cannot get 22 psi in lower gears

GuyGuy · Sep 6, 2009

So it's been a while since I rebuilt my motor and everything is good except for boost.
I've rechecked it all today and I can only get 16psi in second, 18 psi in third and 20-22 in fourth and fifth gear.
can't figure it out.
no boost spiking at all.
could it be that I am underfueled with the Sprint 764's and the low comp. pistons.
I've removed the N239 and unpluged it.
the check valve flows in the direction of the arrow.
any thoughts would be greatly appreciated.

Farfromovin · Sep 6, 2009

A- you have some old outdated Unitronic stage whatever the heck map.
B- lower compression

I'm not sure how those two go together very well. I suggest you contact your local alligator dealer or send your ECU off to a real tuner.

aNUT · Sep 6, 2009

Do you know how much boost is being requested? If it is indeed 21psi, and you're underboosting, this is typically caused by insufficient vacuum to the N75. How much vacuum do you have at the hose that goes into the 'vac' port on the N75?

Also, because you're not running your N18 and N239, it is not necessary to route vacuum and vent lines to and from them. Just run vacuum to the N75 and vacuum reservoir.

GuyGuy · Sep 6, 2009

Farfromovin said:
I suggest you contact your local alligator dealer or send your ECU off to a real tuner.

That part I agree with you 100%

GuyGuy · Sep 6, 2009

aNUT said:
Do you know how much boost is being requested? If it is indeed 21psi, and you're underboosting, this is typically caused by insufficient vacuum to the N75. How much vacuum do you have at the hose that goes into the 'vac' port on the N75?
Also, because you're not running your N18 and N239, it is not necessary to route vacuum and vent lines to and from them. Just run vacuum to the N75 and vacuum reservoir.

Can I check the boost requested with vag-com? I don't have a vacuum gauge to check how much vac I have going to the n75

mojogoes · Sep 6, 2009

Yes i would say a combo of tuning and mostly lack of fueling!

oldpoopie · Sep 6, 2009

check actuator rod and stop adjustment.

aNUT · Sep 6, 2009

Use VCDS to check specified boost. Engine->Measuring Blocks->Group 011

Farfromovin said:
I suggest you contact your local alligator dealer or send your ECU off to a real tuner.

Looking to tuning to fix problems is foolish if you haven't made sure that the hardware is working properly.

The vacuum routing should look like this if you're running a Race Pipe.

GuyGuy · Sep 6, 2009

thanks aNUT, the actuator works fine, the vacuum diaphram is less then a year old and the turbo was cleaned about 2 months ago. AFAIK, everything is nice and clean.

I will figure out how to run a log with measuring block 11 and post it hear.

Farfromovin · Sep 6, 2009

aNUT said:
Looking to tuning to fix problems is foolish if you haven't made sure that the hardware is working properly.

Right, but I'm saying he's got some funky tuning on there. Combined with the "low compression" pistons??? There's more going on here than we know I think.

tivoKlr · Sep 6, 2009

aNUT said:
Use VCDS to check specified boost. Engine->Measuring Blocks->Group 011

Anut, does this give you both requested and measured boost?

Thanks.

vwmikel · Sep 6, 2009

tivoKlr said:
Anut, does this give you both requested and measured boost?

Thanks.

Group 11 gives you RPM, requested boost, actual boost, and N75 duty cycle.

I would also check the actuator adjustment. The symptoms sound like that of a larger turbo with insufficient exhaust volume. So, make sure your vanes are moving completely through their range.

Keebler145 · Sep 6, 2009

I have the same problem
though no where near severe. Secon and third build 18 or 19 usually or close to that but it never builds 22 until late in fourth hear revs wished I knew why toolol

tivoKlr · Sep 6, 2009

Yeah, that's what my car does too, which is why I want to see what the requested value is vs the reported value, especially in 2nd and 3rd gears.

It could be the way my tune is setup, which should be easily answered once I get a chance to run the log and analyze it. Just have to get someone to watch the kids since I'm not sure I want to "go loggin'" with them in the car...

SilveR316 · Sep 6, 2009

20 psi in 1st and 2nd is a heck of a lot of boost. I'm running 25 psi at full load, and my tires slip like crazy when I pass 20 psi in 2nd, and I run extra wide and sticky summers. How are even holding down that kind of power?

Farfromovin · Sep 6, 2009

SilveR316 said:
20 psi in 1st and 2nd is a heck of a lot of boost. I'm running 25 psi at full load, and my tires slip like crazy when I pass 20 psi in 2nd, and I run extra wide and sticky summers. How are even holding down that kind of power?

