Supercharged Vacuum Reading

[Vuu]

Just wanted to get other input on this.

Been slowly chasing a low boost issue for over a month now, and can't figure out why my P3 won't read over 3.5 PSI.

Out of curiosity, what's your vacuum reading at?

Mine used to be around -16 to -18 but now it's consistently at -20 once the car is warm and at idle.

Notes on the boost leak:

I've replaced the BPV, belts, pullies, re-calibrated the gauge with P3 and ACM, and re-seated the plenum twice now. Only things left to do is a pressure test, replace the rubber boots, and dyno.

[tom @ eas]

We've had a handful of cars just have low boost readings, but still make power. The dyno will determine whether the power is still there. It's a problem with the source.

We have replacement velocity stacks that give you a true boost reading at the stack, and allows a fitting to be screwed into place. Simply remove one of the ESS stacks and replace with ours.

[Vuu]

Originally Posted by tom @ eas

We've had a handful of cars just have low boost readings, but still make power. The dyno will determine whether the power is still there.

We have replacement velocity stacks that give you a true boost reading at the stack, and allows a fitting to be screwed into place. Simply remove one of the ESS stacks and replace with ours.

I agree, I need to set up a dyno with you guys now that my schedule has freed up!

How much are your velocity stacks?

[tom @ eas]

Sure thing, PM sent.

[gnjax]

My vacuum reading is usually somewhere between -12.5 and -14 at idle (Braking or A/C can change it slightly). When I had a problem with my T-fitting a few days ago and losing boost my vaccum was way higher, around -18 at idle

[amrazM]

Originally Posted by Vuu

How much are your velocity stacks?

Just an FYI, I replied on your facebook thread. Vacuum varies before and after the throttle blade, on this car to measure the true vacuum AKA sizing a spring for a blow off valve the vacuum needs to be measured in the space between the throttle blade and the cylinder head.

[Vuu]

Originally Posted by gnjax

My vacuum reading is usually somewhere between -12.5 and -14 at idle (Braking or A/C can change it slightly). When I had a problem with my T-fitting a few days ago and losing boost my vaccum was way higher, around -18 at idle

I was skeptical of a pinched line, so I actually replaced the hose with a new one about two months ago. Surprisingly that's when the vacuum start to read -20hg.

Originally Posted by amrazM

Just an FYI, I replied on your facebook thread. Vacuum varies before and after the throttle blade, on this car to measure the true vacuum AKA sizing a spring for a blow off valve the vacuum needs to be measured in the space between the throttle blade and the cylinder head.

I saw the response on there as well, I do appreciate it brother!

Assuming so, the y-fitting at my BOV should just be moved correct? I'd get a more accurate boost/vac reading closer to the plenum.

[Vuu]

Originally Posted by tom @ eas

We've had a handful of cars just have low boost readings, but still make power. The dyno will determine whether the power is still there. It's a problem with the source.

We have replacement velocity stacks that give you a true boost reading at the stack, and allows a fitting to be screwed into place. Simply remove one of the ESS stacks and replace with ours.

Tom, I forgot to ask in the PM, but I figured I would here in case others were wondering as well.

I know I can grab the sensors off of FCP, and the velocity stack from you. However, if you aren't running an AWRON (I'm running a P3 with an analog boost sensor), how would we connect to the fitting for the boost readings? I believe the sensor you buy is the fuel pressure to read boost, and it's an electrical fitting. The P3 is just connected from the analog sensor, to a hose to the Y-fitting that's tapped off the BOV on my current set up.

[SAMM3Y]

Not sure about vacuum cuz the awron doesn't report it but how about pulling the hose off the BOV and plugging the intake side and listen for the boost. I've ran vent to atmosphere and recirc. I've gone back to plugging the intake and leaving the hose on the BOV in the engine bay as it acts as a bit of a whistle silencer. The awron boost gauge is a bit laggy anyway having an audible way of hearing the boost is great. I always check my max values at the end of a rip around to see what it reported too.

