Boost Gauge reading is off

[Valkyrie14]

Originally Posted by larry_g

I have to agree that it looks like you are tapped into the correct location.

Have you been able to confirm that the Hobbs switch is actually seeing boost and working and that the fuel pressure is holding steady?

Is it possible that the FPR or one of the fittings is bleeding off boost pressure?

Is it possible the bypass valve is not closing and you aren't actually getting into boost?

Process of elimination would say the gauge may be bad but it seems odd that the vacuum reading works but the boost doesn't.

No idea. It is all new install. I don’t know how to test any of this. I do know that when I set the fuel pressure regulator by the I’m line pressure gauge I pinched off the vacuum/boost line to set and when I released the line the FP jumped up. So something is going through there.

My tuner tells me I am getting boost and he didn’t flag anything on the fuel system based upon my logs.

How can I test the Hobbs?

[Valkyrie14]

Originally Posted by TheFlyingBananaSS

Maybe a one way valve in the wrong spot?

Where would I look for one of those valves?

I am reluctant to use a brake booster line, as you can tell my projects sometimes go sideways a bit and I would rather not put my braking ability at risk.

Right now I feel like I might not be getting all of the boost potential or benefit of my dual pumps that I should be.

[larry_g]

I guess the best way to test the Hobbs switch would be to see if you are getting voltage at the second pump when you should be generating enough boost. I'm not sure if you would actually see a spike in fuel pressure when the second pump kicks in, that probably depends on the control system setup, but you may be able to see it in an HPT log.

You could bench test the switch but that wouldn't tell you if it's actually seeing any boost with the current install (the real question here).

[Valkyrie14]

Originally Posted by larry_g

I guess the best way to test the Hobbs switch would be to see if you are getting voltage at the second pump when you should be generating enough boost. I'm not sure if you would actually see a spike in fuel pressure when the second pump kicks in, that probably depends on the control system setup, but you may be able to see it in an HPT log.

You could bench test the switch but that wouldn't tell you if it's actually seeing any boost with the current install (the real question here).

I can run a HPT log tonight to see. To be honest without my tuner I don’t know how to read the data very well.

[larry_g]

Originally Posted by Valkyrie14

I can run a HPT log tonight to see. To be honest without my tuner I don’t know how to read the data very well.

No worries, I pay someone else to tune my car. I'm an old school motorcycle carb guy, I spent many hours in a dyno room with them in a past life.

I'm just trying to help your diagnostic thought process...Is the hose getting boost pressure and, if so, why doesn't the gauge see it?

If you can verify the Hobbs switch is triggering the second fuel pump, there must be some boost pressure in the hose and I would look more closely at the gauge. If you can't prove there is boost pressure in the hose, you need to figure out why not. Especially considering it looks like you are tapping the correct port.

[Valkyrie14]

Originally Posted by larry_g

No worries, I pay someone else to tune my car. I'm an old school motorcycle carb guy, I spent many hours in a dyno room with them in a past life.

I'm just trying to help your diagnostic thought process...Is the hose getting boost pressure and, if so, why doesn't the gauge see it?

If you can verify the Hobbs switch is triggering the second fuel pump, there must be some boost pressure in the hose and I would look more closely at the gauge. If you can't prove there is boost pressure in the hose, you need to figure out why not. Especially considering it looks like you are tapping the correct port.

I really appreciate the help. That makes sense. I’m still hoping the cheap gauge I bought is the problem. I will update once I get a fresh log and take a look at the data.

[eLeSthree]

Seeing as how you are seeing vacuum on your gauge, but not boost, I would think you are connected to the wrong place. You are probably connected somewhere before the blower that only sees vacuum.

Easy test. Disconnect your vacuum/ boost line from the T and using an air compressor, VERY GENTLY start applying pressure while watching the boost gauge. It should move from vacuum into boost.

As for the Hobbs switch.. Open the VCM scanner and look for the fuel pressure Channel. The long list of items on the left are all the channels you're setup to scan for. I'm sure your tuner has Fuel Pressure in there. (if not, get a new tuner)

You can either use the same air compressor trick or you can simply use a small jumper wire to ground the hobbs switch. That should kick on your secondary fuel pump(s) and you will see a difference in fuel pressure.

