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2005 3L LL Bean Outback
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Discussion Starter · #1 ·
Continued from What did you do with your 3rd gen...

(Small) Detonations in the exhaust after vehicle has warmed up, very noticeable when car is standing still at the stop light. Also occurs while driving. Less noticeable or even unnoticeable under load. Apparently there's unspent fuel arriving in the exhaust. Could very well be related to a P0420 code that seems to be more frequent as of lately.

So far:
  • Checked the exhaust pipes around the O2 sensors which seem to be firm.
  • Cleaned the MAF sensor.
  • Measured/logged some sensors.
Upcoming:
  • Check fuel regulator.
  • ...
 

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2005 3L LL Bean Outback
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Discussion Starter · #2 ·
Not noticing any fuel smell around the fuel regulator's vacuum line. There is a fuel smell around the vehicle which is probably from the rich condition.

Enabled logging for everything related to O2 in Torque. These are the PIDs that show data points:

PID in TorqueTorque NameExample Value
24O2 Sensor1 Equivalence Ratio0.9888916
34O2 Sensor1 Equivalence Ratio(alternate)0.98788452
ff1240O2 Sensor1 wide-range Voltage2.77050781
28O2 Sensor5 Equivalence Ratio0.99194336
ff1244O2 Sensor5 wide-range Voltage2.76074219
ff1215O2 Volts Bank 1 sensor 2(V)0.45499998
ff1219O2 Volts Bank 2 sensor 2(V)0.45999998

I'm guessing the "wide-range" sensors (ff1240 & ff1244) are the upstream O2/AF sensors. ff1215 & ff1219 would seem to be the downstream O2 sensors.

So these would seem to be the upstream sensors;

PID in TorqueTorque NameExample Value
ff1240O2 Sensor1 wide-range Voltage2.77050781
ff1244O2 Sensor5 wide-range Voltage2.76074219

and these would seem to be the downstream sensors:

PID in TorqueTorque NameExample Value
ff1215O2 Volts Bank 1 sensor 2(V)0.45499998
ff1219O2 Volts Bank 2 sensor 2(V)0.45999998

The "Equivalence Ratio" sensor values would seem to be derived from the AF sensors, being the air/fuel ratio compared to the ideal air/fuel ratio of 1.

As an aside, looking at some of the DTC enable conditions in the service manual, such as for "DTC P1153 O2 SENSOR CIRCUIT RANGE", they seem to require Atmospheric Pressure greater than 75.1 kPa (563 mmHg, 22.2 inHg) to trigger. I live around 68 kPa and mostly only drop to 72 kPa. On occasion, such as yesterday, I do actually drive above 75.1 kPa (around 80 kPa). I guess I could be missing out on codes because of this.
 

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2005 Outback VDC limited 3.0r
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When you say detonation in exhaust, do you mean you hear back fires? Detonation on deceleration or acceleration? Or do you mean you hear pinging on acceleration? A big difference between detonation and pinging. The factory tune pings quite a lot on initial acceleration. Are you running 91 octane? When was the last time plugs where changed?
 

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Fuel in exhaust most likely means no or incomplete combustion in a cylinder from lack of spark, stuck fuel injector, or a damaged exhaust valve/seal. What DTCs are you getting? Is the engine running rough at idle/accel/wot? Check engine light on? CEL flashing?
 

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2008 OB Limited 2.5i, Portland OR USA
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Explanation of the term "detonation" is here - and I'm not sure that's what you are experiencing, which you've described as being in the exhaust.

This is probably damaging your catalytic converters, so it should be addressed very quickly.
 

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2010 2.5 CVT Limited
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It takes quite a bit of raw fuel to gather in the exhaust to ignite there.
I doubt it's a sensor out of range or anything like a weak spark.
Look for a leaking injector.

edit to add: if the fuel pressure regulator is vacuum operated, a tear in the rubber diaphragm would let excess fuel be drawn into the intake stream.
I had a similar situ on a old moto with a vacuum operated fuel shutoff valve. The decel backfires were attention-gertting.
 

