Power valve screws, again.

[bbrandt11]

Hi, I'm a new member but have been lurking for a few years.
Just replaced a 1987 D21, V6, longbox that was my father's truck since new. My son and I restored it about three years ago and he drove it up until a few weeks ago.
It began wanting more and more attention and we decided it was time for retirement, it had worked hard for it's whole life.
We picked up a 2002 QX4, more suitable for his needs, space wise, comfort wise, etc. More like a grown up truck!
The QX4 is great except for a few minor issues that likely are more attributable to the PO's maintenance schedule and we are working these out.
The biggest concern is an acceleration issue, it pulls like a three cylinder.
At moderate to heavy throttle acceleration is slow, it revs to about 3500 rpm, doesn't shift properly and there is the distinct sound of detonation from the engine.
We replaced the spark plugs, with the OE NGK's, no drastic change, the old plugs were pooched.
As the throttle body has to be removed for the #4 plug, decided to clean it up as well, looking in to the plenum I noticed that the center two power valve butterflies were missing, there seem to be witness marks on the shaft that would lead me to think that they were there, once upon a time.
I found the threads regarding the issues with the screws coming loose and suspect that this is what has happened.
I am not too concerned that they are not there, I am really concerned with where they are and how far downstream they can travel.
The engine sounds decent, no random ticks or rattles that would make me think the screws made it into the cylinder or bent a valve but I do have to pull the plenum off just to be sure, and to Loctite the remaining screws and maybe even replace the missing plates.
If the plates came loose, could they make it further in to the intake and cause a blockage?
Would it cause the acceleration issue? More throttle would initially send more fuel until the O2 sensors read it rich because of the restricted airflow on perhaps two cylinders, then lean it out and the detonation would become severe?
Codes pulled sort of suggest the Cats are clogged, but reading the causes in the FSM of these codes it points to intake and/or injector issues as well.
I think that diligence requires that the intake be checked out regardless, other than that I will try a known MAFS and see if that changes anything.
We will work through this, just need to find a good starting point.
Any suggestions?

[Towncivilian]

Welcome to NICO.

Use red threadlocker (permanent) as there's no reason the screws would ever need to be removed in the future. Replace any missing butterfly plates. It is certainly possible for the plates to go missing somehow, see this fateful picture:



Here are additional threads about the subject:

Power Valve Screws Falling Out On 3.5's, 01-04 on the Nissan Pathfinder Off Road Association forums
Threadlocker On Power Valve Screws

Another new member also recently posted about his issue with a power valve screw coming loose, read here.

I'm not sure how one would find out where the screws ended up, thus I don't know what other advice to offer.

Does your QX4 burn any oil? What are the current engine codes?

It's unfortunate that Nissan has not validated that this is a potential issue with the VQ35DEs on our Pathfinders and QX4s. You can try calling 1-800-NISSAN1 to see whether anything has changed regarding their stance on this problem.

[bbrandt11]

Thanks for the response, I think I've read just about everything I could find about the power valve screw problem, and then some!

"I'm not sure how one would find out where the screws ended up."

I'd have to agree with that, there is only one way to find out where they didn't end up and that's the first issue I'm going to deal with.
By all accounts this is a common enough problem that there is no other rational choice, at least if you want to prevent any further harm.
I didn't know about the screw problem when I changed the plugs or I would have taken a closer look into the cylinders when the plugs were out.
The old plugs didn't show any obvious signs of being hit by anything loose in the chamber, they were well past when they should have been changed though by the roughly .055 gap ad deterioration.
I thought at first when I saw that two power valve plates were missing that someone had removed them for some reason I'll never understand, now knowing that this is common problem I just can't wait to see what I find in there.
Some of the related threads get in to the swirl control valve and the symptoms when it's stuck or malfunctioning, the lack of acceleration at anything more than granny throttle and hanging in gear which are both symptoms the truck has.
So if the two plates and screws did travel inward, if they got mixed up in the swirl control valves they could easily jam it up, I'm hoping that's what I find, both plates and all four screws, fingers crossed on this!
It starts well, idles well, no really inappropriate engine noise, maybe a bit of a pulse to the exhaust, revs freely but maybe a bit slowly to redline with no engine load.
When driven it's far more sluggish from stop to speed than it should be, getting to speed is as described by others as pulling a semi trailer with parachute attached, forget about trying to pass another vehicle unless they are headed the opposite direction and under heavier throttle the detonation is severe.
Last night I tried a know MAFS out of a friend's '02 Pathy, no change, had my son take the Pathy for a drive when we were done, when the tires broke loose his words were "Is this what my truck should go like? Holy S--t! I can hardly wait to get it fixed! On the other hand it may save him some money and points with it working the way it does!

"Does your QX4 burn any oil? What are the current engine codes?"

