2005 LL Bean Outback, EZ30 w/5EAT.
225,000 miles. It has been owned for 4 years, but it has been in the family since ’06. I have multiple service records.
For the past 4 months I have been dealing with a recurring check engine light caused by P0171 and P0174 (always both) indicating a weak condition in both banks. I have pursued this problem myself and to a mechanic, but with no consistent success.
This problem first appeared after letting the car sit for about a month and a half (final + Christmas break), roughly 2 years after I had driven the dreaded P0420 code — which I fixed by welding in a new flex pipe in exhaust that was completely detached from the rust. Seeing as these poor codes are often associated with P0420, I first checked the exhaust system and sure enough, the flex pipe I put in had started to develop a small rust hole (thanks, winter salt!). I decided that DIY flex pipe replacement wasn’t the best way to go and got a new stainless exhaust fitted at a shop. Instant reduction in cabin noise so I thought maybe that solved it.
About a week later though the check engine light came on again, with the same codes. After much research on these forums, I got a basic understanding of how these codes work and how to troubleshoot while driving intermittently. Codes would re-appear and activate usually with acceleration, although not particularly heavy (city driving), with freeze frame data showing short term fuel cuts in both banks >20%, and long term fuel cuts of approx. 10%. Around this time I noticed that when I would start the car it would experience what I think is hunting at idle — ramping up from about 2k to 3.5k rpm and then it would drop and jump a bit but stabilize when I put it in car.
This led me to suspect a vacuum leak, based on what I’d read here. Facing weeks of cold weather, I decided to take it to a store to test it out. On the way to the store, about a quarter mile in, I started to lose power and got a check engine light on just as I pulled into the parking lot — not starting. The mechanic certainly focused on the issue and replaced all the spark plugs (I was getting ready to do that anyway and was glad I didn’t have to contend with the H6’s tight spaces). While the car ran a little better, it didn’t fix the problem though, and after a few days of running, the light came back on.
I made another appointment at another mechanic to look at the car, but it was a month out. In between I cleaned the MAF and air filter based on the suggestions I had seen here (the MAF was actually pretty dirty), which did not fix the problem. The flashes came back as pending codes that I would see with my reader, but did not turn on the light. Constant loss of power to the point where I stopped driving.
The new shop took it in and found that the inlet pipe boot was torn really badly on the bottom and there was the remains of a rat’s nest in the area. They said smoke came out like a strainer right when they plugged it in. They replaced this and then re-tested the intake to make sure all was well. They noticed that the passenger floor strap had broken from the frame to the engine.
When I got the car back, I immediately noticed that it idled “normally” again, not increasing in RPM and not moving around. It also seemed to get power back and generally drove like a normal car again. However, after a few days of driving, that bad smell of a check engine light reappeared. Just checked and sure enough, P0171 and P0174.
So now, my thoughts on this and where I would like some help is that I think I definitely had a vacuum leak, and that was affecting performance and contributing to a lean condition, but it doesn’t seem to be the whole story. What seem to be the next possible suspects based on my understanding so far:
— Fuel problem, kill pump and/or clogged filter
— The EGR valve gets stuck open essentially causing another vacuum leak as reckless air enters
— something else entirely, perhaps electrical noting the broken strip of earth and evidence of rats?
Other relevant info: with the window down today I noticed that I can hear a spark plug noise/knock when i’m accelerating at low speeds, it matches the youtube video recordings of the noise very well. Not too loud, but probably important. The valve cover is leaking a bit, especially on the passenger side. I have new gaskets to fix this as the weather is warming up.
I have a code reader and got one of those cables to put Romraider etc on my laptop if deeper diagnostics are needed.
Something I’m missing here and any suggestions to help me keep trying to find the culprit(s)? Of course I’d like to try to get as much of this work done as I can to avoid racking up huge bills at the shop for a fairly old car, but I don’t mind going to a shop. I love this car and want to keep it going, and I love learning about car repair and struggling with it, especially if the weather is good!
In particular, is there any way I can try to figure out if the fuel pump is a problem before I buy a new one or go to a shop? I know the pressure can be tested but I hear the fuel volume is also important. Those pumps aren’t super cheap, so I’m not wild about throwing a new one at will.
More importantly, how worried should I be about this? From what I gather the poor driving can make the combustion chamber very hot, but if I’m carefully monitoring the engine temperature (it hasn’t been hot at all) is this a problem where I should stop driving until it is fixed, or the kind of thing I could drive, just getting lower MPG?
Thanks for any help!
