Ok I've owned this 02 6speed SE for about a month. Aside from some tiny quirks here and there, I've been having an issue with the performance. For a while it was intermittent, now it seems as if the car is "stuck" like this.

When accelerating the rpm's increase, but the power is just not there. The car used to spin the tires effortlessly and used to really open up after 4k, now I have to dump the clutch at higher rpm's just to get anything out of it. Even if I try to keep the rpm's up when changing gears, they just don't want to.

No Check Engine lights, and I've put about 1500 miles on it. The car now has 51k and change. I was thinking maybe plugs, especially because I have a tendency to upshift early when crusing???

I don't know I'm stumped. Any help would be appreciated.

 

Well, the stock plugs are NGK platinum tipped and are usually good for 100,000 mi..

Have you changed your air filter, pcv valve, used fuel injector cleaner, are you using a lower grade fuel?

 

sounds like it might be maf to me

 

Any smoke from exhaust?

With no engine codes, I'd think this is likely due to bad Pre-Cats. Do a pressure test on the cats

 

out of curiosity, what is the pressure test on the cats? vacuum gauge? any decent scanner will be able to tell engine load, and with bad cats the load will be fairly high at idle, i saw 21% load at idle IIRC

 

^^ Exactly what I was going to say. Hopefully member djf240 will chime in because he had the same symptoms and after replacing 2000+ worth of parts, he realized it was clogged precats.

 

No smoke, air filter is fine, pcv fine, no additives, I've filled up with 93 and 87-no difference. Do you guy's have a method to clean the MAF on these, I haven't touched a MAF in 10 years. As far as the cat's or pre-cat's being clogged, would that really be possible at just over 50k miles?

 

Here you go: http://forums.maxima.org/5th-generat...10-w-pics.html

 

http://lmgtfy.com/?q=checking+exhaust+back+pressure

(Not meant as a 'search noob' joke, just a way to show you some different info)

And 20% engine load at idle is normal. I've read that a few times lately on here and haven't jumped on it, but it is. Any of you can go out and fire your cars up and look at it, it'll be around 20% without clogged cats.

"load" of this engine is calculated based on MAF value primarily, and if the Air cant get out of the engine because of plugged cats, then it also can't get IN.

If it can't get IN, then there's no extra air flowing across the MAF sensor to 'indicate' this 'load' that you're referring to. So even though the engine may be 'stressed' or 'loaded' because it can't pump the air out, the way you're checking 'load' in this manner won't show that.

In short, checking 'load' with the OBD2 style testing is useless for this situation, in my experience. I could be wrong. But I CAN tell you again, that 20% is normal load at idle.

 

my denali shows 2% load with the same scanner

 

Does your denali Use a map sensor or a MAF sensor?

My G35 reads 20% load and it doesn't have any cats, at all.

 

the truck is maf, and it has 4 cats. i also tested the car with a vacuum gauge, i got just under a 2 psi variance. but the maxima was getting the 0420 and 0430 codes so i know it had bad cats. ill check the corrected idle load % next time i go to mess with the car

 

Might be a good idea to get the baseline.

My scanner reads 20% load at idle on the Vq30DE-K with all stock Exhaust on but VERY low miles (cats not plugged, no way).
My RWD VQ35DE (G35) with NO CATS at all also reads 20% with my code reader at idle.

Good info to know, either way. Maybe the scanners calculate load different, who knows.

 

There's a predisposition on this forum to suggest mysterious problems are caused by "bad pre-cats". While admittedly (and personally ) an effective rationalization for gutting the pre-cats, or getting headers, I believe that diagnosis is too easy and often wrong.

I'd check to make sure your VIAS valve is still functioning. Or that a load of leaves or other debris isn't blocking your panel filter.

2-cents

 

Oh Rochester, there you go again making logical and rational sense.

Although, when OP stated it doesn't have power and doesn't want to go into and stay in the high rpm range...that *does* at least suggest that clogged (bad) cats could be a potential issue, yes?

