I just bought a used 2001 Subaru Outback L.L.Bean, and the check-engine light is on due to misfiring in cylinders 1, 3, and 5 (right side only). I thought I was getting a pretty good deal even given the CEL risk, but the car is at the mechanic now and he is stumped and telling me I have to take it to a dealer service center.
This is a 6 cylinder with a timing chain. Plugs were replaced and computer reset and the light came right back on. There are no spark plug wires, and I read that the coil packs rarely fail. The engine runs smoothly and seems to have power, but since I just bought the car used so I’m not sure how much power is normal. It has 122k miles.
What could be causing misfires on one side of the engine only? Any ideas?
I tip my hat to your mechanic for knowing he’s beyond his knowledge level.
Since it’s always happening on the same cylinders I’d be inclined to suspect the crank position sensor, but your guy is right, you need a shop that can do some in-depth diagnosis. CPS signals can be monitored along with other signals with the right equipment.
This is a COP. He could, however, have a few coils going out. My thinking was that any mechanica can check for that, so since his suggested he needs the dealer perhaps that possibility has been eliminated. However, whatever it is a fully equipped shop should be able to diagnose it.
You could switch out coil packs to see if it travels but I doubt that’s it. After all, what are the chances three go out, all at the same time and all on one side?
It has got to be something that side of the engine has common to all cylinders…
It could be a vacuum leak of sorts. There’s that breather hose to the airbox that each side has. Not sure what would happen with that line off, leaking or clogged.
I bet this car also has an O2 sensor for each side. Maybe it makes some sort of compensation for one that is bad causing a misfire?
Ok, here’s the update: the mechanic had already swapped the coils-- he said that was the first thing he tried. Sorry I didn’t know that before. The code went away, then he took it for a 4-mile drive and the same codes came back. Cylinders 1, 3 and 5 misfiring. There were no other codes. I mentioned the timing on that side only and said highly unlikely and not worth checking since the car is running smoothly.
Below are the remaining possibilities I’ve culled from this and one other forum. Can any of these be ruled out, in your experience? And which are more likely than others? Remember that the engine is running smoothly and there are no other codes…
some fluke battery weirdness?
igniters?
a crankshaft/camshaft position sensor that’s not providing a consistent firing signal?
O2 sensor? (assuming each side has its own)
fuel injectors messed up due to undercarriage pressure wash?
fuel pressure regulator? (assuming each side has its own)
fuel pulsation damper? (assuming each side has its own)
I doubt very much if this is a fuel problem. And I can guarantee it isn’t a battery problem. That elilminates just about everything on your list except the crank position sensor,
The valves are an outside possibility, but any mechanic can check those with a vacuum gage.
I still think it needs a good engine analyzer. I still think pulses & traces need to be looked at to get to the root of the problem.
I’m curious about the theory on how a crank position sensor would lead to one side misfiring but not the other side? The sensors I’m used to are hall effect sensors which would let the PCU know when the crank was at a certain position (0,360,720, etc), from which it would interpolate the position in between passes of the vane. Given that, a bad sensor would throw off both the left and right banks together… Certainly there could be other sensor designs, dual sensors, or modes of operation, so I’m not saying you’re wrong, just curious.
Personally, I’d be inclined to check the camshaft position sensor - there are two of them on the vehicle, one for each bank. If the one on cylinders 1,3,5 is bad, but the other is good, that might give these symptoms.
I’d also check the knock sensor - similarly, there are two, one for each bank, and if one went bad, you could end up with misfires…
You may be right Eraser. A cam position sensor makes more sense. That would leave the crank sensor as a crank apeed sensor only, and that shouldn’t repeatedly affect the same three cylinders. It’s always good to have somone with specific vehicle knowledge watchin’ over me. The results are far better that way.
Sydeburn, allow me to suggest respectfully that telling the mechanic what to check out is not the best way to go about getting the problem resolved. What I’d recommend is that you give him a detailed description of all your symptoms, any background that you’re aware of, and let him do the diagnosis. let him decide what to check. One of the key things you’re paying him for is his expertise.
Yes, I feel odd suggesting check this or that, but the mechanic is stumped and asked me take it to a dealer service center. I already trust this mechanic quite a bit and would rather not pay dealer prices. He seems open to suggestions.
My feeling is that connecting a vacuum gauge and running a compression test should always be done first.
The vacuum gauge attaches in seconds and will reveal any anomaly instantly. Depending on the gauge reading this would be followed with a compression test.
A vacuum leak (depending on where it’s at) can also lead to problems on one side or the other due to the engine’s Boxer design. This would also show up on a vacuum gauge.
The problem here is that I don’t have specific knowledge of this vehicle, other than it has a V6 and most crank (and cam) position sensors are hall-effect and brutally simple devices.
You could be absolutely correct, because the Subie might have some quirk that I know nothing about.
Naw, I’m probably not correct in the specttifics. Mine were general statements. I’m still of the belief that it’s going to take an engine analyzer and someone skilled in its use to get to the bottom of the problem. That’s a pretty normal process, as you know, but the OP apparently has a level of confidence with his mechanic such that he’d prefer to work with him, offering ideas, than to try another shop. That’s a testament to the honesty of the mechanic, but I’m betting he’ll end up at a different shop. Some shops are fantastic with the basic stuff, but not up to speed on the high tech stuff.
I knew a shop owner that was A#1 with (pre-ABS/stability system) brakes, chassis, and carbs, but really never kept up in a lot of the areas. He’d take on only jobs within his level of expertise and was always busy and highly respected. He retired when it got to the point that there no longer was any old-fashioned technology on the road, when everything was ECUs, COPs, and sensors. He was a good and an honest man.
