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01-01-2021, 10:29 AM | #1 |
Scooby Newbie
Member#: 516695
Join Date: Jul 2020
Vehicle:2008 Impreza 2.5i |
Valve Rattle At High RPM's Under Load (5k RPM+), Faulty VVL Solenoid
I have an engine rattle that I haven't been able to pin down yet, but I have a theory that I'd like to put forth to the group and see what more experienced Subie owners have experienced.
The rattling noise occurs when going up steep grades at high RPM's under load, like 5,000+. A few months back when the noise occurred it set a CEL, P0028 for the Bank 2 Intake Valve Control Solenoid and a noticable "valve rattle" type noise could be heard. I ran a can of BG Engine Performance Restore through the engine to flush out the oil (leftover can from when I worked at the dealership) and so far the code has not come back, but the rattle can still be heard under the conditions I previously said. A little more background, when I purchased this vehicle (2008 Subaru Impreza 2.5i) it had a leaking VVL oil pressure sensor on Bank 2, which was misdiagnosed as a bad head gasket and is how I ended up with the car, as the owner didn't want to spend that kind of money. I made sure to keep the oil level up driving the car back home and replaced the sensor ASAP after getting the car, but I have no way of knowing whether it's been ran low on oil before I took possession of it. So what do you guys think? Could this be caused by a failing VVL solenoid (but not bad enough to cause a CEL) or is it more likely I have engine damage that is making itself known by knocking at high RPM's? Thanks in advance! |
01-01-2021, 02:34 PM | #2 |
Scooby Specialist
Member#: 283429
Join Date: May 2011
Chapter/Region:
South East
Location: Down yonder.
Vehicle:2016 Fuji Sunfire 03 Silver |
You may have two conditions - gummed up i-AVLS (VVL) causing the code and spark knock creating the noise.
Generally you will get the P0026/28 from low oil level and/or sludge. First step for the P0028 is engine flush (Seafoam/Subaru Treatment) then fresh oil & filter change. Really bad cases oil & filter - flush - oil & filter. You say it is valve rattle? Are you sure it is not spark knock (pre-detonation)? The conditions you describe is more indicative of spark knock. Have you tried using a different grade/octane fuel? Tier 1 fuel vendor? Generally if you have valve rattle it is present at all ranges/RPM. One other thing to check - although this is usually below 2500 RPM - rattle from the i-AVLS rocker arms. I have seen techs not pre-load the spring loaded rocker lever and when the i-AVLS rocker is in low lift the mechanism rattles. Wouldn't hurt to check valve lash either. And then there is the timing belt tensioner - again, those usually rattle at idle/low RPM. |
01-01-2021, 10:58 PM | #3 | |
Scooby Newbie
Member#: 516695
Join Date: Jul 2020
Vehicle:2008 Impreza 2.5i |
Quote:
I will try running some 93 octane fuel once the tank gets to around 1/4 full and recreate the conditions to see if it improves/goes away. I do not know the full maintenance history of this vehicle as the Carfax only lists spotty oil changes and air filter replacements, so I don't know if the timing belt and water pump has ever been done, but I plan on doing it within the next month or two. I have also been thinking about doing valve lash when I do the timing belt job, I could not find a maintenance interval for adjusting the valves and I also doubt it's ever been done. And I am a maintenance fanatic and want everything to be "perfect" on my vehicles LOL. I had no freeze frame data stored with the code, nor have I pulled the VVL solenoid to inspect it for sludge, etc., just have ran the BG EPR flush treatment and checked the level weekly. The reason I assumed it was valve train related was because of past experience hearing "lifter ticks" and other similar noises and they come close to the noise my Subie is making, and also because the P0028 code was set while the noise was very prominent and the conditions were where the noise always seems to occur (steep grade going uphill, 5k+ RPM's). I just "assumed" it was losing oil pressure at high RPM's or something similar to that. What is the procedure for preloading the rocker level and how do you check the clearance? I will keep this thread updated and see what happens with the car |
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01-02-2021, 11:00 AM | #4 | |
Scooby Specialist
Member#: 283429
Join Date: May 2011
Chapter/Region:
South East
Location: Down yonder.
