Stuttering at max boost

[aspekt9]

So I just completed my N/T to turbo conversion and took the car for a ride. It drives smooth and pulls hard. Now here's the thing, max boost is 12psi and all the way up to 12psi is smooth and feels great but as soon as it hits 12 psi, it will stay there like it should. However, it only stays there for about 3 seconds and then watching the boost gauge it jumps down to 9 and will climb back up to 12psi again and do the same thing unless I let off throttle or shift. What could be causing it to do this?

 

[VETTE_50_TH]

Boost leak FTL. Or a bad exhuast leak or wastegate creep.

James

 

[95fwdtsi18psi]

Boost leaks are pretty awesome! :

Mine used to do this until I got my tubular o2 housing w/ dump and full 2.5" exhaust. so I'm guessing it was boost creep at work.

 

[aspekt9]

I will do a boost leak test tomorrow. I uploaded a sound file in which you can hear whats happening, it happens twice in the video, it's like the engine pauses when it backs down to 9psi before bouncing off at 11psi again. It really slows acceleration down.


zSHARE - data-2009-6-17-00-16-00.mp3

 

[tsiAWD91x]

sounds like this could be an exhaust/wastegate NOT a boost leakproblem (see the below story JUST to give you an idea if you new to DSMS and turbos). if it is a vac leak it prob a HUGE one enough to effect the idle which i didnt see you mention, What size Downpipe are you running? and what size exhaust? are your running a CAT????? what turbo are you running? Internal or external gate? is the turbo ported?? try just connecting the wastegate (assuming its stock) to JUST the intake manni, so the wastegate directly to the manifold even the "P" on the TB and it should boost to about 8psi max. (assuming your running 14b stock swaped turbo) let me know what happends after you try that, dose it still bounce arround or peak and hold at 8psi. only takes a minute to change this will give us an idea what the wastegate is doing

FYI 2 weeks ago i was working on a 2g with a 20g for a cust. and on the compressor housing near the bottom there was a hole about the size of a BB and it wouldnt let the the system even pressurize 5PSI i mean this B*#$t was BADDD. Im guessing this was supose to be a Nipple fitting for a pressure source that was tapped and not blocked or used WTF (Pulled liek a rapped ape after i fixed it..wow ) but there was no signs of this bad leak, idle wise or driving either "TO" the owners knowladge. BUT!! getting back to the point!!! this did not cause any type of Spike/Creep at all so thats why i feel thsi is a Wastegate/Exhaust problem :thumb:

 

[aspekt9]

It's a 14B turbo internally gated. All the mods are listed in my profile. Right now, I'm only running an open downpipe, 3" all the way and a testpipe and then it ends until I get my catback in the mail. Would this be causing the issue? Also, the turbo is ported and the wastegate hole was ported, but not enough as to cause a seal issue. It was ported because I was worried about creep with the 3" exhaust. I noticed my PCV was not screwed all the way into the head, so I fixed this but haven't been able to test the car out again. If you listen to the sound clip, it's almost like when it hits 12PSI a RUSH of air is let through and then it backs down to the 9 and climbs to 12 again and it will keep doing this as long as I'm at WOT.

Also, the wastegate goes to the MBC and then to the nipple in the J-Pipe. The MBC is unscrewed all the way to run stock boost, which it seems like it does because it stops around 11/12 PSI.

 

[JayRolla]

sounds like this could be an exhaust/wastegate NOT a boost leakproblem (see the below story JUST to give you an idea if you new to DSMS and turbos). if it is a vac leak it prob a HUGE one enough to effect the idle which i didnt see you mention, What size Downpipe are you running? and what size exhaust? are your running a CAT????? what turbo are you running? Internal or external gate? is the turbo ported?? try just connecting the wastegate (assuming its stock) to JUST the intake manni, so the wastegate directly to the manifold even the "P" on the TB and it should boost to about 8psi max. (assuming your running 14b stock swaped turbo) let me know what happends after you try that, dose it still bounce arround or peak and hold at 8psi. only takes a minute to change this will give us an idea what the wastegate is doing

FYI 2 weeks ago i was working on a 2g with a 20g for a cust. and on the compressor housing near the bottom there was a hole about the size of a BB and it wouldnt let the the system even pressurize 5PSI i mean this B*#$t was BADDD. Im guessing this was supose to be a Nipple fitting for a pressure source that was tapped and not blocked or used WTF (Pulled liek a rapped ape after i fixed it..wow ) but there was no signs of this bad leak, idle wise or driving either "TO" the owners knowladge. BUT!! getting back to the point!!! this did not cause any type of Spike/Creep at all so thats why i feel thsi is a Wastegate/Exhaust problem :thumb:

Actually that 20g issue was a boost leak and I still think thats his issue.

