Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

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PattiM
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Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby PattiM » Tue Dec 14, 2021 3:18 pm

My 92 Pathfinder started running rough all the time - sort of like it's running of 5 cylinders, but I think it's a fuel mixture problem. (problem with air mass sensor) The cylinders have good compression and the spark plugs are pretty clean. I took the air mass sensor off, and there is clean engine oil in the rubber boot connecting the intake manifold to the air mass sensor (on the air cleaner). The oil starts about half way from the side openings (two approx. 1/2 inch hoses and one tiny hose) but I can't tell which hose the oil is entering from.

I replaced the PCV valve, but the oil came back. The air filter is also damp with oil near where the air mass sensor draws air in. (The other half of the air filter is dry.) This seems really strange! How is oil getting spit *upwind* of the air mass sensor and oil filter?

(injected V6 engine)

Any ideas where this might be coming from? I ran some Blue Seafoam top-end cleaner into the rubber boot just ahead of the intake manifold butterfly valve. It seemed to clean things up and it ran fine for a couple of days. This is really confusing. There's also a high-pitched whistle that depends on the throttle (foot pedal) position. But this whistle goes away when it starts running rough.

This is what the air duct looks like - does anyone have one of these and could help me know what the two ports on the side attach to? I'm guessing they're part of the emissions control system - but the manuals I have aren't too specific. Thanks.
https://i.ebayimg.com/images/g/DhkAAOSw ... s-l400.jpg
Last edited by PattiM on Tue Dec 14, 2021 6:47 pm, edited 5 times in total.


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VStar650CL
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Re: Oil in air mass flow sensor? (92 pathfinder 4x4)

Postby VStar650CL » Tue Dec 14, 2021 3:34 pm

Most likely a bad PCV Valve, could also be a collapsed hose in the PCV system or a clogged air gallery inside one of the valve covers. It's probably causing your poor performance as well.

PattiM
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Re: Oil in air mass flow sensor? (92 pathfinder 4x4)

Postby PattiM » Tue Dec 14, 2021 6:46 pm

VStar650CL wrote:
Tue Dec 14, 2021 3:34 pm
Most likely a bad PCV Valve, could also be a collapsed hose in the PCV system or a clogged air gallery inside one of the valve covers. It's probably causing your poor performance as well.
As I said, I replaced the PCV valve and none of the hoses seem collapsed. There are three ports going into the air duct - one of them is allowing oil into the air duct, and it's dripping into the air mass sensor and onto the air filter. Which of the three ports (the two you can see in the pic https://i.ebayimg.com/images/g/DhkAAOSw ... s-l400.jpg and one more very small one that seems to go to a vacuum switch of some sort) could oil be coming from?

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VStar650CL
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Re: Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby VStar650CL » Tue Dec 14, 2021 8:52 pm

See if you can blow through the PCV passages from the valve covers into the crankcase. You may have a clogged cover. Oil really doesn't have any route to reach the MAF except via the PCV system, so either your problem is there or something very unusual is pressurizing your crankcase.

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Re: Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby VStar650CL » Tue Dec 14, 2021 9:01 pm

PS - If you don't find any failures in the PCV system, almost everything else that can pressurize the crank is a severe engine failure. Bad/cracked rings, bad exhaust valve seals, cracked heads or blocks, etc. So I'll cross my fingers that you find something simple. If not, next step is compression and leak-down testing.

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Re: Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby PattiM » Mon Dec 20, 2021 8:32 am

VStar650CL wrote:
Tue Dec 14, 2021 8:52 pm
See if you can blow through the PCV passages from the valve covers into the crankcase. You may have a clogged cover. Oil really doesn't have any route to reach the MAF except via the PCV system, so either your problem is there or something very unusual is pressurizing your crankcase.
Thanks! Great! I'll give that a try. I sort of rely on folks' knowledge like this - that "the oil only can go through the PCV system." I replaced the PCV valve which is unique from any I'd ever seen before. it has a pipe fitting on one end that screws into the intake manifold near between two injectors, I think. I'm not sure where the other end goes - I guess to the crankcase somewhere? PCV valves are usually press-fit into the top of a valve cover, right? That's why this seemed so odd.

