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1991 740... Turbo upgrades/replacement?

^ This. With the actuator removed, clamp the rounded nut in a vice, then you can use vicegrips on the rod end to break it free. Once that is off, you can remove the rounded nut & replace it - after you clean the rod threads and apply never-seize to the threads
 
Take the inlet hose off the front of the turbo and you should have plenty of access to the bolts holding the bracket to the turbo. It will be helpful if you have a vice or something else to clamp the actuator in place while you put a vice grip or something on the locknut. Once it’s off you can just remove the nut from the arm and replace it with a hardware store one. I bet it’s M6x1.0 or something common like that.
 
ortho stice said:
Take the inlet hose off the front of the turbo and you should have plenty of access to the bolts holding the bracket to the turbo. It will be helpful if you have a vice or something else to clamp the actuator in place while you put a vice grip or something on the locknut. Once it?s off you can just remove the nut from the arm and replace it with a hardware store one. I bet it?s M6x1.0 or something common like that.
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Fixed it. Sadly adjusting the wastegate actuator made no difference.
The boost bar only goes about 1/4 of the positive pressure.
Waiting for my boost controller to arrive in the mail so I can see exactly how much boost in digital I have at the turbo. Should I put a manual boost controller on it to see if there's a way to increase it? Or should I just replace the turbos? :oops:
 
Have you checked all the basics? All related hoses in good shape/not soft/collapsing/leaking? Air filter, Timing, fuel pressure, plugs, etc??

Could be you have serious cracks in the hotside preventing building boost, but you need to know the status of all related systems. When you removed the inlet hose, did you check for radial play in the compressor shaft? (Not that that in of itself would prevent full boost, just indicator of turbine health).
 
1/4 of positive pressure on the stock gauge doesn’t sound that far off but it’s been awhile since I was running a stock turbo setup. If I remember correctly you had no boost pressure at the beginning of this journey. Stock wastegate spring is around 6-7 psi if my memory serves.
 
ortho stice said:
1/4 of positive pressure on the stock gauge doesn?t sound that far off but it?s been awhile since I was running a stock turbo setup. If I remember correctly you had no boost pressure at the beginning of this journey. Stock wastegate spring is around 6-7 psi if my memory serves.
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There was but it was barely anything. Adjusting preload got me a tiny bit more.

lookforjoe said:
Have you checked all the basics? All related hoses in good shape/not soft/collapsing/leaking? Air filter, Timing, fuel pressure, plugs, etc??

Could be you have serious cracks in the hotside preventing building boost, but you need to know the status of all related systems. When you removed the inlet hose, did you check for radial play in the compressor shaft? (Not that that in of itself would prevent full boost, just indicator of turbine health).
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Yup I checked everything else, replaced lines, filters, fuel pressure regulator, plugs, coils, distributor.
I just did a major overhaul on all the common failing parts to get the car back to stage 0.

I also checked the compressor shaft for any play, and none.

Would the waste gate not be sitting properly?
 
I suppose anything is possible. You could remove the down pipe (just undo the nuts and force it to the side) and look in through the outlet to make sure the wastegate is seated properly and doesn’t have some kind of huge crack.
 
ortho stice said:
I suppose anything is possible. You could remove the down pipe (just undo the nuts and force it to the side) and look in through the outlet to make sure the wastegate is seated properly and doesn’t have some kind of huge crack.
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This would be a great idea, since he could have a clogged cat (and this would immediately confirm) - that would definitely cause the symptom & is more likely than the turbo at this point
 
lookforjoe said:
This would be a great idea, since he could have a clogged cat (and this would immediately confirm) - that would definitely cause the symptom & is more likely than the turbo at this point
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No clogged cat. The car passes SMOG with no problem with flying colors.
I'm thinking perhaps its time for a new turbo. :oogle:
 
Have you pulled the CBV off to check the diaphragm yet? This idea that the turbo is “bad” doesn’t make a ton of sense to me. Why is it bad? How is it bad? Throwing another turbo at it might put you right where you are today.
 
How difficult is to obtain exact psi boost reading and be done with guessing about the turbo?

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Studie said:
No clogged cat. The car passes SMOG with no problem with flying colors.
I'm thinking perhaps its time for a new turbo. :oogle:
Click to expand...

Doesn't test under load, which is when the restriction will **** your backpressure & kill boost

Not hard to unbolt the DP & wedge a screwdriver in there to maintain a gap (leak), drive around the parking lot. You will know immediately if the symptom is resolved.
 
If that is a low pressure turbo the waste gate actuator would be set at about 4 psi. When I was running one of these on my 88 765 I used a washer between the compressor housing and the actuator on each of the 2 bolts to move the actuator as it wasn't adjustable. Ended up with 7 psi.
 
Re-seated the preloading arm to a bit more than half of the hole. Changed the fuel regulator and deleted the sponge in the airbox.

Added a whole tank with some octane boost and injector cleaner, ran the car for a long drive and voila we are back in business!

There is nearly half of the positive boost on the OEM gauge at WOT. Car runs well, flushed the engine, and replaced the oil with Liquimoly 5w40 + MOS2 treatment since we get super cold winters here, and planning to do the coolant tomorrow. Car is idling perfectly.

Will pull the downpipe and get the exhaust worked on over the winter, hopefully, see some more power with this dinky 13c turbo.

I guess it's time for a manual boost controller?! :rofl::oogle::oogle:
 
Alright so the weather is warming up finally and I'm going to install my boost controller that I got with a digital boost gauge.
Does anyone know what kind of T taps do I need for the boost hoses? Would 1/4" for the hoses work?
 
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