Boost fluctuation

Terrencemitch88

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Hey boys!!!

just took my car out on the hi way for a ride and I have noticed that the boost we’ll fluctuate from 0 psi to 5 or 6 psi with the gas paddle in the same spot but once I eased off the paddle or give it just a hair more it we’ll stop. It’s fine around town driving just seems to do it on the hi way.

I have check all around my intake and throttle body there’s no leaks and my mass air is clean.
 

PM-Performance

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No belt slip, I have a metco auxiliary idler pulley

While I agree it’s not belt slip, just because you have that doesn’t mean there won’t be slip.
If I were to guess this sounds like a bypass issue. Could be as simple as vacuum source to the bypass.
That’s where I would start atleast.

Doest it make full boost when you stand on it?
 

SCGallo2

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Keep in mind if you have uncommanded boost, you can overheat the rotors and smoke the blower. You need to limit driving and figure this out.
 

SCGallo2

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I believe you have a Whipple. If so, start here:

Whipple bypass test.jpg

Whipple bypass rear.jpg
 

Catmonkey

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If you're looking at the factory gauge, just ignore it. It really has nothing to do with boost. It's an inferred reading derived from engine load. Unless you're bone stock, and even then, it's not going to be correct. But even if it's the stock gauge, movement shouldn't be erratic. You can't assume it's actually related to boost, however. Have you checked for codes?
 

Terrencemitch88

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While I agree it’s not belt slip, just because you have that doesn’t mean there won’t be slip.
If It were to guess this sounds like a bypass issue. Could be as simple as vacuum source to the bypass.
That’s where I would start atleast.

Doest it make full boost when you stand on it?
Yes It we’ll make full boost once you get on the paddle
 
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Terrencemitch88

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Terrencemitch88

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If you're looking at the factory gauge, just ignore it. It really has nothing to do with boost. It's an inferred reading derived from engine load. Unless you're bone stock, and even then, it's not going to be correct. But even if it's the stock gauge, movement shouldn't be erratic. You can't assume it's actually related to boost, however. Have you checked for codes?
It has a 2.9 whipple gen 3, 127mm jlt , twin 65mm cobra jet throttle body, kooks long tubes with off road xpipe, running an aftermarket ford racing boost gauge it’s tune by hp tuners. Would it probably be in my tune? I tried to phone my tuner but no answer yet.
 

SCGallo2

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yes I have a 2.9 gen 3, I check my by pass today and it’s not stuck close, if the by pass was stuck close or didn’t work properly would I have a wrench light on? Or check engine light?

The bypass actuator is entirely mechanical, works off vacuum or lack of vacuum; I doubt that it would trip a fault, however it might cause other monitored conditions to be out of normal parameters, tripping a fault... I’m really not sure.

The vacuum source is tapped into the upper intake manifold under the back of the blower, doubtful that you can see anything without a small inspection mirror and flashlight. I would double check all connections on the blower for a vacuum leak.

The only other thing I can think of that I would do if i were having this issue is datalog THROTTLE ANGLE COMMANDED, THROTTLE ANGLE ACTUAL, and PEDAL POSITION to see your throttle input and what the car is actually doing. If these were too far out of agreement, I would think it would trip a fault.
 

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