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2005 Outback VDC limited 3.0r
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According to that definition @johnre then it wouldn't be heard in the exhaust, at least that's the way it seems to suggest. Which is something I'm hoping to clarify. I'm glad to see that detonation is getting a strict definition. When I was in trade school and dealing with high performance stuff, detonation could have been pre or post ignition. It's loosely used and confused with spark knock, pinging, back fires.
 

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2005 3L LL Bean Outback
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Discussion Starter · #8 ·
When you say detonation in exhaust, do you mean you hear back fires? Detonation on deceleration or acceleration? Or do you mean you hear pinging on acceleration?
I don't hear backfires and it's not necessarily on acceleration or deceleration. It's not really audible, certainly not a bang, and it's more like hard thumps or jerks, variable in amplitude, coming from the rear or at least behind the driver's seat, seemingly from below the vehicle (presumably the exhaust) and felt in the seat. It's very noticeable when standing still at the stop light. When these thumps, jerks or detonations occur I feel the vehicle noticeably shaking and sometimes wonder whether the driver behind me at the stop light notices the shake(s). I also notice it while driving, but it seems it occurs less when the vehicle is under load (higher rpms). The car has to be warmed up. I'm guessing when the exhaust warms up it starts igniting unspent fuel somewhere in the exhaust.
Fuel in exhaust most likely means no or incomplete combustion in a cylinder from lack of spark, stuck fuel injector, or a damaged exhaust valve/seal. What DTCs are you getting? Is the engine running rough at idle/accel/wot? Check engine light on? CEL flashing?
The only code I recently got was P0420, which I've had since owning the vehicle (5+ years). I'd like to say I would get the code 4 or 5 times a year. I've always cleared the code. Recently, actually since I've been noticing these 'detonations', it seems the code occurs more often, say once every 3 or 4 weeks. The vehicle had been parked (in a garage) for close to 6 months and I would start the engine once every 6 weeks or so and let the engine warm up, but otherwise wasn't driving the vehicle. I started noticing these 'detonations' when I started driving the vehicle following the 6 months of being parked. Initially I attributed this issue to bad/old fuel (I'm using 91 octane), but I've gone through 8-10 tanks of fuel and the issue continues.

Around the time I started driving the vehicle following the "long park", I had a bad coil pack on cylinder #5. That actually threw a misfire code and would produce a repeating jerking effect, different than these 'detonations' coming from the rear, coming instead more from the front of the vehicle and somewhat more frequent than what I'm now experiencing from the rear of the vehicle. The bad coil also caused a noticeable drop in engine power, which I'm not experiencing with this current issue. I still intend to inspect at least the coils as I can imagine more coils may be going bad (vehicle is hitting 185K miles). Plugs (NGK 6481 ILFR6B Laser Iridium) have around 90K miles on them and the plug on cylinder #5 looked surprisingly good when I replaced the coil.
This is probably damaging your catalytic converters, so it should be addressed very quickly.
That's what I'm afraid of.
f the fuel pressure regulator is vacuum operated, a tear in the rubber diaphragm would let excess fuel be drawn into the intake stream.
I pulled the vacuum hose from the regulator and didn't notice any fuel smell. The hose looked good. I should be able to test the hose with a vacuum pump.

I'm currently leaning towards either the coils/plugs or a(n exhaust) leak. If it's the coils/plugs I would expect misfire codes, but perhaps they haven't yet reached a sufficient number of counts to trigger a code. I should have RomRaider working to get some more feedback. I have a smoke/fog machine coming in Friday which may help diagnosing a(n exhaust) leak. Even the gas cap could be an issue. I replaced the cap some 4 years ago, but I'm not exactly sure for what reason, if any. Could have just been a preventative measure.
 

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2020 Onyx
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If it's not audible I'm not so sure your problem is ignition in the exhaust.

Since you're scanning - no misfires?

No transmission codes?
 
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2018 Outback 3.6r touring //// 2004 Wrx wagon 5mt SOLD
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Sounds like a hard misfire to me, but no misfire codes? What is the vehicle and how many miles? Sorry if you posted already.
 

