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 10 Cycling valve? (Read 2250 times)
CW 951
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Cycling valve?
Jun 26th, 2013 at 12:38am
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Ok, I've read and read and read about this turbo/wastegate/cycling valve setup in my 86 951.  I am experiencing relatively low boost, about 1.5-1.6 bar according to the in-dash gauge.  All the vacuum hoses are new and it has a venture delete kit installed.  I unhooked the hose from the cycling valve to the wastegate, drove it, and.....wow!  I wasn't hard on it because I knew about the dangers of overboosting but what a difference!  I could easily 'regulate' the boost gauge at 2 bar with the gas pedal and I never floored it.  The turbocharger is definitely working.

My question is this: is the cycling valve my faulty component or is it something else?  Is there any more testing/troubleshooting I can do to isolate the culprit?

Thanks.
Cliff
  
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eyepoker951
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Re: Cycling valve?
Reply #1 - Jun 27th, 2013 at 4:53pm
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Sounds like you need a new wategate.  Ian sells re-built wastegates.  Lindsey racing has aftermarket wastegates.  You can also re-build it yourself or use shims to fix the leakage.

Max boost pressure is 1.75 bar on your vehicle,  going over that amount will cause damage to the head.  When you get to 1.75 the wastegate should come into play to save your engine.
  

1986 951 - New GQ (thanks to MGJ), 2007 Cayman S - DD spring/summer/fall, 2000 Subaru Forester S - now my winter ride
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Ky951
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Re: Cycling valve?
Reply #2 - Jun 27th, 2013 at 5:22pm
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If the cycling valve is broken, it will fail in safe mode and generally the highest boost you will get is 1.2 bar.  I have run my car with the cycling valve unplugged and that is the result I get.  My system is completely stock.
  
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Re: Cycling valve?
Reply #3 - Jun 27th, 2013 at 11:07pm
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eyepoker951 wrote on Jun 27th, 2013 at 4:53pm:
When you get to 1.75 the wastegate should come into play to save your engine.

So the wastegate should open at 1.75 regardless?  If so, then why is the cycling valve even there?

Don't get me wrong, I am not trying to start a fight here, just asking for a little info before throwing piles of $$$ to solve this minor issue.

From what I've read, there are two ways to 'control' the level of boost; original design cycling valve and aftermarket manual (or electric) boost controller.  Either of these methods are designed to control or 'open' the wastegate thus limiting the max boost. 

Further reading revealed that one way to troubleshoot a low boost issue is to disconnect or pinch the hose between the cycling valve and the wastegate, drive the car, and see if the turbo makes at least 1.75 under part-throttle operation and below 3000 or so rpm.  It warns of overboosting under hard acceleration. 

This test was to make sure the turbo is developing boost, it said nothing about the wastegate opening automatically to prevent boost above 1.75.

Again, not trying to argue, just trying to learn.

Thanks for the input.
  
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Re: Cycling valve?
Reply #4 - Jun 27th, 2013 at 11:09pm
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Ky951 wrote on Jun 27th, 2013 at 5:22pm:
If the cycling valve is broken, it will fail in safe mode and generally the highest boost you will get is 1.2 bar. †I have run my car with the cycling valve unplugged and that is the result I get. †My system is completely stock.

I haven't tried running with it unplugged to see if there is a difference...good point.
Thanks.
  
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Re: Cycling valve?
Reply #5 - Jun 27th, 2013 at 11:12pm
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eyepoker951 wrote on Jun 27th, 2013 at 4:53pm:
Sounds like you need a new wategate. †

Is there another way to test or troubleshoot the wastegate?  I'd like to be 100% sure before embarking on replacing that animal...not to mention the wasted $$ if that was not the problem.
  
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Re: Cycling valve?
Reply #6 - Jun 28th, 2013 at 2:08am
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Clarks has a procedure using pressure. I use a Mity Vac to test the Wastegate per his instructions.
  

Bruce  88 951, Alpine White, Autothority chip, HRE custom wheels, Schnell short shifter, Koni sports, M030 sways
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eyepoker951
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Re: Cycling valve?
Reply #7 - Jun 28th, 2013 at 2:57pm
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Quote:
So the wastegate should open at 1.75 regardless? †If so, then why is the cycling valve even there?

From what I've read, there are two ways to 'control' the level of boost; original design cycling valve and aftermarket manual (or electric) boost controller. †Either of these methods are designed to control or 'open' the wastegate thus limiting the max boost. †

Further reading revealed that one way to troubleshoot a low boost issue is to disconnect or pinch the hose between the cycling valve and the wastegate, drive the car, and see if the turbo makes at least 1.75 under part-throttle operation and below 3000 or so rpm. †It warns of overboosting under hard acceleration. †

This test was to make sure the turbo is developing boost, it said nothing about the wastegate opening automatically to prevent boost above 1.75.


