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sprinkles08, ASE Certified Technician
Category: Infiniti
Satisfied Customers: 22983
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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Infinity g20: I am working on a 2001 infinity g20. the engine

Customer Question

I am working on a 2001 infinity g20. the engine will idle but will not accelerate. on acceleration it pushes air back thru the intake so the maf doesn't see enough air flow. checked the camshafts and they were still in the correct timing. exhaust is not restricted. if I enrich it it will accelerate. tried new injectors no help. fuel pressure is 36 at idle 44 on acceleration. the fuel injector resistor has 12 olms supposed to be 4 to 8 of resistance but I have 12.2 V at the injectors. voltages and ground checks out at maf. coolant temp is correct. o2 is switching from rich to lean nicely. the downstream 02 has a code for not switching but exhaust is very lean. tps is working nicely. could I be getting too much spark advance without cam sensor codes?
Submitted: 2 years ago.
Category: Infiniti
Expert:  sprinkles08 replied 2 years ago.
Hello and welcome to JustAnswer!
If it's pushing air or exhaust back out the throttle body on acceleration then there is almost no chance that you don't have an exhaust restriction. An exhaust restriction or valvetrain issue is the only way you're going to have exhaust and air flowing backward while the engine is running. You almost surely have a restricted catalytic converter. What was one to check for an exhaust restriction?
Customer: replied 2 years ago.
it does this with the ex. pipe off the downstream converter and the egr pipe off the egr valve. i am also a master mecanic and was an instructor this issue makes no sense to me. i am trying another maf sensor. if i pinch off the fuel return line increasing fuel pressure to 60 psi it runs good. i put in new injectors no help. checked timing marks on cams also.
Expert:  sprinkles08 replied 2 years ago.
Do you have the VIN?
Customer: replied 2 years ago.
another maf sensor solved the problem but the defective maf sensor i bought cost many hours of diagnostc time. somehow the lean condition caused the engine to puff air back thru the maf causing me to check camshafts and exhaust system and even changing the injectors. thanks for the input but i told you in my first communication that i checked the exhaust for restriction.
Expert:  sprinkles08 replied 2 years ago.
I'm glad the problem is gone at least for now, but an inaccurate mass airflow sensor doesn't have the capability of reversing airflow through the engine. let me know if you need any more help.