Need some advice on my newly aquired car. - Toyota Yaris Forums

Lux · 07-07-2012, 06:20 PM

Coheed, You might be in luck... I know the these cars practically inside-out.

If you have the equipment, check your fuel pressure, verify that it is 2.3 to 2.8 bar. The backfire is from rich mixture and/or incomplete combustion, could be caused by excessive fuel pressure. The fuel system is not monitored by the ECU, and the MIL trouble codes are not much help due to their simplicity of that era. These engines are also double-spark-- they fire twice per combustion cycle-- which accelerates spark plug wear by twofold; check your plugs and replace as necessary. Proper AFM and TPS testing requires a professional lab scope across the full range, but if you checked them by voltage test at low, mid, and high ranges, then I guess it should suffice.

Verify your firing order as well, because that much fuel igniting in your exhaust system makes me think that some cylinders are just pumping wet (fuel, but no spark).

**edit: sorry, I just noticed you have the 7M-GE, not the 7M-GTE. The fuel pressure for your model is 2.7 - 3.1 bar. Your ignition system is a single-fire only, as well.

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07-07-2012, 06:20 PM	#16
Lux Drives: NCP91 Join Date: Jul 2012 Location: Markham, Ontario, Canada Posts: 114	Coheed, You might be in luck... I know the these cars practically inside-out. If you have the equipment, check your fuel pressure, verify that it is 2.3 to 2.8 bar. The backfire is from rich mixture and/or incomplete combustion, could be caused by excessive fuel pressure. The fuel system is not monitored by the ECU, and the MIL trouble codes are not much help due to their simplicity of that era. These engines are also double-spark-- they fire twice per combustion cycle-- which accelerates spark plug wear by twofold; check your plugs and replace as necessary. Proper AFM and TPS testing requires a professional lab scope across the full range, but if you checked them by voltage test at low, mid, and high ranges, then I guess it should suffice. Verify your firing order as well, because that much fuel igniting in your exhaust system makes me think that some cylinders are just pumping wet (fuel, but no spark). **edit: sorry, I just noticed you have the 7M-GE, not the 7M-GTE. The fuel pressure for your model is 2.7 - 3.1 bar. Your ignition system is a single-fire only, as well.