RPM dip/cut-out in middle of power band - All Gears

[ExNep]

Recently installed (June): JWT Pop Charger Z-Tube 5/16 Motordyne Plenum Stillen Grounding Kit

Symptom (specific RPM depends on how open throttle is): at climbing RPMs engine will cut-out/back off for very brief moment

It's like the throttle/acceleration stalls, not dips.

So in any gear, at any throttle level, as long as the RPMs are climbing at a noticable rate, between 3250 and 4250 (depending on the gear it seems) the RPMs will suddenly stall for about quarter/half second then pop back up and climb as normal.

I have performed the following: Battery unplugged overnight Reset ECU/Throttle Body/Idle Learning following http://www.nicoclub.com/articles.php?id=356397

Any ideas? Sticking throttle body?Bad MAF Sensor?

Please also note : After completing these mods/installs all on same day, I get a whistling/sucking sound at mid rpms with mild throttle. No sucking sound on WOT or over 3500 RPM. Was told this is just the JWT working as it should. Correct?

Thanks in advance!

[Sentientbydesign]

Hmm...

I'd start with intake leaks. Be sure you reinstalled the vaccuum line on the bottom of the z-tube (was previous on the top of the "G" tube).

Also, check to make sure that the plenum spacer was installed properly. Over torquing the bolts, or leaving some out, has the potential to create an intake leak.

Out of curiousity, how is your idle? Is it at 650 +/- 50 rpms? Does is stay put after warm up, or bounce around?

My next statement is BIASED:

The Stillen grounding kits doesn't do anything...I am biased because I produce my own grounding kit. I have been contacted by a few forum members to replace or augment their Stillen kit because they don't experience any gains (usually, the grounding kits DO NOT produce power, they just make the car more responsive).

[ExNep]

Sorry for the delay, I have been casually ignoring this problem now it seems to be worsening and I have been noticing obvious power loss throughout the power band with the rpm needle bouncing throughout the power climb on hard acceleration.

Each gear that I am in has one point in particular (in RPM) which causes the largest lag/dip/jerk. 5th gear it is about 3400, 4th=3650, 3rd=3800 or thereabouts.

Most recently and most notably, why I am getting back on this, when the engine is cold and I get on the freeway at 3500rpm the car travels at 70mph, as the engine warms the speed increases steadily until the car hits 75mph where it sits, as usual. I really tripped out on this the other day. I set the cruise control at 3500rpm and was going 70, then while watching 71, then 72, then 73,74,75 and steadied. NOT NORMAL. (Cruise control has nothing to do with this, happens without it, just what made me aware of the issue)

I'd start with intake leaks. Be sure you reinstalled the vaccuum line on the bottom of the z-tube (was previous on the top of the "G" tube).

After reading this in August I checked the intake, tightened all clamps and nothing changed.

I also reset ECU and performed all related reset procedures.

Also, check to make sure that the plenum spacer was installed properly. Over torquing the bolts, or leaving some out, has the potential to create an intake leak.

It was installed, as far as I can tell, to spec. Torque wrench, nothing dropped, dinged, bent. Everything re-attached and sealed properly.

Out of curiousity, how is your idle? Is it at 650 +/- 50 rpms? Does is stay put after warm up, or bounce around?

Idle is dead calm. In fact, after I installed the kit, the idle was more calm than before. Still has not changed, sits and idles perfectly. Every now and again though you can hear a subtle gap or miss if you listen to the exhaust carefully behind the car.

Aside from returning the car to stock, one part at a time (grounding kit, intake, plenum spacer), is there anything that I can do to diagnose the issue?

Could it be a fuel pump issue which just happened to coincide with the parts upgrade?See FAQ 2 on this page http://www.nicoclub.com/articles.php?id=251205

Anyone out there willing to test out a MAF Sensor swap for 30 minutes?

All help and options are welcome.

[tollboothwilley]

Try removing your grounding kit.

Clean the MAF, could be dirty and getting sporadic readings.

[Sentientbydesign]

What a bizarre problem...

The specific, but varied RPMs make me think it's a load dependent issue.

Is there a decrease in velocity or decrease in acceleration at the cut-out point?

[ExNep]

The specific, but varied RPMs make me think it's a load dependent issue.

Load Dependent? have any resources to read up on this? or information you can share?

Is there a decrease in velocity or decrease in acceleration at the cut-out point?

the acceleration prior to the cut-out point seems handicapped, then there is a slight loss of power/acceleration, then after the cut-out it's like having boost on a turbo where the acceleration is nuts! If you run hard, where rpm's always above 4000, you never notice the problem or lack of power.

btw, one thing I have noticed, ever since I bought the car, that I attributed to driving habits, is that full throttle/pedal to the floor, feels like 95% power but backing the pedal off a bit gives 100% power.

[w8lifter21]

I'll bring this back from the dead to see if there was any resolution .

My G35 5AT is experiencing the same issues, only mods are an Injen CAI and borla exhaust.

-Under load, in the same RPM range, there is a sputter/miss and there is power loss.
-I could rev in neutral and no miss.
-Idle is a little low and if I were to very quickly push the gas to the floor and let go, the RPMs dip down 2-300 RPM before rising.
-Partial throttle/throttle response while driving is also sluggish