Know it sounds crazy, but on a S5, what can be done to make to stock gauge read a max of 12PSI rather than the 8.7. I just get tired of seeing the gauge max out and would like to change that if possible.
Any Ideas?

 

The stock gauge is too small and has no logical scale. If you want to boost that high you should know exactly how much boost you're running. Don't waste your time with it, get an aftermarket one like you should've done ages ago.

 

non-linear doens't mean no-logical

 

On a boost gauge a non-linear scale is next to useless.

 

I imagine something could be done with a variable resistor or similar, and if you calibrated it against an accurate boost gauge it should be fine. I couldn't tell you what to do though

 

I have an aftermarket boost gauge. The car runs right around 11PSI consistently. Just wanted the boost gauge to reflect this, regardless of the scale on the gauge.

 

Dat doesn't mean it's non-logical. Besides.. having a non-linear boost gauge is still better than no boost gauge at all.

 

What I was thinking of is how some guys run a fcd and it naturally fools the ecu into thinking it's lower, therefore the gauge reflects the lower boost. Something like that, but on the other side of the ecu, or output side to the gauge.

 

If you take apart the dash, you'll find that the motors and springs that the gauges go by are pretty much set in their ways, unless you want to start messing with the spring settings and flexibility of the parts in there, which would probably be close to impossible. What you could do, which would still be hard as hell, but more possible, is take the housing off the aftermaket gauge and throw it in the spot of the old one. Wouldn't look to nice, and it might not even fit depth wise, so you're probably going to be stuck with mounting it somewhere else.

 

you wouldn't need to muck with the gauge, just the signal to it.

 

If the car is running 11psi, then you have an FCD, in which case the stock gauge is only going to read up to that anyways, and that is where its maxing out. it's pointless, and a waste of time.

 

Why? If you have an aftermarket gauge who cares if you can't read the stock gauge?

I have no idea what your point is.
The gauge is linear, it's the scale that's not. This is what makes it impossible to get an accurate reading from. It was put there mainly for marketing reasons. The fact that pretty much any increase in boost sends it off the top of the scale means an aftermarket boost gauge is the first thing that should be added when modifiying.

 

Not unless you wired in the FCD just before the ECU in the passenger footwell area.

 

What difference is that going to make?

None...

 

Well.. if you go back and read you just might get it

How do you know the gauge is linear? How do you know the gauge is not? Have you done tests on it? The scale on the oil pressure gauge is non linear too. So I guess the 30, 60 and 110psi marks are crap(well most of us agree to that on our 15 year old cars but what about when the car was brand new?)

I do agree that you need an aftermarket gauge if you are above stock but saying that the stock gauge is useless is careless. Mazda afterall states that you should stop the car immediately if the boost levels go above the top mark. I've never seen that happen before but then again this is a 15 year old car.

 

Just to clear things up, I do not have a fcd, that is why the boost gauge is maxing out.
To me it's not pointless, nor a waste of time, but just thought one of the electrical guru's on here may be able to suggest a shunt or something similar that would reduce the signal to the stock gauge accordingly.
Looks as though I'll do some experimenting.

I also agree with the above. I've owned the car since new and the factory boost gauge and the aftermarket gauge have read the same throughout the years. It wasn't until the recent upgrades have the stock gauge has now maxed out.

Thanks again

 

Then you must have an aftermarket/reprogrammed ECU, otherwise you would have hit fuel cut a while ago.
Something sounds screwed here....

 

The output signal from the boost sensor splits in the ECU harness up above the ECU - one wire goes to the ECU, the other to the instrument cluster.

If you use a "normal" FCD that plugs into the boost sensor, the gauge will max out at +40 - that's where fuel cut is. If you have an FCD that's wired into the ECU, the boost gauge will read "right".

You can also do the same thing with a boost sensor FCD by tapping a wire into the output signal from the boost sensor (before the FCD) and running it to the gauge, which wouldn't be hard. That signal is also handy for running a Super-AFC off the boost sensor instead of the TPS.

With my old HKS FCON that had a boost sensor at the ECU, the stock gauge went to the second "O" in "Boost". Great for comedy value .

The stock boost gauge is far from worthless. Yes, it's worthless as far as seeing how much boost you're running, but if I would have paid attention when mine stopped working (just sat at zero, due to the vacuum hose to the sensor popping off) I wouldn't have blown my first engine. The boost sensor controls ignition advance and retard, and it's a good thing to know that it's working right.

On a bone stock car, it's one way to tell if you have a clogged cat, boost leak, clogged air filter, etc.

Dale

 

You make a very good point. What you're basically saying is that no-one (including you) really knows exactly what the gauge is reading unless it happens to be pointing exactly at the top of the scale. This simply reinforces how useless it is at displaying boost readings.
Careless? You need to put this thread, and this whole forum, into context. Turbonut is running 12psi, well above stock. Almost every person here has modified their car and is running higher-than-stock boost. The stock boost gauge is unable to tell you how much higher you are running, since most people are off the scale.

As Dale mentioned, about the only thing the stock gauge is good for on a modified car is monitoring the health of the MAP sensor. For that it needs no pointless modifications.

I suppose with a lot of effert you could recalibrate the gauge and draw on a new scale, but then all you'd end up with is a very small gauge with one third of the resolution of a typical aftermarket gauge (90deg sweep vs. 270deg sweep).

 

That means the gauge is not useless doesn't it?



Yeah I guess it could be recalibrated but you and I would agree that there's no point to that.

 

I never actually said it was.

 

This question is a bit off of the topic, but why did Mazda put the boost readings in millimeters of mercury? Maybe because the US is the only dumbass nation to not use the metric scale? Why not just put it in PSI rather than mmHg?