[Valkyrie14]

Originally Posted by eLeSthree

Seeing as how you are seeing vacuum on your gauge, but not boost, I would think you are connected to the wrong place. You are probably connected somewhere before the blower that only sees vacuum.

Easy test. Disconnect your vacuum/ boost line from the T and using an air compressor, VERY GENTLY start applying pressure while watching the boost gauge. It should move from vacuum into boost.

As for the Hobbs switch.. Open the VCM scanner and look for the fuel pressure Channel. The long list of items on the left are all the channels you're setup to scan for. I'm sure your tuner has Fuel Pressure in there. (if not, get a new tuner)

You can either use the same air compressor trick or you can simply use a small jumper wire to ground the hobbs switch. That should kick on your secondary fuel pump(s) and you will see a difference in fuel pressure.

Here is where I am pulling the boost line from. The upper stem, I saw on another thread that this was a recommended point for boost. I don’t have a air compressor unfortunately, not yet at least. Where else can I pull boost from, I have tried a couple of locations and I am running out of places.

[eLeSthree]

I'm not familiar with the zl1 blower, sorry. Is boost reporting in Hptuners?

If so, you have the wrong port or a bad gauge. I highly doubt its a bad gauge since it sounds like its reading vacuum perfectly fine. A mechanical boost gauge should sit perfectly on 0 when the car is off.

Why do you need a boost gauge anyway? Boost is going to be determined by your pulley sizing anyway. Once you get it tuned, it wont need monitoring like a turbo car might. I dont have one... just a thought.

[Valkyrie14]

Originally Posted by eLeSthree

I'm not familiar with the zl1 blower, sorry. Is boost reporting in Hptuners?

If so, you have the wrong port or a bad gauge. I highly doubt its a bad gauge since it sounds like its reading vacuum perfectly fine. A mechanical boost gauge should sit perfectly on 0 when the car is off.

Why do you need a boost gauge anyway? Boost is going to be determined by your pulley sizing anyway. Once you get it tuned, it wont need monitoring like a turbo car might. I dont have one... just a thought.

I got the boost gauge to measure how much boost I am getting, which really means did I set up my blower right and making sure it is working. I’m no mechanic, so I always worry I didn’t do things right. So the gauge is a test on if I am getting boost and if so as much as I should be based on my pulleys.

That also involves my other project for the dual fuel pump. How do I know when I hit 4 psi engaging the second pump if I don’t know when I am at 4 psi or greater.

My tuner has limited my channels on HPT to what he looks at, I don’t think boost is on my current channels. I can add in some channels just to see I suppose.

[Valkyrie14]

Made a decision to get a new boost gauge. Even if the gauge isn’t the issue I prefer the look of the AEM gauge, it is on the dash for God’s sake and it should look nice.

I see the AEM gauge has a harness that plugs in with a pigtail. Anyone know what that plugs into? I want to know what I am getting into before I buy it. Also, I am comparing their boost gauge to the boost/fuel pressure gauge. Any reviews?

[TheFlyingBananaSS]

I have AEM boost and air/fuel gauges. They are costly but great quality. Not sure how they wire up my builder did them. I just made the pod mounting bezel for them. Very easy to read with a quick glance at them.

[larry_g]

I have the AEM boost gauge. It comes with a sensor that the wiring connects to. The whipple has a couple of pre-tapped and plugged ports on the back of the lower plenum that are designed for this.

I have seen an adapter for the MAP sensor that has a similar port if your setup doesn't have one.

Sent from my Pixel 5 using Tapatalk

[Valkyrie14]

Originally Posted by larry_g

I have the AEM boost gauge. It comes with a sensor that the wiring connects to. The whipple has a couple of pre-tapped and plugged ports on the back of the lower plenum that are designed for this.

I have seen an adapter for the MAP sensor that has a similar port if your setup doesn't have one.

Sent from my Pixel 5 using Tapatalk

This one?