Does your Defi boost gauge read higher than your ECU logs boost? - TriStateTuners.com :: Home of Tristate Auto Enthusiast

**TROLL** · 09-02-2008, 06:32 PM

Wondering if others experience the same... if you have a Defi boost gauge and you are also able to log your ECU, how do the two pressures compare?
My Defi reads about 23 psi while my ECU logs about 21 psi max... I've heard Defi's read high which is a little disappointing at the price, but wanted to see if others experience this.

Loserkidwac · 09-02-2008, 07:03 PM

Can't say I have experience but just wondering if the gauge and the ecu are taking the reading from the same location...pre and post IC might show different boost levels...if one is tapped off the turbo and one on the intake mani etc...I always try and tap everything off the intake mani...

**TROLL** · 09-02-2008, 07:09 PM

yeah good thought, i forgot to mention that... i have them both tapped off of the intake manifold.

Loserkidwac · 09-02-2008, 07:15 PM

Hmmm....that's interesting...I once had a autometer gauge that read 1psi even when it wasn't hooked up to anything...I found a write up on how to recalibrate it and did so and then to check it I used an air compressor and compared the reading on the tank to the gauge...that method might be able to show if you gauge is reading incorrectly...

JET02WRX · 09-02-2008, 08:09 PM

Bryan which Manifold pressure option are you selecting in RomRaider? FWIW my Omori gauges read 1psi higher than what my logs say. I have my warning light set at 20psi, and it trips all the time...yet my logs never go over 19.

WRXD · 09-02-2008, 08:31 PM

my Defi is almost dead on perfect with what my ECU sees.

**TROLL** · 09-02-2008, 08:35 PM

ah interesting... i'm using MAP (corrected)... I havent even though about using the others. Is there a preferred one to log?

WRXD · 09-02-2008, 08:42 PM

I am reading off MAP as well, reading from my MSD DashHawk and my Defi tapped from the manifold.

JET02WRX · 09-02-2008, 08:59 PM

These are all the options in RR. I don't see MAP corrected? I use MAP (direct) because it says thats the value used by the ECU in its calculations. All of the MRP options seem to be calculations of some sort with the exception of one, but it only goes to 18.4, so i don't use them.

‘Manifold Absolute Pressure’ - this standard SSM parameter will read no higher than about 37 psia.
‘Manifold Relative Pressure’ - this standard SSM parameter is limited to about 18.4 psig regardless of atmospheric pressure.
‘Manifold Relative Pressure (Corrected)’ - This is a calculated parameter (still based on standard parameters) that is limited to about 22.3 psig at sea level. The actual limit will depend on the local atmospheric pressure (37psia - atmospheric pressure). For example, if atmospheric pressure is 13 psi, then this parameter would be limited to 24 psig (37psia - 13 psi = 24 psig).

‘Manifold Absolute Pressure (Direct)*’ - This extended parameter reads the manifold pressure value directly as used by the ECU. As such, it has no effective limit.
‘Manifold Relative Pressure (Direct)*’ - This extended parameter also has no effective limit. It is not the actual relative pressure, however. This parameter assumes sea
level atmospheric pressure (14.7 psi). Although this will not match actual relative pressure if local atmospheric pressure is different from 14.7 psi, it will match the standard units ECU definitions in relation to relative manifold pressure (ex. Target Boost).

ericnjttz · 09-02-2008, 10:49 PM

my defi reads spot on with my EBC cant log my ecu though

**TROLL** · 09-03-2008, 01:54 AM

Woops sorry I'm using MRP (corrected). under Andy at Verocious' recommendation I added a GM 3 bar map sensor so I actually wont be capped at 22.3 psi MRP any longer. However we had to calibrate it and its very close, but not 100% to what the factory sensor read.

By the definitions you listed it seems that MRP (direct) would work well also.

TrboChicsRock · 09-03-2008, 10:05 AM

My Defi gauge used to read 1 psi when the car was off. It never read correctly. I have since switched to a Stewart Warner boost gauge and that reads the same as my GM Map sensor does.

**TROLL** · 09-03-2008, 10:08 AM

Yeah its tough because the GM Map Sensor needs to be calibrated so that could be off slightly, but my Defi gauge sits at like... .5 psi when the car is off. I'm just thinking about it because Subaru guys talk about the safe acceptable boost limit being about 22 psi and I'm wondering if 22 psi logged which is 24 psi on the gauge is ok... or If I should do 22 psi on the gauge which is about 20 psi logged. Eh I guess if its not knocking its not knocking...

Vince@R/TTuning · 09-03-2008, 10:22 AM

Its hard to say but im willing to bet that the 3 bar is reading a lil low and that your defi is closer to accurate. I log boost on the dyno with a 3bar and it always tends to be a lil low(1-1.5lb) lower then all the other gauges or logs that i am using. I log with serveral different systems, not just one, and it always seems to be a lil lower....hope that helps....

JET02WRX · 09-03-2008, 02:19 PM

Quote:

Originally Posted by TROLL

Eh I guess if its not knocking its not knocking...

You'll be fine most likely....that is unless you see this while logging!!!

If so, expect to see your floor pan fall into the street....for some reason....

SovXietday · 09-04-2008, 05:20 PM

Where are you getting power and ground from?

I've seen voltage offsets do some pretty weird stuff, especially with widebands.

