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Just another misfire/rough idle thread...


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If it is a burned valve, it would come and go with temperature as the block warms and cools. I have seen that before.

 

I had a cracked ringland. It would pass compression testing it finally failed one and then a leakdown test confirmed it. I compression tested once I knew something was up. I had a cyl 4 misfire. It wouldn't log any misfires when cruising and accelerating. Only at idle. And even then there were some times it wouldn't at all. I understand why you're asking. And yes it is logical, but if you think what happens inside the cylinder walls, that's all pretty violent stuff going on. And when it comes to cars and car repairs always expect the unexpected.

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After the car warms up you would think the issue would be consistent. What was the car doing that last 5 minutes? I assume you shut the car off when you got home. Rough start? Stutter?

 

The last 5 minutes prior to turning it off was stop/go traffic with a couple red lights and stop signs.

 

When I got home I turned it off a few seconds after completely stopping the car, the idle was smooth (but with a barely noticeable misfire).

When I started it back up after dinner it was immediately idling rough. When I'm accelerating while the idle is acting up it does seem to stutter slightly at about 3k rpm.

 

The soap is for keeping the IC clean. Though now I just pressure wash the entire engine with boiling industrial degreaser and only a light misting of soap on the IC for protection. :D

Also running a garden hose through the throttle body is a great way to get that deep engine clean; forget Chemtool, Seafoam, etc...

 

For future readers: His first tip, and possibly his second tip also, is why people sometimes say "you can't believe everything on the internet".

 

If it is a burned valve, it would come and go with temperature as the block warms and cools. I have seen that before.

 

I had a cracked ringland. It would pass compression testing it finally failed one and then a leakdown test confirmed it. I compression tested once I knew something was up. I had a cyl 4 misfire. It wouldn't log any misfires when cruising and accelerating. Only at idle. And even then there were some times it wouldn't at all. I understand why you're asking. And yes it is logical, but if you think what happens inside the cylinder walls, that's all pretty violent stuff going on. And when it comes to cars and car repairs always expect the unexpected.

 

My issues don't seem to be correlated with engine temp at all.

 

I've experienced smooth and rough idles in cold weather with both cold and warm starts, and I've experienced smooth and rough idles in warm weather with both cold and warm starts. As best as I can tell the engine temp has little to zero affect on the symptoms.

 

When it's in a bad mood and idling rough it is always also idling low, like between 400-700 rpm. It's almost like the ECU isn't reading the idle properly. Don't get too excited just yet, because even when its idling properly the misfire is still present.

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The last 5 minutes prior to turning it off was stop/go traffic with a couple red lights and stop signs.

 

When I got home I turned it off a few seconds after completely stopping the car, the idle was smooth (but with a barely noticeable misfire).

When I started it back up after dinner it was immediately idling rough. When I'm accelerating while the idle is acting up it does seem to stutter slightly at about 3k rpm.

 

 

 

For future readers: His first tip, and possibly his second tip also, is why people sometimes say "you can't believe everything on the internet".

 

 

 

My issues don't seem to be correlated with engine temp at all.

 

I've experienced smooth and rough idles in cold weather with both cold and warm starts, and I've experienced smooth and rough idles in warm weather with both cold and warm starts. As best as I can tell the engine temp has little to zero affect on the symptoms.

 

When it's in a bad mood and idling rough it is always also idling low, like between 400-700 rpm. It's almost like the ECU isn't reading the idle properly. Don't get too excited just yet, because even when its idling properly the misfire is still present.

You have a vacuum gauge?

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My car seems to have the same symptoms yours does with the very erratic yet stubbornly persistent misfire. I've logged some data via the BtSsm app and it confirms what I feel, which is also what you describe; the misfires vary in frequency seemingly at random. I'm subscribing to this thread, hoping that I can learn from what you figure out with your car.
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My car seems to have the same symptoms yours does with the very erratic yet stubbornly persistent misfire. I've logged some data via the BtSsm app and it confirms what I feel, which is also what you describe; the misfires vary in frequency seemingly at random. I'm subscribing to this thread, hoping that I can learn from what you figure out with your car.

 

Good luck, hopefully you'll solve your problem quicker than I am.

 

On our EJ255's are the bank1/bank2 camshaft position sensors interchangeable?

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Good luck, hopefully you'll solve your problem quicker than I am.

 

On our EJ255's are the bank1/bank2 camshaft position sensors interchangeable?

 

Looks like they are the same according to this diagram - see part #6

BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT
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My DD is back on the road so the LGT is back inside the garage patiently waiting for my attention.

I still haven't done the leak-down test... after that I'll take off the intake manifold and try to locate my vacuum leak.

 

Just a nugget of interesting info... the past few times that my CEL turned on was exactly between shifts, somewhere in the ballpark of 4.5-6k rpm (nowhere near idle).

