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Chris(aka-Moose), Nissan Technician
Category: Nissan
Satisfied Customers: 621
Experience:  16 years of experience
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1996 Nissan Quest high nox

Customer Question

1996 Nissan Quest high nox
Submitted: 2 years ago.
Category: Nissan
Expert:  Ricardo Hohl replied 2 years ago.
Hi welcome to just answers my name is ***** ***** i will try my best to help you solve this problem....Lean Fuel Mixture - Lean fuel mixtures cause high NOx.When cylinder temperatures reach approximately 2500°F, NOx levels in the engine-out gasses increase. This condition will typically only exist under a load not at idle. One of the systems used by manufactures to control these temperatures is Exhaust Gas Recirculation (EGR). have you scan the computer for any codes?
Expert:  Ricardo Hohl replied 2 years ago.
another thing that will cause nox is a lean condition cause by lo fuel pressure have you check f/pressure.
Customer: replied 2 years ago.
Hi! thanks for your help Ricardo......No codes in memory,the EGR sistem is working fine,fuel pressure it's 34 and 43 if I discconect the regulator,I don't know if it is normal that when I turn off the car fuel pressure drops to cero.Oxigen sensor works fine and the CAT (The rear one)was replaced but no difference.Are the Injectors restricted? I'm trying to pass smog inspection and nox drops too 700 ppm so,is not low enough.
Expert:  Ricardo Hohl replied 2 years ago.
ok fuel pressure should not drop to sero pressure when engine is switch to off position , there should be some residual pressure on the line for quick restart of the engine this problemis cause by the fuel pump module return valve, stuck open. or a leaking injectors ,this can cause a lean condition upon start up and worm up but wans the rail builds up pressure again it would be ok
Expert:  Ricardo Hohl replied 2 years ago.
to me it seems like you have an egr valve stuk close or the solenoid that controls the egr bypass is not working.
Expert:  Ricardo Hohl replied 2 years ago.
has any body check the egr valve function?
Expert:  Ricardo Hohl replied 2 years ago.
if the egr valve is operable then you must have bad restricted injectors, have you try adding injector cleaners at the tank or have a presurize injector cleaning perform?
Expert:  Ricardo Hohl replied 2 years ago.
did you conect a scaner and check voltage switching between rich and lean levels on the upstream and downstream 02 sensors, and were they the same at both ends or was there almost no activity on the rear
Customer: replied 1 year ago.
Ricardo.....the rear CAT was replaced,the O2 sensor wave its switchin rich and lean on the lab scoop,I have 2000ppm before the first cat and 800ppm after both Cats,????
Customer: replied 1 year ago.
Nox it's about 2000ppm before the first Cat and about 1500ppm you think the first Cat is bad????
Expert:  Ricardo Hohl replied 1 year ago.
sounds like the first cat is not doing its job , thats almost the same on the upstream as it is on the downstream, it should be much lower than that on the downstream.
Expert:  Ricardo Hohl replied 1 year ago.
the secondary Cats are not going to be able to handle that much Nox , thats why your levels of Nox are so hi.
Customer: replied 1 year ago.
Ricardo.....I've been tryng to rate your service and I don't know why I can't not do it
Customer: replied 1 year ago.
Ricardo....I need to rate your service