LSD works for me. Oddly, it's a lot harder to spin 2 tires than 1

robnitro · Sep 7, 2009

Keebler145 said:
I have the same problem
though no where near severe. Secon and third build 18 or 19 usually or close to that but it never builds 22 until late in fourth hear revs wished I knew why toolol

Same thing here... I believe it has to do with fueling or maybe too strong of an actuator spring- sprint .216 w vnt17 here. I can get 22 in 3rd if I start at 2500, but at higher revs it will undershoot and stay there. Better than overshoot IMO, lol. I got rid of my super turbo muffler, and it helps a bit but still undershoot in 1 and 2.. 1 is understandable.
You can try adjusting the actuator a bit shorter. Mine is at the stop at 18 inHG, if I try to lower that, then the actuator is not pushing upwards at the low boost stop when vac is off.
I have no vacuum issues, N18 is disconnected from the loop, vac pump pulls 25 inHG, the n75 is putting about 23 in HG to the turbo at idle.

Still, its faster than when I was spiking to 24 psi with my old program... last night the Acura RSX next to me floored it, I quickly rolled into it, and left it in the dust

GuyGuy · Sep 7, 2009

ok I hate excel but managed to get this graph done, don't know if it's worth anything but here goes.

I also put a print screen version of the log.

robnitro · Sep 7, 2009

It looks like your tune is limiting how much vacuum the N75 provides to the turbo. It may be designed for more fueling, I run the same sprint .216 you do, which are in the middle of fueling.

Example 80% means 20% duty cycle and you can see how the N75 numbers go up with revs. I'm getting about 65% in the log in 2nd at the same point and much closer to requested. The lower the number in the log, the more vacuum is being put to the actuator.

Maybe you can get that re mapped for your fueling? Do you smoke at all?

GuyGuy · Sep 7, 2009

ok I think I understand what you just said robnitro.

I do smoke but I think it's more due to the piston design (machined out bowl) then excess fueling.

GuyGuy · Sep 8, 2009

Well I found part of the problem I hope, there was a small leak in the upper intercooler pipe.

Tomorrow I'll try givin her and she what she does.

Keebler145 · Sep 9, 2009

See mine is finicky this morning I jumped on it and the boost went to 22 but lastnight when I shifted from first to second it lagged to the point that I had to just shift because it wouldn't go past 15 psi. Now Im sorry but that is just absurd. How does it work fine one day but the next it's taking way to long. It just blows huge clouds of black smoke and never boosts. The logs show it's calling for 22 the turbo just won't meet requested

Edit: the actuater moves freely on the turbo it breaks at 4 and fully opens just passed 18

robnitro · Sep 9, 2009

What was the N75 duty cycle in the log when it was not meeting boost? Rolling into the throttle instead of flooring it outright helps me a lot.

Keebler145 · Sep 9, 2009

ehh off the top of my head i'm not quite sure but it was some where around 25 to 30 percent.....

UFO · Sep 9, 2009

This may have nothing to do with the problem at hand, but in my track car (gasser 280Z turbo) I never get full boost in 1st gear because I can't load the engine down enough.

I know,

1) It's a gasser
2) It's wastegated, and not a VNT turbo

Keebler145 · Sep 9, 2009

see i would agree but it does it worse in second and you can tel the car is bogging down cause it's running to rich from lack of boost. Plus on the days it runs right i hit 22 or 23 psi and the car launches like you wouldn't believe. However it only does it when i'm alone on back roads. But when I'm trying to show my friends I hit second step on the gas and the car just bogs down. Completely depressing. I think it's the turbo vanes are hanging and or dragging. Which makes me mad cause the turbo isn't even 3 months old =/

Scott02 · Sep 9, 2009

Keebler, No CEL ?

I'm guessing that the boost deviation in the lower gears doesn't happen for long enough to actually trigger a CEL.

robnitro · Sep 9, 2009

Keebler145 said:
ehh off the top of my head i'm not quite sure but it was some where around 25 to 30 percent.....

You mean the numbers said 25-30% on the log? Its kinda weird how the N75 is indicated... example: 80% in vag com means no vacuum to the vanes and 20% would mean full vacuum. More vacuum to the vanes means more boost.

GuyGuy · Sep 10, 2009

the car does run better now but the higher I rev it when accelerating, the more lag I have when I switch gear. I mean if I'm in third and give her till 4200, when I switch to fourth, I'll have like 3-4 seconds of lag and she smokes like a pig.

when I roll into it. it's pretty much fine, I'll recheck the length of the new actuator with the old one and will try and do a vacuum test to see if the vanes move freely

Keebler145 · Sep 10, 2009

Scott: no cel or any fault codes getting thrown my guess is the same as your's.

GuyGuy: I know exactly what you mean I'm trying to solve the problem myself. I'm wondering if i has anything to do with IAT? if the ecu is cutting back fuel maybe it's cutting back air too? I have no idea really i'm just wild a$$ guessing at this point. I'm seeing Jeff the 19th and I'll get some of it figured out.

Robnitro: No I meant 25 to 30 percent. It's requesting full boost but the turbo is just taking it's good ol' time to respond and then sometimes decides it doesn't even want to meet requested within a long shot.

cannot get 22 psi in lower gears

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