What is the expected vacuum reading at idle? - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

qtwre · 08-12-2014, 09:45 AM

I'm trying to diagnose a potential vacuum leak and it would be good to know what I should be expecting at idle. If anyone could take a look at their boost gauge or obd2 readout it would be most helpful.

Thanks

Admired · 08-12-2014, 10:41 AM

-9.9

HRTROB · 08-12-2014, 10:46 AM

I believe mine is around -60kpa (-17.72 inHg). Defi boost gauge hooked up to the brake booster line.

ecko04 · 08-12-2014, 11:27 AM

I pull ~ -20 @ idle. That's measured using the P3Cars gauge reading from the OBDII port.

sw20kosh · 08-12-2014, 11:46 AM

-20

rb6freak · 08-12-2014, 11:49 AM

-19 AEM Boost gauge, brake booster source. If I recall correctly when I had a vacuum leak I still read the same on my gauge. I found out through the fuel trim in the EcuTek logs that it was most certainly a vacuum leak due to lean AFR's.

Edit: Good read for common vacuum leaks - http://www.ft86club.com/forums/showthread.php?t=62709

ecko04 · 08-12-2014, 11:54 AM

Your idle should bounce a bit but a strong idle is -18 and up

wbradley · 08-12-2014, 12:13 PM

On the new WRX (still FA20 block) at idle the dash boost gauge reads -9PSI, sometimes as low as -10 PSI momentarily.

Probably the same as the FA20 as idle is off boost.

Sportsguy83 · 08-12-2014, 12:50 PM

PSI is not equal to inHG which is what omst gauges read.

Idle should be -18 to -21 inHG.

Sportsguy83 · 08-12-2014, 12:51 PM

Quote:

Originally Posted by wbradley

On the new WRX (still FA20 block) at idle the dash boost gauge reads -9PSI, sometimes as low as -10 PSI momentarily.

Probably the same as the FA20 as idle is off boost.

Similar, but not same because not same motor compression, not same intake manifold siz, etc.

qtwre · 08-12-2014, 01:34 PM

Thanks guys. Mine reads around 20in/hg from my obd2 readout but it still behaves as though there is a leak with a high/bouncy idle when warm.

ecko04 · 08-12-2014, 02:45 PM

Quote:

Originally Posted by qtwre

Thanks guys. Mine reads around 20in/hg from my obd2 readout but it still behaves as though there is a leak with a high/bouncy idle when warm.

Injector scaling and fuel trims may be an issue more so than a vacuum leak. Without knowing anything about your setup though that's just me pissing in the wind.

qtwre · 08-12-2014, 03:25 PM

Quote:

Originally Posted by ecko04

Injector scaling and fuel trims may be an issue more so than a vacuum leak. Without knowing anything about your setup though that's just me pissing in the wind.

Interesting that you mention fuel trims because I find my idle is always reading in the -20s. That means it's pulling fuel, right? While a vacuum leak would be causing it to add fuel? Is -20 a lot?

Here is a short Ecutek log in case you or anyone else is interested in taking a look. My issue is that once the car is warm, when I disengage the clutch (press the pedal) while in motion, it keeps the RPMs at around 2k (sometimes it bounces instead.) Sometimes it even propels me in gear with no throttle at 2k rather than slowing to idle. This persists until I put the transmission in neutral and re-engage the clutch. It will then idle nicely so long as it's spinning the input shaft.

So this log is of me moving slowly in a parking lot, then the clutch pedal is pressed and I'm rolling for a few seconds, then stopping.

I'm going to have my mechanic check for a vacuum leak tomorrow because I can't find one by eye and poking around.

This is with a stock fuelling system and AVO turbo.

Admired · 08-12-2014, 10:45 PM

1 inHg = .5 PSI

08-12-2014, 09:45 AM	#1
qtwre Senior Member Join Date: Jun 2012 Drives: White FR-S Location: GTA, Ontario Posts: 190 Thanks: 15 Thanked 35 Times in 30 Posts Mentioned: 2 Post(s) Tagged: 0 Thread(s)	What is the expected vacuum reading at idle? I'm trying to diagnose a potential vacuum leak and it would be good to know what I should be expecting at idle. If anyone could take a look at their boost gauge or obd2 readout it would be most helpful. Thanks

08-12-2014, 11:27 AM	#4
ecko04 Seems Legit Join Date: Mar 2013 Drives: Toyota Location: Here & There Posts: 855 Thanks: 187 Thanked 438 Times in 250 Posts Mentioned: 24 Post(s) Tagged: 0 Thread(s)	I pull ~ -20 @ idle. That's measured using the P3Cars gauge reading from the OBDII port. __________________ No build thread. I don't want to be reminded of how much money I spent. [insert profound quote here]

08-12-2014, 11:49 AM	#6
rb6freak Senior Member Join Date: Nov 2013 Drives: 23 BRZ Location: CA Posts: 540 Thanks: 546 Thanked 688 Times in 300 Posts Mentioned: 33 Post(s) Tagged: 0 Thread(s)	-19 AEM Boost gauge, brake booster source. If I recall correctly when I had a vacuum leak I still read the same on my gauge. I found out through the fuel trim in the EcuTek logs that it was most certainly a vacuum leak due to lean AFR's. Edit: Good read for common vacuum leaks - http://www.ft86club.com/forums/showthread.php?t=62709 __________________ SecondGen \| FirstGen \| Instagram \| YouTube

08-12-2014, 11:54 AM	#7
ecko04 Seems Legit Join Date: Mar 2013 Drives: Toyota Location: Here & There Posts: 855 Thanks: 187 Thanked 438 Times in 250 Posts Mentioned: 24 Post(s) Tagged: 0 Thread(s)	Your idle should bounce a bit but a strong idle is -18 and up __________________ No build thread. I don't want to be reminded of how much money I spent. [insert profound quote here]

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08-12-2014, 10:41 AM	#2
Admired Senior Member Join Date: May 2013 Drives: 2013 Scion FRS Location: GA Posts: 248 Thanks: 0 Thanked 16 Times in 13 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	-9.9

08-12-2014, 10:46 AM	#3
HRTROB Senior Member Join Date: Dec 2012 Drives: Toyota 86 Location: Manila, Philippines Posts: 458 Thanks: 144 Thanked 271 Times in 140 Posts Mentioned: 13 Post(s) Tagged: 0 Thread(s)	I believe mine is around -60kpa (-17.72 inHg). Defi boost gauge hooked up to the brake booster line.

08-12-2014, 11:46 AM	#5
sw20kosh Senior Member Join Date: Jul 2012 Drives: 2013 Black FR-S Location: SF Posts: 3,030 Thanks: 881 Thanked 2,014 Times in 990 Posts Mentioned: 153 Post(s) Tagged: 1 Thread(s)	-20

08-12-2014, 01:34 PM	#11
qtwre Senior Member Join Date: Jun 2012 Drives: White FR-S Location: GTA, Ontario Posts: 190 Thanks: 15 Thanked 35 Times in 30 Posts Mentioned: 2 Post(s) Tagged: 0 Thread(s)	Thanks guys. Mine reads around 20in/hg from my obd2 readout but it still behaves as though there is a leak with a high/bouncy idle when warm.

08-12-2014, 10:45 PM	#14
Admired Senior Member Join Date: May 2013 Drives: 2013 Scion FRS Location: GA Posts: 248 Thanks: 0 Thanked 16 Times in 13 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	1 inHg = .5 PSI

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