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Discussion Starter · #1 ·
To start, I'm running Stage 1 with a TD04, Viggen intercooler, & a Forge BOV. Base boost is at 5psi. Right now, at WOT I hit 20psi but then fall back to 16-17 psi instead of holding a steady pressure.

From what I've read, it seems like a wastegate issue. Any other thoughts?
 

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Could be numerous things. Boost leak. Failing Turbo. Bad or incorrectly set waste gate actuator. Failing apc solenoid. If it holds in lower rpm and dies off higher you could be maxing the Turbo or even over spooling. That will lead to carnage. I was pushing 15 psi on my factory gt17 when it let go. The compressor wheel litterally exploded.

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Discussion Starter · #3 ·
Wastegate has been adjusted according to stock base boost numbers. I have a spare APC I may swap in. Otherwise I haven't read anything that would suggest a TD04 can't hold at 20psi.
 

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Are you sure stage 1 boost pressure isn't 15psi? Hitting 20 then dropping is called a spike

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Discussion Starter · #5 ·
Are you sure stage 1 boost pressure isn't 15psi? Hitting 20 then dropping is called a spike

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That I'm not sure of. I'm just surprised it would spike 5psi over normal without hitting fuel cut.
 

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With staged tunes they usually remove the ability to hit fuel cut or set the value to its maximum. It is assumed that most people install a wideband system to monitor their air fuel ratios.

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Discussion Starter · #7 ·
With staged tunes they usually remove the ability to hit fuel cut or set the value to its maximum. It is assumed that most people install a wideband system to monitor their air fuel ratios.

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I know it still has fuel cut (played around with a mbc). I'll have to call genuine Saab to figure out what psi i should be boosting to.
 

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Stage 1 should be 16-17 psi. The 20 psi spike is not uncommon. Usually requires some fine tuning of the boost control maps to sort out. Most people just live with it so long as the spike never hits fuel cut. Quite surprising to see a spike like that with so little base boost though, most people have base boost set at around 7 psi.
 

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I know it still has fuel cut (played around with a mbc). I'll have to call genuine Saab to figure out what psi i should be boosting to.
I had a problem little while back where my MBC's ball bearing came unseated after threading in too far and was causing erratic boost. Pull the MBC out and remove the side nipple if it has one and observe if the spring is still centered on ball, and that the ball is still blocking the port.

If you're running a stock IC at higher boost levels, it might be out of it's efficiency range. I know mine struggled @16.5 psi so I upgraded to an all aluminum FMIC which I'd suggest you do at some point.
 

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Sounds perfectly normal to me. Very common amongst folk who run a t5 apc valve. If you wish to have better boost control, switching to a t7 apc will help. You will also need to hard mod the ecu and re program the ecu to allow the t7 valve to be used. Worth doing though as t7 valves are around 5 times less expensive when they need replacing and are considered more reliable.
 

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Discussion Starter · #11 ·
Sounds perfectly normal to me. Very common amongst folk who run a t5 apc valve. If you wish to have better boost control, switching to a t7 apc will help. You will also need to hard mod the ecu and re program the ecu to allow the t7 valve to be used. Worth doing though as t7 valves are around 5 times less expensive when they need replacing and are considered more reliable.
Any write ups on how to do the mod? (I'm at work, otherwise i would search).

Also, I cleaned the purge valve and replaced the hose from the throttle body to the valve. That helped a good amount.
 

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This is the hardware change you need to make to the ECU in order to run a T7 apc valve. There are then two control frequencies that have to be changed in the map that is flashed onto the ECU. Than all you have to do is connect the correct pair of pins to the T7 apc valve and it should operate.
 
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