Exactly - Whats Left?

It seems to me that it is some sort of load.
It would need to be a fairly significant load, however.
"Normal" engine vacuum is 17" - 19" or so.
I should be losing about 1" to my altitude, which means I am losing at least 1" additional inch to something.
The A/C pulls about 1.5" more or less, so the load is less than that.
Turning on all the lights is just slightly less than 1", so it is somewhat more than that.
I guess I should sit down and do the math on the lights.

It would be easier to do the experiment with the battery and alternator wires as I indicated above, but the weather hasn't allowed that.

I have also been having the same problem for several months, even before it started getting hot. I have been distracted by other things with the car since then, most importantly getting a proper tune.

I have never dynoed the car, but it is now registering the same MAF flow rates as other pettit cars. My idle vacuum constantly stays @15-16. I live @90 miles north of PC Beach, FL. Not sure what the elevation is here and I am too lazy to check right now.

Maybe it is because my motor is tired now at 90k miles??
Maybe because my idle is set @1100?

Regardless, if there are any tests I can do to help figure out what is happening on my car or yours, let me know.

The 1100 idle should actually raise your idle vacuum.
Mine goes up to 18" or so at that RPM.

However, I don't have any use for an idle that high and that would be "masking" the "problem" if I did.

Its not really a problem - just an observation. The idle is stupid smooth.
I just have a burning need to understand why the vacuum is low at 800 - 900 RPM (the "normal" idle range).

Its stopped raining, so I'm going to pull the car in and pull the alternator wire and see what happens.

Watch the WEB cam for fire!

Hey Jeff; I have about the same issue - but only when my car starts to warm up; I blamed mine on the fuel trims with my MAF housing issue. I will be following this one too.

Well, mine does drop as the motor warms up - all '8s do that.

OK. I disconnected the alternator.
Vacuum went up a full 1 PSI to -8.1 or so (from the low -7 to -6.9 I had hot before).

Its still low-ish, but 2" of mercury is pretty significant.
I guess I'll have to start looking for loads with the ammeter.

Is the best measure of vacuum determined while the motor is still cold, since it drops once it is warm??

Doesn't matter, as long as you are consistent.
Mazda's number is based on a warm engine.
It will typically drop an inch once it is warmed up.

The warm Vac is the only really relevant one...the engine won't stay cold long :)

What gauge cables are you using for battery relocation?

Hard to imagine a dark 20 amp load somewheres; thinking more like resistance in the charging circuit.

That's a lot of charging resistance though. Can't imagine 4GA wouldn't be be too small?? I have battery in the trunk and used 4GA with no problems evident to date

I'm using 1ga. There is only .2 ohms from the battery positive to the alternator out.

I am now probing around the various circuits, looking for resistance.
I hooked my ohm meter to the alternator wire and ground.
20 ohms. I'm thinking this is bad.
I started pulling fuses and the BTN dropped the impedance to 400+ ohms, so I think I'm on the right track.

OK. Getting closer.
Room fuse in - 20 ohms.
Room fuse out - 2k ohms.

Probably some stupid thing I have installed somewhere.

The search continues.

Of course every god damn thing is on the "room" circuit! Every sub system under the PCM seems to draw on that.
Crap.

WOW You have an inverter running a coffee maker or something ;)

Or something .... :)

https://www.rx8club.com/attachment.p...2&d=1220044965

Lol.

So, I started disconnecting things on that circuit.
Its not the CarPC or its power supply.
Its not the boost controller, the EGT or the WBO2S.

I guess I'll unplug the head unit, the TPMS, the keyless entry and go from there.

lol
That would be quite a vacuum leak if I had to seal the passenger compartment!

Yeah, no aftermarket lighting.
Besides, the low vacuum happens when I'm driving, too.
I don't usually drive with the doors open.
I did pull those harnesses, though. No effect.

I'm running out of things on that circuit.

this thread = Jeff's O.C.D. at it's finest!
:D:

Damn straight! Gots to be seen in the hood. :eyetwitch
Hey Jeff is this low vacuum actually causing a drivability issue? Or is it just the fact that you can't put your finger in it, I mean on it, that's making you go NUTS!:Eyecrazy:

The latter. It isn't affecting anything as far as I can tell. (Other than my sanity.)

I thought so. Well this is your lucky day! I know what it is and how to fix it.










































The car is running,,

Shut the engine off!

If it makes you feel any better, mine sits at 15 on a hot idle. You are not alone... :P

Is it your gage? Have tried measuring a simliar set up with your gauge?

Verified with three gauges - the boost gauge, and two mechanical gauges.

wow , the lengths you go to for something last isn't even a problem .......