09-02-2008, 07:03 PM	#2
Loserkidwac Tri-State Addict Join Date: Sep 2006 Location: SE PA Member #2550 My Ride: 1992 Mazda Miata, 1991 Honda CRX Si LS-T, 95 Civic VX iTrader: (3)	Can't say I have experience but just wondering if the gauge and the ecu are taking the reading from the same location...pre and post IC might show different boost levels...if one is tapped off the turbo and one on the intake mani etc...I always try and tap everything off the intake mani... __________________ MoHawks are Cool To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures. To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.

09-02-2008, 07:15 PM	#4
Loserkidwac Tri-State Addict Join Date: Sep 2006 Location: SE PA Member #2550 My Ride: 1992 Mazda Miata, 1991 Honda CRX Si LS-T, 95 Civic VX iTrader: (3)	Hmmm....that's interesting...I once had a autometer gauge that read 1psi even when it wasn't hooked up to anything...I found a write up on how to recalibrate it and did so and then to check it I used an air compressor and compared the reading on the tank to the gauge...that method might be able to show if you gauge is reading incorrectly... __________________ MoHawks are Cool To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures. To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.

09-02-2008, 08:09 PM	#5
JET02WRX Tri-State Addict Join Date: Jun 2006 Location: Chester Co. Member #2133 My Ride: 2002 WRX Wagon iTrader: (1)	Bryan which Manifold pressure option are you selecting in RomRaider? FWIW my Omori gauges read 1psi higher than what my logs say. I have my warning light set at 20psi, and it trips all the time...yet my logs never go over 19. __________________ 2002 WRX "Fun-Wagon"

09-02-2008, 08:59 PM	#9
JET02WRX Tri-State Addict Join Date: Jun 2006 Location: Chester Co. Member #2133 My Ride: 2002 WRX Wagon iTrader: (1)	These are all the options in RR. I don't see MAP corrected? I use MAP (direct) because it says thats the value used by the ECU in its calculations. All of the MRP options seem to be calculations of some sort with the exception of one, but it only goes to 18.4, so i don't use them. ‘Manifold Absolute Pressure’ - this standard SSM parameter will read no higher than about 37 psia. ‘Manifold Relative Pressure’ - this standard SSM parameter is limited to about 18.4 psig regardless of atmospheric pressure. ‘Manifold Relative Pressure (Corrected)’ - This is a calculated parameter (still based on standard parameters) that is limited to about 22.3 psig at sea level. The actual limit will depend on the local atmospheric pressure (37psia - atmospheric pressure). For example, if atmospheric pressure is 13 psi, then this parameter would be limited to 24 psig (37psia - 13 psi = 24 psig). ‘Manifold Absolute Pressure (Direct)’ - This extended parameter reads the manifold pressure value directly as used by the ECU. As such, it has no effective limit. ‘Manifold Relative Pressure (Direct)’ - This extended parameter also has no effective limit. It is not the actual relative pressure, however. This parameter assumes sea level atmospheric pressure (14.7 psi). Although this will not match actual relative pressure if local atmospheric pressure is different from 14.7 psi, it will match the standard units ECU definitions in relation to relative manifold pressure (ex. Target Boost). __________________ 2002 WRX "Fun-Wagon"

09-03-2008, 10:05 AM	#12
TrboChicsRock Tri-State Post Whore Join Date: Feb 2005 Location: Pennsylvania Member #152 My Ride: 1998 Eclipse GSX, 2012 WRX Premium iTrader: (1)	My Defi gauge used to read 1 psi when the car was off. It never read correctly. I have since switched to a Stewart Warner boost gauge and that reads the same as my GM Map sensor does. __________________ - Jessica 1998 Eclipse GSX 11.2 @ 126 To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.

09-02-2008, 08:31 PM	#6
WRXD Tri-State Post Whore Join Date: Dec 2005 Location: SEPA Member #1156 My Ride: 2013 Ford Focus ST iTrader: (0)	my Defi is almost dead on perfect with what my ECU sees.

09-02-2008, 08:42 PM	#8
WRXD Tri-State Post Whore Join Date: Dec 2005 Location: SEPA Member #1156 My Ride: 2013 Ford Focus ST iTrader: (0)	I am reading off MAP as well, reading from my MSD DashHawk and my Defi tapped from the manifold.

09-02-2008, 10:49 PM	#10
ericnjttz Tri-State Addict Join Date: Aug 2007 Member #5687 My Ride: Z iTrader: (1)	my defi reads spot on with my EBC cant log my ecu though

09-03-2008, 10:22 AM	#14
Vince@R/TTuning Vendor Join Date: Mar 2007 Location: telford Pa Member #3958 My Ride: the one in the back of the shop iTrader: (2)	Its hard to say but im willing to bet that the 3 bar is reading a lil low and that your defi is closer to accurate. I log boost on the dyno with a 3bar and it always tends to be a lil low(1-1.5lb) lower then all the other gauges or logs that i am using. I log with serveral different systems, not just one, and it always seems to be a lil lower....hope that helps.... __________________ Philadelphia Area's Only Authorized and Factory Trained Pro Tuners for:HONDATA:UPREV:APEXI POWER FC:AEM:COBB:ECUTEK To view links or images in signatures your post count must be 10 or greater. You currently have 0 signatures.

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