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Resolved 2G Boost gauge

GSXRunner

Proven Member
150
33
Feb 24, 2013
Queens, New_York
Does anyone have a schematic of the stock alternator gauge on a 2g? I've looked through some incomplete pdf's and only find an idiot light. The reason I ask is because the gauge is very low when the car is idling and when I drive, especially at a higher rpm, it goes way up to max. I though there might be an issue with my alternator, even though the voltage stays around 14V, so I disconnected it electrically and yet it still does the same thing. I don't know if there's some kind of short somewhere in the system or an issue with my ecu, but I need to get to the bottom of this. So if anyone has this schematic, I'd really appreciate it. My car is a 95 GSX.
 

GSXRunner

Proven Member
150
33
Feb 24, 2013
Queens, New_York
Think you’re looking at boost or oil pressure gauge. There’s no gauge for alternator that came from factory.
The one on the left is a boost gauge? LOL I always thought it was an alternator charge gauge because it looks like a pic of an alternator and it has a plus and a minus. You sure about that?

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steve

DSM Wiseman
15,010
1,809
Feb 3, 2002
Boulder, Colorado
I always thought it was an alternator charge gauge because it looks like a pic of an alternator and it has a plus and a minus. You sure about that?

Yep, 100% but it's not a real boost gauge. It is just a simulation based on what the ECU measures the airflow at the current RPM to be and estimates what the boost might be.
 

GSXRunner

Proven Member
150
33
Feb 24, 2013
Queens, New_York
Yep, 100% but it's not a real boost gauge. It is just a simulation based on what the ECU measures the airflow at the current RPM to be and estimates what the boost might be.
I got my car with an aftermarket boost gauge on the A pillar that works well and is marked.

I think it's weird they would put a boost gauge next to an oil gauge. Since the oil gauge is a very critical indicator, I would think they would put an alternator gauge next to it rather than a boost gauge. After all, if your boost is not correct, it's not going to leave you stranded somewhere; an alternator with a broken belt will. So I always thought that to be an alternator gauge. I never really looked at it when I was accelerating, but recently, after suffering an oil leak that killed my turbo, I have had a sharp eye on it when accelerating; which is why I noticed it going up so much. Being a boost gauge definitely explains why it's going up.

In the picture, the ignition is off and it's at its bottom mark. Is this correct? When I turn the ignition on without starting, it goes to about 1/16" above the second mark if I count the bottom mark as zero and I count one, two. Is this correct? Cause I would think that with the ignition on, it would show where the zero point is (where there is no vacuum or pressure). I'd also think that if it's a boost gauge, they would mark the zero point. I have some parts off my car right now, so I can't start it just yet to see where it is at idle.
 

steve

DSM Wiseman
15,010
1,809
Feb 3, 2002
Boulder, Colorado
I'm not sure what your asking at this point. Seems like you being rhetorical.

The gauge does what it does, it's not calibrated for a reason. When you turn on the electrics the gauge moves somewhere close of the middle since there isn't any boost or vacuum (it's at atmospheric pressure), once you start the engine it goes negative and assuming things are working under boost it goes positive. The bottom mark is vacuum.
 

TheDude236

Proven Member
205
113
Mar 15, 2021
Kingston Springs, Tennessee
I'm with Steve here. Are you worried about your OEM gauge being calibrated wrong compared to the aftermarket one maybe? I'd trust that one more for sure anyways.
 

GSXRunner

Proven Member
150
33
Feb 24, 2013
Queens, New_York
It's not really an issue right now. It's just that for the two decades I've owned this car, I've always thought it to be an alternator gauge. Now that I know it's a boost gauge after all these years, I thought it would be helpful to know how it's calibrated and how it works so it can alert me in the future of any issues with the electrical system. I trust the aftermarket boost gauge over this, but if this gauge is doing something it shouldn't because maybe there's an issue with the ECU, I will be alerted. Incidentally, I never saw this gauge go up so high before I rebuild my turbo. I guess I must have picked up a great deal of boost after rebuilding it.
 

Spleen8urLSX

5+ Year Contributor
326
220
Dec 26, 2017
Elyria, Ohio
Just ignore that gauge. Making slight changes makes it do all kinds of goofy things. If your car is anything other than bone stock ignore what that gauge does and there’s no way to make it read boost more accurately if that’s what you’re asking. Like someone else said, if you get ecmlink use it to make it a knock gauge.
 
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