[Vuu]

Originally Posted by SAMM3Y

Not sure about vacuum cuz the awron doesn't report it but how about pulling the hose off the BOV and plugging the intake side and listen for the boost. I've ran vent to atmosphere and recirc. I've gone back to plugging the intake and leaving the hose on the BOV in the engine bay as it acts as a bit of a whistle silencer. The awron boost gauge is a bit laggy anyway having an audible way of hearing the boost is great. I always check my max values at the end of a rip around to see what it reported too.

I've tried, and honestly it's too loud to hear anything.

Plus, I'm running the Vortech blow off valve now and sold the bypass valve, so my intake coupler is plugged up with an expansion plug. There's no recirc.

Are you running the velocity stack to read your boost on the Awron?

[SAMM3Y]

Yes I am.

[amrazM]

Originally Posted by Vuu

Assuming so, the y-fitting at my BOV should just be moved correct? I'd get a more accurate boost/vac reading closer to the plenum.

you should be taking the reading off the line below the plenum, the split line at the fuel tank breather valve to the throttle actuator.

[Vuu]

Originally Posted by SAMM3Y

Yes I am.

Can you send me a picture of how your sensor is connected? I know it's threaded into the velocity stack, but is it connected by a plug?

Originally Posted by amrazM

you should be taking the reading off the line below the plenum, the split line at the fuel tank breather valve to the throttle actuator.

So, when I replaced that line with a new part from the dealer, I made sure to leave it even longer to prevent any kinks in the hose whatsoever. The first go-around had a small kink because I couldn't remove the hose from the OEM fuel tank breather valve and ended up breaking the nipple off of it.

When I did replace everything, I also upgraded that fitting to a gold fitting instead of the plastic T-fitting that comes with the kit.

Since the hose is coming from the T-fitting on the fuel tank breather valve to the Y-fitting off of the BOV, wouldn't it read the same in either location?

[gnjax]

It is indeed the same, i get my readings with the same setup as you currently have (branching p3 sensor with a t close to the bov, with a p3 and a maxflow race bov). It may not be perfect but i see 7+ psi of boost at redline which is approximately what is expected of a 625 kit. If you are way below that you can safely assume that where you are reading from is not the problem, unless something else is faulty on the way.
Are you sure you did the sensor calibration correctly ? press left button once, wait for the 'tap.1' message and press left again, egine off ignition on ? Also did you put bst mode to bst.A on the p3 gauge ?

[SAMM3Y]

Here you go buddy, I've used these metric gauge adapters for a few things through the car too. Recommend picking up a pack. With the awron gauge there's a temp sensor too which goes in at the back. I had to use cylinder 8

[Vuu]

Originally Posted by SAMM3Y

Here you go buddy, I've used these metric gauge adapters for a few things through the car too. Recommend picking up a pack. With the awron gauge there's a temp sensor too which goes in at the back. I had to use cylinder 8

Originally Posted by gnjax

It is indeed the same, i get my readings with the same setup as you currently have (branching p3 sensor with a t close to the bov, with a p3 and a maxflow race bov). It may not be perfect but i see 7+ psi of boost at redline which is approximately what is expected of a 625 kit. If you are way below that you can safely assume that where you are reading from is not the problem, unless something else is faulty on the way.
Are you sure you did the sensor calibration correctly ? press left button once, wait for the 'tap.1' message and press left again, egine off ignition on ? Also did you put bst mode to bst.A on the p3 gauge ?

I have, and I've done it about 6 times now.

I went through the settings with a P3 technician and he advised that my settings were correct as well.

At this point, I have a couple of more possible solutions.

1) Pressure test.
2) New intake boots.
3) All new pullies, tensioners, and belts.
4) Blower rebuild.

I scheduled a dyno next Friday so we'll get a baseline and go from there. Hoping to just out out the power and not worry so much about the reading.