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2005 Outback VDC limited 3.0r
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So it's at idle, and while accelerating a bit? Can you look and see if you have green cup cv axles? If not, the issue may be a cv axle. It's common for aftermarket ones to cause vibrations while at idle. I would check them all for excessive movement too. Any rust streaking coming from the driveshaft(propshaft) u joints? See if the rear trans mount is torn(lift up on the back of the trans).
 

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2005 3L LL Bean Outback
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Discussion Starter · #12 ·
If it's not audible I'm not so sure your problem is ignition in the exhaust.

Since you're scanning - no misfires?

No transmission codes?
No codes other than the P0420 which hasn't come back in the last week or so. I just tried to use RomRaider but it's a bit wonky; I was able to start monitoring values, fuel pressure, etc., but RomRaider stops or else disconnects after about 10 or 15 seconds. If I restart the Logger I can reconnect with the ECU but again it only reads/monitors values for about 10-15 seconds and then stops. Not sure what's going on. I may have to go back to Torque but I believe RomRaider can get more data points than Torque, notably transmission values. I recall monitoring turbine speed some years ago using RomRaider. Could well be something going on in the transmission. I'll see if I can check the fluid level which is not always easy as I don't have level ground anywhere in the area.
Sounds like a hard misfire to me, but no misfire codes? What is the vehicle and how many miles? Sorry if you posted already.
No codes. It's a 2005 H6 LLBean Outback at ~ 185K miles.
So it's at idle, and while accelerating a bit? Can you look and see if you have green cup cv axles? If not, the issue may be a cv axle. It's common for aftermarket ones to cause vibrations while at idle. I would check them all for excessive movement too. Any rust streaking coming from the driveshaft(propshaft) u joints? See if the rear trans mount is torn(lift up on the back of the trans).
It's also while cruising but less noticeable than while idling. Doesn't seem to make a difference if the transmission is in drive or neutral. The front are definitely OEM green cups. I bought them new some 4 years ago. Not sure what's on the rear. The symptoms are very noticeable thumps which I wouldn't qualify as vibrations. I'll have a look but I replaced the transmission mount about 2 years ago.
 

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Discussion Starter · #13 ·
One of these days I need to find level ground and mark the fluid horizontals on the brake and power steering fluid reservoirs. That should allow me to find where the vehicle is level around my house by sliding the right amount of plywood under the wheels that need to be raised. For now, I believe the vehicle is more or less level by getting the rear wheels just a little bit up on these home made ramps.
Tire Wheel Automotive tire Light Black

I seem to have enough ATF:
Automotive lighting Hood Bumper Automotive exterior Motor vehicle
 

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Discussion Starter · #14 ·
Doesn't seem to make a difference if the transmission is in drive or neutral.
I take that back. Just went for a short drive and when I came back home, while standing still in the driveway, I shifted back and forth between neutral and drive. I'm not noticing the issue when in neutral. As soon as I shift to drive it starts shaking/thumping. Shift to neutral and it stops, shift back to drive and it's back. Did that around 10 times and it consistently shows up when in drive and disappears when in neutral. So it seems like it's the transmission. Couple of days off ahead so I'll see what I can discover. I guess I can monitor the turbine rpm and atf temperature but I'm not sure what else to look for. I can drain and fill the atf but I don't believe that's going to fix an issue like this. I can imagine there's something wrong with the torque converter.
 

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Discussion Starter · #15 ·
Can't help feeling a bit embarrassed for qualifying for what now seems to be a transmission shudder as detonations, thumps and shakes . Apologies for throwing people off, and thanks for all the feedback.

Seems these issues sometimes get resolved by draining and filling the atf. I happen to have atf and even the drain plug crush washers, so I did a single drain and fill. 8mm hex to remove the drain plug and after the drain and reapplying the plug I filled 3 qts/bottles + 700ml. I can only cycle through 1st and 2nd gear while standing still. Doesn't seem to have made a difference. I notice every time it shudders the engine rpms slightly and briefly rev up, perhaps ~100rpm. Going to take it for a drive but I don't believe this drain and fill is going to make a difference.
 

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Discussion Starter · #16 ·
Perhaps there's nothing to be embarrassed about.