Vehicle:2016 Fuji Sunfire 03 Silver |
Quote:
The "lifter ticks" you are probably used to are from hydraulic lifters, your Subaru does not have hydraulic lifters, hence the reason for a valve lash adjustment. There is no real service interval for valve lash, although most Subaru instructors recommend around 100,000 miles. Given the fact that EJ engines are prone to head gasket failures a competent tech takes time to adjust valve lash when replacing head gaskets. OK, you have never been behind the rocker cover of a Subaru - It is not so much a preload as it is a black spring loaded lever next to one intake rocker arm on each cylinder. You release the spring to make it easier to remove the rocker assembly. In the photo: The "preload" is when that square tang is behind that round pin to the left of the tang. There is one of those on 1 intake rocker for each cylinder. You perform valve adjustment like any other rocker arm valve train - set the cylinder to adjust top dead center (valves fully closed), and use a feeler guage between the valve stem and rocker tappet. The rocker tappet has a lock nut and threaded screw to adjust the clearance. https://www.subaruoutback.org/attach...-1-png.391473/ |
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01-12-2021, 03:05 AM | #5 |
Scooby Newbie
Member#: 516695
Join Date: Jul 2020
Vehicle:2008 Impreza 2.5i |
Thread Update
I filled the car up from 1/4 tank with 93 octane and drove it around for a day or so to make sure the gas is sufficently mixed in before recreating the driving conditions that made the problem occur before. The higher octane fuel did NOT eliminate the rattling noise that occurs around 5k rpm under heavy load, so I don't feel that is it spark knock, although the car did seem to have less power at those rpm's, as if it was pulling timing to correct for spark knock. Also whenever the noise started it was accompanied by an "oil burning" type smell that even my girlfriend noticed and pointed out, I don't know if that helps at all but I thought I'd include it. Based on my experience as a mechanic, I'm guessing I need to check valve lash and do a valve adjustment to see if that makes any difference, but I am not experienced with Subies, so what do you guys feel would be prudent to look at now that I've eliminated one of the potential causes? It's definitely some sort of engine noise. Last edited by jimmy12345678; 01-12-2021 at 04:59 PM. |
01-16-2021, 11:32 AM | #6 |
Scooby Newbie
Member#: 516695
Join Date: Jul 2020
Vehicle:2008 Impreza 2.5i |
Another update
This might be related, but the car has has an intermittent, occasional misfire at idle ever since I've owned it and I've not been able to determine the cause. It's not enough to set a misfire code, but my experienced mechanic feel knows what a misfire feels like, haven't put a lab scope on it yet to see if I can "catch" a miss on one of the cylinders (2 channel Pico). Seems to happen more when the A/C is on, such as in the summer or when running the defroster. Don't know if the two issues are related or not. Again not familiar with Subarus, although basic engine concepts remain the same across all makes. Didn't know if anyone had seen this problem before or if there was a common issue that caused this. |
01-30-2021, 08:13 AM | #7 |
Scooby Newbie
Member#: 516695
Join Date: Jul 2020
Vehicle:2008 Impreza 2.5i |
Anyone have any ideas on what I should check next in order to figure out this problem? I'm at a loss for words and don't know where to go from here given my inexperience working on Subarus.
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01-30-2021, 11:18 AM | #8 |
Scooby Specialist
Member#: 283429
Join Date: May 2011
Chapter/Region:
South East
Location: Down yonder.
Vehicle:2016 Fuji Sunfire 03 Silver |
Sure it' not just a heat shield on the exhaust?
Based on the other things you looked at we are back to spark knock. If it happens under load/acceleration that is most likely spark knock. Primary cause for that is air/fuel going lean. I understand you fixation on valves but if you had a problem in the valve train it would most likely happen at all times. Do you have the capability to see real time fuel trims? Be curious to see what they are cruising at operating temperature as well as the A/F sensor and O2 sensor under load. also check fuel pressure. Have you tried unplugging the MAF and driving it? Does it still happen? |
01-30-2021, 11:56 AM | #9 | ||
Scooby Newbie
Member#: 516695
Join Date: Jul 2020
Vehicle:2008 Impreza 2.5i |
Quote:
I found something that COULD explain my issue in another thread on this site, tell me if this makes sense to you or if it's gibberish: Quote:
I've checked all the heat shields on the vehicle and none are loose or rubbing on anything (been burned by loose heat shields before on customer's vehicles) along with the P0028 code setting during the noise occurring makes me certain is it a legitimate problem. Have not tried driving with the MAF unplugged, what exactly would it mean if the problem went away with the MAF unplugged? I WILL get to the bottom of what is causing this issue, I might not be the best diagnostic tech but I'm stubborn enough to not give up when there's a problem LOL |
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01-30-2021, 02:06 PM | #10 | |
Scooby Specialist
Member#: 283429
Join Date: May 2011
Chapter/Region:
South East
Location: Down yonder.
