OK - My 740 turbo had just made a great run down the on-ramp. I opened the throttle up a little to get up a hill and noticed something wrong. I could not get any boost. The car runs fine(i.e. no smoke & no drama, just no boost)and revs great. I did read the FAQ's. I checked for:

1. split hoses (which were just all replaced in January),

2. broken CBV (plugged it and got no boost)

3. took off the Dawes device (just in case)

4. Turbo does spin freely

The other things to check for in the FAQ were:

Faulty Wastegate or controller (how do I check that for this year?)
Plugged cat (can a car go 65 mph at 4500rpm with a plugged cat?)

I of course have the usual little funds and would like to fix it myself.


Thanks to all who reply.
Phil

Here is what it looked like when I got under the car. It was a 30 second fix with a small cotter pin. Unfortunately the 30 second fix was ofset by the 2 hour gas filter replacement that I decided to do while the car was up. Working under the car 100 degree weather while sweat drips down the back of your neck and into your eyes as you try to get leverage on a varnish encased filter was a life altering experience. Wait maybe that was the gas fumes.....

-Phil

Well I gotta hand it to the members of this forum. The answer was given here. I was able to get a look under the turbo and the actuator arm did fall off. The wastegate just flaps back and forth while the car is off. If there is a spring to hold it open or closed it isn't on my turbo.

Thanks much to the guys who called it dead on.

-Phil

I have 87 745 with a mitsy turbo, I had the exact same thing happen and it was the waste gate arm. the arm comes out of the actuator and connects to the waste gate in the exhaust manifold, on mine this is under the manifold. What happened was that the cotter pin that held the assembly together rusted away and the arm disconnected, leaving little to no boost. It sounds very similiar to your situatiuon because of the sudden loss of pressure. Does you gauge read little pressure? (below the yellow)

let me know if you find anything!!

mike 87' 745T

Wow- I thoughtif the actuator arm fell off that the boost would max. Yeah, my gauge reads no boost at all. HOw do you get to the arm? I can't even see it from the top.
-Phil

If the actuator arm disconnected from the wastegate, you'd have TOO MUCH boost. Look elsewhere.

Do you hear the turbo at all?

Take off the intake - see if the turbine is free to move. Possible you lost your turbo. Happened juyst like that on my '89. Just stopped working, just after an accerelation.

doesnt the wastegate open to divert exhaust gas away from the turbine, essentially lowering boost pressure? and if so wouldn't a car loose pressure if the gate was disconected and allowed to flap wide open anytime exhaust was flowing. Is there supposed to be some kind of spring apparatus holding it closed? When my gate arm became diconnected the gate simply flapped around and didnt allow my turbo to spool up really very much, but as soon as I reconnected it the pressure was back.

Let me know if my thinking is off or my car is just wacky!!

thanks
mike

Yeap, you're right (I'm also "tbone"). Sorry about that, I was thinking of the HOSE to the wastegate, which if it falls off will give you some hairy acceleration for a short time.

If the rod from the waste gate actuator is not connected to the waste gate armature, you might experience exactly what you are experiencing. Hope that's all it is.

I did take off the intake hose and the turbine does spin freely. I think I can hear the turbo but that might just be the CBV.

Phil

You can only get to it from under the car, wait till it's stone cold and get under there and you will see a rod up there somewhere connected to the turbo, it should all be connected and not stuck open or shut.