VQ35 Power Valve Riddle (w/ answer)

[IncidentalOffroader]

-OK all you VQ engine owners, see if you are knowledgeable enough to solve this riddle.

 

-The answer is in the second post.

 

-If you don't have time for riddles and want to cut to the chase, skip to the third post.

 

-Those who have been referred here by the "Highest Milage/Oldest VQ, Problems w/VQR50's" thread will already know the answer.

 

The riddle:

Kyle finally carved out a weekend for checking out the power valves in his Pathfinder. There was a manufacturing defect where some VQ35 engines did not have the valve mounting screws secured with thread-locker. The fix was simple, but labor intensive: remove the upper part of the intake and apply thread-locker to the valve screws.

 

As he eased off the clutch and slowly maneuvered his 2001 Pathfinder SE 4WD into his work area, he thought how lucky it was of him to have joined the NPORA forum recently. Otherwise he would have never known about this issue, and could one day have had a sudden catastrophic engine failure. In fact, some screws may have already fallen out, and the implications were just too disturbing to consider. Yet again, it was quite possible that the screws were adequately secured and there was never any problem, in which case ignorance would have been bliss. With mixed feelings over the value of having too much information, along with a feeling of suspense over what he would find, he shut off the engine, shifted out of first gear, set the handbrake, and started the task.

 

Kyle worked methodically, guided by the Nissan FSM and an excellent write-up of the

procedure by BowTied

. He had never gone so far into this particular engine, so he went slowly. But he was having fun. He also thought of the money he was saving by doing the work himself. Finally, he unscrewed the last bolt holding the upper intake and lifted it. The moment of truth had arrived: would he see the power valves all securely held in by their screws? Or would he see missing screws, or even missing valves, like one of the more shocking photos that was on NPORA? He looked down at the lower intake ports where the power valves were and was astonished to see....

What did Kyle see? See the next post for the answer.

[IncidentalOffroader]

Answer: Kyle saw nothing. There were no power valves in the lower intake bypass ports.

 

Apparently there are no power valves on VQ engines mated to manual transmissions for this year of Pathfinder. See the next post for supporting info.

 

Mentioning the clutch and shifting from first gear were the clues to realizing that Kyle's Pathfinder had a manual transmission.

 

This story is based on a true event. (Does anyone need any thread-locker compound?)

[IncidentalOffroader]

There are no power valves on VQ engines mated to manual transmissions.

 

The screenshot below is from page EM-10 of the Nissan FSM for either the 2001.0 or 2001.5 Pathfinder. It shows the upper (8) and lower (2) parts of the intake manifold collector, and the throttle body (10).

The "Variable induction air control valve control actuator" (14) controls the power valves in the "lower intake manifold collector" (2). The actuator has a note, "A/T", which I take to mean automatic transmission. (If you have a VQ/manual transmission of another model year, you should double-check with the corresponding page in the proper FSM.)

 

Here is a picture of a VQ in a 2001 Pathfinder SE 4WD with a manual transmission.

The plastic cover has been removed and nothing else. Compare this photo with BowTied's first photo in http://npora.ipbhost.com//index.php?s=&amp...st&p=277553. In BowTied's photo, the power valve actuator is the round thing with the hose at the lower left. In my picture above, the actuator would have been in the red box. The missing actuator is consistent with the FSM, and implies that there are no power valves.

 

Here is definitive proof: a picture of the lower intake manifold collector.

Compare this to BowTied's 7th photo in his write-up. There is no trace of power valves having ever been there. There even isn't a crossbar for the valves to mount on, nor holes in the manifold body for the crossbar to run.

 

Hope I've saved other VQ manual transmission Pathfinder owners some time and worry.

 

An unresolved question: is there a different part number for VQ35DE engines for manual transmissions? This would be relevant to anyone wanting to do an engine or transmission transplant.

[wspinks]

Thank You!!!!! I was going to do this in the coming weeks, before a long road trip in June. You saved me a lot of time.