Also what types of plugs, wires are you running? Almost sounds like it misfires when the boost doesnt stay solid. Im guessing boost leak and bad plugs.

I also just relised this was an N/T. What ecu are you using? What tuning have you done with the maf-t? Do you have a wbo2? Do you see knock on your logger?

 

[aspekt9]

I'm runing NGK BPR7ES and NGK Wires. The plugs are gapped a little over .028 maybe it's too loose of a gap? Also, I have my fuel pressure set to 26PSI with the vacuum line connected, is this too small a pressure to run and perhaps I'm not getting enough fuel?

TIMA	FTRL	FTRM	FTRH	FTO2	O2-R	TPS 	MAFS	ERPM	KNCK
34.00º	81.12%	91.26%	91.92%	36.66%	0.88V	17.25%	150.96Hz	2187.50rpm	0
35.00º	81.12%	91.26%	88.92%	32.76%	0.84V	17.65%	150.96Hz	2187.50rpm	0
34.00º	81.12%	91.26%	88.92%	32.76%	0.68V	20.00%	182.41Hz	2218.75rpm	0
29.00º	81.12%	91.26%	88.92%	53.04%	0.10V	56.86%	503.20Hz	2406.25rpm	0
17.00º	81.12%	91.26%	88.92%	99.84%	0.92V	96.86%	578.68Hz	2625.00rpm	0
18.00º	81.12%	91.26%	88.92%	99.84%	0.94V	100.00%	666.74Hz	2937.50rpm	0
19.00º	81.12%	91.26%	88.92%	99.84%	0.94V	100.00%	767.38Hz	3218.75rpm	0
20.00º	81.12%	91.26%	88.92%	99.84%	0.94V	100.00%	912.05Hz	3531.25rpm	0
18.00º	81.12%	91.26%	88.92%	99.84%	0.94V	100.00%	1132.20Hz	3875.00rpm	0
18.00º	81.12%	91.26%	88.92%	99.84%	0.92V	100.00%	1465.57Hz	4312.50rpm	0
18.00º	81.12%	91.26%	88.92%	99.84%	0.90V	100.00%	1603.95Hz	4875.00rpm	0
19.00º	81.12%	91.26%	88.92%	99.84%	0.90V	100.00%	1603.95Hz	5437.50rpm	0
22.00º	81.12%	91.26%	88.92%	99.84%	0.31V	100.00%	1603.95Hz	6156.25rpm	0
18.00º	81.12%	91.26%	88.92%	99.84%	0.90V	10.59%	113.22Hz	5687.50rpm	0
45.00º	81.12%	91.26%	88.92%	99.84%	0.88V	25.88%	402.56Hz	3812.50rpm	0
33.00º	81.12%	91.26%	88.92%	67.08%	0.92V	22.35%	327.08Hz	3562.50rpm	0
40.00º	81.12%	91.26%	88.92%	32.76%	0.90V	16.08%	207.57Hz	3593.75rpm	0
40.00º	81.12%	91.26%	88.92%	31.98%	0.92V	14.51%	113.22Hz	3593.75rpm	0

I know I'm a little rich too. I'm using a MAF-T in blow-through and a pocket logger to log trims. No knock though.

 

[JayRolla]

Drop that gap too around .026. Do a boost leak test and get back to us. If using stock 1g ecu, set that FP at 36psi with the vacuum line disconnected. You may be a little low on FP when boost is hitting.

 

[turbo BMW]

that is no boost leak, or boost creep, or exaust leak or anything like that. That is a plain as day dead missfire. The reason the boost is dropping is because the motor is cutting out so it is momentarilly freespooling. Then boost drops and it starts lightin fires agian.

Cause I would suspect to be spark blowout or a loss in fuel pressure, or being excessivly rich or lean.

