My 2005 6mt G has had codes p1166 and p1273 lean codes for years now. I have test pipes but I read you can get rid of these codes with a tune. I did that, also because I was worried it was actually lean, but the code didn't go away and the mechanic said it's probably because of the test pipes. Would I be able to buy some high flow cats and put them on without a retune? I assume it would be richer. Am I right in thinking this could possibly make the codes go away?

 

Rich/lean doesn't have anything to do with your catalytic converters, by switching to test pipes you'll throw catalytic EFFICIENCY codes for the sensor 2 (downstream O2 sensor) P1146, P1166.

So the P1166 is merely because the switching time on the sensor is insufficient because of no cats. You can install O2 sensor non-foulers which will usually help eliminate those codes, basically it's just a little extension bushing that moves the O2 sensor away from the direct stream of airflow in the test pipe. This causes the air around the sensor to not move around so much. Sometimes you need to use two non-foulers and screw them both together to move the sensor even further away, just gotta play around with it.

However P1273 is for the upstream sensor 1, those two O2 sensors are your air/fuel ratio sensors. These ones DO need to be working correctly and not throwing codes.

I would start by pulling all 6 spark plugs and visually inspecting them to see if bank 1 (or one specific cylinder) is actually running lean.

There's a lot of reasons you could be running lean on one bank, fuel injectors spraying different amount on one cylinder, exhaust leak from engine-header or header-test pipes, vacuum leak on the intake plenum, etc. Start with the plugs because you can visually see what's going on inside each cylinder.

 

My tuner said I was only running lean in the higher RPM but he fixed it with the tune. I've had 90 degree non-foulers installed since day 1 but I've heard they don't work on the revvup ECU. Am I wrong for thinking installing either HFC or cats will resolve both codes? Would that risk blowing my engine bc it would run rich as the cats would be gone and it is tuned for not having cats?

 

HFC or cats won't correct the P1273 lean bank 1 code. They would resolve the P1166 catalytic efficiency code but I would recommend just adding another non-fouler (add a straight one to the existing 90 degree one) to the test pipes.

Start troubleshooting why you're running lean on bank1.

I'm also curious why your car is throwing P1273 anyways? That's a non-revup code. I thought all the rev-up ECM threw codes P0130 to P0133 for the bank1sensor1 O2 sensors? Are you sure it's actually a rev-up engine? You have the waffle print on the exhaust cam magnet retarder cover?

 

I thought my tuner would be able to diagnose any lean issues. It is definitely a revvup with a cd009, I looked up the vin and have the intake/exhaust timing cover. Itll throw p1283 as well.

 

Ok apparently it was 2006 when they changed those diagnostic trouble codes.

So you're throwing lean codes for both banks, first step is check for any vacuum leaks, I would smoke test the intake but you could check for any obvious visible problems by removing all the PCV hoses, the PCV valve, inspect for rips/cracks/loose hoses/etc. Same with the intake tube.

Next up is watching fuel pressure, you might be dropping at high rpm. Get a fuel rail sandwich adapter from Z1 Motorsports and hook up an electronic gauge you can temporarily put in the cabin to watch pressure while you drive, or if you have access to a dyno put on a mechanical and make a few rips while you watch pressure.

If it's a fuel pressure drop your strainer baggy sock on the pump might be clogged up or the pump might be starting to fail. If pressure is good then it's something else.

How many maps do you have on your tune, try switching back to a stock map to see if maybe it's just a bad tune. Who is doing the tune?