2009 Mazda CX-7 P0302 Misfire At Idle Only

2009 Mazda CX-7 with a P0302. The misfire mode 6 data shows it misfiring very frequently at idle for the first 15 mins until the engine is warmed up. The oscilloscope wave shows the ignition coils and the fuel injectors all good. The car has new spark plugs. The misfire stays on cylinder 2 even after moving coils and plugs around. Any help is greatly appreciated.

Thank you.

Brian

intake manifold gasket leak? hit the number 2 runner where it meets cyl head with propane while it's missing and watch for the o2 to go rich. depending on how short the window is to test, you may have to opt for smoke machine.

I will do that test for sure. I do have a smoke machine as well. I will watch the O2 sensors and fuel trims. Thank you.

Brian

2.3L turbo? These engines LOVE to carbon their intake valves.

A pressure pulse sensor in the intake would confirm a carbon deposit issue. If that's not available, go straight to pulling the intake and cleaning the valves. If they've never been cleaned, they'll be nasty. :lol:

I have a pressure transducer; would that work? What do you exactly mean by a pressure pulse sensor in the intake? Would this cause the misfires to only happen when the engine is cold?

Thank you.

Brian

BLEE wrote: I have a pressure transducer; would that work?

Which one, exactly? A Pico WPS500 would work, but a Fluke PV350 would not.

What do you exactly mean by a pressure pulse sensor in the intake?

A delta sensor, First Look Sensor, like that. It's a canister with a piezo disk that's very sensitive to pressure changes. This is a known good capture taken off a '15 Equinox. Relative compression in red, intake pulse in green, #1 sync in blue.

Would this cause the misfires to only happen when the engine is cold?

Absolutely. Carbon deposit issues usually show up worse when cold.

There are other issues that can cause that, of course, like a leaking head gasket or intake manifold gasket. Intake gaskets are pretty solid on these, IMO. You can check for a head gasket by getting the engine hot, pulling the plugs and pressurizing the cooling system overnight. Look for coolant in the morning.

Thank you for the info. I made a pressure transducer that I have used for in-pressure cylinder testing for plugged cats. Are you using the pressure transducer in the cylinder? Pulling the plug out and putting in the pressure transducer?

BLEE wrote: Thank you for the info. I made a pressure transducer that I have used for in-pressure cylinder testing for plugged cats. Are you using the pressure transducer in the cylinder? Pulling the plug out and putting in the pressure transducer?

That might work? But in my experience, carbon deposit issues usually don't show up very well on in-cylinder captures. The pressure pulse sensor on an intake port usually works better because it's measuring the breathing ability of each cylinder.

That makes sense. I may have to do that. Thank you.