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-   -   overboost switch question/wastegate malfxn (http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/574528-overboost-switch-question-wastegate-malfxn.html)

zaidigonzo 11-10-2010 07:29 AM

overboost switch question/wastegate malfxn
 
I just put on RarlyL8 headers and ditched the GSF($250 if anyone is interested, only 300 miles on them and have heat/ I could not get rid of small exhaust leak)
Before the header change, I swore I could hear my wastegate open and whistle with the glass down when the boost gage hit 1 bar(I have a 1 bar spring in stock wastegate with new diaphragm)
Now if I hit max boost which seems to come so much faster than before, It just shuts OFF and I almost hit my face against the steering wheel. I assume Im exceeding the max boost and the switch is shutting it off to protect the engine...
Is there anything that could have caused this just from switching to new headers. The car runs and boosts great, just the boost shuts off abrubtly on max boost. My gauge is the little stock boost gauge that flattens at 1 bar so I dont really know how much boost Im at when the car does that. I do know it did not do it EVER before and I could hear the loud "psssssttttt" sound on the drivers rear side on max boost. Any ideas on what to check?
Thank you,

Apparently all I needed to do was put extra gaskets on the GSF headers to make them seal but I was sick of it so I got the new system.

Black_Hat 11-10-2010 08:06 AM

1991 c2 turbo I too just put on RarlyL8 headers
I had to ditch the 1 bar springs Tial 46 mm waste gate
I went with a .9 bar spring blue
I now have peaks of 14.6 as measured by my zietronics
I have yet to log my afr's and sustained boost
headers are ...beyond my expectations ...sound is awesome

matsuzaka 11-10-2010 08:17 AM

I've read these types of comments on this forum before about over boost situations. It's my understanding that there is also a bypass valve on the intake side, does this not come into play in these situations?

Black_Hat 11-10-2010 08:32 AM

nope

CIS needs to keep track of all the air

mark houghton 11-10-2010 10:44 AM

My thoughts for what they're worth.

Ditch the 1.0 bar spring and try a .9. Overboost "spikes" are fairly common when going to a good free-flowing header system.
Second, get a decent boost gauge that tells you with confidence how high your boost is going. The overboost cutoff switch - when new - I think will activate somewhere between 1.2-1.4 bar. An old switch, on the other hand, may activate sooner. Again, you need to know exactly where your boost is at in order to decipher if it's an oversensitive switch or if indeed you're running high boost spikes.
Third, about this loud "psssssst" sound you're used to hearing. Unless you are running with an external blowoff valve modification that vents to atmosphere, you will never hear that tell-tale Ricer psssst when you shift gears and the valve opens. The stock system includes a recirculation valve that keeps the boost contained and doesn't allow it to vent to atmosphere. You should hear nothing when shifting....and should hear a nice loud roar when you've reached maximum boost and the wastegate opens to divert some un-muffled exhaust.
...and one more thing: Make sure that you have the boost signal hose connected between the IC and the WG. Your overboost could be as simple as that....the WG not opening at all.

zaidigonzo 11-10-2010 03:32 PM

there is one hose from the top of the wastegate going to the bottom of the IC.
Another hose comes from the bottom of the waste gate and goes to engine compartment and is open to air. Are these hoses switched? or do they go as is?
the boost sensor switch is the round orange one under the IC right. Has a drivers side connector with a wire to it and the passenger side one has no wire to it. Is this OK?

A930Rocket 11-10-2010 03:37 PM

Sounds like the WG is plumbed properly. The hose on the side is vented to atmosphere. The hose on top get pressure from the intercooler.

The boost sending unit should have only one wire to it (as does the overboost sending unit).

The ivory colored sensor is the overboost sensor and the one with the red cover on it is the boost sending unit

Quote:

Originally Posted by zaidigonzo (Post 5666780)
there is one hose from the top of the wastegate going to the bottom of the IC.
Another hose comes from the bottom of the waste gate and goes to engine compartment and is open to air. Are these hoses switched? or do they go as is?
the boost sensor switch is the round orange one under the IC right. Has a drivers side connector with a wire to it and the passenger side one has no wire to it. Is this OK?


zaidigonzo 11-10-2010 03:45 PM

thank you... will keep checking
may need a .9 spring if all else fails....... This didnt happen before but I had GSF headers with a small exhaust leak and it was warm. Now its RARLYL8 headers and cold air, so may be that its too much boost. It doesnt really happen unless I hit WOT and keep it there. The boost comes fast and smooth and pegs the stock boost gauge to 1 bar without cutting out. But if I keep it there then it cuts out...
so boost spring vs overboost sending unit

zaidigonzo 11-10-2010 03:55 PM

where is the overboost sending unit?

zaidigonzo 11-10-2010 04:05 PM

I dont have a yellow overboost relay. My car is 84. Is that "normal"?

mark houghton 11-10-2010 04:19 PM

Quote:

Originally Posted by zaidigonzo (Post 5666831)
where is the overboost sending unit?

