Re: Low turbo boost - '86 5KCSQ

[George Simmons <gsimmons@sjm.infi.net>]

Thanks for your reply.

Re altitude, I'm at 6400ft (near Lake Tahoe, CA).

I pulled the oil dip stick and the engine promptly died; now I'll try your leak detection suggestion.

Thanks again.

Robert Myers wrote:

> At 03:03 PM 10/16/97 -0700, you wrote:
> >The boost on my car maxes out at 0.9 these days vs about 1.4 a few miles
> >ago.  I've performed the checks listed in the Bentley manual and have
> >come to suspect either the wastegate or the wastegate frequency valve.
> >The boost behaves the same whether I disconnect the electrical
> >connection to the frequency valve or not.  Before I pay my mechanic a
> >visit, does anyone have any suggestions?
>
> Check for leaky fuel induction system.  Simple procedure attached.
>
> I'm surprised at only 0.9 bar.  1 bar should be "normal" with a huge leak.
> Are you at a high elevation?
>
> > I'm also interested in the actual operation of the frequency valve; two
> >vacuum(pressure?) hoses in, a vacuum(pressure?) hose out to the
> >wastegate, plus a two terminal electrical connection from the engine
> >control unit.....   Anyone know the theory of operation?
>
> The WGFV applies pressure to the outer side of the WG diaphragm.  In effect
> it acts as an added spring to reinforce the metal spring and allow greater
> boost pressures than just with the spring alone.  This added boost
> capability is controlled by the WGFV which is, in turn, controlled by the ECU.
>
>                                                   ------------------------------------------------------------------------
>
> To check for vacuum leaks:
>
> 1.      Let the car idle (if it will) and pull the oil dipstick.  If the engine dies (or falters severely) there is probably a leak.  (The system will compensate for some leakage but when the large added "leak" of the open dipstick hole is present it's too much leak for it to compensate for sufficiently.)
>
> 2.      If a leak is indicated, with the engine idling, spray the various rubber parts both on the intake system and the pollution control stuff with ether based starting spray.  (You know, the stuff your grandfather sprayed down the carburetor [remember those?] of his old DeSoto on a -10F morning.)  When you spray the leaking region the rpms will pick up.  This will help indicate the area to search for the leak.
>
> Caution!  Warning, Will Robinson!  Ether is extremely flammable.  Work outdoors away from sources of ignition.
>
> Note: Some have used an unlit propane or butane torch in place of the ether.  Take your pick.  Either works.
>
> 3.      A very common spot for leaks to develop on turbo cars is the intercooler --> throttle body hose (looks like the "Michelin Tire Man").  Actually remove it and do a close inspection - particularly the bottom side where you can't see it when it's installed in the car.
>
> 4.      While this hose is off, feel the inside.  A coating of oil is normal but there should be no grit or small bits of metal.  If there is, you probably have troubles with the turbo itself.
>
>                                                   ------------------------------------------------------------------------
>
> ___
>    Bob
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