Vehicle:2016 Fuji Sunfire 03 Silver |
Quote:
Please clarify, you never confirmed after the oil flush/change - do you still get the P0028 or not? I assumed it went away (my bad for not asking). If you still get P0028 then swap the oil pressure switches on the oil control solenoids from left to right then drive it. Does the P0028 come back or does it change to P0026? Then we can proceed further. One step at a time. Driving with MAF unplugged puts ECM in limp mode. A preprogrammed fuel mixture/ignition timing based soley on engine speed and throttle position. It is assumed that if the engine runs relatively normal in limp mode the engine is relatively good shape mechanically and the issue is related to engine control sensors and/or wiring for sensors. Lets sort the P0028 first if that is still happening. |
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01-30-2021, 05:41 PM | #11 | |
Scooby Newbie
Member#: 516695
Join Date: Jul 2020
Vehicle:2008 Impreza 2.5i |
Quote:
No, I have NOT gotten the P0028 code since doing the oil flush back in November (over 2k miles put on since then), nor have I ever gotten a P0026 code either. The noise was occurring when the MIL came on and shortly after I pulled the code and it was the P0028. The code has not come back but the noise still remains and is easily replicated, and I know that sometimes intermittent problems fail to set any MIL's. I can record the noise as well as all the live data PID's needed to get to the bottom of this. Last edited by jimmy12345678; 01-31-2021 at 11:00 AM. |
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01-31-2021, 12:45 PM | #12 | |
Scooby Specialist
Member#: 283429
Join Date: May 2011
Chapter/Region:
South East
Location: Down yonder.
Vehicle:2016 Fuji Sunfire 03 Silver |
Quote:
Without hearing the noise IN PERSON (don't waste time with a video) all I can give you is what it could be. Normally anything mechanical will be a persistent thing, not intermittent within a very narrow operating range as you describe. First thing based on what you tell me is spark knock. Spark knock is always associated with acceleration under load like climbing a hill. This can be the result of carbon buildup in the cylinders or a lean condition. You could try an upper engine carbon cleaning to see if that helps. It is sprayed into the intake while the engine is running. On your model I spray in through the canister purge hose nipple on the driver side of the throttle body. You will be looking for Intake Valve Cleaner or Upper Engine Carbon Treatment in a spray bottle. Try this next. |
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03-15-2021, 10:20 PM | #13 |
Scooby Newbie
Member#: 516695
Join Date: Jul 2020
Vehicle:2008 Impreza 2.5i |
Update
Okay, still having issues with my Subie, which I'll explain below.
It's still making the rattling noise at high RPM's, but now on a recent road trip the car would barely climb a hill, I had to pick up speed and play with the gears to keep up my speed enough to climb any steep grade, had to use my flashers a couple times because the car just wouldn't keep up with traffic. Did manage to make it home. It set a MIL approximately 45 miles from home after poor performance and fuel economy for the entire trip (around 19 mpg, whereas last summer we averaged around 29-30 under similar driving conditions). I also noticed that the car would "surge" when I'd manually shift into 4th gear at times and it still wanted to rev high and had no power in 2nd gear, and next to no power in 3rd. The codes stored in the PCM were a current P1153 O2 sensor circuit/range performance B1S1, a pending P1153 and a P0171 system too lean code. Just got back home this evening so haven't had time to diagnose anything yet, but my "gut" is telling me it's a failing fuel pump based on the driveability issues. I'm still at a loss. Will be doing some diag work tomorrow but what do you guys think of this new development with this issue? |
03-16-2021, 08:19 AM | #14 | |
Scooby Specialist
Member#: 283429
Join Date: May 2011
Chapter/Region:
South East
Location: Down yonder.
