Boost Gauge Help Needed

[nlowell]

Hey all,

I need some help with my boost gauge. I installed a vacuum manifold from the brake booster line (see pic 1). I installed a 3/8" T and brought the 3/8" line into the manifold where then connected out a line to the KW bypass valve and another line to the ProSport electrical sender filter and unit.

All I'm getting on my boost gauge is "-29" at idle then with any throttle it flashes to "---". I've read every post I can find to resolve.

Here is what I've tried:

• Verified I'm on the correct side of the check valve (see pic 2)
• Replaced cheap clear vacuum line with a thicker line
• Blew into the electrical sender and verified that boost does show on the gauge
• Verified all vacuum lines are straight with no bends or kinks

My car is an automatic. The brake booster line does not go to the manifold. The port on the manifold that has the brake booster line on a manual transmission car has a cap on it. Instead the brake booster line runs past the manifold and enters the engine on the passenger side (see pic 2 and 3).

Why would I only be getting vacuum from this point?
I'm on the correct side of the brake booster check valve right?
Should I just give up on this spot and pull boost from another spot?
Where would that be?

Thanks all!!

Pic 1 - Manifold



Pic 2 - Brake Booster T



Pic 3 - Brake Booster Hardline



Pic 4 - Brake Booster Engine Entry

[enjetek]

Car should be under vacuum at idle its normal since you have no positive pressure. Once things start spooling you will get on the positive side. Hmmm. I would think the brake booster line would be fine.

[Sportsguy83]

The perfect source for the vacuum manifold was the capped nipple on top of the manifold because no need to tee into brake booster.

I really have no idea why would your setup not work other than a bad gauge.

I would get a barbed hose coupler to restore brake booster line and remove that T and take the boost source from the capped point on top of manifold.

[J_kennington]

When you say "under any throttle". Are you actually out driving the car? Or in the driveway, car in neutral, and reving?

[King Tut]

My advice is remove that crappy ProSport gauge from the equation and sell it to some Subaru owner. Were you utilizing this setup prior to installing the boost gauge? Is your bypass valve working properly since it is also hooked up to your vacuum manifold? I would get a mechanical boost gauge and hook it up and see what it says. You should be in the -19 to -21 inHg area at idle. Does anyone with a ProSport gauge know what the "---" means?

[lucid215]

what prosport gauge are you using? i have ran theirs in multiple cars and never had a issue with them. sounds like a bad source. try what @Sportsguy83 recommended

[nlowell]

I will try that, thanks guys. I'm running the prosport evo premium and I was testing with WOT runs on the freeway. Since the gauge shows boost when I blow into the sender I'm pretty sure the gauge is fine.

[nlowell]

That worked! I now show proper boost on my gauge. I can confirm that on my automatic, I am getting nothing but >30 lbs of vacuum from the brake booster line. Crazy...

[Sellout]

Brake booster should have a check valve somewhere in the line so it's always kept under vacuum. That's probably what the issue was...

[zkv476]

I thought the check valve was in the brake booster's inlet but I suppose if there was a check valve before the booster and you tapped after that it would hold vacuum. That's strange though. My Vortech kit uses the line coming from the brake booster as the BOV vacuum line but that would only work if it was always at manifold pressure and the check valve came after. Strange strange.

[Sellout]

I've never actually had to find out where that check valve is, but now that I looked back and saw that he verified that he was on the correct side of it in the OP, I can see that I'm clearly guilty, in this case, of the thing that always irritates me about online forums. Bad reading comprehension...

Carry on.

[DHitHim]

Originally Posted by Sportsguy83

The perfect source for the vacuum manifold was the capped nipple on top of the manifold because no need to tee into brake booster.

I really have no idea why would your setup not work other than a bad gauge.

I would get a barbed hose coupler to restore brake booster line and remove that T and take the boost source from the capped point on top of manifold.

What capped nipple are you talking about?

[Amputechture]

I just installed a prosport boost gauge on Sunday. Didn't work at first. That clear vac hose they provide is probably a 1/8 of an inch in diameter inside...completely useless besides putting a half inch of it around the nipple on the back of the gauge to be able to use a 1/4 vacuum hose that ended up allowing the gauge to get a proper feed.

[Sportsguy83]

Originally Posted by DHitHim

What capped nipple are you talking about?

That was more than two years ago, so I THINK I was talking about the PCV connection on top of the manifold. I think I said "capped" because I had it capped with a vent to atmosphere catch can.