Testing the overboost protection switch
 

How do I test the overboost protection switch to make sure that it vents through the top of the switch in an overboost situation?

-Joe

testing
 

Hi Joe,

the switch in the manifold: I fixed a hose from the compressor to the thread of the switch and checked with gauche and voltmeter. 1.2 bar I think.

the valve on the firewall: blow in from the manifold side and check the way to the IP. Give 12 V to it and check whether the way to IP is shut and the valve is vented.
For a short test you can hear the click when giving 12 V.

Tom

I believe the switch on the manifold itself is fine. How do I give the switch on the firewall 12V?

the switch on the manifold brings ground to the valve.
Just disconnect the socket of the manifold switch and bridge to ground. Then you should hear the click of the firewall valve.
Or: disconnect the socket of the firewall valve and test the pins. The BL/YL/RD should give you +12V the BR/BK, leading to the manifold switch should give you nothing until the shut off pressure is reached.

To believe that the mainfold switch is o.k. is not enough in my opinion.
I feel better being sure it works.:D

Tom

Mine hasn't even been hooked up since I bought the car. I 'm doing fine without it.

Until your engine blows up.

I think it would have blown by now. I put about 70,000 miles on the car without it. The last 10,000 or so with a boost gauge hooked up and a controller dialed in to about 14psi.

you will continue to be fine too, until your wastegate hose breaks, developes a leak, or pops off. Then you have problems.


The overboost solenoid is a failsafe if that ever happens.

I just went out and tested it. That sucker didn't pass the tests, looks like I'm going to have to go out and get a new one. Thanks for your help everyone.

-Joe

Don't you mean if it gets kinked or blocked?

no...the wastegate actuator uses boost pressure to overcome spring pressure holding the wastegate closed and open the wastegate when pressure is greater than that spring pressure (wastegate is a bypass to the exhaust turbine of the turbo) take that away from a leak or whatever (hose off) and it never opens continuing to build boost up to the limits of the turbo or until the motor goes bye-bye. Whichever comes first.

It has occurred to me that one might use the manifold pressure switch (overboost sensor) to switch a small piezo siren (e.g., one of the Mallory Sonalert units) located in the cabin. These can be had surplus for cheap, and many models are loud enough that they would be hard to ignore.

That might be just the ticket for someone who is (1) really cheap and/or (2) philosophically opposed to the stock overboost protection plumbing arrangements.

slightly off topic
 

So one of those dawes devices just plugs right into the small (what 10 inch long, 1/2 inch thick) line that goes from the turbo to the wastegate controller?

I'm on the road now, several hundred miles from my car. Just trying to get an idea of what is where.

I will install a boost gauge to check function before spending the few bucks on the dawes device.

I plan to T into the boost line right where it goes from the banjo bolt, into the overpressure sensor.

JP

all the Dawes device does is bleed off boost pressure in the line that goes to the wastegate actuator....be warned that you are going to get oil all over that side of the bay after a time as boosted air includes blowby and oil mist from the valve cover and it will get messy after a while...if your boost is 10-11 psi you will gain nothing by cranking it up higher. Speaking from someone who has used one on my W116...in conjunction with IP modifications.

Thanks
 

I guess i have to have patience.. something in short supply when it comes to fixing up this cool car I just got.

:)

I will see what the gauge reads when i get it. I think the most effect will be the ALDA adjustment... as the car is sluggish pre boost. It still has the factory seal on at 169k

How do I tell which kind of turbo I have?

More threads to search now.. :)
JP