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Old 05-11-2010, 09:06 PM   #1
blowbyu24
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Default Boost dropping after full boost is reached

Ok everyone, this boost issue has been a work in progress, so I will fill you in and hope someone can help

Brand new Boost control is a eboost2, turbo is gt40r with twin 38mm wastegates with 17psi springs

The issue started before the new boost controller so I know it is not the boost control, something is causing this. What is happening is full boost is dialed in but right after full boost it is dropping down to 17psi then back up to 19, then levels out. I have not been able to have any luck getting it to hold boost. I ran just the one wastegate port and it was even worse lowest boost was 14psi, so I have both nipples of the wastegates tied into the eboost2 and it is the best since having the eboost2 in.

Things I know
New solenoid, plumbed correctly, rpm correction already dialed in(obviously not helping), eboost2 boost settings correct for those that know...sp45 wg10 (really low gain to not cause a boost spike), sensitivity 15 to cause steady boost

Major issue/things i am not sure about
I don’t know if a small boost leak could cause this type of problem, there isn’t a large leak because there are not other signs..idle, hydra, tune, boost control other than dip is steady. Most reading I have done on the issue causes 1. full boost is not obtainable or 2. boost tapers to redline, not really my situation.

Next step is to create a boost leak tester, but anyone have any other ideas because i am not sold on the boost leak cause

Code:
rpm        boost
4150	19.03
4200	20.26
4250	20.88
4300	22.1
4300	22.1
4400	22.1
4400	21.49
4550	20.88
4500	19.65
4600	19.03
4650	19.03
4700	17.81
4750	17.81
4750	17.81
4850	17.19
4900	17.81
4900	17.81
4950	19.03
5000	19.03
5000	19.03
5050	19.65
5150	19.65
5200	19.65
5250	19.65
5250	19.65
5350	19.65
5400	19.65
5400	19.65
5500	19.65
5500	19.03
5550	19.65
5600	19.65
5650	19.03
5700	19.65
5750	19.65
5800	19.65
5800	19.65
5900	19.65
5900	19.65
5950	19.65
6000	19.65
thanks everyone for looking
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Old 05-11-2010, 10:48 PM   #2
subSTIaru
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your waste gate is to small it cant get the extra gases out fast i enough so you get boost creep and than it starts flowing out and regulates it salfe
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Old 05-12-2010, 02:31 AM   #3
NSFW
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I have no idea what's up with your boost controller.
If you were using the stock ECU I'd say add more WGDC in the area where boost is low.


But damn... 20psi at 4200 from a GT40.

I should have gone twinscroll.
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Old 05-12-2010, 07:36 AM   #4
blowbyu24
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Quote:
Originally Posted by subSTIaru View Post
your waste gate is to small it cant get the extra gases out fast i enough so you get boost creep and than it starts flowing out and regulates it salfe
hmm. The only problem is I have had the boost before where it hits 22psi and stays pretty solid to redline, never this bad.

Quote:
Originally Posted by NSFW View Post
I have no idea what's up with your boost controller.
If you were using the stock ECU I'd say add more WGDC in the area where boost is low.


But damn... 20psi at 4200 from a GT40.

I should have gone twinscroll.

yeah I hear ya wgdc, spool is pretty nice for a large turbo. I have the boost correction where it is supposed to raise boost after a certain rpm. Nothing seems to do the trick. I did forget to mention it seems like this problem was getting worse and worse with the drop off after 22psi until I used both tial wg nipples and that stopped it from dropping to 14psi
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Old 05-12-2010, 10:11 AM   #5
B4 ST
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An issue with the boost solenoid perhaps?
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Old 05-12-2010, 10:32 AM   #6
blowbyu24
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Quote:
Originally Posted by B4 ST View Post
An issue with the boost solenoid perhaps?
i thought the same thing, but this is a brand new solenoid we are dealing with...i am leaning towards something mechanical, it happens right after full boost even if it is a high rpm pull where full boost it 6000rpms vs a 2500rpm 4th gear pull
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Old 05-13-2010, 06:21 PM   #7
blowbyu24
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anyone with any other ideas?
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Old 05-13-2010, 08:20 PM   #8
Fongers
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Pretty sure this is what is happening:

1 - your WG spring is too small (or just not tight enough) to hold over 17 psi consistently. Thus, under constant above 17psi presurre, it is blowing open. Try tightening it.

2 - By looking at your boost pattern, you are over boosting since you are probably running 100% WDC to get to your peak but then it's not holding b/c the spring itself is then popping open.

3 - Solve this with a stronger/tighter spring and then you want to tune your WDC from really high (80-100%) when building boost to a more reasonable level (under 80%) once you've flatlined your boost. It should almost look like a cross over with the WDC dropping right before you can get to peak boost.

EG:

rpm boost WDC
3800 9.5 100
3850 10 100
3900 12 100
3950 14 95
4000 17 92.5
4050 18 90
4100 18.5 87.5
4150 19.03 85
4200 20.26 82.5
4250 20.88 80
4300 22.1 80
4300 22.1 80
4400 22.1 80
4400 22.1 81

Continues with 22 psi but maybe some tweakes +/-10 WDC depending on how your engine/head breathes with your cam setup and all...

good luck

Last edited by Fongers; 05-13-2010 at 08:26 PM.
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Old 05-14-2010, 10:29 AM   #9
blowbyu24
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Quote:
Originally Posted by Fongers View Post
Pretty sure this is what is happening:

1 - your WG spring is too small (or just not tight enough) to hold over 17 psi consistently. Thus, under constant above 17psi presurre, it is blowing open. Try tightening it.