 

Netflix keeps rebuffering during old episodes of Top Gear. I'm thinking it's my pre-cats.

 

Yeppers

 

Im assuming the VIAS valve is the little thing on the end of the intake manifold? I actually think that might be the issue. When the car first started driving poorly, I popped the hood and did an quick check of everything and manually opened and closed it. The car drove much better.

Is there any way to check if the valve is functioning properly? I also opened and closed it while the engine was running, and nothing changed.

 

If you can open the valve manually, then allow for the spring to close the valve unencumbered, then the valve mechanics are likely fine. And if you don't have a CEL for the solenoid, then that's likely fine, too. If there were a vacuum leak between the solenoid and the valve, then you would likely throw a CEL. If there were a vacuum leak between the UIM and the vacuum tank, you would (probably ) throw a CEL. So maybe the vacuum tank has a small leak, or the line from the tank to the solenoid.

All of which is total conjecture predicated on looking for your problem at the VIAS. I'm not a mechanic... this is just opinions based on personal research for my old car.

With all the crap necessary to support a vacuum actuated valve, you got to wonder why Nissan didn't design the VIAS with an electric motor, rather than a vacuum and a spring. But then, I'm also not an engineer, LOL.

 

BTW, for virtually the cost of shipping, you could purchase a VIAS Block-off Plate (BOP), and remove your VIAS valve entirely. It's not an uncommon modification, although usually something done in conjunction with other power mods that compensate for the loss of low-end torque.

 

Perhaps I'm misinterpreting, from the OP, it sounded like you have a serious lack of power. Not just a few HP.

VIAS stuck, not working, etc, will not cause a drastic power loss, we're talking about maybe 2-10 HP at most, not something you'd really notice unless it was coupled with some other issue.

Again I might just have mis-read the OP. If you're talking about nit-picking levels of power loss then there's a pile of things it could be.

 

Definitely a big loss of power. Looked into the BOP mod, not really trying to mod anything until I can have the car driving without issue for at least a month! Still driving, like crap, sometimes worse than others. Nowhere near what the car was driving like originally.

 

at first startup of the day, when the engine is cold, does it seem to be better, and get worse the more its driven?

 

Well then it's not the VIAS, like Tuner said... "big loss" doesn't apply to VIAS issues on the 5.5 gen.

 

Are you able to take a WOT video with gauges in view from stop to 60 mph (ish)?

It would be nice to get a more accurate idea of 'how much' power you're down. Can you elaborate?

Signifigant power loss with no CEL on this car is most likely the pre-cats, Rochester is right, it's been thrown around as an 'answer all' lately, reminds me of the "it's your MAF"
BUT that could be attirbuted to age of the car and general mileage ranges on average. It's not strange for issues to pop up in bulk on an old car like this. IMO, pre-cats need to be tested, not just 'assumed'. Especially if you're not doing the work yourself.

Another cause would be excessive blow-by (Worn rings). This will show on a compression test, and that's another test I'd recommend. Before or after pressure testing the exhaust.

 

Like I've said before, the car just hit 50k, I really doubt it's blow by, and I find it hard to believe that the cat's are clogged as well with such low mileage. The car is in almost pristine condition. Driving it again tonight it just isn't what it was, the rpm's climb, but the speed(mph) isnt there. It's still "quick" but before it was a beast.

I would also be doing the work myself, as I am a mechanic, I just don't work in a shop anymore and I'm not up to date on alot of newer cars, and my tools are basic. I'm going to clean the MAF on my day off tomorrow and see if that helps.

 

A good mechanic never assumes anything

 

Maybe one of your rear calipers is seized, where you're ripping up a pad & rotor and don't even know it. Or your TB isn't opening up like it should.

Or maybe I should just shut up and find my "not a mechanic" T-shirt.

Anyway, good intentions and all that.

 

Cleaned the MAF sensor. No difference. What do you guys think about disconnecting the battery to possibly reset?

 

A fuel problem maybe? In tank filter?

