Slight pedal press, boost shoots up - weird boost gauge behavior

[Andrey Sidorov]

Hey lads, I run a procharger system on my 3v with race bypass valve and fuel return system with aeromotive vacuum fpr. Since i got the car like 4 years ago i always had a weird behavior of my boost gauge- let me explain. The system has a vacuum distribution block (if it makes sense) from manifold that splits into 2 vacuum lines - 1 goes straight to the fuel pressure regulator, another goes to the bypass valve. The line that goes to the bypass has a t-fitting through it where the exit goes to boost gauge (hope that made sense). So the problem that i had since day one - on previous motor and on the new one is that even at low rpm if i press the gas like 15-20 percent in it will shoot up to almost max boost which is around 10 psi, same thing with wide open throttle - 10 psi right away which is max i can have with current pulley even at low rpm. Car drives very well, boost feels gradual, no weird behavior, bypass works as expected, no surge, but that gauge weirdness kind of freaks me out sometimes. Does it suppose to work this way?, i understand its a vacuum gauge and it changes with throttle input, but still 10 psi at 2000 rpm wot lol? I redid vacuum fittings with plumbers tape, still same behavior. Lito pointed out to me this recently when i sent him logs with video of afr and boost - logs look good, but what gauge shows isnt. Recently i had instances where gauge was capping at 7psi instead of 10 as well. Anyone has an idea what it could be? gauge , vaccum leaks, or maybe the whole setup is wrong? Video of wot 3rd gear to 4k rpm attached, maybe im just confusing myself and its normal
https://drive.google.com/file/d/1se_YCGFIBY6dnv4XZKmiSPhCNHv_E2P7/view

 

[Forty61]

No basis in any knowledge or science but I personally would want a direct line from the motor to the gauge with no manifolds, splits etc..

 

[86GT351]

Change he routing to make the gauge line direct to it from engine. What companies gauge is it?

 

[redfirepearlgt]

first thing i would do is relocate to another tap point to monitor vac/boost. if that fails try a secondary source...meaning a different gauge or means of measuring boost and vacuum with another device. third begin investigating the bypass valve for issues.

i am assuming this is a mechanical gauge since you did not state.

 

[07 Boss]

Try and run it off the other vacuum line or get a manifold with 3 outlets. I run my gauge off of a T from the FRPS without any issues but I also have an electric gauge. Also don't have a ProCharger and can't remember without looking where I tapped for the bypass valve.

 

[Andrey Sidorov]

Change he routing to make the gauge line direct to it from engine. What companies gauge is it?

Aeromotive gauge, thats what i thought would be the best way, im not sure where to line it from tho, the way it is setup now is the way procharger recommends it with their supplied manifold vaccum block from driver side lower port on the front of the manifold

 

[Andrey Sidorov]

Try and run it off the other vacuum line or get a manifold with 3 outlets. I run my gauge off of a T from the FRPS without any issues but I also have an electric gauge. Also don't have a ProCharger and can't remember without looking where I tapped for the bypass valve.

Never thought of it, actually yeah, will try to run it from fuel pressure sensor vaccum line, maybe there is just to much going on in the manifold that i have from procharger - regulator, bov and gauge all run from one manifold, then i changed gauge to t fitting from bov and plugged the hole in the vaccum manifold, it made it better, but still some weird shananigans happen

 

[Andrey Sidorov]

Never thought of it, actually yeah, will try to run it from fuel pressure sensor vaccum line, maybe there is just to much going on in the manifold that i have from procharger - regulator, bov and gauge all run from one manifold, then i changed gauge to t fitting from bov and plugged the hole in the vaccum manifold, it made it better, but still some weird shananigans happen

Actually another question, while we are on the topic - the stock intake manifold that i have now the driver side bottom port is what is procharger vaccum manifold is connected to, but the top port goes to some vapor canister, not sure what that is, i might be wrong, but cant i just disconnect it and run the line from there?

 

[Andrey Sidorov]

No basis in any knowledge or science but I personally would want a direct line from the motor to the gauge with no manifolds, splits etc..

I would want that too, but im not sure where i can plug stuff in considering i need 3 vacuum sources then for Gauge, regulator and bov

 

[Laga]

For those of you tapping into the vacuum line of the FRPS, this is from the Edelbrock website.

“CAUTION: Never cut into the vacuum lines leading to the fuel rail pressure sensor and bypass actuator, on the driver's side of the manifold, for the purpose of tapping in a boost gauge. Interruption of the vacuum signal to the fuel rail pressure sensor can affect the fuel pressure reading to the PCM, which can result in engine failure! Furthermore, this port reads pressure before the intercooler, and therefore is before the inherent intercooler pressure drop. Readings from this port will always be approx. 20% higher than what the engine actually sees.”

This is not in the installation manual, but on the FAQ section of the website. I had my boost gauge initially “T”ed into the FRPS line and experienced the 20% drop when I switched. I don’t think this will happen with a Procharger intercooler, but it’s not an ideal place to get a boost measurement. And leaks or malfunctioning boost gauge can cause a false signal for the fuel pressure.

 

[Andrey Sidorov]

For those of you tapping into the vacuum line of the FRPS, this is from the Edelbrock website.

“CAUTION: Never cut into the vacuum lines leading to the fuel rail pressure sensor and bypass actuator, on the driver's side of the manifold, for the purpose of tapping in a boost gauge. Interruption of the vacuum signal to the fuel rail pressure sensor can affect the fuel pressure reading to the PCM, which can result in engine failure! Furthermore, this port reads pressure before the intercooler, and therefore is before the inherent intercooler pressure drop. Readings from this port will always be approx. 20% higher than what the engine actually sees.”

This is not in the installation manual, but on the FAQ section of the website. I had my boost gauge initially “T”ed into the FRPS line and experienced the 20% drop when I switched. I don’t think this will happen with a Procharger intercooler, but it’s not an ideal place to get a boost measurement. And leaks or malfunctioning boost gauge can cause a false signal for the fuel pressure.

Thanks for the info, didnt do that yet, so eliminating frps vaccum from possible sources