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sly · 11-13-2018, 01:43 PM

@Matt@Cosworth has suggested I may have a leak. He has personally tweaked the tune and according to a log I took a month ago, fuel trims were normal. Long term was close to 0 and short term varied but averaged 0 as well. So I don't suspect the tune is causing a problem with fuel trims.

I also wanted to add that I have changed out the factory fuel pump with a high volume pump. Matt says fuel pressures look normal. I had been getting good fuel trims with this pump when I took the log a month ago. So I don't suspect the fuel pump.

Mods include Cosworth midpipe and axle back exhaust. Basically everything after the factory header is a Cosworth exhaust. I still have the factory header. I have added the Forester oil cooler and, of course, the Cosworth supercharger with intake manifold.

Could a mechanical problem with the engine cause this? I may try the propane again to look for a leak. Maybe replace the O2 and AFR sensors (although I hate random parts swapping).

I also tried plugging the PCV valve temporarily and the intake port for it on the throttle body. No effect on fuel trims. Pumping the brake peddle makes the fuel trims go more positive which I would expect as it does introduce a vacuum leak. But the trims reduce back to 30% when I stop pumping the peddle.

11-13-2018, 01:43 PM	#2
sly Senior Member Join Date: Dec 2015 Drives: 2016 Cosworth 2.2 BRZ Location: TN Posts: 335 Thanks: 89 Thanked 198 Times in 124 Posts Mentioned: 10 Post(s) Tagged: 0 Thread(s)	@Matt@Cosworth has suggested I may have a leak. He has personally tweaked the tune and according to a log I took a month ago, fuel trims were normal. Long term was close to 0 and short term varied but averaged 0 as well. So I don't suspect the tune is causing a problem with fuel trims. I also wanted to add that I have changed out the factory fuel pump with a high volume pump. Matt says fuel pressures look normal. I had been getting good fuel trims with this pump when I took the log a month ago. So I don't suspect the fuel pump. Mods include Cosworth midpipe and axle back exhaust. Basically everything after the factory header is a Cosworth exhaust. I still have the factory header. I have added the Forester oil cooler and, of course, the Cosworth supercharger with intake manifold. Could a mechanical problem with the engine cause this? I may try the propane again to look for a leak. Maybe replace the O2 and AFR sensors (although I hate random parts swapping). I also tried plugging the PCV valve temporarily and the intake port for it on the throttle body. No effect on fuel trims. Pumping the brake peddle makes the fuel trims go more positive which I would expect as it does introduce a vacuum leak. But the trims reduce back to 30% when I stop pumping the peddle.