First thing I’ve found that explains something I was curious about from the beginning. I've been looking at the Mazda shop manuals for the RX-8, and apparently, the oil pressure gauge is just a switch (IE an on or off value only, no actual range of values). That would explain the ECU controlling the gauge cluster oil pressure meter the way it does.

Hopefully Mazda will offer this as a real pressure gauge in the future, as well as a battery gauge in the future, as accurate readings on both of those are sorely missed by me.

Can anyone else comment on the accuracy of my deduction?

Regards,

OverLOAD

 

OverLoad - you have it absolutely right. (And a search on OIL GAUGE will show previous discussions of this.) The question is if it is possible to put in a real sensor and make it work. It seems like it would be way too much effort. I also like your idea of a real ammeter for the battery rather than the good old idiot light. Ah well ....

mm

 

I don't think I made my original statement as clearly as I should have.

Whiele there have been many threads on the gauge itself being basically a glorified idiot light, the guage itself is a rather fine looking and capable piece of machinery.

What I should have clarified, is that it appears to me as though the oil pressure sending unit itself is just an on/off unit, while the gauge display is obviously capable of displaying a wide variety of values, there are only two possibilites that it might see, thanks to the selection of a rather limited on/off pressure meter.

This is from what I can tell at least. Does anyone know anything about the oil pressure sender unit?

Regards,

OverLOAD

 

something like this

 

OverLOAD:

I'm with you - Idiot lights should be idiot light - not idiot lights looking like gauges. Real sports cars should have real analog oil gauge, temp gauge and ammeter.

Mazda - are you listening ???

... if not can you say aftermarket?

In fact when I had an aftermarket Boost gauge installed in my RX-7 - I had the tuner place a analog voltage gauge where the old Boost gauge had been. The NA model had that type of gauge in the dash

John

 

datel makes very good and somewhat expensive guages.

 

I think that OverLOAD is asking if there is any way of using the existing Oil Pressure Gauge to display an actual Oil Pressure reading. Perhaps just by changing the Oil Pressure sender.

 

I'd love to have a real oil pressure gauge. I wish the sender unit could be replaced with one that will make the gauge to show the real pressure.

However, that MIGHT not be possible. While I realize that the two cars have nothing to do with each other, I'd like to tell about an example where this did not work.

In the 1993 and 1994 model year, Ford Probes had a real, fluctuating oil pressure gauge. In their infinite wisdom, Ford decided with the 1995 model year to dumb down the gauges to the same idiot light-like ones we have now in the 8 (perhaps because they were tired of idiotic people bringing their cars to the dealer complaining about 'fluctuating oil pressure' )

I remember some people posted on the Probe board that they tried to use the sender unit from earlier cars, but apparently, the new gauges were different too - and they did not work properly, or at all.

I'm afraid this MIGHT be the case with our gauges as well... wish I'd be wrong in this.

 

Overload, you must be dreaming.......
Forzda considers that just 'too much information'!
They even use it as an indicator light.....to verify that you have the latest ECU (WDM) update/flash.
If you turn on the ignition, without starting, then pump the brakes 20 times in less than 8 seconds, the trouble codes will be erased...and IF you have the latest program, ('L' I believe) it will confirm the erase by 'flashing' the oil pressure gauge, from '0' to 'normal' and back to '0'.
It is official, it is a dolt light.
.
.
.
doc

 

Anyone noticed how the temperature guage moves in increments? I've watched it (hey, it's something to do when stuck in traffic) and it definitely seems to move smoothy by a few degrees, wait and then move another few degrees. What do you want to bet that the oil pressure gauge and the temperature gauge are the same electrically? If so, I bet the oil pressure gauge can be made to show any value you want it to. Right now the ECU is probably generating the, what is it 60% (?) value. Miata owners had the same problem but they were able to substitute the oil pressure sender for a real one that measured, well *pressure* and through some re-wiring managed to get the gauge to display the actual oil pressure. I've been thinking of submitting the oil pressure gauge to the www.thisisbroken.com web site but I don't want to give people a reason to criticize the RX-8!

Based on my premise about the temperature gauge I've got to think that the oil pressure gauge can be made to work correctly. A sports car with a frickin idiot gauge for oil pressure, give me a break!

 

Yup, I'm aware of that capability, I've seen my oil pressure gauge do some funny stuff when my room fuse was blown.. All my gauges would swing to the maximum value, and then fall back to normal. Kind of odd.

Here's what I'm thinking... The ECU definately wants the value from that one oil pressure sender switch (the ok/low level reading..) to determine what the pressure is. If you were to add a Y valve to the connection point for the stock switch, and add a nice oil pressure sender unit, which connected right up to the oil pressure gauge (disconnecting the factory PCM connection to the OPG) you could have a gauge that read real values.

In the service manual, they even show a service routine that gets the actual oil pressure value by replacing the switch with a real gauge, for testing. It seems a bit odd to me to need to do that. The factory gauge is pretty nice, but the only problem is that it has arbitrary graduations. Even if you hooked up a decent oil pressure sender to the OPG on the instrument cluster, how would you read the value? I guess you'd have to calibrate it against another OPG to says that lowest tick = x, highest tick = y, each incremental tick = y-x/number of ticks...

