I have this weird hesitation that I haven't been able to track down.

It happens between 4k-4500rpms. Happens at part throttle and WOT. It's sometimes worse than others, but when it's normal to bad, the passenger can even feel it. It feels like the car kinda bogs down, then after 4500-4700rpms (~4700 is when the intake cam switches) it opens back up and seems to be ok, but maybe still not 100% to redline. It's been happening for a while and i haven't been in any other similar cars to compare, i'm not 100% sure, but it feels ok. Anyways, with that aside, here's what i've tried...
I've checked the cap, rotor, and wires. Replaced the plugs, put in a test pipe (thinking clogged cat?) and neither has helped. My MAF seems to be ok, as I've checked the voltage and it's still reading high enough at WOT at high rpms. I tried cleaning it too, but it didn't seem to make much of a difference. Cleaned out my TB at the same time too. MY TPS appears to be ok as well, it sits at .54 and goes up to 4.2 or so at WOT. doesn't appear to do anything funky at 4000-4500 rpms, nor does the MAF. My timing doesn't seem to go weird their either. Cleaned the filter on my HS CAI too. Oh, I replaced my fuel filter about a year ago with a huge 300zxtt one, i have another one to install, but i don't think that's the problem?

BTW, I have a Consult II right now to troubleshoot, but i'm kinda out of ideas.

I don't want to throw more money at it, if i don't have to... The TPS is rather cheap to replace, and I think there is another MAF I can use to test with.
Is there anything I'm missing?

Have you watched what the timing is doing during that drop in power? I have a really bad dead spot from 2000 - 2500 that pisses me off sometimes. I watched it with the nProbe, and the timign drops to like 5 degrees, then back to the 30s.

Run the car with the cams not switching for a couple days. Then let us know. I bet its the cams switching to early creating a flat spot.

The timing stays about the same, really doesn't change right there. That was my first thought too, but it doesn't appear to change at all... I need to keep monitoring it though.

Also, the cams aren't switching that early. I have a dummy light on the dash that lights up when they each switch and the intake cam doesn't switch until about 4700ish.

Drove with the consult plugged in on the way home too, don't see anything out of the ordinary, but i'll keep looking. I'm going to try that Seafoam cleaner through the manifold, hoping that there's maybe some carbon/crub built up that's causing the weirdness and the seafoam will clean it all out and make it run like normal again.
Eric and Steve, thanks for the input!

I guess I'll just let everyone know what I find....

try it with out actvating cams if it does it

i get it aswell without cam activation, but im running de ecu with ve injectors so i think thats whats wrong with mine. it goes rich all of sudden then a tad leaner on the A/F graph. I'll see what happens when i get the PFC tuned

I tried it with the cam solenoids unplugged, but it still feels weird right between 4000-4500ish. It didn't seem as bad, but then again, right after the hesitation there isn't the nice surge of power from the cams activating either. It just stays smooth all the way to redline. It's very strange... I'm gonna drive to work and back with the consult hooked up tomorrow as well.


Edit: HAHA! This whole time I've been forgetting about one thing... My Gen 3 HS Header has a nice crack in the primary where the 1 and 4 cylinders merge. I'm thinking this could be causing it? That may also help explain why it happens worse/more when the car is FULLY warmed up, say like after 10-15 miles+ on the highway, etc.. and not right when it first comes up to operating temp.... DOH!

When I was running my old Stillen 2nd-gen header, I had a nasty hesitation right around 3k rpm. With the HS Gen VI, that hesitation is gone.

Edit: HAHA! This whole time I've been forgetting about one thing... My Gen 3 HS Header has a nice crack in the primary where the 1 and 4 cylinders merge. I'm thinking this could be causing it? That may also help explain why it happens worse/more when the car is FULLY warmed up, say like after 10-15 miles+ on the highway, etc.. and not right when it first comes up to operating temp.... DOH!

I was going to suggest looking at the speed the O2 changes. But if you have a leak then that could be it as well.

The 02 seems to switch normally. Under normal driving it's always hopping back and forth.
Could an exhaust leak actually cause driveability issues? It's right on the weld where the 1 and 4 cylinders merge, so i'm thinking it may be messing up exhaust scavenging causing that issue? But it seems like a pretty big issue, for an exhaust leak, but i'm thinking it may just be where the leak is at? I just don't want to throw a lot more money at it, if I don't have to... I already have some set aside for a downpayment on a daily driver, the more I use to fix my car, the higher my new payments will be :(

It's right on the weld where the 1 and 4 cylinders merge

Is that before or after the 02 on your car?

Any air entering the exhaust would merge with the exhaust gasses that pass the o2 sensor, after the sensor. The leak would happen on different exhaust tubes/runners so it doesn't really affect the 02 sensor at all.

Well, it's definitely not running rich... plugs a bit on the lighter side. I replaced the fuel filter again last night and it seems to have helped a lot. I'll see how it does at lunch and on the way home from work tonight. I hope it was just a bad filter I installed before and that fixes it, but I guess we'll see.

its hard to tell if its running rich from the plugs. it burns lean at idle, so even 30 seconds of idling will burn the plugs back to white. you need to check the plugs right after running it.

the leak can cause faulty O2 readings and making it richen up, creating your hesitation. if air gets in, that makes the O2 sensor "think" you're burning rich. i will be installing my VVL in 10 days, with a G6, so i will let you know how it clears everything if you were unsure if it fits with A/C, etc. other than that, try getting that thing rewelded there, you're gonna want to fix it anyway.

have you tried turning the VVL down? try to set the VVL engagement before this hesitation and see if it goes away.

The fuel filter fixed 99% of the problem. I'm an idiot... but I did just replace it recently, so i just didn't think a HUGE 300zxtt filter could go bad/get clogged taht quickly. I will check out everything else still though too. As soon as our G35 gets back at work I'm taking it to the dyno (maybe as high as 350rwhp?) and I'll have a wideband hooked up to that, and i'll have someone drive my P10 over and I'll double check that while i'm there...

yeah, makes sense. i know you pretty much have to kill the motor at WOT and check the plugs then too. Luckily I live out in farmland right now, so i can sorta kinda do that :-)

I did mess with the VVL points and turned it off completely. Didn't really change anything. But like I said... stupid recently installed fuel filter kicked my ass this time... =) Oops.

The fuel filter fixed 99% of the problem.

Good news. I would reset the ecu and that might solve that last 1%

yeah, makes sense. i know you pretty much have to kill the motor at WOT and check the plugs then too. Luckily I live out in farmland right now, so i can sorta kinda do that :-)

What kind of farms do they have in AZ.

What kind of farms do they have in AZ.

Cactus :tongue:

The fuel filter fixed 99% of the problem. I'm an idiot... but I did just replace it recently, so i just didn't think a HUGE 300zxtt filter could go bad/get clogged taht quickly.
ever fill up when the truck is there? when they fill it up, many times our wonderful shit gas (AZ's gas is formulated very similiarly to CA's) puts a nice sludge on the bottom of the tank and when they fill it, it knocks the sludge loose. now, i am pretty sure they have filters capable of filtering this out, but you're putting your gas tank's sludge factor in their hands and their maintenance routine.

also, your own tank can sludge as well and this may get knocked loose. my mom's car ate 2 fuel filters before it was happy...

Flowers, hay, alfalfa, corn, cotton, cattle, etc.. There's a lot of agriculture here, they pull water from the rivers in other parts of the state for irrigation (a lot comes from the Colorado River). There is a lot of farmland here, contrary to popular belief it's not ALL desert, but lately all the farm land around the city is quickly being sold off to housing developers.