Edited by StkmltS
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I have the same issue, it's been parked since March, it started when changed the spark plugs with Denso iridium, throwing codes p0303 and p0304, returned back to old spark plugs, recheck the gap, changed the spark plugs, new set of wires, change the ignition coil, clean the fuel injectors, check the pressure in fuel lines, change the throttle body, change the rear O2 sensor, finally I changed the MAF, forgot to mention that I changed the fuel filter too, we thought the cause was the fuel as the car was idling fine with fuel aditive till reached the point of nothing help...with all of that still have misfire on cylender 3 and 4, both didnt move...still didnt get the time to do a compression test...probably this week...I am thinking in draining the fuel tank and add a new fuel? if didnt help will take it to dealer...
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I have the same issue, it's been parked since March, it started when changed the spark plugs with Denso iridium, throwing codes p0303 and p0304, returned back to old spark plugs, recheck the gap, changed the spark plugs, new set of wires, change the ignition coil, clean the fuel injectors, check the pressure in fuel lines, change the throttle body, change the rear O2 sensor, finally I changed the MAF, forgot to mention that I changed the fuel filter too, we thought the cause was the fuel as the car was idling fine with fuel aditive till reached the point of nothing help...with all of that still have misfire on cylender 3 and 4, both didnt move...still didnt get the time to do a compression test...probably this week...I am thinking in draining the fuel tank and add a new fuel? if didnt help will take it to dealer...

Welcome to the fourm!

 

That's really strange that it started when you changed spark plugs and it didn't go away when you put the old plugs back in. Maybe your problem has something to do with how they're sealing, not the actual plugs themselves.

 

Have you inspected (and cleaned) your two camshaft position sensors and your crank position sensor?

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I THINK I have similar issue. Here is my log of what has happend:

 

5/4/15- Bought car. 2 blocks off the lot check engine light, lack in power, and nasty noise from turbo.

 

5/5/15- P0021 & P0011

Result- Confirmed Bad Turbo

 

5/11/15- Changed Turbo, Coolant, and Oil/Filter

NOTE: Oil was black and filter was tough to get off (Don't think they kept up with regular oil changes)

 

Same Day- P0301, P0303, P0304

 

5/12/15- Changed Spark Plugs

 

Same Day- P0301, P0304 (Got rid of misfire in bay 3).

 

5/15/15- Took into mechanic

 

Supposedly they checked the injectors, coils, plugs, and MAF.

 

Still no solution, they told me it must be internal. However, it doesn't lack power or have any "engine shakes" (For lack of a better term". My buddy is a tech for Volvo, went though the Nascar program in NC. I had him check it out at Volvo and he couldn't find anything either. He says the way that it drives, he is highly doubtful that it is internal. Just stumbled on this thread and it seems to be very similar.

 

Let me know if you have thoughts on anything that you have learned in your process. P.S. your well documented process HAS helped me think through possibilities. I appreciate it!

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- Cyl 1: 13.0% (median 13)

- Cyl 2: 22.4% (median 21.5)

- Cyl 3: 13.6% (median 13.5)

- Cyl 4: 20.6% (median 22)

 

Like you suspect, cyls 2/4 seem like they aren't holding compression as well as they should be. If the misfire only happens when the engine is warm, my guess would be valve clearances have become too tight, and they should be inspected, replaced if necessary, and the clearances adjusted.

 

If you're going to go that far, you may want to pop the pistons out to check the ringlands anyway (it's pretty easy if you've gone that far). Then you should know what you're dealing with.

 

But it seems like pulling your engine is in your future :(

BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT
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Like you suspect, cyls 2/4 seem like they aren't holding compression as well as they should be. If the misfire only happens when the engine is warm, my guess would be valve clearances have become too tight, and they should be inspected, replaced if necessary, and the clearances adjusted.

 

If you're going to go that far, you may want to pop the pistons out to check the ringlands anyway (it's pretty easy if you've gone that far). Then you should know what you're dealing with.

 

But it seems like pulling your engine is in your future :(

The misfire is always present.

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The misfire is always present.

 

Right. Still could be a toasted valve. It could be ringlands too, but usually you get high oil consumption with that, and observe smoke/blowby coming out of the oil fill tube when you remove the cap.

 

Sorry if it's been covered, but you already tried swapping the following various items with another cylinder, but the problem didn't move?

Injector, Coil, Plug

BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT
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Right. Still could be a toasted valve. It could be ringlands too, but usually you get high oil consumption with that, and observe smoke/blowby coming out of the oil fill tube when you remove the cap.

 

Sorry if it's been covered, but you already tried swapping the following various items with another cylinder, but the problem didn't move?

Injector, Coil, Plug

 

Based on everything I've read online my oil consumption is very typical for this car/year/mileage. I've never seen smoke come out of the filler tube, but during the leakdown test that's where I heard the air escaping (for all cylinders).

 

I've swapped the plugs, coils, and injectors, and I replaced the original IM gaskets with the new(er) part# gaskets.

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dunno :( sounds like an internal issue causing the misfire (which pretty much is narrowed down to valves or ringlands)

 

But can I back way up and ask when this started (at 97k miles) had any work been done to the car? Any mods at that time?

BtSsm - Android app/Bluetooth adapter. LV, logging, gauges and more. For 05-14 Legacy (GT, 2.5, 3.0, 3.6), 02-14 WRX, 04-14 STi, 04-14 FXT, 05-09 OBXT
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I bought the car last June with about 96k miles on it, I'm the third owner. The previous owner said no mods other than window tinting, and carfax shows owner #1 was a company that had all regular service completed at Subaru stealerships. As far as I can tell everything has always been stock with the exception of wear-and-tear items. There aren't any odd holes in the interior indicating removed mounts/gauges, and all original engine bits/wiring are where they should be and look like they've never been touched.

 

Other than a few LED bulbs and my new clutch (WRX setup) the car is bone stock.

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  • 2 weeks later...
Four days ago, I changed the spark plugs #3 and 4, seafoam the engine with a half can...the results are amazing...car runs smooth and stable...i reset the codes of misfire and didnt have them back since, however i used the car for only 7 miles, probably should drivr it for longer distance and see if the problem has solved.
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