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Brando
 
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Boosting to the moon

Yhe other day I replaced the w/g spring to the .8bar from the .6bar. The it boosted past 1bar and once it reached past that!! This at a real careful and watchful shakedown. So I came home and changed the spring back but noticed boost was going higher than before and approaching scary(.9bar) on a .6bar spring. Same store tonight but now it's boosting unchecked other than my right foot letting off before full boost. Can't drive the car till I sort this out. Is it the diaghram?

Old 01-28-2012, 06:09 PM
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Crotchety Old Bastard
 
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Stupid question, did you re-attach the vac/boost line? Make sure the banjo fitting is tight.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 01-28-2012, 07:10 PM
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Brando
 
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Well I guess it's not that stupid. I removed the w/g and felt like maybe I should unfold the diaphragm. Did that and then replaced the w/g and tightened the banjo again, tightly but suspect a leak? I had it working good for a couple pulls then it let go again. Boost to 1 bar plus. I'm skittish is u don't let it boost long like that. Get out quickly but something's not right.
Old 01-28-2012, 07:48 PM
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Brando
 
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I replaced the crush washers with new copper ones. Worked for a few minutes then resumed to over boost the spring.
Old 01-28-2012, 08:57 PM
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use a bicycle pump with a gauge to test your wastegate
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87 carmine red 930 | 57k | B6 modified IC | GHL headers | custom exhaust | VEMS EFI | carrera intake w/ flipped TB | LS2 coils | EBC | K27-7200 (soon to be replaced by GTX3071
Old 01-29-2012, 03:20 AM
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Crotchety Old Bastard
 
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Yes if you're having these problems a bench test is prudent.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 01-29-2012, 03:40 AM
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Quote:
Originally Posted by RarlyL8 View Post
Yes if you're having these problems a bench test is prudent.
Yup. The wastegate is a simple device, and easy to test. If the unit itself passes a bench test, then it is likely hooked up incorrectly, or there is a kink or obstruction in the boost "signal" hose. Can we assume that your car has factory wastegate plumbing? You don't have any aftermarket boost controller bits, do you?
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Old 01-29-2012, 05:57 AM
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Something aint right for it to work for awhile, then quit working. Apparently you do have the boost line connected to the corrrect bango (the one on the side, vs. the top one that just goes to atmosphere).

Upon inspection, your diaphram doesn't have a small tear does it? The only other thing might be a worn valve guide which could let the boosted air escape instead of pressurizing the diaphram and opening the valve as it should.

When you bench test, you'll most likely hear some air escaping through the guide. SOME air is probably normal, a lot of air is not. Also, you will probably need more than .8 bar (12 psi) of air pressure to open the valve on the bench. That's normal since there is no exhaust pressure present. It's been my experience that around 16-17psi is needed when bench testing, depending on age/condition of the WG.

You could leave the WG in the car and with the engine running, simply add a known amount of pressure via the hose connected to it and listen for the WG to open.
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Old 01-29-2012, 06:04 AM
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Did you take a good look at the diaghram when it was out ??
Old 01-29-2012, 08:08 AM
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My guess is definitely a leak at the WG. Boost pressure is on one side of the diaphragm, and the other side is presumably atmospheric reference. Spring holds the "gate" closed until the tension is overcome by boost pressure on the diaphragm, which then pulls the stem up. Doesn't take much of a leak to screw this up. Small leak = boost creep.

I use a Mity-Vac to test mine. Just put a low pressure gauge on the pressure side of the Mity-Vac, and pump it up til you get to the desired pressure. You can do this running or not running.

I used to use the air compressor with a very low pressure regulator on it, but they always give a big puff at first before the regulator starts working. It's a cheap regulator. Bicycle pump is also a good idea.

I also use a little of that silicone schmutz that we use for the camshaft seal o-rings on the o-ring in my Tial.
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Old 01-29-2012, 02:58 PM
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I also use a little of that silicone schmutz that we use for the camshaft seal o-rings on the o-ring in my Tial.
When in doubt, Tial is there to save the day.
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Old 01-29-2012, 03:09 PM
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Brando
 
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I did inspect. The diaphragm is ok looking. The guide did look somewhat suspect but not obvious.
I'm leaning toward the boost hose. It's not connected to the intercooler since i haven't got one. The hose is connected to te throttle body but I'm thinking it's not optimal. When I start to close the throttle boost starts to show higher even when it was working well. So I think I need to make some changes there. I can't figure out how to get a good pressure with my compressor. 18psi is lower than I think I can control. I'll try it though.
One thing to consider Is that it all happened after I put my intake pipes back on from a valve adjustment and some rocker shaft work. The vacume lines were disconnected but only set aside so I don't know. Odd but I don't know.
Old 01-29-2012, 03:43 PM
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Shouldn't the signal hose be connected prior to the throttle body?
Old 01-29-2012, 08:25 PM
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Quote:
Originally Posted by Ronnie's.930 View Post
Shouldn't the signal hose be connected prior to the throttle body?
Yup, the closer to the turbo, the better.
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Old 01-30-2012, 02:25 AM
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You actually want the wastegate boost hose connected before the throttle body because it is preferred not to supply vacuum to the wastegate diaphragm.
In order to maximize the boost going ot your engine you should take the signal after all your pressure drops thru the intercooler and plumbing so ideally taking the signal off the outlet side of the intercooler is best. But away from the throttle plate so you dont see any vacuum signals.
Traditionally most all intercooler designs have a fitting on the inlet side of the intercooler that you get the signal from but then you lose some boost going into the engine manifold because of pressure losses kicking the wastegate open prematurely.
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Old 01-30-2012, 09:29 AM
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Brando
 
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Intresting, would it be better to gave an aluminum bung welded to my intake pipes?

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Old 01-30-2012, 10:24 AM
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Brando
 
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That is an initial fitment of a 2 inch pipe, it's now a 2.5" but looks the same.
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Old 01-30-2012, 10:26 AM
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Brando
 
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Turns out my wg hose is from the other side of the throttle body, the underside. And my hose has no leaks. It's tight. My boost gauge and blow off valve is attached on the t/b before the butterfly.
I feel the w/g hose is messed up but that's not what's causing my issue.
Old 01-30-2012, 05:25 PM
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Brando
 
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I'm going to thread a barb into my intake pipe and jbweld it and see if that helps.
Old 01-30-2012, 05:27 PM
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Quote:
Originally Posted by quattrorunner View Post
Turns out my wg hose is from the other side of the throttle body, the underside. And my hose has no leaks. It's tight. My boost gauge and blow off valve is attached on the t/b before the butterfly.
I feel the w/g hose is messed up but that's not what's causing my issue.
The BOV should really be connected after the TB, so it gets the full vacuum with engine overun when you lift off the throttle and the plate closes. Your boost gauge is fine connected where it is pre-TB...how about just puting in a "T" at that same location and hooking in your WG feed line before you go boring a hole in your piping?

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Old 01-30-2012, 05:39 PM
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