The old PCV valve "rattled" when I shook it, so it was likely still working. So the clog must be in the hose somewhere.

Otherwise the car runs GREAT (when the MAF sensor isn't messed up). I did have a compression check and was told that's OK. It isn't using any oil, and not smoking or anything.

Could a test be to leave off the O-ring sealed oil filler cap? That would prevent pressurization of the block (but defeat emission controls). My brother used to talk about "tanking the block" or heads or whatever. Does someone have a system that blows hot steam through the block to melt the petrified oil there? (well, steam is probably a bad idea) The old PCV valve seemed kind-of groty - black congealed oil - even though the valve itself wasn't frozen. I'm not sure what the previous owner did to get the oil to mung-up like that into a jell. I've changed the oil a bunch of times after only a thousand miles or so, but it still comes out black - so I'm guessing it's really dirty in there.

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Re: Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby PattiM » Mon Dec 20, 2021 9:17 am

VStar650CL wrote:
Tue Dec 14, 2021 8:52 pm
See if you can blow through the PCV passages from the valve covers into the crankcase. You may have a clogged cover. Oil really doesn't have any route to reach the MAF except via the PCV system, so either your problem is there or something very unusual is pressurizing your crankcase.
Oh, wait - the PCV valve screwed into the intake manifold near the injectors
https://www.fixya.com/cars/t7351833-pcv ... 992_nissan
...but I'll still check the tubing coming from the PCV valve to see if it's clogged.

This is WAY downstream of the throttle valve - so there doesn't seem to be a path from the PCV up to the rubber boot connecting the throttle body to the MAF sensor. OTOH: the rubber air boot has TWO 1/2-inch tubes coming into it. The oil seems to be coming from one of those two.

EDIT: It looks like the PCV valve tube crosses under the intake manifold to the top of the passenger-side rocker cover near the back of the engine. One of those two 1/2-inch tubes coming from the air duct/boot thing goes straight to the front of the same rocker cover - so I guess that's an air *inlet* for that rocker cover? It seems like that would be the most likely place for oil to get to the MAF - it comes into the air system only a few inches from the MAF.

EDIT-2: OK, the other tube goes to something called an "Air regulator" on the side of the engine.

Maybe I should try "blowing out" the PCV tube?

Or maybe just give up and take it to a willing mechanic (if they exist) to check the PCV hoses? I'm told Pathfinders of this era are difficult to work on.

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Re: Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby VStar650CL » Mon Dec 20, 2021 5:26 pm

PattiM wrote:
Mon Dec 20, 2021 9:17 am
It looks like the PCV valve tube crosses under the intake manifold to the top of the passenger-side rocker cover near the back of the engine. One of those two 1/2-inch tubes coming from the air duct/boot thing goes straight to the front of the same rocker cover - so I guess that's an air *inlet* for that rocker cover? It seems like that would be the most likely place for oil to get to the MAF - it comes into the air system only a few inches from the MAF.

EDIT-2: OK, the other tube goes to something called an "Air regulator" on the side of the engine.

Maybe I should try "blowing out" the PCV tube?
Yah, the VG engines weren't the easiest to work on, they were all PITA's in one way or another. Here's a diagram of the PCV system from the '93 SM, but I'm pretty sure it's the same back to '89. There should be a crossover tube from the other rocker cover as shown in red. Those tubes, the valve, the breather box, and the baffles in the rocker covers all need to be clear, anything plugged in any part of the system will cause oil to regurgitate in one or more places.

93 Path PCV System.png

PattiM
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Re: Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby PattiM » Tue Dec 21, 2021 8:54 am

GREAT!! Thank you. I've got to try all that!! I think this car was driven for years in Phoenix where especially high under-hood temperatures may have congealed oil vapor on the rocker arm cover internals and in the PCV system.

