What caused this?

[AZPete]

Normal driving, then engine went into only-fast-idle with DBW accelerator disabled (Limp-home mode?). I limped home at 25 mph. Codes:
PO171 System Too Lean (Bank 1)
PO303 Cylinder 3 Misfire Detected
PO304 Cylinder 4 Misfire Detected

Any guesses? This is a bone stock 06 WRX 2.5 turbo that's been running well until this sudden change, so did some wire just came loose? No gas leak.

[6t8dart]

Sounds like a lack of fuel to two fuel injectors. If it was ignition, then it would be too rich.

Possible causes:
Poor wiring connection for a bank of injectors.
Bad (or disconnected) O2 sensor.
Computer fault.
Dirt in fuel clogging injectors (or filter).

[STiPWRD]

Are the spark plugs new? Might want to pull them out and check them. Otherwise it could be an air leak letting more air into the system after the MAF.

[AZPete]

I've got to ask some dumb questions: What is Bank 1? Cylinder 3 is right-rear and cylinder 4 is left-rear, right? I'm looking for something that controls only the rear cylinders, right?
The spark plugs are new. Boyd tank, fuel lines, filter are new with fresh gas. In the diagram it looks like the wiring connection to injectors are individual so I don't see a connection effecting both #3 and #4. Could an air leak after the MAF effect just cylinders 3 and 4?

[Rasmus]

Cylinder 1 is Right Front
Cylinder 2 is Left Front
Cylinder 3 is Right Rear
Cylinder 4 is Left Rear

> Could an air leak after the MAF effect just cylinders 3 and 4?

The only way I could see this happening would be to have a crack in the cylinder head. Like right near or on the spark plug holes. Which would be weird and rare so I doubt it's that.

If you had leaks after the MAF but before the turbo the whole system would run lean.
If you had leaks after the Turbo and before the valves the system would run lean off boost. And run rich on boost. Not just 3 or 4 though. All of them.

Even if you had a hole in the intake runner in the TGV above cylinder 4 it would effect all the cylinders.

Your codes make me think it's a fuel injector issue. Like the fuel injectors aren't squirting? Aren't getting a electrical signal? Are clogged? Or fouled on the tips? The fuel rails are clogged before those two injectors?

[walt555]

I've heard of a dirty MAF throwing misfire codes. What kind of air filter do you run? I killed a MAF on my old RS running a cone filter(the type with fiber wire mesh and when you touch it, it has a thin oil film on it). Like you it went into limp mode. tried to clean it with brake cleaner but it didn't help. don't know what codes it threw, I didn't have a reader back then. ended up replacing the MAF and changing back to the stock air box. So on my 02 wrx stock box with a PVC 90 into the fender well and stock type paper air filter still on original MAF. I do throw a misfire code now and again but that's more due to my piggyback EM.

Hope this helps

Walt

[Sgt.Gator]

I'm betting on a Vacuum leak. Check all your vacuum lines closely. Especially the infamous blue Tee under the intercooler. Also check the air intake inlet pipe to turbo connection. The hose can slip off partially and cause a leak. If you are using a T-Bolt there that's probably the reason, they are known to not work right on that connection.

[longislandwrx]

I agree I think its a fuel issue.

are you using the boyd provided aeromotive fuel pump? I know at least one failed.

do you have a fuel pressure gauge? Are you using the factory pump controller?

I'm guessing your fuel pressure is dropping either pump or regulator issue. also check the vacuum reference hose to the FPR






http://forums.nasioc.com/forums/show...ighlight=p0171

[redfogo]

+1 for Aeromotive fuel pump check if you have it, they are terrible high failure rate!

One thing not said yet is check your O2 sensors as well I think both rear and front are required for fuel calculations on the 06 WRX.

[Bob_n_Cincy]

Hi Pete,
Nobody has stated the obvious fuel issue.
Is it possible the fuel sloshed around and thew pump sucked in some air?
Bob

[AZPete]

Thanks guys! I've got lots of things to check this weekend! I'll let you know what I find but so far all I know is I should get at least a 12-pack.

