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Old 03-16-2021, 08:19 AM   #26
Elbert Bass
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Member#: 283429
Join Date: May 2011
Chapter/Region: South East
Location: Down yonder.
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2016 Fuji Sunfire 03
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Quote:
Originally Posted by jimmy12345678 View Post
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?
So now you have a lean code? I don't see mention of that before - is this something new? So it is possible it is spark knock from a very lean condition. I had mentioned checking fuel trims before. Your lack of response on that led me to believe they were acceptable.
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.
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Last edited by Elbert Bass; 03-16-2021 at 11:00 AM. Reason: adding info
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Old 03-16-2021, 06:22 PM   #27
jimmy12345678
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Member#: 516695
Join Date: Jul 2020
Vehicle:
2008 Impreza 2.5i

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Quote:
Originally Posted by Elbert Bass View Post
So now you have a lean code? I don't see mention of that before - is this something new? So it is possible it is spark knock from a very lean condition. I had mentioned checking fuel trims before. Your lack of response on that led me to believe they were acceptable.
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.

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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Old 03-19-2021, 03:24 AM   #28
jimmy12345678
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2008 Impreza 2.5i

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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.
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Old 03-19-2021, 07:40 PM   #29
Elbert Bass
Scooby Specialist
 
Member#: 283429
Join Date: May 2011
Chapter/Region: South East
Location: Down yonder.
Vehicle:
2016 Fuji Sunfire 03
Silver

Default

Quote:
Originally Posted by jimmy12345678 View Post
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.
You talked about adjusting valves sometime earlier - did you ever do that? If not it could be a tight valve. That could explain the codes, the wild fuel trims, the misfire...
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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Old 03-30-2021, 09:05 PM   #30
jimmy12345678
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Member#: 516695
Join Date: Jul 2020
Vehicle:
2008 Impreza 2.5i

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Quote:
Originally Posted by Elbert Bass View Post
You talked about adjusting valves sometime earlier - did you ever do that? If not it could be a tight valve. That could explain the codes, the wild fuel trims, the misfire...
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.
Yes I did check all the valve clearances on both banks once I'd pulled the valve cover to verify that I was on TDC for each cylinder, all were in spec (0.008 for intake, 0.010 for exhaust). Currently have the heads pulled and at the machine shop getting the head pressure tested, cleaned up and new valves and valve guides installed. Once I have them back and reassemble everything I will repeat the leakdown test again and post the results. Hope to have them back within a day or two and have the car back together by the end of the weekend.... we'll see how that turns out.
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Old 04-25-2021, 01:41 PM   #31
jimmy12345678
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Member#: 516695
Join Date: Jul 2020
Vehicle:
2008 Impreza 2.5i

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Well I FINALLY got to the bottom of what was going on with the Subaru. In short, it was a clogged secondary catalytic converter, because after reassembling the heads, setting valve lash and putting the engine back together I still had the same ratting noise and at this point the car would barely drive above 40 mph.

I ended up cutting out the secondary converter and test driving it to see if the problem had gone away and the subie drove like a brand new car. Ended up welding in a universal converter and now all is well.

If I would've tested back pressure I could've found this a lot easier, but I feel like the clogged converter has been the issue all along and it being plugged up is what burned out the exhaust valves.

Thanks for your help through all this!
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