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Slow to build boost L28et with Stock T3


hwvigo

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After months of trouble shooting and replacing parts my L28et is running better, but now a new issue has reared its head that was not seen before due to other running issues. My car builds boost VERY slow will not hit 10 PSI in tell 5500 rpm. And I was wanting some input for the gurus of the Z world.

 

Any info would be a big help thanks.

 

car info: stock L28et, stock turbo , 2.5'' exhaust with factory 90/90 o2 housing, same side intercooler with BOV  and no leaks , DW225 fuel pump , all new connectors on engine harness. and a MBC. and its a AUTO TRANS

 

post-19246-0-96514600-1442347439_thumb.jpg

 

 

video of boosting issue. 

 

Edited by hwvigo
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Couple things come to mind.

 

In the videos some shifting is going on, are you at WOT? Unless you romp on it, it isn't too hard to imagine a slow boost build up.

 

Slipping trans could also prevent the engine from putting out load which is needed for higher boost, does MPH and RPM correlate pretty well in a certain gear?

 

Mechanically speaking there are a couple places it can happen. Either a boost or an exhaust leak. 

 

Boost leaks would be limited to pipes connecting the turbo to the intake, so AFM, AFM gasket, blow off valve, intercooler silicone joiners, etc come into mind. What kind of BOV are you running? Some of the knock off ones have really poor sealing surfaces and could be a massive boost leak.

 

Exhaust leaks would be limited to the turbo manifold, exhaust gasket, or turbo gasket. 

 

A likely culprit seems to be the waste gate. If the waste gate is failing to stay closed for some reason it would take a lot of exhaust to get to the wanted boost pressure. That can be a failure of the waste gate, an incorrectly installed MBC, a cracked turbo housing, cracked/warped/chipped waste gate flapper thingy. 

 

Pretty much you have to pick a side and start working backwards. You can buy or build yourself a pressure tester to pressurize the charge pipes and intercool to see if the boost leak is caused on that side. If it isn't then you would have to move onto the exhaust side.

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1: car is Wot.

 

2: transmission was just rebuilt 2500 miles ago. Mph and RPM correlate very.

 

3: I have checked for boost leaks and exhaust leaks and none are present we blow off valve that is currently on there is a knock off but I have a 1gen DSM I have installed and it dose the same.

 

4: the way state has been tested off the car and opens exactly at 7 psi, and the MBC is installed correctly.

 

5: intercooler, and charge pipes held 30 psi for 2 hours with no leak down.

 

There is a possibility there could be some damage to the turbo I'm not seeing such as internal failures of the wastegate flap. Couldn't exhaust restriction cause this sort of issue just trying to think outside the box.

Edited by hwvigo
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Clamp off the line going to the wastegate actuator and take it for a spin to see how quickly it builds boost then.  With the wastegate stuck shut, it should build boost quickly, just be careful and let off whenever boost gets high.  

 

Agreed, I would disconnect vacuum from the wastegate all together.  Do a pull in 4 gear at say 40 MPH, and when it reaches boost that's higher than normal, I'd let off.

 

Now this may be silly, but it has happened in the past.  Did you have any blockage in your piping?  I had a customer with a 300zx TT in the past that was scheduled for the dyno, but couldn't make any boost past 6 psi.  Come to find out, when he installed the intercoolers, he never removed the packing stuff.  Fortunately enough, the stuffing was bigger than the intercooler piping, and it never made it out of the intercooler.  

 

We boost leak tested the car, and it passed, until I removed the bumper and intercooler to check, and viola, found it

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Agreed, I would disconnect vacuum from the wastegate all together.  Do a pull in 4 gear at say 40 MPH, and when it reaches boost that's higher than normal, I'd let off.

 

Now this may be silly, but it has happened in the past.  Did you have any blockage in your piping?  I had a customer with a 300zx TT in the past that was scheduled for the dyno, but couldn't make any boost past 6 psi.  Come to find out, when he installed the intercoolers, he never removed the packing stuff.  Fortunately enough, the stuffing was bigger than the intercooler piping, and it never made it out of the intercooler.  

 

We boost leak tested the car, and it passed, until I removed the bumper and intercooler to check, and viola, found it

Wish I could make a 4th gear pull its a AUTO car, the IC has been inspected , I will try removing or clamping off the line to the gate and see what it dose.  

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I suppose if the exhaust was restricted enough, it could theoretically slow the turbo since the exhaust would have a hard time moving out and spin the turbine, but to have that much restriction I would imagine the car would really struggle to even start or run. Some hearsay, but I've heard of plugged catalytic converters, I'm not sure if you are even running one so I want to lean away from that. 

 

If their are no leaks, then I would check the waste gate actuator as well, basically something is keeping the turbo from spooling up to speed correctly. It eventually gets up to speed, but at a really high RPM means you are leaking exhaust past the turbo, but eventually you get enough exhaust into it that it essentially spikes itself to your desired level.

 

The wastegate could move freely, but once installed in position it might be binding somehow. Forcing the waste gate shut would be a good test as well. Just be mindful of the boost gauge and AFR so you don't run massively lean. 

 

I'm almost tempted to say it sounds like the MBC is installed backwards? You have more boost, but it really doesn't seem like you are building it till much later, where it should be building pretty quickly and hopefully tapering it off. 

 

Should look like....

    _______

  /             \______

/

 

Immediate and eventually the spring pushes the wastage open bleeding bypassing the exhaust.

 

Seems like right now 

          _ ---

     _ -

_ -

 

You are building up slowly which to me says that you are somehow instead of keeping the diaphragm closed, you are helping to keep it open. Maybe the wastgate spring is broken? Is the slow boost only with the boost controller installed or is it the same even with the stock setup?

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Yea it is a bit difficult to install that incorrectly with the diagram and all. With it removed if it isn't working or building boost correctly then I would be more confident that it has to do with the factory wastegate, I would say the spring might be the culprit, but I think it is a sealed assembly so you would have to just order another wastage diaphram assembly thing.

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Yea it is a bit difficult to install that incorrectly with the diagram and all. With it removed if it isn't working or building boost correctly then I would be more confident that it has to do with the factory wastegate, I would say the spring might be the culprit, but I think it is a sealed assembly so you would have to just order another wastage diaphram assembly thing.

""wastage diaphram assembly thing."" is possibly the best description ever! 

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It seams I have some checks to make now and I really need a AFR gauge. I will delete the MBC and see what happens, I know The MBC is installed correctlyattachicon.gif$(KGrHqNHJEgE8oY,psQNBPV8-1ZjnQ--_1.GIF,   But we will see what happens.

 

I can get you one, whether it be speedhut, aem, innovate.  I'm also trying to work out a deal with wide-band.com for their apsx widebands (which are super cheap, I believe $135?).  If I can get dealer pricing from apsx, then you'll get it for a bit cheaper

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Could fuel low fuel pressure cause this issue, I noticed yesterday that it seamed to be lean popping, its like it just falls on its face when it gets over 7 psi.

 

Yeah lower fuel pressure could be the cause of it.  I'd just rent a fuel pressure gauge from an auto parts store to check it out.

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