Drove about 30 miles after the atf drain and fill and it felt somewhat worse than before. After a bit more driving it was getting really bad. The symptoms were also showing up when in neutral. It was getting harder to accelerate from a stand still, with shaking and jerking and an overall loss of power. Eventually the cruise light came on but no check engine light. Shortly thereafter the CEL came on. Pulled over and was expecting another P0402 or perhaps something related to the transmission, but instead I got a P0306, cylinder 6 misfire detected. Could still be something going on with the transmission but this seems more like what's going on. After replacing the coil on cylinder 5 I was warned the other coils would probably be failing soon. I still have a spare coil pack that I got from the mechanics who also gave me a free coil pack for cylinder 5. Cylinder 6 seems to be one of the more difficult coils/plugs to reach but it should be easier than dealing with a transmission issue.
 

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2020 Onyx
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Several of us thought it might be misfire instead of "exhaust detonation" but the only take-away is to not jump to conclusions - even if one might jump to the right conclusion right off the bat, always good to be open to other possibilities and you have been.

Still in the investigation stage - when the car gets put into gear, it's supposed to tell the engine to idle up so that it doesn't drop RPM too much. When you go in gear is it dropping RPM excessively and that's part of the thumping or jerking?
 

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Discussion Starter · #18 ·
Several of us thought it might be misfire instead of "exhaust detonation" but the only take-away is to not jump to conclusions - even if one might jump to the right conclusion right off the bat, always good to be open to other possibilities and you have been.
I was actually thinking more about confusing one phenomenon with another, not about confusing one cause with another, even though my writing may have convoluted the phenomenon with the cause. For some reason I was thinking about identifying the sound of geese as a cocktail party, even though that example also convolutes the phenomenon with the cause.
Still in the investigation stage - when the car gets put into gear, it's supposed to tell the engine to idle up so that it doesn't drop RPM too much. When you go in gear is it dropping RPM excessively and that's part of the thumping or jerking?
I never noticed excessive RPM dropping. I seem to have gone through 2 stages of this issue; initially I'm feeling the thumps without much or even any noticeable drop in power and the thumps seem to be coming from below and the rear of the vehicle. This lasts for weeks if not months. Then, yesterday, the 2nd stage started with excessive thumping which is now also coming more from the front of the vehicle. In this 2nd stage I'm noticing power loss or else the power being supplied intermittently. At this point I get the misfire code. The only effect I've noticed on RPMs, which is limited to the 1st stage of this issue, is that when a thump occurs the RPMs actually seem to briefly go up a bit, say by 50-100rpm.

I replaced the coil on #6. The replacement has a boot with a reinforcement which makes it harder to bend the boot while installing. This was making it difficult to get the replacement on #6. From left to right: What came out of #5 several months ago, what came out of #6 today, and the replacement.
Gesture Asphalt Finger Pink Road surface

I was already considering removing the coil on #4 to get more space to install the coil on #6, and was also curious to see the condition of #4. So I removed coil #4, put the coil with the reinforced boot on #4, and installed what came out of #4 on #6. Seems to have worked but clearly what came off of #4 is also in bad condition. From left to right: What came out of #5, what came out of #6 and what came out of #4 which is now installed on #6.
Everyday carry Jewellery Tints and shades Wrist Strap

Placed an order with the dealer for 4 replacements but they don't have them in stock and will only seem to arrive on Monday. Kind of want to replace the remaining 4 asap.
 

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Those coils do need replacement whether they were the geese or the cocktail party. Will be very interested to see if these fix it or not.
 
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Discussion Starter · #20 ·
I cancelled the order at the dealer for the coils. Drove by those mechanics who previously had gifted me 2 coils. Picked up 4 more coils from them for a good price. Also got a free spark plug wire for the legacy; the rodent always chews on the same wire and always at the same spot, so this time I don't have to buy 3 extra wires I have no use for, like last time the wire was chewed on. Also got an axle cap which otherwise goes for $ 20-30 at the dealer. Got a small extension which may allow me to get the ratchet on the spark plug socket. Car drove surprisingly well after replacing coil #6, so I treated her to a car wash. Looks like I'll be replacing coils tomorrow.
Circuit component Auto part Gas Magenta Wire
 
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