Where to tap in for boost gauge?

[Beerman]

Installing my AEM boost gauge and wondering if it's best to tap into a line before or after the throttle bodies?

The line on the intake airbox is easy to get to, but there looks to be a vacuum line behind the throttle bodies that's connected to a fuel pressure regulator. Is that the better place to tap in?

Thanks

 

[MrSled]

The line that comes off the Throttle bodys and gets routed down over the air box and over the charge tubes should be the line you want to TEE into.

 

[WVTurboLTX]

I was thinking the same as MrSled when I looked at mine today. Yamaha is just reading the port on the muffler side only. You can see their sensor on a bracket on the throttle boddies. If you didn't want to risk messing with the line over the air box you could probably pull the cap on the clutch side intake port and put a hose on it. Pretty sure the one over the air box runs the bypass valve.

 

[MrSled]

I was thinking the same as MrSled when I looked at mine today. Yamaha is just reading the port on the muffler side only. You can see their sensor on a bracket on the throttle boddies. If you didn't want to risk messing with the line over the air box you could probably pull the cap on the clutch side intake port and put a hose on it. Pretty sure the one over the air box runs the bypass valve.

Basically on a MPI trail turbo the Blow-Off would work like the by pass valve using the same line.

 

[Beerman]

I'm not getting any vacuum on the gauge, so it's either the sensor or where I tapped in. Need to try something different.

 

[Beerman]

Ok, sensor works for both negative and positive pressure (used my mouth). Can feel vacuum is pulling from line where I tapped in. I'm stumped.

 

[MrSled]

Ok, sensor works for both negative and positive pressure (used my mouth). Can feel vacuum is pulling from line where I tapped in. I'm stumped.

View attachment 122828

Thats strange. Follow that line to the throttle bodies, is there a censor at the throttle bodies ?? U should be able to pull one of the nipples on the throttle bodys and run it there as well. But you will not read boost until you are actually loading the motor and it spooling.

 

[Beerman]

Odd, I know. I'm going to try tapping in someplace else and see what happens. I know boost won't build until under load, but I'm not getting a vacuum reading on the gauge at idle or decal on the track stand, that isn't right. Will let you know what I try.

 

[WVTurboLTX]

Like Mr sled said try uncapping another port on one of the throttle bodies and plugging in there. That line you are using goes to a selenoid. Who knows what happens to the pressure on the line when the selenoid fires. It might dump the pressure to relieve it from the fuel pressure regulator. With out a proper shop manual it's kinds hard to tell.

 

[Beerman]

Like Mr sled said try uncapping another port on one of the throttle bodies and plugging in there. That line you are using goes to a selenoid. Who knows what happens to the pressure on the line when the selenoid fires. It might dump the pressure to relieve it from the fuel pressure regulator. With out a proper shop manual it's kinds hard to tell.

That line tees into all 3 throttle bodies and isn't regulated as far as I can tell. The other capped port on the TB was going crazy between positive and neg pressure, so that's a no go. Bought a Bosch vacuum test gauge to verify things. The engine - through that line - only pulls ~3 in of vacuum at idle, which seems really low. The AEM gauge or the sensor isn't very sensitive to vacuum as it sits at 0 and then you'll see it flash 3 and back to 0. I hooked everything back up the way I had it and revved it on the track stand and let off, vacuum shot to 10-12 for a second. On all of Evo's dyno testing the engine is pulling 10 in vacuum on a mechanical Stack gauge, so I still think something is wrong - I'll call OSP tomorrow and ask Jim unless others chime in and say this is expected.

 

[MrSled]

That line tees into all 3 throttle bodies and isn't regulated as far as I can tell. The other capped port on the TB was going crazy between positive and neg pressure, so that's a no go. Bought a Bosch vacuum test gauge to verify things. The engine - through that line - only pulls ~3 in of vacuum at idle, which seems really low. The AEM gauge or the sensor isn't very sensitive to vacuum as it sits at 0 and then you'll see it flash 3 and back to 0. I hooked everything back up the way I had it and revved it on the track stand and let off, vacuum shot to 10-12 for a second. On all of Evo's dyno testing the engine is pulling 10 in vacuum on a mechanical Stack gauge, so I still think something is wrong - I'll call OSP tomorrow and ask Jim unless others chime in and say this is expected.

I really think you are in the correct spot.. if you hold the brake and give it some throttle it will see boost.

 

[**sj**]

fwiw just verifying you are on the back side if the throttle bodies...thats what the engine sees in boost...not before the butterfly

 

[Beerman]

fwiw just verifying you are on the back side if the throttle bodies...thats what the engine sees in boost...not before the butterfly

Hey SJ, I did. It's the line that ties all 3 throttle bodies' pressure together and then routes to the fuel pressure regulator. I did like Mr Sled said and ran it with the brake a little and it made 4 psi and then when I let off hit 12" vacuum, so all seems good. I just thought there would be a lot more vacuum at idle, thus me thinking something was wrong.

 

[MrSled]

Hey SJ, I did. It's the line that ties all 3 throttle bodies' pressure together and then routes to the fuel pressure regulator. I did like Mr Sled said and ran it with the brake a little and it made 4 psi and then when I let off hit 12" vacuum, so all seems good. I just thought there would be a lot more vacuum at idle, thus me thinking something was wrong.

Awesome!! Glad it worked out

 

[@123]

k so if i understand good the picture beerman post is the good place for the tee? thks...