[FUELER]

hahahha great post!

[keelhaul]

I tore my 2002 5-speed down to attempt the fix last summer and found some butterfly valves that I thought were the powervalves. I took off the top and bottom plenum chambers(no valves within), and way down in the intake manifold were 6 butterfly valves with 2 screws each. I now see that those were in fact the swirl control valves and not the powervalves as depicted in Bowtied's pictures? Since I did not have the intake manifold gasket and did not want to remove the fuel rail I just counted screws, cleaned out the intake plenum and reassembled, and all the while feeling that I failed in my objective to locktite the powervalve screws. I guess since I don't have them I didn't fail! I wonder if the lack of the powervalves in the 5 speed VQ's is part of the 10hp difference between the MT and AT engines.

 

BTW great post and links

[BowTied]

Great post! Thanks for kind comments on my write up. I am new pathy owner and myself didn't know there was a difference in the engines based on MT/AT, cool to know!!!!

[02silverpathy]

Sweet! these are the pics without the cover that I couldn't find! Look how they capped all the vacuum lines that operate the actuator...but all the lines still run right to it! Great Find!!

 

So now Riddler, Riddle me these!!

 

Is this really why the HP is greater but the TQ is lower in a Manny....and why didn't Nissan just make a different intake for the manual or why on Earth did they not just leave the valves in?

 

Your super find gets me thinking all of the ????'s

Edited April 17, 2008 by 02silverpathy

[GhostPath]

Yes, this is why the power ratings are different. The engine is drawing most of its air through the short intake path. Good for HP, not so good for torque.

 

Why make a different manifold for a variant that's going to be a small percentage of sales? The vast supermajority of Pathfinders are going to be automatics. Better to save money by using the same casting and not machine it for the power valves it can't use.

 

As for why the power valves aren't there - IIRC, the opening and closing of the power valves is dictated by input from the transmission control computer... which manual transmission Pathfinders don't have. Why go to the added expense?

[IncidentalOffroader]

Ghosty, your explanation makes it all come together now. Though I'll have to take your word for it on the length of intake path vs. HP vs. torque... that's way beyond the scope of my knowledge!

 

Who knew that owning a VQ R50 would be such an exercise in manufacturing forensics?! Add this to what I had to go through with the ignition coils.

[vq35]

WOW! this is something I posted (the diff between auto and manual engines/hpvstorq/tow capacity) at NICO about a billion times and I happen to join this place and BAM! i get the answer, great post by the way and very helpful!!!

 

Now, HOW the hell do i convert me manny 01 se 4x4 into auto set up without catastrophy and has anyone done this? Is it feasible? and possible cost of parts n labr??!

 

any help would be Greatly appreciated

 

thanx

[navygz19]

Now, HOW the hell do i convert me manny 01 se 4x4 into auto set up without catastrophy and has anyone done this? Is it feasible? and possible cost of parts n labr??!

 

 

thanx

 

I would say you'd be the first, as far as I know.

[laxman0324]

WOW! this is something I posted (the diff between auto and manual engines/hpvstorq/tow capacity) at NICO about a billion times and I happen to join this place and BAM! i get the answer, great post by the way and very helpful!!!

 

Now, HOW the hell do i convert me manny 01 se 4x4 into auto set up without catastrophy and has anyone done this? Is it feasible? and possible cost of parts n labr??!

 

any help would be Greatly appreciated

 

thanx

You want to go to auto? I think you could find someone somewhere who would love to have a VQ35 manual and trade you their auto...If you wanted a VG33 auto Id be all over it :tonguefinger:

[vq35]

I re read everything and guess i would be lucky to just stay with me manny (as i just noticed that the control for these power valves is dictated by the auto tranny computer) so feasibility is out the door!!

i guess now i have a different question and this is - does anyone make a cam geared for more low end torq!!?? I also noticed that these bloody power valves are responsible for the HUGE towing difference between the two (i think around 1500 less for the manual!!)

