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Discussion Starter · #1 ·
I just got a 1989 supra turbo, I've been messing around with it for close to a week now chasing a code 34. Abnormal boost pressure. The car seems heavy at low rpm and once the boost kicks in its great until the boost gauge gets pegged and the cel turns on and the car shudders violently. I can let off the gas and get back on it and its fine until the boost catches up. Then the same thing happens. It has a factory replacement ct26 turbo and an aftermarket bov. Everything else is stock for the most part. All the research I've done everyone swears up and down its a boost leak in the ic piping. I've checked and rechecked and pressure checked and everything seems great. Can someone explain how a leak cause an overboost code and the appearance of too much boost?
 

· ƒ=1/2π(√k/m)
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Get an air compressor and air pressure regulator you can slowly increase pressure.

Attach it to the wastegate actuator. Slowly increase the air pressure and observe the actuator arm.
Note when the arm starts moving.

You mentioned the gauge is "pegged".
That means you're over boosting past 8 psi.

You may have a shimmed wastegate, or something else not right with the turbo.

Let me know what you find.
 

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Discussion Starter · #3 ·
I used a hand vacuum pump and pressurized it, it starts to open around 5 psi and is fully open at almost 9 psi. Do I need to find a way to get it to be fully open earlier? As far as I have been able to find through the forums the fuel cut out shouldn't be until 10-12 psi on a stock car.
 

· ƒ=1/2π(√k/m)
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Fuel cut and boost pressure can be mutually exclusive (with an AFM). For example, you can have a boost leak, and still trip the system because the AFM sensor is reading heaps of air but it’s not making it to the engine.

Do you have an aftermarket downpipe or exhaust?

The gate should be open 100% by 6.5-7psi.
 

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Discussion Starter · #5 ·
The down pipe does appear to be an aftermarket peice of sorts, homemade Straight pipe through the cat. If I try to get the valve open early with the actuator I'm likely to have it partially open at all times, is that a concern?
 

· ƒ=1/2π(√k/m)
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The down pipe does appear to be an aftermarket peice of sorts, homemade Straight pipe through the cat. If I try to get the valve open early with the actuator I'm likely to have it partially open at all times, is that a concern?
I’m willing to bet your problems are associated with the exhaust.

It would be nice to know what actual boost it’s producing. Through a peak-hold gauge, or other device.

Is this downpipe and elbow restricting the movement of the flapper of the wastegate any?

On a cold night, with an open exhaust, it’s quite common to hit fuel cut. (Everything else stock. )
 

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Discussion Starter · #9 ·
The turbo based on part number is a stock replacement ct26 turbo. Intended to bolt right in no adjustments nessicary. Looking at the elbow for the exhaust, it is factory. After that the flex pipe looks factory but the cat was cut off.
 

· ƒ=1/2π(√k/m)
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With an open exhaust (even stock elbow), boost pressure can climb. I think I was getting about 10psi.
After you get the gauge in and see how much boost it's making, I think it would also behoove you to check for boost leaks.

You can make a tester pretty simply with some PVC pipes and rubber couplers. (I'll find one and link it here.)

The fuel cut could be a combination of open exhaust and a boost leak.
 
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