2009 Murano - Intake Manifold Part

[Ptroiano]

Can anyone tell me what the round disk shaped part on top of the intake manifold is? It's on the upper back of the manifold. I hear and feel vacuum coming out of the sides and I fighting a p0171 lean error code.

[VStar650CL]

If you mean one of these guys, they're the power valve actuators. They do have rubber diaphragms which can leak, but the ones on your Murano aren't replaceable separately. You need to buy the whole plenum.

[Ptroiano]

No, if you look behind them on the top rear. You can see a round shape that is the piece I'm looking at.

[VStar650CL]

If you mean this then it's a mold plug in the resonator portion of the plenum, a leak there means the plenum is cracked. If you mean something else, post a pic.

[Ptroiano]

That's the piece. So there should be no leaks there?
I hear and feel vacuum there.

[VStar650CL]

I've never tried to remove one so I don't know if it's a molded insert or a threaded plug, but it definitely shouldn't leak. It's possible it's threaded, you could see if it will spin and tighten.

[Ptroiano]

Ok thanks, but that most likely is causing my p0171 code

[VStar650CL]

Sure. P0171 is almost always from a vacuum leak. The only other common cause is bad gas.

[Ptroiano]

I removed the intake and can't find any obvious cracks. Any chance anyone has removed that piece? I don't want to force it. No thing to try a a smoke test I guess.

[VStar650CL]

I talked to several other techs at the shop and nobody recalls ever seeing a leak from that plug. So if yours is leaking, it's a rare bird.

[Ptroiano]

Thanks, I'll do the smoke test and see what happens.

[Ptroiano]

I did the smoke test and can't find any leaks. I put the machine in different places but nothing. I have replaced the upstream o2 sensor but couldn't get the downstream one off. I'm able to get the socket on the sensor with the breaker bar but when I try the losen it the socket rides up and slips off. I have no way to push down. Any ideas on how to replace that one? Not sure what else to try since it doesn't look like a vacuum leak.

[VStar650CL]

If you're using a slotted socket, get a worm drive radiator clamp and tighten it around the base of the socket so it can't spread when you torque it. Since you're replacing the sensor, you can also just cut the wires and use a big box wrench.

[Ptroiano]

I did the smoke test and can't find any leaks. I put the machine in different places but nothing. I have replaced the upstream o2 sensor but couldn't get the downstream one off. I'm able to get the socket on the sensor with the breaker bar but when I try the losen it the socket rides up and slips off. I have no way to push down. Any ideas on how to replace that one? Not sure what else to try since it doesn't look like a vacuum leak.

[Ptroiano]

So do you think it could be the downstream sensor?

[VStar650CL]

It's a lot less likely than some other things. Besides its main job of monitoring the cats, the ECM only uses the downstream sensor as a double-check for the upstream A/F. When there's confusion it's usually because the ECM is blaming the wrong sensor, but you'd be getting a sensor code and not a lean code. Besides a vacuum leak, some other things you can check are exhaust pinholes (particularly near the A/F sensor), MAF calibration, PCV Valve, low fuel pressure, and bad gas (particularly too much alcohol). Pinhole exhaust leaks on the back bank aren't easy to check, so you might want to use smoke for that. To check the MAF, I'd recommend checking the flow at an above-idle RPM, then perform an IAVL and see if the reading changes at an identical RPM.

[Ptroiano]

Ok, found out there was two codes P0171 & P0172. So since we had the o2 sensor for downstream your recommendation to use the hose clamp worked. My son was able to replace the downstream one. He drove the car for about 150 miles and now we are getting P2A03 and a P0138. We need to get the car inspected so these code are prevent a passing grade. Any ideas on next try?

[VStar650CL]

Sounds like the downstream sensor is either the wrong part or DOA off the shelf. P2A03 is a "rationality" problem with the front A/F sensor signal. So that might have a problem too, or the rear sensor readings may be causing it. As I mentioned earlier, the ECM cross-checks the A/F by way of the rear HO2S, so there's a good chance the rear sensor is causing both codes.

[Ptroiano]

The downstream sensor was the wrong part. It's really hard getting the correct ones, everybody seems to describe that different. Not sure why it's so hard to call them bank 1or 2 upstream or downstream. Anyway we did get one from orielies. That sensor seems to have fix the issue. Been driving the car for a week with no codes. So it definitely fixed the issue. Again thanks for all the help.

[VStar650CL]