What a pain in the butt. It's easier to get an aftermarket gauge pillar, and an aftermarket gauge, and plug in another oil pressure sender to the engine. Mazda, please give me back a real OPG! (included with the Sport or GT package option maybe???)

Regards,

OverLOAD

 

OverLOAD - After thinking about this one some more it occurs to me that the gauge and sensor might be just fine. If I were going to dumb down the oil gauge I would just change the algorithm in the ECU to change the response of the gauge to the sensor to a binary function. If that is the case then the gauge could be "fixed" by changeing the algorithm in the ECU.

So there are two things to check. First someone needs to check the line coming from the sensor itself and see if it is providing a full range analog signal (I would bet it is). I don't have the equipment to do this, but maybe someone else does. The second thing to check is the actual code in the ECU. I don't know how you go about doing that, unless CANZOOMER has that ability.

My .02.

mm

 

Wasn't an OPG included on that 3 gauge pod that was circulating around here a couple months ago? It was around $1300 I think but if it housed a REAL OPG then there has to be away to change out OP sending units without freaking out the ECU...someone from Japan should be able to tell..cause it looks as though that is a hot item over there and I can't see justifying $1300 for another idiot "light" so it must be reading true values...if it contains a OPG that is...i can't find a picture of it here anymore...

 

I believe that the Mazdaspeed gauges use a seperate oil pressure and temperature sending unit that installs under the oil filter.

 

Zoom2X - Do the Mazdaspeed sending units go directly to the Mazdaspeed gauges? I'm guessing they do.

mm

 

Could you go over that again? When you say replace the switch, are you talking about the stock oil pressure sender? And when they put a full range pressure sender in, are they reading the pressure on the stock gauge, or from a separate guage attached to the newly installed pressure sender (bypassing the ECU altogether)? Someone would have to try that guage to see if it will actually work with a sender (remember folks, senders and guages aren't mix and match). On my '99 Miata, I replaced a similar on/off type sender with a compatible variable sender. The factory guage only has a few "tics" on it, and I had to adjust the needle so that I can get a general idea of where the pressure is. I'm not going to get much more accurate than that without replacing the stock guage with an aftermarket one, but it does what I want (shows me the fluctuations between different operating conditions, loads, and rpms in a stealth installation).

---jps

 

Yes. The service manual has a tech pulling the stock pressure meter/sender unit off completely, since it's apparently just a dumb swtich, to replace with a calibrated full-range gauge.

The thought is maybe we can put a second sender/pressure gauge unit in parallel with the stock unit, preserving the ECU's happiness, and keeping the low oil lamp off, and routing that new pressure gauge and sender to the stock gauge...

OverLOAD

 

My doubt on this is that the service manual only has two values available listed for the OPG: OK, and LOW. Plus there's no ECU capability to determine what that value is. That why the service manual has the procedure of replacing the sender unit with a mechanical gauge for mechanics testing purposes instead of hooking up a diagnostic tool to the OBD.. It's worth testing like you say tho.

 

But - hasn't it been reported that the latest ECU reflash uses the oil pressure gauge to indicate a NV RAM reset by sweeping the OPG full range and back? In other words, it's capable of controlling the gauge to more than just the OK and LOW positions?

Regards,
Gordon

 

I don't disagree that the gauge itself has 100% of the required capability, and that the ECU can make it do whatever it wants it to do..

Just that the ECU only know two positions of granularity about the actual oil pressure: OK, and LOW. This is a result of the oil pressure sender unit on the engine block.

OverLOAD

 

I agree completley!

said it before and I'll say it again ...

I’d really like to see (as an optional if it can’t be standard) a complete fully functional gage display pack that clearly and accurately shows the normal and abnormal state of things with regards to: engine temperature, voltage/battery (Hey Mazda, there's room right now for a voltage/battery gage that will fit tastefully in the dash by the oil temp gage ...and as of now it's IMHO sorely missing) and oil pressure with an analog speedometer (or some kind of digital indicator that replaces the swing of the needle- maybe some kind of horizontal bar graph underor above the digital speedometer readout screen or else a digital light ring around the edge of the tach gage)!

I'm open to start a letter-writting campain to get this done! Anyone else?

 

Almost hate to say it but I have quickly grown to like the digital Speedometer - all the other should be analog and fully functional IMHO. Not opposed to a graphic / numberic speedo.

John

 

That's another reason I miss my 1990 Probe ... all true gages and the tilting dashboard !

 

Okay, I understand that the sender is replaced. What still isn't clear is whether:

A) The tech hooks up the new sender to the stock wiring and reads the value off of the stock guage in the instrument panel, or:

B) The tech hooks up a separate guage to the new sender, bypassing the stock wiring altogether, or:

C) Something else...

---jps

 

The answer is B. The new sender has it's own, separate Analog, mechanical gauge. That's what we want.. but that's what it looks like to me.

OverLOAD