 

im planning on cat back and KnN CAI, but thats minimal (altho nicer sounding) and i want MORE TORQ!!

ANY HELP WOULD BE APPRECIATED, THANX

[inanima]

This is really good to know. Was dreading having to deal with this. One more (or less as it may be) reason to keep the PF.

'01 Manual owners unite!

[flash45]

I was going to consult the local dealer about this too seeing as my mileage was getting to that point too. I was hoping to hear some knowledgeable news from them but this is much easier! thank u thank u! *Whew!*

Icing on the cake for preferring manual transmission...

[LovemyPathfinder]

thx guys! u saved me a lot of time and money!

[BowTied]

I re read everything and guess i would be lucky to just stay with me manny (as i just noticed that the control for these power valves is dictated by the auto tranny computer) so feasibility is out the door!!

i guess now i have a different question and this is - does anyone make a cam geared for more low end torq!!?? I also noticed that these bloody power valves are responsible for the HUGE towing difference between the two (i think around 1500 less for the manual!!)

 

im planning on cat back and KnN CAI, but thats minimal (altho nicer sounding) and i want MORE TORQ!!

ANY HELP WOULD BE APPRECIATED, THANX

 

 

I don't think the power valves dictate the towing capacity, it is more about the strength of the cltuch and manual trans (and likely warranty claim mitigation).

 

You might find that you can get the low end you want by changing your gears instead of the cam. THe VQ has dual over head cams (4) and they are variable valve timing I think. Not something to mess with IMHO.

 

 

To you guys who are happy to find this info: go spread the word that NPORA rocks!

[colinnwn]

I don't think the power valves dictate the towing capacity, it is more about the strength of the cltuch and manual trans (and likely warranty claim mitigation)

This is exactly right. The manual tranny is plenty stout. Nissan probably put a less aggressive clutch in the Pathfinder to make it easier to drive, but that also means it slips more off a standing start, which is bad for towing and longevity. I'm pretty sure a previous owner put a really grabby clutch in mine, because it is a bear to drive smoothly without clutch chatter when empty, but driving it while towing is silky smooth.

[Alkorahil]

Incidental is correct.....

 

VQ35DE/AT

14010-4W10A MANUFACTURING DATE 06/01-END

 

 

VQ35DE/MT

14010-4W020 MANUFACTURING DATE 01/00-END

 

 

Two different parts based on if it is manual or auto.

In addition, 14010-4W10A supercedes to 14010-4W10B. I have read about this issue many times on here, yet we have never had a vehicle in here with this issue.

[vanuatoo]

I have read about this issue many times on here, yet we have never had a vehicle in here with this issue.

 

And how many vehicles did you have approximately?

[MY1PATH]

Though I'll have to take your word for it on the length of intake path vs. HP vs. torque... that's way beyond the scope of my knowledge!

I belive it works like this;

Air goin into the intake has a "charge", it doesn't want to stop going, so when the air hits the closed valve that charge turns arround an goes back up the intake runner where it charges another cyl or turns arround again when the valve opens again. A short runner means less distance/time b4 that(small) charge can return good for higer rpm and HP(more small charges). A lonng runner means more distance/time and also the length of the runner allows for a greater charge better for lower rpm and forcing allot of air in the the cyl to generate torque.

 

with that concept in mind, for the non-power-valve VQ's, could a block of plate installed between the the upper and lowere short-runner side to taget torque with no adverse effects?

I assume in a condition where both long and short runners open the charge would take the shortest path in but either path back thus lessinging the "charge" effect.

[jjonez]

This 7 year old thread really put my mind at ease. Still one question though: swirl valve screws. I have no idea what a swirl valve is but apparently some people also threadlock these screws when doing the power valves. Is it even worth the effort to do this since I don't have power valves in my 5-speed? Thanks.