Interesting Idle Vacuum Correlations PART 2
08-26-2008, 09:41 PM
#1
Interesting Idle Vacuum Correlations PART 2
I've always felt that my idle vacuum was a bit too low.
It always came up a bit when I went to places with a bit less altitude, but there are other RX-8's here and their vacuum is higher. Even other MM turbo cars are higher, so its not the scroll, manifold or anything like that making back-pressure.
My current motor (and the one before it) ran perfectly and have good (or in the case of the current motor - crazy good) compression.
They are well-oiled and are totally normal in every way.
The idle is stable, smooth and regular.
There are no misfires, the ignition at idle is OE and the A/F is, too.
However, my idle vacuum is about 15" hg. It really should be at least 16 or 17 at minimum.
I tried going to a good set of stock coils (just to eliminate that possibility) and there was no difference from the BHR setup.
So, while charging my battery and flashing my PCM, I noticed something.
When I started the car, the current from the charger stayed in the 17 amp range!
When I stopped the motor, it dropped to 4 or 5.
Thinking that it could be something to do with my battery relocation, I moved the charger to the front of the car near the alternator and tried it again.
Same thing.
I tried a different alternator.
No change.
I spent several sessions with the motor chasing potential vacuum leaks with propane, carb cleaner and other solvents.
Its tight as a drum. No leaks.
I jacked up the OMP just to see the difference and, besides a ton of smoke, there was no change.
So, I am out of ideas.
Inspire me.
It always came up a bit when I went to places with a bit less altitude, but there are other RX-8's here and their vacuum is higher. Even other MM turbo cars are higher, so its not the scroll, manifold or anything like that making back-pressure.
My current motor (and the one before it) ran perfectly and have good (or in the case of the current motor - crazy good) compression.
They are well-oiled and are totally normal in every way.
The idle is stable, smooth and regular.
There are no misfires, the ignition at idle is OE and the A/F is, too.
However, my idle vacuum is about 15" hg. It really should be at least 16 or 17 at minimum.
I tried going to a good set of stock coils (just to eliminate that possibility) and there was no difference from the BHR setup.
So, while charging my battery and flashing my PCM, I noticed something.
When I started the car, the current from the charger stayed in the 17 amp range!
When I stopped the motor, it dropped to 4 or 5.
Thinking that it could be something to do with my battery relocation, I moved the charger to the front of the car near the alternator and tried it again.
Same thing.
I tried a different alternator.
No change.
I spent several sessions with the motor chasing potential vacuum leaks with propane, carb cleaner and other solvents.
Its tight as a drum. No leaks.
I jacked up the OMP just to see the difference and, besides a ton of smoke, there was no change.
So, I am out of ideas.
Inspire me.
08-26-2008, 10:36 PM
#5
I gonna actually try pulling the alternator belt completely.
It might be an electrical load.
The only system I can think of that is only running when the motor is on that can pull that kind of current is the EPS.
I need to do some metered diagnostics to the wiring if it turns out to be electrical.
It might be an electrical load.
The only system I can think of that is only running when the motor is on that can pull that kind of current is the EPS.
I need to do some metered diagnostics to the wiring if it turns out to be electrical.
08-27-2008, 12:17 PM
#7
Administrator
iTrader: (7)
ponder this I shall.
08-27-2008, 02:54 PM
#8
Lubricious
Join Date: Oct 2003
Location: SF Bay Area, California
Posts: 3,425
Likes: 0
Received 4 Likes
on
4 Posts
Air bypassing the throttle?
Idle rpm are normal?
I'm not sure about the battery charger thing; maybe just a red herring. Did you try that on another car? Maybe it's just behaving differently with the running engine due to voltage. It's trying to charge what it sees as a 15 volt battery instead of a 12 volt?
Idle rpm are normal?
I'm not sure about the battery charger thing; maybe just a red herring. Did you try that on another car? Maybe it's just behaving differently with the running engine due to voltage. It's trying to charge what it sees as a 15 volt battery instead of a 12 volt?
Last edited by Nubo; 08-27-2008 at 02:57 PM.
08-27-2008, 05:23 PM
#9
No, that's a supercharger thing. 
No "idle bypass" or anything like that.
Yep, totally normal, smooth, stead and no dips or anything. Like glass.
Yeah, I dunno.
An alternator load is the only thing I can think of at the moment.
The FSM says either a vacuum leak (which I cannot find) or bad compression (and mine is around 130 per combustion chamber).
So, I'm still stumped.
When it cools off this afternoon, I'll pull the alternator belt and see what happens.
No "idle bypass" or anything like that.
Yep, totally normal, smooth, stead and no dips or anything. Like glass.
An alternator load is the only thing I can think of at the moment.
The FSM says either a vacuum leak (which I cannot find) or bad compression (and mine is around 130 per combustion chamber).
So, I'm still stumped.
When it cools off this afternoon, I'll pull the alternator belt and see what happens.
08-27-2008, 06:15 PM
#12
Registered
And is that with the air filter in place (guessing at a dirty filter)?
This is a new engine, so I would guess that there no defects after the throttle body that would impede airflow.
That's my two guesses. Next!.
This is a new engine, so I would guess that there no defects after the throttle body that would impede airflow.
That's my two guesses. Next!.
Last edited by jeffe19007; 08-27-2008 at 06:23 PM.
08-27-2008, 06:44 PM
#14
Registered
I was hoping that the intake, being something, maybe, in common between engines was an answer.
Other than that, my old knowledge says the tune can affect the idle too. But I don't want to go there for fear of getting in way over my head!
Other than that, my old knowledge says the tune can affect the idle too. But I don't want to go there for fear of getting in way over my head!
Last edited by jeffe19007; 08-27-2008 at 06:48 PM.
08-27-2008, 06:50 PM
#15
Power!!
Maybe take a step back and list all the things that affect idle vaccum and walk through them 1 by 1.
Intake leaks
Intake restrictions
air density
rotor sealing
AC load
Alternator load
water pump
oil pump
Idle RPM
What else?
Intake leaks
Intake restrictions
air density
rotor sealing
AC load
Alternator load
water pump
oil pump
Idle RPM
What else?
08-28-2008, 01:39 AM
#23
Asshole for hire
iTrader: (1)
Join Date: Jun 2006
Location: Colfontaine, Belgium
Posts: 3,214
Likes: 0
Received 3 Likes
on
3 Posts
can you look at your PIDS/DTC
DTC B1318 is over/under voltage for the module
the PIDS might tell you something as well
C1099 - Abnormality detected in control current from EPS control module to EPS
motor.
DTC B1318 is over/under voltage for the module
the PIDS might tell you something as well
C1099 - Abnormality detected in control current from EPS control module to EPS
motor.
Last edited by paulmasoner; 08-28-2008 at 01:41 AM.