To rule out the first, take the gap down to .020" (this sounds really tight but it will work, trust me) If that doesn't take care of it check the resistance on the plug wires and try another coil to make sure you don't have corroded wires or a weak coil or something stupid like that

If that checks out put in a fuel pressure guage somewhere you can see it while driving. I like to just put a tee in the fuel line and attach a hose to a $3 water pressure guage from the hardware store. then run the fuel line out the hood and zip tie it to the wiper in front of you. Go take it for a ride, you should see the pressure rise with boost pressure, if it drops at all you need a better pump.

Lastly I have also watched several cars do that when they are run way to rich. Usually around 10.3:1 or so AFR, they will start doing that. People are scared of AFR's so they run them pig rich because they are afraid of blowing it up but there really is no need for anything less than 11.5 or so.

 

[JayRolla]

that is no boost leak, or boost creep, or exaust leak or anything like that. That is a plain as day dead missfire. The reason the boost is dropping is because the motor is cutting out so it is momentarilly freespooling. Then boost drops and it starts lightin fires agian.

Cause I would suspect to be spark blowout or a loss in fuel pressure, or being excessivly rich or lean.

To rule out the first, take the gap down to .020" (this sounds really tight but it will work, trust me) If that doesn't take care of it check the resistance on the plug wires and try another coil to make sure you don't have corroded wires or a weak coil or something stupid like that

If that checks out put in a fuel pressure guage somewhere you can see it while driving. I like to just put a tee in the fuel line and attach a hose to a $3 water pressure guage from the hardware store. then run the fuel line out the hood and zip tie it to the wiper in front of you. Go take it for a ride, you should see the pressure rise with boost pressure, if it drops at all you need a better pump.

Lastly I have also watched several cars do that when they are run way to rich. Usually around 10.3:1 or so AFR, they will start doing that. People are scared of AFR's so they run them pig rich because they are afraid of blowing it up but there really is no need for anything less than 11.5 or so.

How would 10.3:1 afr cause this when stock afr on a dsm is 9.5:1.

Ive seen a constant studder from running real rich but its usually a lot richer than 9.8:1.

I agree after listening to the video that its a misfire. I would not drop gap too .020 right off. With his low boost he should be fine at .028 or a little under. I run 30psi at .026 gap. If he does have to go to .020 to fix the issue than its covering up a weak spark problem. .020 should not be needed untill 45+psi is being run.

Also on a dsm running pump gas we like to run around 11.1 afr at leanest. This allows for the most boost and timing usually. Anything leaner will just knock. Boost and timing will always make more power than a lean afr.

 

[aspekt9]

Okay so I pulled the plugs, they had carbon built up on the bottom which I'm assuming is indicitve of running rich and they were gapped at like .032, so I regapped them down to .028 and took her back out. It seemed she stayed at 12psi a little longer, maybe around 5 seconds or so and then it the same thing happened. My fuel trims say FTRL 81% FTRM 94.95% FTRH 94.19%. At idle sometimes I can hear a low muffled pop sound coming from the exhaust, backfire? For the life of me I can't get this thing to lean out maybe I'm doing it wrong. First I set AUX 0 BASE 2 for 450 injectors all the other nobs are in the middle. Then I reset the ECU so all the trims read 100% and then go for a drive and let the trims settle in and then I see okay I'm running rich so I pull over adjust the idle and wot knobs two clicks to lean it out but i don't see any change on the logger? Does this sound like a misfire issue or a rich issue? Fuel pressure is at 26-28 PSI with hose attatched and 37 with it off. Any ideas guys? I appreciate the help.

 

[JayRolla]

Yes you are running real rich. That is most likely your issue. Probably way richer than 9.5:1. You should really get a wbo2.

If I remember right all knobs should be at zero for stock injectors.

 

[aspekt9]

Just an update, I leaned out my WOT and MID knobs a little more and took the car back out on the highway. Did a 5th gear pull WOT boosted all the way to 12PSI and STAYED THERE!! So it seems it was because the car was running too rich. Now I just have to figure out why when I lean it out my logger reports the trims as like 81% 94% 81%... Nice to know my porting job works when running an open 3" downpipe haha. thanks for all the help guys, I appreciate it. I'm definitely going to invest in a Wideband now so I can see WTF is going on.

 

[JayRolla]

The first trim is just cruising so you are pig rich during cruise. Pull a little fuel out with the base knob and see if trims change.

That guy above was right that it was a rich studder. But not from running 10.3 afr. You must have been real rich.