Originally Posted by SAMM3Y

Here you go buddy, I've used these metric gauge adapters for a few things through the car too. Recommend picking up a pack. With the awron gauge there's a temp sensor too which goes in at the back. I had to use cylinder 8

Thank you so much for this!

[tom @ eas]

Originally Posted by Vuu

Tom, I forgot to ask in the PM, but I figured I would here in case others were wondering as well.

I know I can grab the sensors off of FCP, and the velocity stack from you. However, if you aren't running an AWRON (I'm running a P3 with an analog boost sensor), how would we connect to the fitting for the boost readings? I believe the sensor you buy is the fuel pressure to read boost, and it's an electrical fitting. The P3 is just connected from the analog sensor, to a hose to the Y-fitting that's tapped off the BOV on my current set up.

Assuming the P3 has a rubber line for a reading from the pressure sensor (we don't sell P3), you can just plumb a barbed fitting into the stack. We can show you once you come in for your dyno.

Originally Posted by gnjax

It is indeed the same, i get my readings with the same setup as you currently have (branching p3 sensor with a t close to the bov, with a p3 and a maxflow race bov). It may not be perfect but i see 7+ psi of boost at redline which is approximately what is expected of a 625 kit. If you are way below that you can safely assume that where you are reading from is not the problem, unless something else is faulty on the way.
Are you sure you did the sensor calibration correctly ? press left button once, wait for the 'tap.1' message and press left again, egine off ignition on ? Also did you put bst mode to bst.A on the p3 gauge ?

We've had a handful M3s on the dyno that will read low boost, but still make power. No rhyme or reason as to why, as most cars read correctly. Other than tapping the manifold directly, the velocity stack is the easiest and non-obtrusive way to get a true reading.

[gnjax]

Originally Posted by tom @ eas

Assuming the P3 has a rubber line for a reading from the pressure sensor (we don't sell P3), you can just plumb a barbed fitting into the stack. We can show you once you come in for your dyno.



We've had a handful M3s on the dyno that will read low boost, but still make power. No rhyme or reason as to why, as most cars read correctly. Other than tapping the manifold directly, the velocity stack is the easiest and non-obtrusive way to get a true reading.

Yeah i might pick up one as i will need to plug an hobbs switch soon too and it just seems cleaner to do it from a velocity stack. I sent you an e-mail about it actually but maybe I can ask here so everyone can see the answer, I just wondered what the exact dimensions of the threads are and if it is in metric or imperial ?

[tom @ eas]

Originally Posted by gnjax

Yeah i might pick up one as i will need to plug an hobbs switch soon too and it just seems cleaner to do it from a velocity stack. I sent you an e-mail about it actually but maybe I can ask here so everyone can see the answer, I just wondered what the exact dimensions of the threads are and if it is in metric or imperial ?

Metric, as Awron displays were using BMW sensors. M10x1.0 and M12x1.5.

[jdamore]

Isn't it possible to read the MAP sensor (obd) and compare it to the P3?

[Vuu]

Bumping my old thread.

Still never fixed the issue. Still chasing the leak

[Scharbag]

Originally Posted by Vuu

Bumping my old thread.

Still never fixed the issue. Still chasing the leak

Sorry if you said you did, but have you pressure tested the plenum in the car?

I recently moved my P3 to a tap on the back of the plenum. Still testing but it is hard where I live as long, straight roads with no traffic are very rare.

When I boost tested my plenum to 10PSI I found every velocity stack coupler leaked a little.

Boost seems to read ok. I no longer see vacuum but I know I do not have leaks now after fixing everything. I still feel that sometimes it wants to make boost then it doesn't. Very odd. A new shop is supposed to be opening up locally with a dyno, so I will wait to test there some more.

Superchargers should be simple. Only other thing I can think of is a bad BV seat from time to time or belt slip. I have ordered new tensionsers as they are cheap-ish and easy to change. This will rule out belt slip for sure.

It is frustrating but stay with it. When you sort it out, you will be so happy!!