It's not a sending unit, it's a simple pressure sensitive switch that's normally closed. It's mounted on the boost recirculation manifold, beneath (or maybe beside) the IC on it's left side and toward front of the car. Hard to explain, and mine is no longer in the stock location.

I cropped it out of a larger picture to at least show it's appearance (sorry so small, but cropped after all). Ivory colored, single white wire going to it. Find it, remove it, hook an ohm meter to it, put air pressure to it gradually and see at what pressure it "opens".

http://forums.pelicanparts.com/uploa...1289434701.jpg

mark houghton 11-10-2010 04:29 PM

Quote:

Originally Posted by zaidigonzo (Post 5666848)
I dont have a yellow overboost relay. My car is 84. Is that "normal"?

As to your yellow relay question, I think the '84 may have used a red or black circular relay similar in appearance to those found in the trunk. Here's another picture (disclaimer: Not mine, so please don't sue me!) of where the yellow would be located. You may have a round one in its place.

http://forums.pelicanparts.com/uploa...1289435299.jpg

zaidigonzo 11-10-2010 04:39 PM

ok! Thank you! found it. Cleaned the connection and clamped it tight. Still cuts off on sustained boost.
Yes, I have a round red fuel pump style relay instead of the rectangular yellow one.
I guess Ill try replacing the overboost unit and see. I have a spare new red relay so I could check that too. The car shuts down when I disconnect the white wire to the overboost switch so its working under normal situations.
The stock waste gate has a new heavy duty diaphragm and 1 bar spring installed not more than 600 miles ago so I doubt it just failed.
Perhaps the overboost switch is bad or too much exhaust flow plus 1 bar spring= overboost reached before the spring opens the waste gate..?

mark houghton 11-10-2010 04:42 PM

Quote:

Originally Posted by A930Rocket (Post 5666789)
Sounds like the WG is plumbed properly. The hose on the side is vented to atmosphere. The hose on top get pressure from the intercooler.

Uhhhmmmm Rocket Man....either one of us is getting old or some brain fart won't let me think correctly, but I believe the top of the WG is vented to atmosphere and the side is the boost signal port. Damn, now I'm going to have to crawl under the car to look-see. I hate it when this happens:confused:(brain fog)

zaidigonzo 11-10-2010 05:02 PM

cool! maybe thats my problem......
let me know if you find out how yours is plumbed Mark. Thank you ALL

s5uewf 11-10-2010 05:04 PM

Mark, I agree. I think the IC routes to the side (at least for Tial WG) and vents through the top.

http://www.tialmedia.com/documents/w3_tial_wginstall.pdf

mark houghton 11-10-2010 05:41 PM

Quote:

Originally Posted by s5uewf (Post 5666972)
Mark, I agree. I think the IC routes to the side (at least for Tial WG) and vents through the top.

http://www.tialmedia.com/documents/w3_tial_wginstall.pdf

I stewed about this all the way home from work tonight (what....I lurk on this forum during work? Shame on me!). First thing getting home, grab a flashlight and check out my Tial....yep, boost signal on the side. I'm almost certain it's the same as the stock WG but I certainly could be wrong. One thing about this forum, we all support eachother to the max and - guess what - we're not shy if something sounds amiss.

zaidigonzo 11-10-2010 06:00 PM

just switched the hoses. Going for a drive to see.........

zaidigonzo 11-10-2010 06:11 PM

CAR IS FIXED!!!!!
switched wastegate hoses. AWESOME!!

mark houghton 11-10-2010 07:06 PM

Quote:

Originally Posted by zaidigonzo (Post 5667083)
CAR IS FIXED!!!!!
switched wastegate hoses. AWESOME!!

Ahhhh....if life were only such a simple fix. Happy for you, now get out and rod the ***** out of her!!!


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