Problem with Boost Dropping off at higher RPMs..B16G

I posted this on tuners but no one is helping. Since it is GVR4 specific, I was wondering if I could get some thoughts here...

I have posted bits and pieces about this in other threads but it is now my primary problem. Please no comments about multiple threads on the same topic since this is a new primary issue.

I have set my MBC at 22 psi with my Big 16g. By 4500 rpm, boost drops to 20 psi. By redline, it is at 17 psi.

I have replaced the MBC just in case it is an issue and still have the same problem.

I have Boost Leak Tested the system with a 6 gallon compressor and have been able to take the pressure up to 30 psi. I do hear air from the valve cover oil cap when I remove it even when timing is set to 30 degrees ATDC. It is not as bad as others have described and I don't want to go broke spending too much money and time on valve stem seals if it not the cause of the boost fade. In fact, I have read that hearing some air from the valve cover opening during a BLT is normal. All BLT are performed cold.

Compression is 161-165 across the board.

I have replaced the throttle shaft seals and put RTV over the BISS Screw opening due to boost leaks. I put the one way check valve to the PCV as well.

My BLT situation is far better than it was before overall and I am not so sure I want to continue to blame boost leaks for this issue.

I have also gotten a Dodge Modded BOV (I really think it looks more like the Dejon but others say it is Dodge Modded).

All of this and I still have the above Boost Fade Problem. In fact, someone else had or has an identical issue:

Is Boost fade normal? - DSM Forums: Mitsubishi Eclipse, Plymouth Laser, and Eagle Talon Forum: DSMtalk.com

All of my mods are in the signature. (Note the 40mm Tial Wastegate). The spring is 16 psi. The wastegate is apparently 10 years old. I contacted Tial to find out more about it since the previous owner installed it. Maybe the spring is tired after that long? (They didn't seem too worried about it).

Could you all give me your thoughts?

Thanks!

Mods are:


Ported Big 16G Turbo, ETS FMIC & Piping, XBC MBC, Custom 2.5" tubular SS O2 housing with 40mm TiAL wastegate, turbo back Buschur 2.5" mandrel bent SS exhaust and CATCO cat, 1G DSM shifter with 2G DSM shift knob, Autometer Vacuum/Boost Gauge, Nordskog oil pressure gauge, custom turbo oil return line, FRAM airhog air filter, Mighty Max oil filter housing for relocated oil filter, M1 15w-50, HIR 9011 and 9012 bulbs, fog lamp delete, Warlboro 190 lph pump, Fuel Pump Rewire, FIC 650 injectors, Alarm with turbo timer and remote start built in, Innovate LC-1 Wideband O2 with guage, Triple gauge pod below radio, removed insulation under carpet, vented carbon fiber hood and carbon fiber hood pins. Socketed EPROM ECU with Ostrich and ROM emulator, Stutterbox and Check Engine shift light, using RT Tunerpro for tuning. Palm iiic w/mmcd hardwired into car (charges battery too), JDM GVR4 trans from Noyan, PTT twin disc clutch and flywheel with organic discs, SS Clutch line, Dejon Stop Leak Kit for BOV, Stock Head and Cams

 

[SouthCaliVR4]

My first recommendation would be to drop the cat & see if that helps.

 

Dropped it and it behaved just the same. I should have mentioned that sorry!

 

[SouthCaliVR4]

so you ran it off just the down pipe & had the same issue? or did you use a test pipe, in which case what muffler are you running?

 

I ran it right off the downpipe and had the same issue. Thanks!

 

[SouthCaliVR4]

Next suggestion, put a vacuum gauge between the filter & turbo, see if you're pulling any vacuum there your intake/filter could be the restriction, sorry not familiar with that type Fram filter but I know their replacement types have caused some cars to run rich enough to fail emissions.

 

Good idea, couldn't I run no filter up the road quickly just to duplicate that without a vacuum gauge? Airhogs are supposed to flow better than K&N but I am up for a try.

 

[SouthCaliVR4]

Yup

 

Thanks...pebbles are my responsibility! I'll just run it carefully up a paved road and turn right around once I verify! I will be back to report tomorrow. Please stick around.