2 - By looking at your boost pattern, you are over boosting since you are probably running 100% WDC to get to your peak but then it's not holding b/c the spring itself is then popping open.

3 - Solve this with a stronger/tighter spring and then you want to tune your WDC from really high (80-100%) when building boost to a more reasonable level (under 80%) once you've flatlined your boost. It should almost look like a cross over with the WDC dropping right before you can get to peak boost.

EG:

rpm boost WDC
3800 9.5 100
3850 10 100
3900 12 100
3950 14 95
4000 17 92.5
4050 18 90
4100 18.5 87.5
4150 19.03 85
4200 20.26 82.5
4250 20.88 80
4300 22.1 80
4300 22.1 80
4400 22.1 80
4400 22.1 81

Continues with 22 psi but maybe some tweakes +/-10 WDC depending on how your engine/head breathes with your cam setup and all...

good luck
really good thoughts, but the only thing is, i haven't changed anything, it just over time got worse and worse, it used to hit 22-23 psi then only taper to 20 right around redline which i am fine with for my street map, not this hold 22psi for a split second....here is more of the log

Code:
 (rpm) tps  (psi)  wastegate PID (%)
3000	102	1.84	0
3050	102	2.46	0
3050	102	2.46	73.6
3100	102	2.46	74
3100	102	2.46	74
3150	102	3.07	74
3100	102	3.07	73.2
3150	102	3.07	74.4
3200	102	3.07	73.2
3200	102	3.68	73.6
3200	102	3.68	73.2
3250	102	4.3	73.6
3250	102	4.3	73.6
3300	102	4.91	73.6
3300	102	4.91	73.2
3350	102	5.53	72.8
3350	102	5.53	73.2
3400	102	5.53	73.2
3400	102	5.53	72.8
3450	102	6.14	73.2
3450	102	6.75	72.8
3500	102	6.75	72.8
3500	102	7.37	72.4
3550	102	7.98	71.6
3550	102	7.98	71.2
3600	102	8.6	71.6
3600	102	8.6	71.6
3700	102	9.21	71.2
3750	102	9.82	70.4
3750	102	10.44	70
3800	102	11.05	69.6
3800	102	11.67	69.2
3850	102	12.28	68.8
3900	102	13.51	68.4
3950	102	14.12	67.6
3950	102	14.74	66.8
4000	102	15.96	66.4
4050	102	17.19	64.8
4100	102	17.81	64.4
4150	102	19.03	63.6
4200	102	20.26	62.8
4250	102	20.88	62
4300	102	22.1	61.6
4300	102	22.1	60.8
4400	102	22.1	60.8
4400	102	21.49	61.2
4550	102	20.88	61.6
4500	102	19.65	62.8
4600	102	19.03	63.2
4650	102	19.03	64
4700	102	17.81	64.8
4750	102	17.81	65.2
4750	102	17.81	65.6
4850	102	17.19	65.6
4900	102	17.81	65.2
4900	102	17.81	64.8
4950	102	19.03	64.8
5000	102	19.03	64.4
5000	102	19.03	63.6
5050	102	19.65	64
5150	102	19.65	64
5200	102	19.65	64
5250	102	19.65	64
5250	102	19.65	64
5350	102	19.65	64
5400	102	19.65	64
5400	102	19.65	64
5500	102	19.65	64
5500	102	19.03	64

Last edited by blowbyu24; 05-14-2010 at 10:45 AM.
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Old 05-14-2010, 12:43 PM   #10
Fongers
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The fact your map is setup right tells me that if nothing changed, then it really is the wg not staying closed... try tightening the springs a notch or two and see how that serves you. Remember, these things are operating at 500F+ so they do eventually wear out a bit.
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Old 05-14-2010, 08:34 PM   #11
MattPersman
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Default Boost dropping after full boost is reached

I don't have twin scroll but I had issues with the bpv leaking under boost I would change the spring or try to shim it more. Just my thought
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Old 05-15-2010, 04:51 PM   #12
blowbyu24
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Well my bud and I did a boost leak test and found two leaks. One the nipple back under the throttle on the drivers side of the intake mani, it had a gash in it and my air temp sensor on my fmic piping was leaking. Buttoned them up and lowered the sensitivity on the eboost2 now it hits 22 and stays stready now. I sure had odd symtoms of a boost leak. Thansk everyone for ther input
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Old 05-16-2010, 06:35 PM   #13
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For future readers :

Don't know what your setup is but this is how it should be : You must use a 3 port solenoid. It will have 2 outputs. One is open at 0% WDC while the other is open at 100% WDC. The output that is open at 100% WDC goes to the top port on both wastegates. The output that is open at 0% WDC goes to the side port on both wastegates.

So at 100% WDC you are sending maximum pressure to the top ports of the wastegates which along with the spring pressure is resisting exhaust gas back pressure. If exhaust gas back pressure is still over powering this setup, you need to increase the spring force in the wastegates. Or increase flow through the turbine by increasing nozzle area or changing turbine wheel specs.
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Old 05-17-2010, 01:34 PM   #14
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Glad you were able to figure it out about the leak! I had the something similar happen to me and it turned out to be my WG even though I was searching for a leak for months... 2 ways to skin a cat!
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