ReStylin

iTrader: (1)

So after getting the Momentum ST kit installed. I am still trying to iron out some problems.

Problems, at 2500rpm it has a lean spot, Ive been told its to do with the PMAS maf and that its fairly common.. I have most of that problem ironed out.

SOMETIMES up top, in full boost, it feels like its hesitating, I cant very much discribe the feeling other then that.. It doesnt feel likes it making full power, it very slightly chuggs/hesitates, (A passenger thought I was losing traction) but I wasnt. In my old S4, when it misfired it felt alot like this did. But I am not throwing any misfire codes.

Now Ive talked to a few ppl and the general consensis is that the MAF Location on the Momentum kit is
1. To close to the BOV
2. To close to the bend.

Now could this be a spark plug problem (Improper gap, the plugs that came with the ST kit were used, 1 stage colder NGK, my mechanic didnt touch the gap on them to my knowledge, I wasnt there and its sunday so I cant ask him, I am assuming they come pre gapped. But I also assume he checked the gap)

Would buying a Uprev GT maf fix this? could it just be the PMAS which everyone is telling me is a garbage maf. Should I move the MAF placement higher towards the TB?
How far away should it be from the BOV, Right now its about 3 inches away.
How far should it be from the Bend?
Below is a picture of where the placement of MAF is from the BOV and the bend on the kit.

Resmarted

iTrader: (2)

you basically said it yourself, might as well start with spark gap. You should have the tools for that anyway, and it is really easy to do.

konrad

iTrader: (15)

maybe its knock on higher RPM ? does uprev pull timing with knock?

ReStylin

iTrader: (1)

Thing that bugs me, it only happens sometimes.....

It didnt happen once when the car was on dyno, or getting tuned, or with the tuner in the car after we left the shop.... but 5 mins after leaving the tuner, it happened....

Sometimes if I turn off the car for a few seconds, then its fine for a few minutes. Then it returns... but if I pick someone up to show them the problem, it doesnt present itself haha.

binder

iTrader: (8)

you will load the car more on the street than on the dyno so that could be the case with a misfire.

I would start with the plugs. if they aren't iridium i would gap them down further. the -11's come with .044 gap which is huge unless it's an iridium. Even on the iridiums i gap them down to .030.

I never had a problem at 2500 with the pmas. i wouldn't change it out for the uprev maf just on that basis alone. It sounds like it just needs some tuning or it's osmething mechanical at 2500 rpm. Did you remove the fuel dampers and upgrade the fuel system? sometimes it does that when the dampers are removed.

and yes, the maf should be further from a bov or a bend. There is too much turbulence caused by those things and it will disturb the airflow the maf receives. I would make it at least a foot from those objects if at all possible.

ReStylin

iTrader: (1)

Would the MAF being so close to these things make a different when at WOT 4-5-6k rpm?

Boosted Performance

iTrader: (14)

A tial BOV is built so it opens at high vacuum (depending on spring selection), so no it will not be a problem at all while accelerating. Spring size is determined by reading vacuum at idle, while engine is warm.

Here is a Tial BOV spring chart:

http://www.streettunedmotorsports.co...ring_chart.jpg

kacz07

iTrader: (15)

Restylin, air velocity might not present the same airflow disturbances at lower rpms. Just a thought.

ReStylin

iTrader: (1)

http://www.youtube.com/watch?v=togdP...2&feature=plcp

Here is the video of it being tuned.

binder

iTrader: (8)

When WOT the tial won't be open so air won't be going out the BOV but the fitting and cutout for it on that bend on the exact same side of the maf right before it will cause the air to tumble and become turbulent as it flows past that BOV union.

It's just a bad idea to have a maf in an area that has so much disturbed air. The thing is there aren't other people (at least not a big number if they exist) that are having the same issues you are just due to the momentum kit. Therefore i'm not entirely sure it's a design flaw that a tuner couldn't get around if other people are making it smooth.

DaveJackson

iTrader: (5)

There is something to this, for sure. I think guidelines for flow control are something between 1.5-5 internal diameters of distance downstream before an element like a MAF is installed. I'd never thought of this before but with so little space, I'm surprised more people don't have problems. Like you said, it's probably something that a tuner can cancel out.
A "flow straightener" just upstream would probably work fine, but they cause a bit of a pressure drop. They are soooo simple. Essentially just load that section of tube with chunks of McDonalds straws pointed in the direction of flow until it's full and looks like a honey comb. The turbulent eddies get broken up and forced to point straight through the straws creating more laminar flow.
Unfortunately, without a joint right there, you can't play around with this and it would suck to melt a straw on the hot wire anemometer! I hope you figure it out, though!

djamps

iTrader: (1)

MAF is not the issue. PMAS is a perfectly good MAF in the hands of a competent tuner (in fact handles way more HP than the Uprev GT) .

2400rpm you say? Have you deleted the OEM fuel dampeners?

https://my350z.com/forum/tuning/4848...-what-the.html

binder

iTrader: (8)

That was exactly my question earlier. Although he is only having it in 1 spot not all 3 spots with those of us that were affected it still could be some fuel issues. For one spot i would lean more towards a tune issue than fuel but i wouldn't ever dismiss the idea completely.

ReStylin

iTrader: (1)

Stock fuel rail, and no fuel return. Dampeners were not removed.

Today I took out MAF and blew it off, plugged it back in and it worked perfectly for about 20 mins... Then problems started to resurface.

DaveJackson

iTrader: (5)

^ Careful blowing it off as those suckers are pretty fragile. Did you use the magic cleaner? Because that's the stuff you need to be sure it's clean. (I think it's just acetone but the "magic cleaner" is cheap enough that I'd just buy it).

ReStylin

iTrader: (1)

I used my mouth.

dj lizard

iTrader: (6)

hmmm wired ....... I had no issues with the maf nor anything else...
but it might be cuz I'm running an aftermarket rails/returnline/regulator..

binder

iTrader: (8)

see if you can borrow a maf from someone else.

if not then use some maf cleaner from the auto parts store on it. Also i would use electrical connector cleaner on the wiring connector to the maf.

ReStylin

iTrader: (1)

Noone has a PMAS I could borrow in the Ottawa area.

For some reason when I took the MAF out and blew in it, and then hooked it back up, it worked perfectly until yesterday.

djamps

iTrader: (1)

Could you post a screen shot of your fuel map? Could also be sh!tty injectors assuming you've swapped them out. Newer DW injectors have a new design and seem to not perform well at low loads.