I appreciate your thoughts.

I have some other thoughts as well, but don't like to feed into things because I have a tendancy to get people off of target.

I'll list them anyways:

1) Pre-turbo exhaust leaks
2) Incorrect Cam Timing
3) Some weird ECU tuning (my XFD file has all kinds of boost parameters in it)..not sure if any of them can control boost though...target boost is one of them
4) Worn Wastegate spring
5) Pinch or hole in wastegate diaphram
6) Too much ignition timing (not sure about this one)
7) Boost Controller is Tee'd off of the BOV line.

 

[SouthCaliVR4]

1) Pre-turbo exhaust leaks

Slower spool or if bad enough could cause an inability to reach max boost, I think since you're reaching max boost for a while I doubt it.

2) Incorrect Cam Timing

Possible, easy enough to check.

3) Some weird ECU tuning (my XFD file has all kinds of boost parameters in it)..not sure if any of them can control boost though...target boost is one of them

I don't see how it could control boost if you're using an MBC.

4) Worn Wastegate spring

Also possible but I would think again you'd not reach full boost at all.

5) Pinch or hole in wastegate diaphram

See above.

6) Too much ignition timing (not sure about this one)

I was pondering that as well but I would think you'd hit knock before you affected exhaust flow significantly /ubbthreads/images/graemlins/dunno.gif

7) Boost Controller is Tee'd off of the BOV line.

mine is J-pipe to wastegate actuator, only way I have ever done them, others will chime in.

Anyway, my list of musings to your list of possibles

 

Previous owner said to take a look at knock as it was knocking like crazy at only 16 psi. Maybe I just am not hearing it due to the external wastegate hmmmm. Wow that is scary!

I will check the cam timing marks and hopefully they line up.

I might just go with a 2g timing map for a while to test this out and make sure it's not ignition timing related!!

This is of course after I run it without the air hog in place.

I will get the BOV tee situation sorted as well.

Thanks so far...feedback coming.

 

Could a "Bad" Turbo cause these symptoms?

 

Well it is definitely not the Fram Air Hog...took it for a spin and did the same thing.

 

[Barnes]

Quoting SouthCaliVR4:

5) Pinch or hole in wastegate diaphram




This would actually cause over boosting.

 

Thanks, well it is not ignition timing either...pulled timing back to 2g map and still the same issues.

 

how mig are your intercooler piping and front mount? you may jsut be experiencing pressure drop due to too large a volume for the turbo to fill up top rpm where the motor is taking air faster then the turbo is able to push/fill a larger frontmount and piping. this may seem odd. but as a test. route your piping without teh intercooler. and see if the problem goes away. this happened to me before on ym rb20 240. i had a bastard 20g wiht a gargantiun frontmoutn. and would get to 30 and start dropping. after i tested the no front ount problem was gone. so i ended up buying a precision 6262 for the car and kept my big frontmoutn. needless to say. it was a solid 30 all the way to redline.

 

I have been waiting for someone to post this. I have always held this scenario in the back of my mind. I have read it....in fact this guy here has the same issue. It is IDENTICAL to mine in every way.

This is the intercooler and piping that I have, the sizing etc is mentioned within:

click

I could have sworn that someone said that they used this with a Big 16g here and was able to hold boost with no drop at all whatsoever to redline.

Someone else on dsmtalk has this exact "problem".

Take a look here:

click

 

[thecman02]

What does your wideband say when your boost tapers?

 

I have a rough idea, but I don't want to give you inaccurate information. I think it runs 10.8:1.

I think it runs substantially leaner than the map that is loaded. The map is set for a rich 9.x:1

Should I go run it from 3000 at WOT and report back?

 

your afr's... as critical as they are to the motor and performance. should not be a reason for your pressure drop. i know i have a low post count. but im willing to bet you its the small turbo unable to keep the intercooler and piping filled and still supply psi to the motor. its not a bad thing. but it is affecting your higher end hp numbers. and as with your tune. it could cause it to richen up since its tuned for the 20 psi at WOT and is eventually seeing 16. but thats also based off if you have a fuel management system thats not modern enough to see the differences and adjust accordingly... i . e an safc.