The wastegate does not automatically open, it requires a vacuum to open it up.  By pinching off the line from the cycling valve to the wastegate you keep the engine management system from activating the piston to open the gate.

Since you can get boost up past the regulated max of 1.75 bar then you know the turbo side is patent, free of leaks.  Wastegate failure occurs because the spring that keeps the gate (valve) closed securely is weakened.  You can use a bandaid of placing shims to increase the pressure on the valve seat to prevent leakage.

Give Ian a call and he can set you up with a new or refurbished wastegate or shims.
  

1986 951 - New GQ (thanks to MGJ), 2007 Cayman S - DD spring/summer/fall, 2000 Subaru Forester S - now my winter ride
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dpoul34
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Re: Cycling valve?
Reply #8 - Jun 29th, 2013 at 10:53am
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I had/have a similar problem and ordered everything vacuum related new.  Hoses, venturi delete, cycling valve, etc. and still haven't put anything in, 18 months later (it's removing that manifold that freaks me out).

My in-car gauge reads a little past 1.5 when boosting.  Not having driven another 951 leaves me wondering where it's really supposed to be.

I always throw around the idea of deleting the valve and modding things out a bit and then reality sets it and I leave it stock.

I do know that there are way more things that it could be on low boost than the cycling valve or waste gate.  i've researched this topic til I was blind.
  

1987 951 56000 miles Black Beauty (Stella)
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Re: Cycling valve?
Reply #9 - Jun 29th, 2013 at 12:28pm
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Thanks for all of the info/suggestions.  I have driven 2 other 951's and both of them had a very noticeable boost increase over mine.  Both showed about 1.75-1.8 on the gauge whereas mine shows 1.5 or so.

I will disconnect the electrical plug from the cycling valve to see if that makes a difference.  If the boost drops to 1.2 or so, I know the valve is working.

Again, thanks for the input.

Cliff
  
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dpoul34
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Re: Cycling valve?
Reply #10 - Jun 29th, 2013 at 12:36pm
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Please report findings.  I'm curious to see how this plays out.  It may push me towards playing with mine more deeply.
  

1987 951 56000 miles Black Beauty (Stella)
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Re: Cycling valve?
Reply #11 - Jan 25th, 2015 at 11:37pm
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Ok, time for an update.  Sorry for the looooong delay but this issue really wasn't on the top of the priority list.

Short story...new cycling (timed delay) valve fixed the low boost.  I didn't do any other parts changing prior to this but I troubleshot it by disconnecting the hose going to the WG and it boosted very well.  She pulls like a freight train now with new cycling valve and indicates 1.75-1.8 on the gauge.

Yeah, I'm excited now!!!  Cheesy Cheesy Cheesy Cheesy Cheesy
  
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Ronin-951
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Re: Cycling valve?
Reply #12 - Jan 26th, 2015 at 2:58pm
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She's a slippery slope CW, Boost is addicting for sure. The new Proverb of "Reliability is inversely proportional to Modification" keeps me out of that game, but I certainly enjoy a crisp Winter Day for the added push. Cheesy
  

'Princess' of the Inland Empire, virgin '86, Lady in the City, Ho on the Hiway, Pace not Race!
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Re: Cycling valve?
Reply #13 - Jan 26th, 2015 at 4:59pm
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Ronin-951 wrote on Jan 26th, 2015 at 2:58pm:
She's a slippery slope CW, Boost is addicting for sure. The new Proverb of "Reliability is inversely proportional to Modification" keeps me out of that game, but I certainly enjoy a crisp Winter Day for the added push. Cheesy

It sure is...the boost, that is!  The PO did new vac hoses and venture delete, that is the only mods.  I plan to keep it relatively stock and reliable.  It starts every time and is a great road-trip car with working a/c, heat, and cruise...and it now has its 'kick' back in operation.  Hopefully it will continue to be reliable with little more than routine maintenance.
  
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Re: Cycling valve?
Reply #14 - Jan 26th, 2015 at 9:03pm
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I'd highly recommend a boost enhancer.  If you set it low, all it does is make sure the wastegate stays completely closed until it's needed (with the stock setup, the wastegate is never completely closed).  You can adjust it to add more boost, but you're obviously aware of the potential downsides to that....  I have mine set so it moved the maximum boost (on the gauge) from about 1.7 to 1.8, but the biggest difference is in the lag reduction.  It's not completely gone, but it does reduce it.  $100 and 5 minutes to fit or remove.
  

1986 951 almost completely stock, boost enhancer mod.
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