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ViPEC Commanding Incorrect Wastegate Duty Cycle

seattle express

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Hello all,

I have an issue that's causing the car to limit boost. Here's the story, I hope you'll bare with me:

The car was tuned for 30psi maximum boost and has run on that setting for years without a problem. Recently, my transmission failed, so I decided to swap in a bigger better one. After the swap was completed, I drove the car normally for a while to break in the new trans and clutch. When I attempted my first full throttle run, I noticed the boost wouldn't exceed 20psi roughly. I tried a couple of more times in the following days and it wouldn't boost more than spring pressure which is 18psi.

I decided to check my WG DC. My WG DC table has 50% DC which tapers down to 37% as the RPMs climb. So I logged WG DC while doing a WOT run and found that the ViPEC commands 85% for stage 1, then 95% for stage 2.... 

The car built boost fine for years... I checked the wastegate plumbing and it looks fine. The photo below shows how it's routed.

I feel like I'm at a dead end and I'm out of ideas.. I appreciate your help!


Image result for wastegate boost solenoid diagram

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There is something wrong with your wastegate/turbo/plumbing/boost valve.  You are in closed loop mode so the numbers in the wGate DC table is just the starting point that the ecu uses as it enters stage 2.  The ECU is winding more DC in to try to bring your boost up to target but the boost is not responding.  Either there is a big leak or the wastegate is stuck open.

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  • 2 weeks later...

Adam, I checked the hardware. No leaks in the turbo manifold. Everything is sealed up. I put a pressure gauge on the line from the boost solenoid COM port to the top port of the wastegate and it's getting high pressure. I tested the boost solenoid and it switches just fine. I ran pressure to the top of the and bottom ports of the wastegate and the valve moves just fine. Everything works mechanically when tested.

Another thing I tried was to increase wastegate spring pressure to see how it responds. It boosted at the higher spring pressure just fine but it wouldn't boost more than that. It's limited to spring pressure only for some reason.

I'm honestly stumped. I have no idea what's causing this. What other variables should I be looking at here?

Maybe a hairline crack in the turbo manifold is causing this? But if that were the case, why would it hold the higher spring pressure? I'd imagine it would boost the same between low and high pressure springs.. Also a crack that small wouldn't be able to leak out enough exhaust pressure to drop that boost THAT much..

Is this the correct vacuum line routing for my ECU settings? I'm almost positive this is how it was before the issue started.


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What happens if you put the Aux to test on so the solenoid is at 100%, This should give you as much boost as the turbo will make assuming all is plumbed correctly and the solenoid turns on. (be ready to pull out of the run as boost is effectively uncontrolled) 

If you don't get the boost then it points to plumbing or faulty solenoid.

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Simon, I put a pressure gauge on the line that connects from boost solenoid COM port to wastegate top port. The wastegate top port is getting high pressure. So I know the solenoid is working, otherwise it wouldn't allow boost to that line.

Also, after driving the car for 9 years on the same settings, I know exactly what the wastegate sounds like when it cracks open during a WOT run. I'm not hearing it open anymore. It's closed throughout the whole run but it's not building the correct boost...

It's already commanding 85-95% DC but I'll still try a cautious WOT run with Aux set to test (on) as you had recommended just to see if it makes any difference.

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Update: I pressure tested both top and bottom port to the wastegate. The top has a small hiss and the bottom rushes air at a good pace out of the valve guide. So I sealed the airgaps in the top port and  I clamped the vacuum hose to the bottom port shut. That way, all boost was directed to the top port which was supposed to keep the wastegate valve shut. I also set the boost solenoid Aux to 'test (on)' so that the solenoid would allow full boost to the top port. I thought to myself "surely, I'm set now!"... 

The result... No luck.

I am truly humbled. I have NO idea what's causing this.. The only thing left I can think of is a cracked manifold, but I took it off and visually inspected it for cracks and couldn't find any. 

In response to the possibility of an exhaust restriction, I added an exhaust valve last week, but this issue's been going on before adding the valve. I also disassembled the exhaust and verified the valve isn't stuck. The exhaust is 4" diameter which is overkill for the power I'm making. I doubt it's restricted.

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