My Impreza (269k EJ22 - 5 Speed) has intermittently hesitated especially on those damper/snowier days. Felt like the plug wires were due for replacement. Since it was so mild I didn't bother to replace them until yesterday. My wife was driving it home and it stalled out on an intersection. Started back up, but the issue seemed to be getting worse. I swapped the plug wires but got no change.

 

Today we took it to work. It was pretty goofy on the way. The power would lag and surge and lag and surge. Sometimes rhythmically and sometimes random. On the way home it stalled on me once. I played with it a bit. If I put the clutch in and coasted, it would stall out, then re-engage the clutch and it ran again. It went back and forth from bucking all over the place under load to smoothing right out and being normal.

 

Stopped at auto-zone to get the CEL code pulled. Code is P0420. CEL has been on for over a year. I generally ignore them unless the car shows issue.

 

Would an o2 sensor cause this much bucking and issue with the car? Or is this a blocked cat? Or any thoughts on the next best step?

Not likely.  NGK Plugs, Subaru or NGK plug wires, Subaru Coil.  

 

Daughters 99 Impreza just went through the same thing and it turned out to be the coil.  

I'll give that a try. I have a spare coil from an EJ18. I'll see if that works enough to test it out. Plugs are cheap so I'll probably throw a set in there just to hit the reset button.

Check the intake tubing. Make sure it's clamped tight. Make sure the large hose for the IAC is firmly attached.

Check for loose vacuum hoses too.

Do you have a spare MAF sensor you can try?

Edited February 23, 201313 yr by Fairtax4me

My Impreza (269k EJ22 - 5 Speed) has intermittently hesitated especially on those damper/snowier days. Felt like the plug wires were due for replacement. Since it was so mild I didn't bother to replace them until yesterday. My wife was driving it home and it stalled out on an intersection. Started back up, but the issue seemed to be getting worse. I swapped the plug wires but got no change.

 

Today we took it to work. It was pretty goofy on the way. The power would lag and surge and lag and surge. Sometimes rhythmically and sometimes random. On the way home it stalled on me once. I played with it a bit. If I put the clutch in and coasted, it would stall out, then re-engage the clutch and it ran again. It went back and forth from bucking all over the place under load to smoothing right out and being normal.

 

Stopped at auto-zone to get the CEL code pulled. Code is P0420. CEL has been on for over a year. I generally ignore them unless the car shows issue.

 

Would an o2 sensor cause this much bucking and issue with the car? Or is this a blocked cat? Or any thoughts on the next best step?

 

Those are the exact symptoms I had on my Loyale and it went on for a few weeks without a code and then threw an O2 sensor code. I replaced the sensor and now it runs fine, no code, no bucking like a bronc.

 

Here is a discussion on this code P0420:

 

http://allwheeldriveauto.com/subaru-check-engine-light-and-code-p0420-explained/

 

One of the proposed solutions is "start with the higher octane fuel, some driving at higher RPMs at lower

speeds and see if you can breath a little more life out of your

Catalyst."

 

The guy in the discussion tried that advice and it worked. Certainly a free thing you can try out. Good luck.

Edited February 23, 201313 yr by MR_Loyale

Well no dice on myEJ18 coil. Has a different wiring setup. Any idea if I can swap over the coil from a Phase II EJ25 motor from my wifes 2000 outback? I would prefer to not just buy stuff to see if it fixes it.

 

or if an o2 sensor from a 93 Impreza with the 1.8 would match my 97 2.2? I may sound lazy but at the moment Wisconsin is getting pounded with snow and the furnace on the house is pumping minimal heat. Not ideal conditions for working in the driveway.

 

 

All else fails I'll bite the bullet and take a trip to the yard.

I wouldn't rule out the crank angle sensor.

Good thinking. I saw that pop up in a search somewhere. It was an easy enough swap and I had a leftover from the 91 legacy. Swapped it in and no difference made. So I think crank angle is ruled out.

Can I get a read on whether it's the o2 sensor by disconnecting it? What would I expect to have happen running without the sensor connected? Pretty sure it hasn't been right for a while but the behavior seems extreme for a faulty sensor.

Edited February 27, 201313 yr by AdventureSubaru

If you have a meter that will log the voltage you can back probe the sensor wires and record voltage. 

 

Or if you have a computer that will record voltage, that will tell you what the state of the system is.

Unplugging the front O2 sensor should set default the ECM to a failsafe mode. It will run on preset fuel and spark maps which should allow it to run, but it not at optimal performance or economy. It's certainly worth a try if you have no other leads.

You might unplug the sensor, then disconnect the battery - for 15 minutes or so to reset the ECU.

Unplugged the sensor, disconnected the battery for a while. Started her up and still no better.

 

Getting a decent amount of smoke from the engine bay with the hood popped. Smells like the usual seperator plate leak onto the cat. Was thinking maybe head gaskets. Exhaust smells normal. Oil looks normal. Coolant looks normal.

 

Likely causes as I'm seeing it -

 

Coil

MAF

blocked cats from burning oil or HG leak.

 

Would I be seeing this from a head gasket failure?

Nope.

Check PCV breather hoses for splits where they meet the valve covers.

Hoses by the valve covers look fine.

 

Changed the plugs today. The old ones were bosch and were pretty ugly. May have smoothed things out a bit but the engine is still hesitating.

