2003 Subaru Outback H6 (3.0), getting random misfire codes on all 6 cylinders. 

 

Still idles okay (But sounds rough) no loss of power. 

 

Showed P301 - P306 codes, as well as 2 of the cylinders showed misfire/lean fuel code. 

 

Had tech test fuel pressure with gauge it was fine (39 psi), I replaced fuel filter with new Subaru Filter. 

 

I filled up tank to full to see if that would make a difference and it still ran the same. 

 

No loss of power that I can notice under acceleration. 

 

256,000 Miles on the car. 

 

(about 8 months ago 3 of the injectors (2,4,6) were replaced with genuine OEM subaru ones. ) However symptoms here were misfire in only 1 cylinder

(About 6 months ago 3 of the Coil's were replaced with genuine subaru ones - can't remember which sides ) - However symptoms here were misfire in only 1 cylinder. 

 

Fuel Pump was replaced 3 years ago (It had failed completly) and was replaced with a used one from a Low Mileage Subaru H6. 

 

 

Any suggestions on what else to check? Normally I have a master subaru tech that can diagnose and fix for me, however he is tied up for the next 2 weeks. 

 

 

Spark plugs? How old? What kind?

 

At that mileage the timing chain guides may be worn and have allowed the chain to jump a tooth. There are inspection holes in the cover which can be removed to check the timing. Timing chain work is a major job on that engine.

Spark plugs were replaced about 1 year ago with subaru ones. 

Timing chain tensioners were replaced about 2 years ago. 

 

Master tech listened to the engine when he had a few minutes yesterday, he said it's not timing or chain tensioners/guides. 

Spark plugs? How old? What kind?

At that mileage the timing chain guides may be worn and have allowed the chain to jump a tooth. There are inspection holes in the cover which can be removed to check the timing. Timing chain work is a major job on that engine.

Major cluster of grounds on the intake, rt side, on top...

Could be bad spark plug wires shorting out.

Woah, all 6 cylinders has to be somethign that can affect it all.
Fuel - beginnings of a cracked fuel pump cap and oring failure?

Electrical (as CNY_Dave pointed out)
Timing (mechanic suggests this sounds fine).

 

 

Could be bad spark plug wires shorting out.

The H6's don't have spark plug wires, but they have COP's which would be unlikely for all 6 to fail.

Vacuum leak?

 

only at idle? maybe IACV?

Tech finally has some time to look at it next week. I ordered 6 used injectors just to have on standby as he thinks there might be something going on with the injectors. He's going to check injectors along with fuel pump, although seems as if fuel pump is unlikely because pressure seems to be okay. 

 

Coils were replaced not too long ago with subaru ones. 

 

Hopefully won't be to difficult of a fix. 

 

Will post results once he takes a peak

Edited August 22, 201411 yr by dbullen

This time don't bin the used parts, someone will always want spares!

Car was fixed, issue was fuel injectors (3 of them), carbon build up, he did a cleaning of all injectors and car is running great now. 

 

I guess reason all 6 were misfiring was because pressure regulator was on the side that had the issue, and was some how affecting the other injectors

Edited September 4, 201411 yr by dbullen

nice, thanks for the feedback. 

 

do you know how they verified it?  did they test or guessed?

 

so you ended up replacing all 6 injectors?  3 awhile ago and the other 3 now?

Edited September 4, 201411 yr by grossgary

3 were replaced a while back, all he did this time was clean them all (3 were really built up with carbon) and 3 were okay but cleaned anyways. 

 

He visually inspected fuel pump and also tested it, checked fuel pressure, checked a number of sensors (cam shaft, crank shaft sensors I believe), may have checked a few other things, and finally ended up by process of elimination at fuel injectors, so he took them out, saw the carbon build up and cleaned everything. After putting back together it ran smooth and no more codes. 

Edited September 5, 201411 yr by dbullen

thanks again for sharing that - good to know that's something to possibly check.

 

woah - the build up was clear visually and externally?  crazy.

what's that from i wonder.

I think cardoc or some other guru once said he could see xtra carbon inside EZ30 engines that didn't get premium fuel.

 

???

What is your oil change interval and how often have you changed the PCV Valve?

Coking can come from several sources.

 

-One is never chaining the PCV valve. If you have an engine that tends to coke you should replace it once a year to be on the safe side.

-Reduce the oil change interval from 7500 miles (or more on some engines) to 5000 miles. The oil itself may be fine at lubricating right up to and past 7500 miles, but the additives have broken down.

-Try a hotter spark plug as you may not be burning off the (normal) residual oil left on the valve stems. This is a problem on direct injection engines especially (Subarus do not do DI).

-A different brand of fuel (stop using the cheap gas). All gas is the same but the additives are not.

-You may need to actually press the go pedal to the floor once in a while (highway on ramps) to help clean out the carbon.