks again for all of the great advice!
 

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2017 VW Golf SportWagen 5MT
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Some use seafoam and others. I'm a fan of relying on combination of good fuel and hard driving to clear out internals. Chevron already has techron in it's gas. As far as knock sensor -- there should be no knock or need to retard timing in the first place.

Stan
 

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you are right stan there should be no knock but if there is and op has a knock the knock sensor should be stopping it and his obviously isnt. as for the seafoam it works to a degree.
 

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2002 Forester
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Discussion Starter #17
UPDATE: Don't know if anyone is still looking at this post, but I located the original cause of the engine knock. After running the 93 octane for 5 fill ups, the knock came back as strong as ever. It always happens after about 15 to 20 seconds of load on the engine from driving up a steep bridge. The knock sensor checked out fine, and the OBD never through a code.

I thought I'd eliminate some other possible causes for running poorly. I replaced the fuel filter, plugs and wires. When I pulled the #3 plug, I noticed a brown discoloration on the ceramic. The other three plugs appeared normal. The next day I approached that steep bridge and proceeded up the incline. Hey, no knock. I got on the gas and really tried to make the engine knock. Smooth as can be. My only thought on the cause of the knock now was that the plug was running hot and would cause the cylinder to fire due to the tip glowing red hot and pre-igniting the fuel during the compress stroke. Thanks again for the support!
 

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Thanks for the followup post. Many don't update w/ their solution which leave most folks unsatisfied.

Re your problem, I once purchased a used 94 Chevy Suburban and drove on a long trip. I noticed some rattling under load which sounded vaguely like engine pre-detonation and decided to check engine when I stopped. While pulling on the plug wires I noticed a small noise. I borrowed some tools and found about half the plugs loose in their threaded holes! Fortunately no thread damage and car ran fine after cleaning, regapping, and re-installing the plugs.

Regards
 
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