Vehicle:2016 Fuji Sunfire 03 Silver |
Quote:
Did you get freeze frame data from when the P0171 set? are both long and short term trims high positive numbers? Yes, fuel pump is a possibility. You will need to check fuel pressure to verify. It may not be evident at idle and only show low pressure during the rattle under load. In fact, I have seen water in fuel filters cause that. Fuel flows fine under normal load but as soon as you increase demand for fuel flow (accel up hill or heavy load) the water in the filter media will only let's so much fuel through and pressure drops. The amount of water won't be much, could be accumulation of moisture over the years from condensation in the tank. It doesn't take much to soak the filter and block fuel flow. That is the drawback with a single ended fuel supply and a "lifetime" filter in the the tank on the pump assembly. Last edited by Elbert Bass; 03-16-2021 at 11:00 AM. Reason: adding info |
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03-16-2021, 06:22 PM | #15 | |
Scooby Newbie
Member#: 516695
Join Date: Jul 2020
Vehicle:2008 Impreza 2.5i |
Quote:
The P0171 (which went from "pending" to "current" on my test drive tonight) is a new code for this vehicle. I observed tonight that when the low power/surging conditions happen (along with the rattling) that my fuel trim numbers jump all over the place, from -28 to 28, the car also goes from closed to open loop at times while this occurs, though not always. I didn't have my Autel scan tool at home tonight, only my old Innova 3140 that reads live data, so I'll try and get some data PID pics of when this is occurring. I can also feel a slight miss both at idle and while driving when it surges, it's had pending P0303 codes before, but not enough to set an active code. Have access to an oscilloscope too, so see about getting some secondary ignition waveforms to put up. I did check fuel pressure with my Actron gauge, teeing into the fuel lines just past the regulator, and I had a steady 50-52 psi running pressure (spec is 49-50, I figure that's within range) even when the low power condition occurs. I also verified fuel volume delivery by jumping the fuel pump relay on the passenger side under the dash and I got roughly 9 quarts in 1 minute, well within the spec, so fuel pressure/delivery isn't my issue. Thought I was onto something..... Last edited by jimmy12345678; 03-16-2021 at 07:21 PM. |
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03-19-2021, 03:24 AM | #16 |
Scooby Newbie
Member#: 516695
Join Date: Jul 2020
Vehicle:2008 Impreza 2.5i |
Okay, I did some more testing today and I'll post the results:
Volumetric efficiency testing yielded 55.18% on the first test run, 58.79% on the second, indicating either a real or false engine breathing issue. I checked the MAF sensor voltage waveform with my scope and while it had the initial around 4 volt spike, it did not build up voltage as high as a "known good" from the Pico library. Cleaning the MAF made no difference to the waveform output, so I thought I'd go at it as if the breathing fault is real. I also checked and cleaned both the grounds on the intake plenum and the main battery ground under the throttle body, no excess corrosion was found, nor was the issue resolved. As far as the fuel pressure test went, I had the gauge ran from under the hood and taped to the windshield so I could watch it while I was driving, and the pressure never dropped below 52 psi while running, so I'm confident that fuel isn't the issue. My fuel trim numbers, however, were all over the place when giving the car throttle, jumping all the way down to -28 and then back up to 0, with the car going in and out of closed loop at times, though not consistently. Fuel trims did this anytime throttle was applied. I verified that the timing was on with my scope via cam/crank correlation, so I know that mechanical timing is correct on the engine. After that I did a relative compression test with my Picoscope and the results came back completely normal, then it was onto the actual compression testing, which yielded 195 PSI for cylinders 2 and 4 (Bank 2) , and 210 PSI for cylinders 1 and 3 (Bank 1) (cranking for at least 5 revolutions with the throttle held open each time). The approximate 15 PSI difference between banks perplexed me, so I moved onto doing a leakdown test. This is where it got interesting, as cylinder 1 yielded a 15% leakdown, with a faint noise heard from the intake and some blow by coming from the oil cap. Cylinder 3 yielded 40% leakdown, with a bit more noise coming from the intake and roughly the same coming from the oil cap. After that I checked cylinder 2, which showed a 55% leakdown with lots of air coming from the intake, the blow by from the oil cap was roughly the same as bank 1. Cylinder 4 also showed 55% leakdown from the intake as well. I'm assuming this indicates burnt intake valves, and therefore a valve job is needed, but I wanted to see what others think of these new findings. I know that a lean condition can cause burnt valves, but can burnt valves induce a lean condition? Would explain the leakdown numbers and poor VE. Last edited by jimmy12345678; 03-19-2021 at 03:41 AM. |
03-19-2021, 07:40 PM | #17 | |
Scooby Specialist
Member#: 283429
Join Date: May 2011
Chapter/Region:
South East
Location: Down yonder.
Vehicle:2016 Fuji Sunfire 03 Silver |
Quote:
You seem to be distracted by these big faults when most times problems are the simple things. You need to get back to basics here - check the valve lash before you go any further. Worst thing is you are out $20- $25 for 2 rocker gasket/bolt seal kits. BTW: it is normal for the ECM to go open loop at WOT. |
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