410 replies to this topic

[LukeFranky]

Now the car is just messing with me.

P0171 came back. Doesn't come on as easily as before though.

The only symptoms are high fuel usage, surging on boost 3-6 PSI and a slight misfire at idle.

A few thoughts:
I know my cam shaft sensor has had earthing problems. Could it be a suspect?

I've tried two other MAF sensors, one OEM and one aftermarket, both make the car run rich under boost with no error codes. The original MAF lets the car run smooth but brings on the P0171 eventually.

Both o2 sensors were replaced less than a year ago. Might try the old front sensor which was only failing to heat on start up.

I noticed the cat converter has been replaced at some stage with a non-OEM one, anther possible cause?

Could it just be a bad tune? I bought the car with a bad primary turbo but it drove fine with good fuel economy. The P0171 started as soon as I replaced the turbo. It has an EcuTek badge.

Are there any cheap scanners that will give me readings of o2, MAF, coolent temp, etc? Mine only gives me codes and battery voltage.

I might also start looking around for a stock air box and replace the rest of my vac lines that aren't silicone yet.

I know that's a lot to read, sorry guys.

[Robbks]

-If it's been tuned and then had other airflow mods done it's going to need to be re-tuned.

-Any time you swap a sensor or airflow part make sure you perform an ECU reset

-You can buy a VAG-COM cable for about $30 and use RomRaider on an old laptop to view lots of engine data.

[LukeFranky]

Hmm, what to try next?

Pay out for a tune at the risk the problem is elsewhere?

I've already spent a fortune on the car. I can't keep buying and replacing parts.

Also, a point of interest. Is a BOV ever meant to be half open/closed? Since installing the silicone intake I have been able to hear the BOV. On partial throttle I can hear boost recirculating. Is this normal?

[Robbks]

the BOV sits a little bit open under high vacuum.

So you have installed "airflow" mods since getting the car (silicone intake, etc)
the car needs to be tuned for the mods. simple.

You would need to confirm if it does in fact have an ECUtek tune onboard, if so a re-tune should not be too expensive, but you would need to make sure it is 100% mechanically perfect,

And yes I'm going to keep beating this dead horse.
cut your losses and either flog off the car, or Convert it to single turbo and enjoy hassle free boosting.

You can spend twice the money troubleshooting a small issue with a $50 part on the TT system, than you would have converting it to single at the first sign of trouble.
having spent 10 years around TT Subaru's and their problems I've lost count of how many have just been on-sold or traded in with "unfixable" problems

[LukeFranky]

I just got quoted $1500 for a retune...

 

Might just live with it. Biggest issue is the fuel consumption.

[LukeFranky]

Would a bad tune give me a random misfire at idle?

[Jimbo]

I think it might be all to do with the tune.

Any changes outside of the parameters of the tune will cause unstable behavior. The ECU is trying to establish the state of tune which it's been tuned for, any changes are going to freak it out. At least, on the stock tune on the ECU there are greater boundaries for adjustment and it will adapt to small changes.

I think a good place to start would be to have the factory tune re-implemented.

Quick edit. I have noticed you haven't mentioned the throttle position sensor or idle control sensor (A-C has it, not sure on D-E, someone should be able to confirm).

Perhaps check voltages to make sure they're working correctly?

[Jimbo]

Also did you get to re-plumbing the PCV lines correctly?

[LukeFranky]

Thanks Jimbo. I checked the voltages on the TPS. Looked ok me. What range is good?

I haven't looked at the idle control valve. Does it only affect idle air flow or can it trigger problems with any type of driving?

What are your thoughts on temp sensor? I've seen this mentioned as possibility.

How can I go back to stock tune? Is it possible to just unplug the ecuTek chip so I can switch back and forth? I assume it has a chip somewhere. Correct me if I'm wrong. I haven't had much to do with tuning.
Oh yeah, I did replumb the PCV lines. I think I did a good job of it too.

[LukeFranky]

I just made a discovery. The phenolic washers for the intake manifold bolts that came with phenolic spacers aren't strong enough. They're falling apart under the pressure of the bolt head. Probably needed some metal washers on top on of them.

[Jimbo]

Would this mean the manifold is lifting lol ? That'd make it run whacked as hell, dunno if that would trigger P0171

[cowie165]

Ref: Aftermarket cat

RevDE runs two O2 sensors, right? One up front and a second off the cat? I have RevA-C so can't check if it goes into the cat or into the exhaust itself. Wait one, will check the manual.

 

Edit: wrong laptop. No manual. Luke try checking your exhaust and confirming whether there's a second O2 sensor plugged in there.

[Jimbo]

I think the rear 02 sensor purpose is purely to let you know if the cat gets flogged, front one does all the jibber-jabber.

[LukeFranky]

The manifold isn't lifting up Jimbo, but the bolts had lost some tension. Possibly causing an air leak. Might be why the car ran so good after putting putting back together and now gets the code again more easily.

I tried another cam sensor from a NA motor. It looked identical but I can't be 100% sure it is correct and it only made the problem worse.

I think it is bad wiring. I have an extra earth attached near the cam sensor which improves its operation. I only have a bluetooth scanner but the cam sensor does throw a code if I dissconnect the extra earth.

What do I do about the bad wiring? Pull it all out and rewire the lot?...Yuck.

I also have a spare O2 for front and back. The spare front one works but the heater element is gone. The back o2 sensor goes into the exhaust before the cat I think.

[LukeFranky]

Yup. Goes in before the cat...
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[LukeFranky]

"is best left to an Auto electrician" - Challenge accepted