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jt1 jt1 is offline
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Check Valve in Diverter valve line?

I'm working on my 83 Euro 930, which is stock except for cams. It's primarily used for DE events with a few street miles. The problem I'm chasing is that boost threshold rises as engine temp rises. By the end of a DE session, there is a 4 or 5 second delay from throttle application until boost begins to build. My first thought was the wastegate was sticking, but after purchasing another wastegate and replacing it, that possibility has been eliminated. Next thought was that the diverter valve is sticking when it gets hot. Today I removed the diverter valve and cleaned and inspected it. It appears fine. The piston moves freely under its own weight, and there are no scars or scratches on the piston or housing. The end seals appear to have been recently replaced.

I also have a complete CIS system off an 84 Euro 930. Comparing it to the 83 system on the car, I discovered the 83 has a check valve in the line from the intake to the diverter valve, which is not present on the 84. The check valve is oriented so that vacuum from the intake will pass to the diverter, but no air under pressure can go from the intake to the diverter.

Is it possible that the check valve could be holding the diverter valve open? If so, how could engine temp be a factor? And lastly, does anybody know if this valve is supposed to be there on an 83, but not an 84?

Thanks for your help.

John
Old 10-05-2008, 12:22 PM
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Could you post a picture of check valve? BOV plumbing is very complicated on these cars an mine also had some sort of check valve whose function I never really understood. Easiest way would be just replacing it with other check valve or removing it. Maybe it's membrane gets stiff when subjected to heat? Also, fully open BOV during full throttle will force turbo into overspin, as it will recirculate the air.

Is it the one on lower left?

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Old 10-05-2008, 02:37 PM
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jt1 jt1 is offline
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Neither of my systems have the component shown in your pic. Of course, I bought both of them used!

Mine is plumbed into the line:





It is a simple one way check valve. It seems that the only way the diverter valve would close is by leakage past the check valve and by the piston.

John
Old 10-05-2008, 03:06 PM
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Quote:
Originally Posted by jt1 View Post
Neither of my systems have the component shown in your pic. Of course, I bought both of them used!

Mine is plumbed into the line:





It is a simple one way check valve. It seems that the only way the diverter valve would close is by leakage past the check valve and by the piston.

John

yeah you're right. there should be no check valve in that line
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Old 10-05-2008, 03:36 PM
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My car did not have that plastic angled check valve.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 10-06-2008, 12:18 PM
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jt1 jt1 is offline
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To follow up, I took the car to CMP Thurs, and it ran like a champ. You could tell a little heat soak affecting the stock IC by the end of a session, but the delay in the boost threshold is gone.

This begs the question, why was the check valve put there anyway? it certainly had a negative effect on the performance of the car.

John
Old 10-18-2008, 03:00 PM
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Quote:
Originally Posted by jt1 View Post
To follow up, I took the car to CMP Thurs, and it ran like a champ. You could tell a little heat soak affecting the stock IC by the end of a session, but the delay in the boost threshold is gone.

This begs the question, why was the check valve put there anyway? it certainly had a negative effect on the performance of the car.

John

Congrats!! CMP is great! I ran my first PCA club race there in a little NA 944 years ago. Great place, almost like 2 tracks in one...

Who knows on the check valve, people do weird stuff. I built the engine in a tricked up 930 years ago that had a fuel pressure damper plumbed into the WUR fuel line, I never quite understood what he was trying to do but the owner said it cured a surge at high boost in 3rd gear?? I'll never really know for sure
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Old 10-18-2008, 06:09 PM
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RE: the FP damper, I think Mercedes used it too.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 10-19-2008, 02:17 AM
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