No noticeable burning oil from the exhaust, still too early to figure out oil consumption.
The codes point at the cat efficiency, so the clogged cat issue may be the problem, it would make sense that it could cause it to run this way but how do you tie that to the fact that it will rev with no load?
I think that making sure the intake system is as it should be is a given, that's tomorrow's task, then check out the exhaust system end of it.
On principle alone, a new fuel filter is in order as well, pretty inexpensive security!
What they teach in first aid, breathing, bleeding and bones in that order!
Just an analogy that does kinda apply here!

Any direction is much appreciated!

Bryan

[Towncivilian]

The fuel filter is a possible cause regarding sluggish acceleration, but that usually only impacts the ability to achieve higher RPMs.

Make sure the throttle plate is not partially open at idle. Perhaps try adjusting the accelerator wire according to page FE-3 of the FSM.

If the only current code(s) is P0420 or P0430, it's possible that the cat is clogged. I believe one way of telling is to check if the catalytic converter is glowing with the engine at operating temperature. See EC-338 for possible causes of the cat efficiency codes if you haven't yet.

You used NGK spark plugs, correct? Also, you could have simply removed the idle air control valve below the throttle body instead of removing the entire throttle body to access the fourth spark plug.

[bbrandt11]

"The fuel filter is a possible cause regarding sluggish acceleration, but that usually only impacts the ability to achieve higher RPMs."

I'd have to agree, and not just because you're the moderator!

"Make sure the throttle plate is not partially open at idle. Perhaps try adjusting the accelerator wire according to page FE-3 of the FSM."

Good suggestion, think I'll check the TPS as well and anything else that bears tinkering.

"If the only current code(s) is P0420 or P0430, it's possible that the cat is clogged. I believe one way of telling is to check if the catalytic converter is glowing with the engine at operating temperature. See EC-338 for possible causes of the cat efficiency codes if you haven't yet."

I read through that, P0420 and P0430 do point to the intake system as well as the manifold cats, just a matter of picking a starting point I guess.
Is the chance that the cats are so plugged that it would cause this?
This truck did pass an E'test within the last 1 1/2 years, could the cats go that quickly?

"You used NGK spark plugs, correct?"

NGK PLFR5A-11, I have an inherent bias toward NGK anyway from many years of Japanese bikes.

"Also, you could have simply removed the idle air control valve below the throttle body instead of removing the entire throttle body to access the fourth spark plug."

It's a new vehicle to me so the tips and tricks have yet to be discovered!
Beside that, how would I have ever found out all this wonderful stuff that I'll be dealing with tomorrow?
The throttle body was pretty scungy anyway, the screws didn't feel like they had been out in a long time so at least that was one task out of the way.
I'll post how it all turns out.

[Towncivilian]

Well, if one or more power valve screws went through the cat(s) then I'd think that could certainly cause problems... other potential causes are excessive oil consumption fouling the cat, or a lot of misfiring occurred at some point and thus a glut of unburnt fuel entered the cat.

I'm not sure whether there's a part number for the butterfly valves or the power valve screws themselves, I'm having difficulty finding either on Courtesy Parts' website. It's possible that the acceleration issues are being caused by the missing butterfly plates, since there is obviously no control of the two intake runners with the missing plates.

Good luck!

[bbrandt11]

Not a really tough job, just basic wrenching and swearing!
Removed the upper plenum, looks like the picture above, just 4 plates missing from different locations.
Removed the lower plenum, found 1 plate in #3 runner, 3 plates in #6, removed them with a magnet.
Not even going to guess why 3 of them ended up in the one runner!
Pull the fuel rails and intake, on principle alone, also easier to make sure all the swirl control valve screws are tight, they were.
Installed all the plates, Loctited screws, cleaning up everything to go back together.
The loose plates wore away some of the aluminum on the split in the intake ports.
Not thrilled about what the condition of the valve seats and faces may be but at this point that's the way they are, for now.
On to reassembly.

[Towncivilian]

Multiple plates ended up in one runner in a case reported in one of the threads I linked. As to how that actually occurred, I'm just as perplexed as you. Glad everything went smoothly.

It might have been wise to replace the PCV valve while you had the lower intake manifold off. Had I known that you were going to remove the LIM I would've suggested that. When I put threadlocker on my power valve screws, I only removed the UIM. The valves require a considerable amount of force to move, so I was not concerned about dropping a screw. Of course, removing the LIM might've been more comfortable since I had to crouch on the front of the engine to access all 12 screws, and I ended up replacing the PCV valve several months later so I ended up doubling the effort for nothing.

[CanuckQx4]

Is there a test to see if you have a failed PCV??

[Towncivilian]

Is there a test to see if you have a failed PCV??

Remove the PCV hose and put your finger over the opening, you should feel vacuum and hear a hissing noise at idle. Though this is just about impossible given the horrible location of the PCV valve and its hoses. If you have the PCV valve itself off the engine, you can shake it to see if it makes a rattling noise. If it rattles, that usually indicates that it's fine.

