I was doing some pulls earlier today to tune for my new cat-back and I noticed that my VAFC-II seems to lose it's RPM signal once it goes above 6000 RPM.

This was in third gear, and it happened two out of three times. About 10 minutes ago, I tried to do some 2nd gear pulls, and guess what, the VAFC-II worked perfectly fine above 6000 RPM all four times. This problem seems to be more common in third gear.

The VAFC-II simply shows "0 RPM", and does not make any corrections.

Here is a picture of my air fuel curve, with the vertical line being 6000 RPM, at 14.09 seconds. You can clearly see the AFR drop to like 12.4 after the VAFC-II stops working.



Does anyone know what could be causing this? Anyone else have this problem?

I'm thinking that it could be interference in the wire or something...idk

Oh, and another thing that I noticed, is that the throttle plate does not close as the RPM's approach redline, as some theories suggest. I don't know if this has been confirmed before, but I figured I'd throw it out there. My VAFC-II get its throttle input from the TPS sensor directly, and it showed 95-100% all the way from 1200 RPM to 6600 RPM.

 

check your Tach wire. Make sure the ecu connector is securely fastened and all the tapped wires.

How much fuel are you taking off at 6000 rpm? 12.12 isnt bad, maybe you just need to take away more fuel. I believe mine is -6 around 6k-6.5k.

If you clearly see 0 RPM after 6k, then something is really wrong, and no i've never heard of this problem besides not being able to trim fuel after a certain rpm.

 

I actually have mine set to -6 at 6400+ RPM also. When the VAFC-II decides to work above 6000 RPM, it leaves me with a 12.8-13.2 AFR at 6000+ RPM.

I'm 100% positive that it's the VAFC-II, as I have videos of the VAFC-II next to my wideband during some pulls, and you can see the VAFC-II say "0 RPM".

You're probably right about it being something with the connectors. They all looked fine though, and I soldered them up properly and used heat shrink, so I have no idea at this point...

 

It can be a defective unit. I friend of mine just went through 2 bad ones and my cousin went through 1 before they got a good one.

Do you have the wire connected to the actual tachometer or to the ECU harness? Try swapping them then check if the problem is the same. If it is, you could have a bad vafc. The only time something like this ever happened to me was when my connection wasnt proper.

EDIT: one more thing. When this "cut" happens at 6k, does the car still rev out like its supposed to? or does it act like a 6k rev limiter?

 

It's very common with the SAFC-II as well, myself and SR20DEN have brought this up many times. We've seen it in both our logs and dyno, etc.

The SAFC2 just requires a reboot and everything is fine. I know when it freaks because the peak hold feature only shows 6k or so even though I know I was @ 7k. So yeah.

 

Ahh I see. The car revs out just fine, and my actual tach shows the proper RPM (+500).

I believe I tapped the tach signal right off of the ECU harness...

I guess I'll just have to deal with it. I just got rear ended today, so maybe I'll get a Technosquare reflash with the z33 CVTC maps and make myself a SSIM with some of the extra money (my dad owns a body shop)

 

PICS!

 

Doesn't look bad in that picture, but everything under there is pushed in. The guy's truck bumper went right above my rear bumper. I plan on getting the 2001 black tails and the replica AE rear lip. My dad owns a body shop, so I should be able to make a couple bucks off this whole thing...

 

Hm... I have to check mine out. Mine never did that. I have AEM UEGO and everytime I floor it I usually check the gauge to see if my a/f ratio is in good range.

 

fyi i had this issue in my old car, i needed to use an msd tach adapter, bc the piggy back ecy i was using lost the signal after about 6k , no matter where i got the signal from, weir, bc my current car is fine safc reads all the way through, could be some wire degragation of the signal but i have seen it before. tach adapter wired into the main coil power wire solved the issue