A) I know this is a re-post but I have a slightly different take on this now.
B) I also know I have an i35, but more people go to the Maxima pages than the Infiniti - figured I'd get more help here.


OK, so I think I found a connection to my own car's issue with uber-power when running cold and "blah" when engine is warmed up.

The system that loops exhaust is what I believe is the culprit. Before the car can warm up, the engine loops exhaust through the pre-cats. When the engine is at running temp, the loop is shut off and exhaust flows freely out the tailpipe. (If this is inaccurate, you only know this because you understand the concept I'm getting at.)

Point being, I had a serious oil leak from a gasket that was leaking into the spark-plugs and several other places in the engine. This has since been fixed (to the tune of $1200) but I'm wondering if this could have had an adverse effect on the catalytic converter should it have absorbed a significant amount of oil. Is it possible that is is clogging exhaust gas and not allowing the car to breathe properly when running at operating temp.

Could this also affect shifting? The car seems to not be breathing well, so could this be what's making the car not know when to shift?

Ultimate Question: Could the catalytic converter be the root of all evil here?

 

plz dont tell me you paid 1200 to have a leaking valve cover replaced?

 

So what you are saying is that when your precats warm up they clog your exhaust system some how?? The reason for your cars sluggish performance could be many thing, air filter, fuel filter, old spark plugs, maf,

 

My car does the exact same thing. Although mine is a 6 speed, it still runs very sluggish when fully warmed up. Im not trying to hijack your post, but maybe if we are having the same issue we can figure this out.

 

If it's only when warmed up and less than 30% throttle & under 3k rpms primary o2's could be to blame.

 

It's innacurate, because there is NO device that loops any exhaust gas, it is always flowing through the pre-cats & main cats. Even on cars that do have an egr, but your's doesn't anyways. You should gut your front pre-cat anyways to save your motor, but I highly doubt it's the problem.

 

No. $1200 fixed a few other things as well - including replacing all of the O2 sensors and 1 or 2 coil packs among other things.

 

Its actually at wide open throttle when it hesitates.

 

try useing fuel injector cleaner. it sounds like you guys have fuel injector problems

 

What is your oil consumption like? If you are burning a quart more than every 2000 miles or so, I wouldn't be surprised if all three cats are at least partially clogged by now.

 

Knock sensor?

(Yeah, I know i claim that in every other thread too haha)

When it's cold the engine is in closed loop so it's ignoring the 02s and KS. If the KS is dead/dying, your timing will be severely retarded once it enters open loop and goes into safe mode.
It doesn't throw a CEL, so you'll never know. Plus, if the V isn't out of range you won't get a code, anyway, but it could be telling your ECU it's knocking.

Just another stupid thing nissan did (no cel for safe mode).

 

A) Yes. My car eats through oil like a mother.

B) Fuel injector cleaner never seems to do much of anything (in my opinion).

C) Is the knock sensor something that gradually goes bad?, or is it one of those things that is or is not working with no kind-of working of in between?

D) Thanks for your responses once again - I really do appreciate the help when it comes to getting Foxy to run better again.

 

Now that I think about it (and have done some more research on pre-cats) I'm becoming more sure that the catalytic converter is our issue.

As stated on Wikipedia: What is a pre-cat?
To put it quite simply, the pre-cats sit before the main catalytic converter in the exhaust system and help to keep the harmful emissions as low as possible for a short period after you start the car up.

This leads me to believe that because the car runs best when using ONLY the pre-cats, that it actually is the main cat that needs to be replaced. Although pre-cats can be clogged by oil leaks, so can the main cat, hence the lack of power when the car is using the main cat. Am I correct in my thinking here?

 

If the main cat is clogged then i would think it would run bad all of the time because exhaust is running through it all of the time, not just when its warmed up. Im thinking possibly a knock sensor because i use premium fuel in mine and it still pings a little bit.

 

I guess its not a bad idea to replace the knock sensor either way. It's bound to go at some point, but could the sensor really limit power that severely? I mean, on the highway, if I'm going faster than say, 60, I have NO top-end power for passing. Might as well be driving my mother's 1996 4cylinder Camry at this rate.

Also, the pre-cats reuse the exhaust until it burns up all the harmful emissions that build up when the engine is off - so yes, it always uses the main cat, but during the car's warm-up stage, not all of the exhaust is going out the tail pipe. What doesn't exit out the tailpipe is being constantly recirculated by the pre-cats (hence the "loop" I was referring to earlier). Meaning, there is more strain on the main cat once warmed up.

 

Im not sure about the loop your talking about. But yours does what mine does, at highway speed there is no top end for passing.

 

Sucks don't it?

 

yes it does... the car runs like nothing else when its not fully warmed up.

 

Exactly. I don't even remember when I noticed it was this bad because it was such a gradual change over time. I do remember being able to make the tires chirp at 30mph if I floored it. Now it barely moves. It almost feels like a less drastic form of "limp mode."

Hmmm... limp mode issue?... Naaw.

 

It could be the knock sensor.... going into limp mode

 

Yes, if the KS is dead there is NO power. Your experiences are IDENTICAL to what I encountered. Your mpg should be atrocious in the city, too.

 

Oh it is f***ing awful. I'm at 300 miles or less on a full tank.

 

BTW, forgot to tell you to stick a 470K resistor into the KS connector. Just follow the wire that comes out between the "V" in the block (the crevice). If your power is instantly restored, then that's your issue. I run mine bypassed like that.

 

Will a bad Knock sensor make it ping even tho i use 92+ octane? I notice it only pings after its been fully warmed up also, plus the hesitation... I have noticed i dont get as good gas milage than i used to. I used to get about 400 miles per tank. Now im lucky to get 300

 

Sounds like both our cars have the same illness. When I got mine, it had 34k miles on it and was getting almost 450 per full tank even.

Korn - As far as the resistor goes, is your knock sensor connected at all? And did you just connect the resistor to the + and - wires that go to the sensor?

 

Unplug the KS, fold the leads in half to make them thicker, then stuff them into the male connector and put some tape on it (just in case). I've ran my old car bypassed and my current one for several thousand miles. I do it b/c I don't trust the KS/ecu not to retard timing.

 

How much does a new sensor cost?

 

$100-$150 (Depending where ya buy it)

 

Should be less on ebay.

 

I dont really like buying stuff like that off ebay. I would rather pay a little more and get it at an auto parts store.

 

I bought a maf, KS and (for someone's 4th gen) injector, coils and KS. They were OEM as stated on the listing. I'm not paranoid when they have 99 or 100% feedback.
I don't trust auto stores and especially not junkozone. They like to box up used parts.