My max doesn't seem to be getting enough fuel at higher rpms above 3500-4000 rpms and I was wondering if anyone has any thoughts on this. Would a bad oxygen sensor do this or would it affect the whole rpm range? Could this be more likely a fuel pressure problem, fuel pump or fpr?

 

What makes you think that it's running lean?

 

loose nut behind the steering wheel?












j/k

 

I don't know for sure but I have a new knock sensor and subharness installed so that rules that out. About the only thing I haven't changed is the oxygen sensor. I just installed a new WP Y-pipe and the car runs great until about 3500 and it really get hard to go any faster without standing on the gas pedal. I have good compression, 180-185 on all cylinders. I had both heads off about a month ago and had them machined along with the exhaust manifold surface to get a good seal at the head. All new manifold studs and the rest of the hardware to go with it. Replaced all of the valve seals to fix a problem with burning oil. All fuel injectors tested fine but one was spilling fuel so I changed that injector. I have a smooth idle now. Everything seems fine. Also, replaced upper timing chain tensioners. All in all more than $1000 worth of work. All problems fixed except it seem to really doesn't like to run above about 4000 rpm. Clutch was replaced almost a year ago with an oem Exedy, no slipping. I guess I am guessing right now until I can get the fuel pressure tested.

 

Oh yeah, rebuilt vtc's.

 

How about some ideas, anyone?

 

Where's your timing at? Try playing around with that maybe? I'm not sure but I think 3500-4000 is where your timing is supposed to be the most advanced.

 

Yeah, I played around with the timing a little but now I have it set back to stock ( not advanced at all). I also have new coils and ngk copper plugs. I cleaned out the IACV as well. It sound like I may be getting a little detonation at higher rpms unless the gas is on the floor too. I'm running 93 octane right now. Also, it did this before I did all of the work I just completed, I just assumed it was the knock sensor but that wasn't it.

 

Well,the little magic 3500 rpm number has me thinking along the lines of vtc's/knock sensor...Both these items turn off in the 3500rpm range..

Btw..It is possible to get a new knock sensor and be bad...Especially if they are dropped/treated roughly during shipping/stocking...

 

Here is a couple of pics from my last project.

Heads Removed:


Clean heads installed:


The heads looked awesome when they came back from the machine shop. I didn't get them ported or anything, it was just hard to believe they were the same heads. Thanks guys.

 

You are right. I hope that is not the case but I will recheck the knock sensor as soon as I get a new meter (broke my old one). Also, the vtcs are just rebuilt and I guess I could have screwed them up some way. Do you still have any spare vtc's I can rebuild?

 

Yeah i still have them...

 

What kind of muffler do you have in that picture by the way? How much for the vtcs?

 

The muffler is oem,i just put some s/s tips on it[got them at the pep boys on kingston pike rd. ]

$20 shipped on the vtc's...

 

I was saying in another thread about the knock sensor bypass thing http://forums.maxima.org/showthread.php?t=487528 something you can try untill you get around to installing a new KS. It's always better to replace it but it works untill you can. At least you can see if it helps your performance at all...

 

Do not do the KS bypass, you may ruin your engine! Its for lazy fools!

Have you checked your fuel pressure? It could be something as simple as the regulator or filter.

Also check your temp sensor connector, it may be corroded.

 

I don't plan on doing a KS bypass but I am going to check it again. The KS and the subharness are both new so unless the ks was damaged when shipped it should be ok.

 

As Indicated above, 4k RPMs is where the VTCs are activated ( or deactivated, I don't remember). Make sure the VTC solenoids are working and are getting current to activate and/or are moving freely ( pull, activate with battery and see if plunger moves freely). Did a previous owner short them?

 

I'm a novice, but did you check your Fuel pump regulator? Maybe its not allowing you the fule you need. My car is doing just as you described.

 

to check the ks, use the obd. the ks is the only code (i think) that doesn't give a check engine light. if its bad you get a code 34