 

I used some carb spray to see if I could hunt down a vac hose leak. I may (Not sure since the hesitation is intermittent) have gotten some results near the Idle Air Control. Trouble is, I wiggle hoses and move stuff around trying to get something to happen (Stall/rev whatever) and I can't get anything consistent. So it might just be coincidence.

 

On another note, the ABS pump is humming (Sounds like speaker feedback) Any chance this is related?

Edited March 12, 201313 yr by AdventureSubaru

Hoses by the valve covers look fine.

 

Changed the plugs today. The old ones were bosch and were pretty ugly. May have smoothed things out a bit but the engine is still hesitating.

 

I used some carb spray to see if I could hunt down a vac hose leak. I may (Not sure since the hesitation is intermittent) have gotten some results near the Idle Air Control. Trouble is, I wiggle hoses and move stuff around trying to get something to happen (Stall/rev whatever) and I can't get anything consistent. So it might just be coincidence.

 

On another note, the ABS pump is humming (Sounds like speaker feedback) Any chance this is related?

 

 

There's a TSB about the ABS pump relay. Try a search for that.

try front 02 senser mabee is runing lean bet thiss on the 2.51s alot when 02 gets shorted to lean side were the plugs very clean ?

You probably have a plugged cat. My Foerster set the 420 code and I drive it like that for about 20k. It strayed bucking and stalling and feeling gutless. I pulled the cat off and looked inside and the honey comb had melted down, restricting about 60% of exhaust flow...

change front 02 senser and try it have had very good luck with telling customers to run preimium gas to fix 420 code helps to clean the catts but takes at least 3 tanks and drive hard. If catts are melted down they will rattle inside and exhaust will sound funny. Also have had good luck removing catts and preshure washing them out and reinstall cost a 1$ at the local car wash with new gaskets and no leaks

good ideas here. The front 02 sensor has been disconnected with no apparant change. Still worth trying to swap in a new one?

 

This car wont make it through one tank of gas, let alone three. It got pretty bad, pretty fast. Went from minor annoyance every once in a while to nearly undriveable. I'll see if I can't get a look at the cats to see what's up.

 

Once they are apart, anything in particular that I'm looking for? I have seen plenty of cats, so looking for any particular color other than just breaks/blocks?

 

Hoping the exhaust comes apart easily. Some of it is welded together.

change the 02 senser and look for damage to catts and materals blocking them. The car must have a 02 or it cant learn the 02 tells the ecu how mutch 02 is left in the exhaust so the ecu cant addjust mixture no 02 gos into default or limp mode

Plugged cat will affect high RPM and heavy throttle driving first. If you can redline the engine in second gear and keep accelerating, cats are fine. If a plugged cat gets so bad that it affects off idle and low part throttle driving it will glow red after a short drive, and the high rpm test above will be a very determinate test.

You can check for a plugged cat with a vacuum/ pressure gage. Hook it to the intake manifold and check engine vacuum at idle. Increase engine speed to about 2000-2500 rpm and hold it there for 1 minute. The vacuum gauge should stay steady near or slightly above the vacuum reading from idle. If the reading slowly drops during the whole test it is due to back pressure in the exhaust system which could mean plugged cats.

Another test is to Get a few brass adapters from a hardware store and thread a barbed nipple into the O2 sensor hole in the top of the front cat. Stick a vacuum gauge on it with a hose long enough for you to see the gage inside the car. Start the engine and watch the needle. At idle you should have no back pressure in the exhaust system. The needle should sit still or waver back and for the between pressure and vacuum. Raise engine rpm to about 2000 and watch the needle. It should be no more than a few psi. If the reading is high psi, or the hose pops off of the gage, there is excessive back pressure in the exhaust.

change front 02 senser and try it have had very good luck with telling customers to run preimium gas to fix 420 code helps to clean the catts but takes at least 3 tanks and drive hard. If catts are melted down they will rattle inside and exhaust will sound funny. Also have had good luck removing catts and preshure washing them out and reinstall cost a 1$ at the local car wash with new gaskets and no leaks

Please tell me why running a cooler burning fuel (higher octane) in an engine not designed with enough compression to fully combust anything past 89 Octane would clean ANYTHING out???

 

 

It was Probably just the hard driving

 

 

http://en.wikipedia.org/wiki/Octane_rating

Edited March 16, 201313 yr by kn33

Really has nothing to do with octane. It's in the detergents they add to the higher priced fuel. Engines that require higher octane fuel need more additives and cleaners in the fuel to help keep the combustion chambers clean. Carbon buildup in the combustion chamber increases compression, and provides a burnable substance that will retain heat. Both of which will lead to detonation and internal engine damage. Because of that the fuel companies add extra goodies to the higher octane fuels, at the request ($$$) of vehicle manufacturers looking to avoid warranty repairs on engines damaged by carbon buildup from poor quality fuels.

Has to do with whats left over after the combustion process less carbon and deposits in the premium feul octane is erelavent and burn temp is erelavent its the leftover crap in the feul that is important. The feul we get here is realy poor so the perium feul is a step up and not just premium chevron or mohawk 94 premium as it has some ehanol in it witch will burn cleaner it did seem to work still no 420 codes on the test 02 forester and it used to throw a 420 every 2 days and is driven at a idle by a 70 year old man so rpms dont think it sees any

Figured I'd close this thread out with the end results. The CEL was a red herring in the mix. Fuel pump was to blame. I pulled one from a nice 97 Legacy sedan with just over 100k. It fit just fine but the fuel pump motor was much bigger than the one from my Impreza. Anyway. Plugged it all together and the car is running normally again.