FWIW: I had the compression checked and it's nominal. Plugs look nominal. So I should find clogs in the crankcase breather system.

There's also this thing called an "Air regulator" that my Chilton and Haynes manuals don't really talk much about. But it doesn't seem to connect to the crankcase, so I don't think it's a suspect? (Oil can't get in that way.)

BTW: What manual is that? The Nissan shop manual?

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Re: Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby VStar650CL » Tue Dec 21, 2021 9:20 am

You're most welcome. Basically you're looking for anything that's blocking or obstructing any part of the PCV system. Like I mentioned, blow through the baffles to make sure they aren't sludged, etc. One thing to be aware of is that rubber hoses can delaminate and collapse on the inside without much evidence on the outside. If any of your PCV hoses seem to pinch or deform slightly when the engine runs, or you find a "soft spot" in an otherwise healthy hose, suspect a hidden collapse that's only happening when vacuum is applied.

The air regulator is part of the enrichment system for cold starts, basically the equivalent of a choke on a carb motor. People in warm climates often block or remove it without issues. It's only peripherally related to the PCV, but I suppose it could cause blowby issues if it was stuck rich and polluting your oil. That would probably cause blackened plugs and gas in the oil, though.

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Re: Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby VStar650CL » Tue Dec 21, 2021 9:23 am

PattiM wrote:
Tue Dec 21, 2021 8:54 am
BTW: What manual is that? The Nissan shop manual?
Yep. I couldn't find that section here in Nico, but it's in the EC section of the FSM.

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Re: Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby PattiM » Sat Dec 25, 2021 12:46 pm

VStar650CL wrote:
Tue Dec 21, 2021 9:23 am
PattiM wrote:
Tue Dec 21, 2021 8:54 am
BTW: What manual is that? The Nissan shop manual?
Yep. I couldn't find that section here in Nico, but it's in the EC section of the FSM.
Could you look in your manual for the two 1/2 inch diameter inlets on the air duck and see what they're connected-to? I found that the one closest to the air filter housing connects to the front of the passenger-side rocker arm cover, but I can't figure out where the other one goes (the one closer to the intake manifold).
It looks like this:
https://s3.amazonaws.com/rparts-sites/i ... a7a202.JPG
(in that image, the bent tube is the one nearest the air filter box)

I'm also not sure where the little 1/8 inch tube goes either...

Thank You!!

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Re: Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby VStar650CL » Sun Dec 26, 2021 8:30 am

I'll have to look on Tuesday, I'm not at the shop and don't have access to ASIST. If I haven't posted anything by around noon Tues, freshen-up this thread to remind me.

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Re: Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby PattiM » Thu Dec 30, 2021 10:56 am

VStar650CL wrote:
Sun Dec 26, 2021 8:30 am
I'll have to look on Tuesday, I'm not at the shop and don't have access to ASIST. If I haven't posted anything by around noon Tues, freshen-up this thread to remind me.
Thank You! I'd really appreciate that. I'm hoping that whatever is putting oil into the MAF sensor is what is causing this engine to run rough. It used to run rough only occasionally (once every couple of months for a few minutes). Now it's constantly running rough. Plugs and compression are OK - so it's some feedback in the engine control system... :(

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Re: Oil in air mass flow sensor? (92 pathfinder 4x4 V6)

Postby PattiM » Wed Jan 19, 2022 11:56 am

I replaced the MAF sensor and it didn't seem to make any difference. Something is making this engine run rough. Could it be something in that maze of rubber hoses and sensors?

Also, there's a high-pitched whistle that varies with accelerator pedal position - as if it's coming from the butterfly in the intake manifold, but it's so loud it must be coming from a tube somewhere. When the engine runs smooth, the whistle is there at idle; when the engine runs rough, it's gone at idle.

The engine always idles smoothly. Roughness increases with increased accelerator pedal depression.

To me, this says something to do with air flow - maybe a sensor isn't allowing the proper air/fuel mixture. (This is why I thought of replacing the MAF sensor.)


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