Boost Unstable.

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sjbsuperman1425
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Boost Unstable.

Postby sjbsuperman1425 » Tue Aug 28, 2018 10:25 am

I have a S14 T28 BB turbo with stock wastegate actuator and recently I've been having issues with my boost pressure fluctuating, spiking, or just being lower than normal. I tested the boost controller (HKS EVC-S) and it functions properly. The solenoid works at specified settings and warning function works at set pressure. The issue I'm having is when I set the offset on the controller the other day, it was holding 10psi in all gears just fine. A day later, in hot/humid weather, it was working but after about 20 minutes of highway driving it started to drop 1-1.5psi. Now today, cooler/rainy, it is boosting 12psi or more. I understand it's not huge jumping numbers, but it just seems unstable and I'm pretty certain changes in weather shouldn't create that much of a change on boost pressure. I put pressure to the wastegate itself bypassing the controller solenoid and it moves feely and I didn't notice anything wrong there. Could the internal spring of the wastegate or the diaphragm be failing and causing these issues? I'm really stumped at this point and just looking for input.

Thanks guys.


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Re: Boost Unstable.

Postby sjbsuperman1425 » Wed Aug 29, 2018 5:22 am

I would like to add that turning the boost controller off, the turbow/wastegate holds about 6psi and doesn't creep. Very puzzled because this makes me want to say there is a problem with the boost controller.

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Re: Boost Unstable.

Postby float_6969 » Wed Aug 29, 2018 6:46 am

To me it sounds like a faulty/failing MAP sensor for the boost controller. Is it integrated into the controller, or is it separate. Specifically, it sounds like the barometric compensation side of the sensor is failing. If the sensor is external, there should be a small hole in the housing of the sensor somewhere. Make sure that hole hasn't gotten plugged or covered up somehow.

I could also be a grounding issue. If you have a bad ground associated with the controller, your boost levels may not read correctly and the boost won't be stable.

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Re: Boost Unstable.

Postby sjbsuperman1425 » Wed Aug 29, 2018 7:18 am

I guess I wasn't even aware of such a thing as barometric compensation. The sensor is separate from the controller, but is mounted in a spot that does tend to get dirt there so I will have to check that and double check the ground.

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Re: Boost Unstable.

Postby float_6969 » Wed Aug 29, 2018 8:13 am

Most MAP sensors have it integrated into them. The old GM sensors didn't, and so they would have two sensors. The one connected to the manifold, and then another that was just open to the air. They later figured out that if they exposed the back side of the pressure transducer inside the sensor to atmosphere, it would self compensate and the extra sensor was superfluous... At least that's what I read on the internet once, LOL!!!

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Re: Boost Unstable.

Postby sjbsuperman1425 » Wed Aug 29, 2018 9:48 am

Interesting information. That's how the boost controller's pressure sensors work on most if not all boost controllers?

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Re: Boost Unstable.

Postby float_6969 » Wed Aug 29, 2018 10:31 am

From what I understand, yes.

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Re: Boost Unstable.

Postby sjbsuperman1425 » Wed Aug 29, 2018 4:49 pm

I check the sensor and there isn’t another port for ambient pressure. I popped the cover on it off and there is only a circuit board so I’m assuming it’s good since the pressure it shows corresponds with my analog gauge in the dash. I put some pressure to the wastegate and that holds air as well no leaks. The solenoid also is functioning properly when key on engine off and air is applied. I did all these tests and took it for a drive and it held 9.8-10.1 psi strong in any gear.

I’m baffled to say the least. Maybe something is starting to fail and I just can’t reproduce the sequence of events needed for it to act up. It’s also not as hot or humid today as it was 2 days ago. Michigan is crazy like that

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Re: Boost Unstable.

Postby float_6969 » Thu Aug 30, 2018 6:50 am

Well that's annoying, LOL!!! Intermittent issues are always such a PITA.


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