Extreme loss of power at 7100 rpm. Help needed!
 

Hey guys wondering if anyone is having problems with their sc stage 1 or 2, at 7100 rpm my boost and power just plummet. It is about *100 whp and +1 lb of *boost of loss every dyno pull and this always occurs *like clockwork at 7100 rpm. Seb and I are racking our brains trying to figure it out. We believe it's a software issue. I believe we are going to send the logs to uprev / Sam on Monday.
Please let me know if anyone has any knowledge / experience / advice.

Note: I have a gtm sc stage 2

It would probably help if you posted what type of SC kit you were using. Stillen, GTM, etc?

what's the last thing you guys messed with? pulley change, retune, etc

Updated OP with the kit I have.


This issue occurred when we swapped to the ark exhaust from
Invidia (which was more restrictive). We have also swapped the pulley to a 92 mm one but the sharp decline started once the exhaust was swapped out.

weird, i swapped my HKS out back to stock without retune and still runs the same.

did you retune it after the pulley change though?

He did a few changes as far is timing. But this sudden drop of power occurred before pulley swap and it was just after a new exhaust. I don't think the ark is a bad exhaust but I'm think something is just not sitting right in the tune/ecu. Not to mention that coop has one on his TT g37.

We went from 460 whp peak to 340 And then it shows to start building up power again

I dunno. When I first bolted on the ARK Grip exhaust there was no dramatic reduction, although from a nearly flow through GTM exhaust to that, I did not feel a gain. Possibly a slight loss, but not 100 whp, and they were able to tune it back up. We did not do a back-to-back.

That said, a drop of this caliber sounds very much like a fuel cut in some form. One of the better changes I made was when I asked Sam to raise the fuel cut (RPM limiter in effect) to 7800 RPM from 7500. The car wanted that extra and it used it. He did NOT want to go this high, but I assumed all responsibility.

Got a graph?

Coop

Perhaps your belt may be slipping

It would help if you data logged via UpRev so that you can determine what your MAF is reading , timing adjustments, as well as what your A/F ratio is reading. Two things come to mind; one that a coupling is leaking and a less restrictive exhaust or even a major exhaust leak could be the cause. But a 100 HP loss is staggering and I would expect something else related to the A/F ratio. First things is to datalog, as the data will always show the problem.

My tuner seb data logged the runs the maf is reading 4.0+ volts? Like 4.5

That sucks man. Hopefully it can get fixed. Let's hope the tranny can be able to hold that extra power. You might see a slight gain not much using a different pulley.

Well in only making 8.9 psi max

Is your transmission or torque convertor shot?
I assume you have a automatic transmission.

+ or - 0.5 volts on your MAF air flow is a huge difference. Expecially with the 3" intake piping. Plus if your boost is low, I would automatically be looking for a boost/vacumn leak in your couplings/connections or the boost relief valve could be sticking.

I doubt my trannys shot it shifts fine and no matter what hp or gear pull its always 7100 rpm. No matter if it's 350 who or 410 or 390 or 450

Anyway I'm confident in gtm uprev and my tuner. Im just hoping I can make this problem go away quicker

I'd have to agree with with what Zat Zuma is saying about checking for boost leaks. I've already had to retighten some of my couplers on my GTM Stage 1 kit. What kind of AFR's #'s are you getting?

I know of a guy on another car platform that had a very similar problem - supercharged setup, in the upper revs power just dropped off for no obvious reason. Turned out a plastic section of his intake was bending shut from the pressure at the upper RPMs, closing off the intake somewhat. I doubt that's your problem, but it's another thing to look for. Sounds like it has to be some sort of mechanical problem because anything tune-related that would cause that seems like it'd be fairly obvious to the tuner.

This would help us understand.

Coop

Will work on getting a chart Sorry didn't see your post earlier!

Hmm, that is very interesting, only reason I think it is software related is that it always happen 7100 rpm..Like the train is NEVER Late lol.

Sounds a lot like the SC belt is slipping to me. However, if it's at an exact RPM every time, I suppose that's less likely.

do you have a 7at or 6mt ??

if you have the 7At , you might have the same exact problem that I had for a complete year , no one was able to figure out what was the problem and it got worst by the time went

I had the luck of blowing my 7 AT at the drag strip and when they did the replacement they saw the flywheel which was badly cracked !!!

in the beginning when I noticied the problem it was at the beginning of winter , at that time we supposed it was some bad batch of winter gas.
but the problem never went away during the summer so we tried soo many thing.

by replacing the flywheel and tranny , I do not have that big extreme loss of power

mine was always like a clock at 6800-7000 and losing 40-50whp
then I started to have another other dip in power at around 4500rpm

Im only NA power with the 7AT ,

Ive seen a few other guys having a cracked flywheel .

I have a 7at, did you start to build up hp towards redline? mine dips then starts to build up right before redline.

look at it ,,,
2 line shown when I had the problem and fully tuned the best we could
and the better one is after I got the car back from the dealership (flywheel and tranny replacement)
Nissan 370Z Forum - Megan370z's Album: Dyno Day 28 Nov 2011 (Dynojet vs Dynapack 3000) - Picture

Looks somewhat similar but mines way more dramatic, BUt I don't suffer any loss till 7100 rpm, i actually gained 40 whp throughout the power band and about 30 peak tq and 40 midrange.

remember you are FI and im only NA ! so yeah the number seem more dramatic on yours but its about the same.

remember that dyno sheet show the last time I was fully tuned with the cracked flywheel that has been cracked for almost a year...
It didnt show much of any problem in the mid range at the beginning ,, only at 6800+

Hmm Ill keep an eye on it, hopefully thats not the case..

I hope so too. That's gonna be a fat repair bill

Ya.......... Funny thing is if that happened then Ill be wondering if it was from day to day driving or my SC... loL!

isnt 7100 about the time the factory rev limiter kicks in? that could be a clue to your problem.

I think it's 7500? 7600? Mines set to 7700 I believe

nop 7500 is.
he should not lose 100whp ike he does say .
something is going on somewhere

Was there a resolution to this problem? What's up?

Coop

He's parting out his car

lol so it must have been the tranny.

Sad that this seems to happen to everyone that runs into an FI problem.

Starting to wonder if the SC is putting to much tq to the tranny of the at7.

this is a good post, having the $ to support the kit will be needed.

Nothing for sale on the G37 forums. What's your intel?

Kosstick: Defend yourself! :icon17:

Yes. These are costly performance upgrades.

Coop

haha! here you go! :hello:

For Sale Biggest Part out EVER? *GTM SC KIT INSIDE* - MyG37

For Sale 2010 G37 S Coupe GTM STAGE 2 SC - MyG37

Lol guys my tranny is fine. I'm actually going to a runway event this Saturday. Just decided I want to save up for the gt500! As far as the power loss I believe it is a faulty maf sensor!

Love the assumptions but they are incorrect lol