Boost problem after new turbo

[TURB0]

I recently upgraded to an Evo III 16g as well as supporting mods. The car was running awesome. I got a decent tune on it running about 16psi for a few days. Then upped it to about 19psi with still no knock and an overall safe tune. Then my car began stuttering under load, and eventually just about all the time. So I ordered new plugs/wires and that problem was fixed. However now it seems the car will not build as much boost in lower gears. 1st gear builds about 10psi and starts falling towards redline, 2nd to 12psi, still falling towards redline. However in 4th and 5th it will hold 19psi steady. Any input? Thanks.


p.s. Tested for boost leaks...none.

 

[Eastwood95]

I know boost varies with engine load (ie. gear) but it shouldn't be that big of a difference. Did this just start happening out of the blue?

Try turning the boost back down and see what levels you're running in all gears again...

 

[TURB0]

Yes it just started happening out of the blue. I even today ran the boost directly from the wastegate actuator and bypassed the MBC to get essentially the same result

 

[wvturbo2]

Could you have an exhaust leak or something? Causing it not to spool til your at a higher speed and gear ? I have no idea it just seems weird to me.

 

[oldman]

1. Check your timing marks then perform a compression test.

2. Describe in detail the process and the results of your boost leak test.

3. Did you perform the leak test after the turbo install and before the problem, or after the problem.

4. Have you check the turbo for shaft play and free spin.

5. like already mentioned by wv, have you check for pre-turbo exhaust leaks?

6. Which MBC and is it connected to the BOV line.

 

[TURB0]

timing and compression check are scheduled for tommorow. However it still idles flawlessly at 750rpm, so I wouldn't think the timing would have skipped a tooth or anything.


I boost leak tested after the install as well as just after the problem occurred. To test it I just spray down all possible leak areas with soapy water and pressurize the system to 20psi and make sure my boost gauge verifies it.

Turbo shaft is still solid, no oil or anything on the blades either.

I will check for pre turbo exhaust leaks tomorrow as well. What would main culprits be? cracked manifold? Banjo bolts from the turbo loosening and creating a gap maybe?

Its the turboXS bleeder style MBC. And yes I am running the line T'd off of the BOV line, which I know isn't the best but there is no nipple to run it from on my current licp or anywhere on the turbo. However it held boost fine forever on my 14b and for a bit on the 16g.


Thanks for the input guys.

 

[oldman]

I boost leak tested after the install as well as just after the problem occurred. To test it I just spray down all possible leak areas with soapy water and pressurize the system to 20psi and make sure my boost gauge verifies it.

I was helping someone else tonight who swears up and down that he was able to pressurize his intake up to 25psi, after further questioning, it turns out that his compressor regulator was set to 80 psi , let's make sure that is not the case here.

I will check for pre turbo exhaust leaks tomorrow as well. What would main culprits be? cracked manifold? Banjo bolts from the turbo loosening and creating a gap maybe?

Anything including cracked manifold or turbine housing and flange/gasket leaks before turbo, even an unsealed flapper, can have great effects on your turbo spooling.

Its the turboXS bleeder style MBC. And yes I am running the line T'd off of the BOV line, which I know isn't the best but there is no nipple to run it from on my current licp or anywhere on the turbo. However it held boost fine forever on my 14b and for a bit on the 16g.

Worst combination ever!!!! I just found you a huge vacuum/boost leak. This what I've posted in the past about tapping your BOV line.

1. BOV line was previously thought to be better and more accurate because it's the pressure the engine sees when in reality it doesn't matter because boost gauge is already measuring manifold pressure regardless where you reference your MBC.

2. Long route vs short route, increased chance of boost spike.

3. Turbo protection. In a case of developed boost leaks in your intake tract, tapping BOV line will result in turbo spinning out of control while boost gauge till maintains full boost. Where as a compressor source will open wategate sooner while registering pressure drop on your boost gauge.

4. This is the most important one. Tapping your BOV line will result in an opened BOV under WOT because of pressure bleed through the MBC's wastegate pressure relief hole. The situation gets worse when using a bleeder type like the TurboXS units because it's also a vacuum leak which can lead to idle surge as well as compressor surge.

 

[romeen]

And yes I am running the line T'd off of the BOV line, which I know isn't the best but there is no nipple to run it from on my current licp or anywhere on the turbo.

Here are some suggestions for installing a nipple for a boost source.

http://www.dsmtuners.com/forums/showthread.php?t=255444

 

[TURB0]

Ok, the compression is mid 150's across the board so that seems ok.

And yes, I had the compressor set correctly, haha

I will get right on correcting my MBC setup, however it is weird to me that it would run seemingly fine for so long and then all of a sudden give me problems. I also have no idle problems what so ever.

I inspected the exhaust manifold and turbo housing to the best of my ability and could find no cracks. Is there any easy way to test for pre turbo exhaust leaks?

 

[romeen]

I inspected the exhaust manifold and turbo housing to the best of my ability and could find no cracks. Is there any easy way to test for pre turbo exhaust leaks?

As you know, you can visually examine for black, sooty deposits around the flanges/gasket areas.

But I have found that running a can of Seafoam through the intake will identify even the smallest exhaust leak (the smoky byproduct of the cleaner when burned will find it's way out of just about any opening). And of course you will be getting the added benefit of cleaning out your intake. If you want more info there is a large, ongoing thread about it. Or just let us know if you're interested.

 

[oldman]

And yes, I had the compressor set correctly, haha

And what does "correctly" mean?

I inspected the exhaust manifold and turbo housing to the best of my ability and could find no cracks. Is there any easy way to test for pre turbo exhaust leaks?

You can do what DMV inspectors do by placing a cloth or cardboard at the tailpipe while another person look for leaks when the car is at idle OR make another tester that fits your tailpipe and do a reverse boost leak test.

 

[phillip]

drill n tap a nipple on the j-pipe. That's how the factory has it on the 1g's conect that n the wastegate. Screw the mbc all the way out n run it. it should be your lowest boost setting. then turn it in after each pull, till u have it correct.

 

[fuzzydoodle]

Just thought this would fit in here. I'm having the same sort of problem after a t28 install on my tsi in first as soon as any boost hits the car cuts out an jerks real bad then all dash lights come on ex. cel. but if i let off when this happens it resumes running fine (i ported my o2 & exhaust man. but dropped the exhaust manifold on the pavement after looking at it i found a crack it looks old but it goes through i dont know if it happened when i dropped it. i dont have bigger injectors in (was just to get it running because the ol t25 blew). but i dont think it would have anything to do with the injectors, i checked all ic fittings all are tight no leaks. hopefully someone been through this has any help...

 

[oldman]

Just thought this would fit in here. I'm having the same sort of problem after a t28 install on my tsi in first as soon as any boost hits the car cuts out an jerks real bad then all dash lights come on ex. cel. but if i let off when this happens it resumes running fine (i ported my o2 & exhaust man. but dropped the exhaust manifold on the pavement after looking at it i found a crack it looks old but it goes through i dont know if it happened when i dropped it. i dont have bigger injectors in (was just to get it running because the ol t25 blew). but i dont think it would have anything to do with the injectors, i checked all ic fittings all are tight no leaks. hopefully someone been through this has any help...

BOOST LEAK TEST!!!!

Visual inspection doesn't work.