[bbrandt11]

The intake end of this got back together Saturday, no big problems, checked the PCV, it moves, would have replaced it if I had remembered to buy one before I started.
This didn't cure the acceleration problem, it's a bit better but not as it should be.
I ran out of time to change the fuel filter, besides the truck was dripping (we had some snow) and I really didn't feel like a salt shower.
The oil level was down more than it should have been three weeks after an oil change, topped it up and I'll see how quick it drops.
The truck has 282,000 Km (about 175,000 miles) on it so given that 8 screws most likely passed through I'd be surprised if some damage wasn't done.
I'll see what changes with a new fuel filter and then investigate the cats.
Hoping for the best, but I think I'll see what's around for a lower mileage engine, likely a sensible move.
Are there options other than QX4/Pathfinder engines, perhaps from the cars? Presumably the pans and oil pickups would be different but they can be changed.

[Towncivilian]

How much oil did you need to add? Did you fill to the full mark on the dipstick? I hadn't really realized the quantity of screws that fell! 8 is crazy. Looking for a lower mileage engine is a wise idea. As far as I know, nobody has swapped another engine into our VQ35DE equipped R50s yet.

[bbrandt11]

I put about 1 1/2 liters in, to the full mark.
I did my best to hunt around in the ports with a magnet, nothing came out on it.
I'm going to pull the plugs and have as good a look at the pistons as I can to see what kind of marks are in there, trying to scrounge a borescope to get a better look.
Hmm, ZX350 engine?
Likely cammed different, maybe different heads, intake and other bits but it would likely be built to be more of a revver than a torquer but I would guess the block would be the same.
As long as the engine comes out of something that has it mounted the same direction, the mounts would likely be different for a transverse mount application.
Probably easiest to find a wrecked Pathfinder/QX4.

[Towncivilian]

There are likely a considerable number of condemned Pathfinders & QX4s as a result of the recent strut housing recall, but nobody knows the fate of them yet. It would be ideal if they were able to be parted out - you'd no doubt find a decent engine that way.

So, about 1.58 quarts within 3 weeks? How many miles were driven? That sounds crazy excessive - anything more than 1 quart within 1000 miles is often deemed excessive by manufacturers. As you said, there's no doubt that there has been damage as a result of the 8 screws. Have you tried calling 1-800-NISSAN1 to see if they'll do anything at all? The answer will probably be no, unfortunately, but it doesn't hurt to try. Maybe if they receive enough complaints they'll look into the issue and possibly create a recall, but that's a long shot.

[Towncivilian]

Anything new to report?

[bbrandt11]

Haven't gotten back at it to figure anything more out.
Still has a lack of acceleration and the detonation noise or whatever it is.
It does run a bit stronger but far from what it should be.
The oil is down to the half way mark on the dipstick after 2 weeks, not a good sign but it could always be worse!
The plan is still to get a look in the cylinders and do a compression check, put the new fuel filter in, check the TPS and make sure the power valves and swirl control valves are actuating as they should.
Then get a temp reading at the front and back of the cats, if there is a big difference then loosen them up at the inlet and see if there is a power difference.
Step by step!

[bbrandt11]

Solved, so far!
Two new cats, it now has the guts that it should have and actually feels like it's breathing again.
Have to see if the oil consumption decreases and what else turns up.
Replacing the cats, not "that" bad a job, once you get the heat shields off so you can get at the nuts and bolts that attach the cat to the manifold and you don't break any of them, I only broke two despite liberal dosing with penetrating goo.
If all goes well, the screws that attach the heat shield to the cat can be removed, if you have snake hands and can get at them,
If not, there is very little space to get in to cut, chisel or torch the screws off of the top side of the cats, HUGE PITA!
The old cats were toast, not broken up but the front face of the media was eroded severely.
I'll post some pics soon.

[Towncivilian]

Great to hear it!

I had forgotten to mention that a possible cause of oil consumption is the passenger side valve cover baffle - read here. Of course, one can't discount the possibility of damage caused by the power valve screws, but one might as well rule out other options.

[bbrandt11]

The valve cover baffle is on the list, at least "most" of the major known maladies are dealt with now, I hope!
Just going to let my 55 year old body recover from doing the stuff it did at half that age!
Moral of the story - the more you do, the more you will be able to do, it just takes longer to recover!
I'm seriously looking at getting a 2 post hoist, I somehow end up "playing" with enough vehicles that working under them on jack stands is getting to be REALLY annoying, not to mention that the lack of mobility when you are on your back really hampers doing the work.
That's likely the reason I like working on my bikes more, you don't really have to crawl around under them!
Does it make sense that if the cats or exhaust are overly restricted there would be increased back pressure and there could be increased crankcase pressure as well?

[bbrandt11]

So the Q is whole again and working as it should, almost!
One 112,000 "new" engine, 2 new aftermarket cats and it's a real truck and decent to drive.
Just have to sort out why it's getting the swirl control valve code.

Bryan

[Towncivilian]

Glad to hear it! Undoubtedly you applied threadlocker to the power valve screws of this 'new' engine at some point?

Start with checking the swirl control valve solenoid vacuum hose; it might be clogged.