 

I think I'm going to stop giving you advice because you're not taking it.

 

Thanks for your help, but what advice have you given me other than check the cats? I don't have a scanner, not quite sure how to check them, and doubt they are clogged at just over 50k on the car. I've owned vehicles with clogged cats before and it doesn't even drive like that. No I can't take a video at WOT of the guages and hold the steering wheel and shift at the same time, I don't even have a video recorder.

I mean damn is this one of those forums where if you ask for advice or help, it means you don't know anything?

 

If I'm Assuming you've checked the most basic of things, because you're a mechanic (Air filter, spark plugs, vacuum leaks, exhaust leaks)

THEN, I'll recommend again:

1. Pressure test Cats
2. Compression Test
3. More info.

I know you said you can't do as I suggested with the video camera, that's fine. As a mechanic you must understand, to properly diagnose a problem you need to first understand the problem. If I get a vechicle to work on and all I know is: Customer says "lack of power".
Then I'm going to road test it before ANYTHING. I need to know how bad it is, where the power is gone or if it's the whole range, under what engine load, temperature and condition, and so forth.

Otherwise the only thing I can do is simple Low Power checks, Which I already listed for you above. All the stuff in brackets and Compression and Backpressure tests.

Other than that I need to check O2 Sensors, Knock sensors, and so on.
It's almost 2013. You're a mechanic? You should have a scantool, period. You can't work on/diagnose cars properly without it anymore, period.
Smart Phones have "free" (under $5-10) applications that will turn your phone into a $80+ Scanner. All you need is the Bluetooth USB port from Ebay for under $20.

Disconnecting the battery is a good idea, try it. But even if it fixes it, it doesn't tell you much. And the issue will likely come back. The only case this may be untrue is if a sensor threw the car into a lower-level Limp mode, and that sensor doesn't act up again for quite some time.

Again, worth a shot, just make sure you leave it for at least 24 hours.

 

Thanks. In my defense I haven't worked at a shop in a decade, and don't own a smart phone. I don't work on or diagnose cars for a living at all, I just keep my own vehicles running(mostly carbureted) and do whatever mod's to them that I can. My good friend who is a mechanic doesn't have time for me right now. I do have a compression tester, but I'm not going there yet.

As far as checking the pressure on the cats, like I said I'm not sure how to do it. Last vehicle I had bad pre cat's on melted the DPFE valve, then blew the hose off the new one.

Like TriniMax said, is there a fuel filter on these anyway?

Thanks for all the suggestions, the help is appreciated.

 

Yes, it's very inexpensive, and accessed under the back seat, integrated with the in-tank fuel pump. When purchasing it from Nissan, be sure to call it a "fuel strainer", not a fuel filter.

Here's one of the best write-up on replacing it: http://www.shiftice.com/fuel_filter.html

 

I did get the impression that you were an 'ol boy' with this stuff. Nothing the matter with that at all, but electronics run cars, they have for a while now. So if this is something that is beyond your reach or 'want' to understand that's fine too, but if you're working on anything post 1995 you need to either pass the buck or 'learn up',

No offense or insult meant, it's just the way cars are now. And if it's not precats or compression or vacuum leaks, it's most likely electronic.
But if you refuse to do vacuum, compression and precat tests, then I really can't help very much more, maybe someone else can.

And I already posted the Google search link for how to test Backpressure, TWICE.

 

It's a car forum, so anything can happen. Good advice, bad advice, helpful, snarky, funny, rude... all the above. Filter out what you need, and try not to invest too much emotional attachment to the process.

As for Tuner, he's a smart guy who knows his way around these cars. So if you can get his attention (when he's sober ), it's usually good advice.

 

*Update* Haven't had much time to work on the car between my work and life, yet I decided to run 93 octane through it. The lack of power started getting ridiculous and got worse the longer the engine was running. After a few tanks full of 93 octane the car seems to be back to normal. The car is fun to drive once again!

 

Knock sensor?

 

Clutch?