[Subaruoutbackh6]

Tried new sparkplugs and nothing. Tried good working coils still nothing. Had an O2 sensor coding off and on for awhile so replaced both of them still nothing. Last thing I tried was a new fuel filter and checked fuel pressure. Pressure was around 45psi and when I took vacuum line off fuel pressure regulator it jumped to 50psi. Book said to plug vacuum line and it should go up 3-10psi when I pluged the line it did nothing.
Car runs real rough at idle and wants to die when I try to take off from a stop sometimes it does die. When driving down the road doesn't sound bad but you can tell it still has misfiring cylinders.
Any advice and help would be appreciated as I'm at the end of my rope with this car. Thanks.

 

[CNY_Dave]

What are the actual codes?

Some of the symptoms align with a bad TPS sensor.

 

[Subaruoutbackh6]

Don't have actual code numbers but the tech I had look at it said it was showing codes for misfires on 4 of the cylinders.

 

[1 Lucky Texan]

hmmm - many posibilities. maybe knock sensor?, maybe try a vacuum gauge test - valves may not be closing or ???

how many miles? any work.wrecks.mods before this started happening?

Have you inspected the fuel pump for a bad cap and o-ring?

 

[cardoc]

Misfires have many different root causes.

Sensor feed from the MAF, ECT, TPS and MAP/BARO will tend to make the car run rich or lean = misfires. You don't have an electronic throttle, so idle control is based on IAC position, which if not opening enough will cause missing at idle. One way or another, its starvation of air or fuel, or missing fire from the ignition.

PCV valve, but it usually doesn't cause multiple misfires. If its clogged it will throw off the air calculations.

If it didn't run hot, I would discount compression.

Any noise from the front of the engine? Loose timing chain, guide, stuck tensioner will will cause retard of timing at idle and allow for smoother running at high rpm due to late cam rotation. This will also flood out cylinders at idle causing a miss.

The knock sensor won't cause misfires at idle and allow for smoother running at high rpm. The knock sensor detects detonation through vibration of the engine. The vibration from a misfire causes the plates in the sensor to separate, increasing the resistance and lowering the return voltage to the computer. The computer calculates the vibration with cylinder ignition and determines which cylinder is missing. If the knock sensor fails, usually cracks, it will stop sending a base signal to the PCM and you would have a knock sensor code. It does nothing for base timing or ignition because it doesn't know engine speed. It just vibrates at high velocity all the time regardless of rpm. When the sensor fails, the PCM ignores it. Subaru is the only car I know of that you can replace a knock sensor and start the car and the MIL immediately goes out with the first turn of the key.

 

[idosubaru]

one with multiple misfires that i saw was repaired when a few of the coils were replaced.

what is strange (i just met with the owner a few minutes ago ironically), is that when we swapped the coils, it did not fix the issue, it did not "move" with the coils as one would expect...but somehow replacing a few of them fixed it. i can't recall which were replaced, they weren't cheap, but it fixed the problem.

another cause of multiple misfires i've seen on this motor would be severe carbon build up in the head.

Misfires have many different root causes.

i can say with certainty it won't be a bunch of the things you mentioned like the PCV valve, compression, or timing chain guides. he needs help narrowing it down, he's already had it to a mechanic and had some work done to it (plugs, fuel pressure tested) - listing all possibilities doesn't help, we could come up with 50 things that it "could" be. tips on how to narrow it down or which are most common on this engine is what he needs now that the obvious hasn't helped.

 

[1 Lucky Texan]

maybe oil leaking into the spark plug tubes?

 

[CNY_Dave]

one with multiple misfires that i saw was repaired when a few of the coils were replaced.

what is strange (i just met with the owner a few minutes ago ironically), is that when we swapped the coils, it did not fix the issue, it did not "move" with the coils as one would expect...but somehow replacing a few of them fixed it. i can't recall which were replaced, they weren't cheap, but it fixed the problem.

...

That makes it sound like the connectors on the harness were weak/making bad connection or something similar.

 

[Subaruoutbackh6]

No oil in spark plug tubes though the valve covers are leaking. Don't know if the o-ring on the fuel pump could cause this but I'll try it seems easy enough and cheap. Don't mind the cheap try's. I put all new coils on it and nothing luckily I'm in the parts biz so I was able to return them. Just borrowed a block test tool to see if I have a cracked head or blown head gasket will post back after I do this.

 

[Glennda5id]

What are the actual codes. Get them from your mechanic or got to Autozone and get it scanned for free.

 

[Subaruoutbackh6]

Well the tool didn't have the right adapter to work for my car. I'll have to see if one of the parts stores loans them out tring not to drive it anymore than I have to don't want to cause further damage. I may see if someone at my work has one I can borrow, the shop has one but it only works in GM vehicles.

 

[CNY_Dave]

GM has a special connector for ODB-II? I thought it was fully standardized.

 

[Subaruoutbackh6]

No the computer they use only works with GM. It's called a tech-2 it may work for other cars but the software if only for GM

 

[cardoc]

It would be highly unlikely that with 4 cylinders misfiring, the head gaskets are leaking. That would mean both heads. Look for something common to all the cylinders.

And, it may be miscommunication, but my previous list was for narrowing it down, not suggesting all those things are the problem.

Things to check: AIR, FUEL, FIRE, mechanically. Then check outputs from the sensors. This is one of those things where a technician needs to look at live data to narrow it down. Sorry, but unless you can record a data stream and post it, you will have to check parts one by one. Check, not replace, until you find the failure.

If you know how to use a multimeter and want a detail on pinpoint test of engine control sensors, let me know.

 

[cardoc]

Fuel Trim

Once you get a scan tool that can read the live data, look at the reading for STFT and LTFT. Ideally, it should be +/- 5%. If not, a positive trim means the comp is adjusting for lean, adding fuel and negative means rich and it reduces fuel. If its rich, could be too much air or sensor failure. Lean, not enough fuel or sensor failure. The greater the trim number, the more the computer compensates up to 37.5%. The trim reading will tell you what you are missing.

Now, failure of a sensor could be cause for the PCM to add/reduce fuel causing the "miss". Too much fuel=fouling, not enough=no explosion. Barometric pressure is how the PCM determines altitude and makes adjustments. MAP determines the absolute pressure, ECT determines the fuel state open or closed, TPS determines throttle open/closed, AF sensors determine the ratio of air/fuel in combustion, CMP determines injector timing.

The computer makes adjustments based on info it receives. If you don't have a vacuum leak, good fuel pressure and flow, ignition system is good, then you need to look at the data stream to determine where the fault originates. The AF sensor is where I would start if fuel trim is in the double digit area.

And, I just thought it, is your's EGR equipped? If so and the valve is stuck open, it creates a vacuum leak.

 

[cardoc]

I forgot: Actron makes a scanner that talks to all vehicles for under $250.

 

[cardoc]

Fuel Trim and Ignition Descriptions.

 

[cardoc]

H6 Pinpoint Test

 

[1 Lucky Texan]

^^^^^ thanx !

saved to read later.

 

[Subaruoutbackh6]

Well finally figured it out it was a dead cell in the battery never thought to check it because it's only around a year old and never had trouble starting. Thanks for all the help and advice.