[Wayne Presley]

one TGV staying shut

[ssssly]

Would have to be both TGVs since the cylinders are on opposite sides of the engine.

Have seen this happen when an intake manifold wasn't tightened properly. The intercooler connection kept the manifold tight enough on the IC side, but the engine rock allowed air into the 3 and 4 cylinders when the car wasn't under boost throwing the code.

It would be a strange fueling issue if you are using the stock rails. The fuel path is 4-2-1-3. Not impossible for the first and last injector to clog or fail at the same time but would be strange.

Would also be a strange wiring issue. Since it is one cylinder on each half or the harness. Again not impossible but would be a crazy coincidence.

Another common cause of the P0171 code is the FPR vacuum line coming off the intake manifold.

[AZPete]

SOLVED! From all your suggestions I checked a lot of stuff - Fuel pressure, fuel filter, fuel pump, MAF, air filter, intake leaks and spark plugs. I found that my engine supplier, AJW, had installed the wrong spark plugs! Then, after a smoke test (with a You Tube home-made smoke machine) I discovered that the rubber bushing of the #4 injector was not seated correctly, creating a vacuum leak. New bushing solved it! Reading back through the suggestions . . . STiPWRD had it nailed with both spark plugs and vacuum leak. Sgt Gator and ssssly were the next smartest. Thanks to you all!! But, no thanks to AJW for causing these problems.

BTW, a vacuum leak at #4 injector can also effect #2 and #3. I don't know why but I don't care, now that all misfires are solved and A/F is normal.
Thanks again, guys.

[STiPWRD]

Glad you're back up and running!

[Sgt.Gator]

That's great. Vacuum leaks can be a pain in the rear to find. The smoke machine was a good idea. I bought one off eBay and it found my problem in 10 seconds.

[AZPete]

I agree, Sgt. I tried spraying Brakleen around the intake hoping for an increase in rpm, then water hoping for a drop in rpm, but neither worked. The smoke test found the vacuum leak instantly! I made a smoke machine from an old paint can, 2 hose nipples, some plastic tubing and a bicycle pump - cost $3.20, thanks to You tube!

[Loring]

Just some more input on these codes:

Firstly, on a car with only one precat o2 sensor, only a p0171 will set. There is no p0174, even though there are two banks.

Second, an ignition misfire can cause a lean condition, from the perspective of an o2 sensor. A partial burn may cause a high or low o2 voltage but a dead miss from an ignition misfire will always cause a low o2 voltage. O2 sensors don't sense fuel, and an air fuel mixture that goes through a cylinder with no ignition will exit as it entered, roughly, at about 15-19% oxygen, which will yield an HO2S voltage well below 300mV. That said, it's entirely possible to run your car rich enough to set a lean code, if you can take it that far.

AJW is making quite the rep for themselves, hmm?

[Wayne Presley]

AJW is making quite the rep for themselves, hmm?

AJW sold one of my customers a 5 speed with a Quaife limited slip differential. I opened it up to re seal the case and there was a stock open diff in it...

[mac1]

Figure I would post here what I'm up to. In an effort to make it to FFR show in a couple weeks, I'm hoping I can get this sorted. THis is a '06 WRX-T

Originally this code would pop up after some hwy pulls but caused no drivability issue at all. I clear the code via COBB v3 and wait for it to pop up again.
after a few weeks of occasional driving I started to think it was just AVN fuel quality related and the COBB tuning.

One morning as we get ready to head up to Sedona, it wants to die on me in the driveway, I check under the hood and all seems legit, I say the hell with it and go.
Up in Sedona the code was returning and I started to note LEAN afr's. I pull over and found a fuel leak at the Y split between FPR and individual rails. So I limped it home although it drove fine on the hwy and no issue at WOT, I had my extinguisher ready and it was a rather small leak

Next week I fix the fuel leaks and to my surprise it is still leak at idle like 19 afr and runs rough and stalls. Searching I found it could be dirty MAF or bad 02 in my case cause no vacuum leaks. I clean the MAF but no luck, now the AFR reading on the COBB is stuck on 14.7 and doesn't move. As of today I ordered a Denso upstream 02 sensor.

crossing fingers.