I need help with diagnosing a VI problem.
I have a 2002 3.5.
I dont think mine is activating, if i rev it up to redline and watch the valve it will move for about a half a second and then go back to stationary. It does this at about 5200 rpm. I had a dyno done a while back but the hp drops at 5200 instead of going up. i only ended up with 187hp and 201torque or something like that.
I have a homemade intake but when i did the dyno it was stock.
any help would be apreciated.

 

what kind of dyno was it done on? mustang dynos will typically show lower numbers. also i thought 2k2 had a lower cross point for the vi. i know mine is somewhere around 5100-5200 but ive been told 2k2 is lower like around 4500. if you dont mind doing this kind of testing, i would find a 2k2 with the same tranny and run him and see if he pulls on you in higher rpms.

 

Did you get a graph with your dyno? If so can you scan it and post it? Keep us posted on what you figure out, I'm afraid I have a similar problem, sometimes I feel a slight loss of power right around 4k, sometimes not. My problem is intermittent, so I can't put my finger on it yet. When it does this I can feel the engine is weaker and slower to rev to redline. Other times it pulls harder. Since it is so intermittent I have always just chalked it up to heat, but I'm starting to wonder..

 

I bet it is your VI. my dyno dropped at 5200 also on my '02 and I've acknowledged that it is my VI causing the problem..

 

i have been told the VI cross over for 2k2-3 is right around 4k. if you losing power at 5200 then something else might be the culprit unless the VI is working intermitently.

 

Somebody enlighten me please...I always thought 2k2-2k3's don't have variable intake. Variable valve timing, yes. But not variable Intake. Am I wrong here? Do 2k2-2k3's have VI?

 

okay...yes 2k2 2k3 do have VI activates at about 3000-3500 rpm, ive dyno'ed mine and watched that actuator do its job.

Tita6: i would have that hestiation TSB done to your car and make sure they change your MAF sensor. That 4000 rpm lag or loss of power, that happens intermittently, is one of my symtoms for a failing MAF sensor. It might get worse to the point where going over 4000 rpm will be very slow. Or your'll go into limp mode soon. I'll bet 5 bucks this will happen wihtin 6 months.

 

From all of my dynos, the switchover point for the Manual Tranny + VQ35 happens at 3300 RPMs when under WOT acceleration. It takes until 3700 RPMs to fully open.

 

Yes they do

 

Thanks for the info. I had the TSB done a couple months ago but they didn't replace the MAF. I had a 200-mile interstate drive today and I was able to repeatedly wind out 3rd and 4th gear full throttle; sometimes it's so weak in the upper rpms that it seems like I would never be able to redline 4th. Other times, up hills even, it pulls REALLY hard in that same rpm range. Totally intermittent.
I will see if I can convince those idiots, I mean, friendly service guys at the dealership to replace it under warranty. Man, I thought I was going to have to duct tape them to their desk and start pulling teeth with their pliers to get them to do the TSB. It was worth it though.

 

do the desk and pliers thing..it'll be alot faster. Faster getting your car worked on...or faster way to void your warantee...dunno. But i like that idea.

 

I guess this cross over point is true, i find that my car starts to pull real hard at about 3800RPMS (which at that point, the frankencar intake starts to really growl)..

ED

 

yeah, the switchover point is 3800 for the vq35. I know I've read though of a couple instances where people with failed VI noticed dropoffs after 5200 in the dyno though. I tested by disconnecting VIAS and running my car to find that there was no difference in performance than when it was connected.. It's a loose idea, but I'm going with it in hopes of fixing things.. David, if I find a fix for mine, I'll let you know. It seems we're having about the same problem.

 

Sorry had to re install my whole computer,
I do have a dyno chart, it was done in about jan-feb
i dont know how to set up a link though, i dont have a web site.
My brothers girlfriends mom also has a 2003 3.5 and it does the same thing with just clicking and then going back. I hope that that is how they are suposed to work, because if not then they are just using another thing to get sales.