Boost controller vs MAP

[CGASTON]

I have a question and wondering if anyone would happen to have experienced the same issue. At idle my car is registering -13# vacuum and my tru-boost is reading -10#. So that is a difference of -3# vacuum. I have the MAP tied into the vacuum block with it own line and the "tru boost" with it on line. So here is a question.

1. So the purpose of the scanmaster is to read the atmospheric pressure (Pa) within an engine. So does the scanmaster\PL at anytime covert the Pa to gauge pressure (Pg)?

2. I know that the "tru boost gauge" calibrates itself every time you turn on the key to zero Pg (14.6 psi of Pa) and takes into account the atmospheric pressure that we deal with everyday. So with this said, the scanmaster\pl should read -14.6 psi Pa from the atmospheric pressure from within the motor when the gauge reads 0psi, engine 0ff. The amount of oxygen at my level is 85% (4600ft). Yet, I can not figure out why they read differently... Can someone help me out on this one. Secondly, I may have forgot to write something. Let me know!!!

 

[Blazer406]

I think you are getting confused......

Vacuum is usually measured in inches of mercury..... and boost is measured (usually) in PSI..... so it technically isn't -10 psi.

The MAP is the absolute pressure..... not gage pressure. If you have ever tinkered with a FAST, on the main VE table, it has kPa on the left going up.... and "0" is real close to 100 kPa........ this is kilo pascals absolute. Most engines with medium cams idle in the 25-40 kPa range which is an actual pressure number......

I might have confused you more than not.....

I would think the SM is reading off the PL MAP input.... which is similar to the FAST, howver, I'm not familiar with how the SM reports that pressure.

 

[TurboDave]

I have a question and wondering if anyone would happen to have experienced the same issue. At idle my car is registering -13# vacuum and my tru-boost is reading -10#. So that is a difference of -3# vacuum. I have the MAP tied into the vacuum block with it own line and the "tru boost" with it on line. So here is a question.

1. So the purpose of the scanmaster is to read the atmospheric pressure (Pa) within an engine. So does the scanmaster\PL at anytime covert the Pa to gauge pressure (Pg)?

2. I know that the "tru boost gauge" calibrates itself every time you turn on the key to zero Pg (14.6 psi of Pa) and takes into account the atmospheric pressure that we deal with everyday. So with this said, the scanmaster\pl should read -14.6 psi Pa from the atmospheric pressure from within the motor when the gauge reads 0psi, engine 0ff. The amount of oxygen at my level is 85% (4600ft). Yet, I can not figure out why they read differently... Can someone help me out on this one. Secondly, I may have forgot to write something. Let me know!!!

First, some clerification is in order:
When you say -13# and -10# in the opening paragraph, I assume you acctually mean 13 in/HG vacuum and 10 in/HG vacuum.

I'm a little confused by all the numbers you're throwing around so here's what I know. The scanmaster/Powerlogger combo read the same as a normal combound vacuum/boost gauge. In my case, for example I run a Westach vacuum/boost gauge, and my scanmaster, which gets it's info now from the powerlogger reads exactly what my boost gauge does. It's even smart enough to do the conversion from PSI, to In/Hg (vacuum) when it goes into vacuum.

Does your Powerlogger, get it's manifold pressure from the same source that your tru boost does?? Do you have a known good mechanical gauge to hook up to see how it reads compared to PL and tru boost??

 

[SloGN]

Have you verified that the voltage going to the map sensor is getting a clean 5 volt signal? For every tenth of a volt the input voltage is is low from 5V is the output will be reduced by that same tenth 0f a volt thru out the complete scale from vac to boost. The Powerlogger just has a set scale that it uses to turn sensor output voltage into a psi #.

There is no correction factor that i'm aware of in the power logger software to compensate for the voltage error.

But if it were me i would worry about it. What's the boost pressures read on both units are they 3 psi off into boost? if not then i would worry about the vac stuff reading two much different.


HTH

 

[CGASTON]

First, some clerification is in order:
When you say -13# and -10# in the opening paragraph, I assume you acctually mean 13 in/HG vacuum and 10 in/HG vacuum.

I'm a little confused by all the numbers you're throwing around so here's what I know. The scanmaster/Powerlogger combo read the same as a normal combound vacuum/boost gauge. In my case, for example I run a Westach vacuum/boost gauge, and my scanmaster, which gets it's info now from the powerlogger reads exactly what my boost gauge does. It's even smart enough to do the conversion from PSI, to In/Hg (vacuum) when it goes into vacuum.

Does your Powerlogger, get it's manifold pressure from the same source that your tru boost does?? Do you have a known good mechanical gauge to hook up to see how it reads compared to PL and tru boost??

Dave, Sorry I got a little carried away and forgot to add this. Thanks for clarifying ( 13 in/HG vacuum and 10 in/HG vacuum). Yes this is correct. My 3bar MAP is in the stock location and gets it pressure from its own dedicated line. And the tru boost gets it own line as well. So I don't understand why they are not reading the same when they are booth feed from the vacuum block. I am going to connect my mechanical gauge up tonight and check both the PL and tru boost against it.

 

[CGASTON]

Have you verified that the voaltage going to the map sensor is getting a clean 5 volt signal? For every tenth of a volt the input voltage is is low from 5V is the output will be reduced by that same tenth 0f a volt thru out the complete scale from vac to boost. The Powerlogger just has a set scale that it uses to turn sensor output voltage into a psi #.

There is no correction factor that i'm aware of in the power logger software to compensate for the voltage error.

But if it were me i would worry about it. What's the boost pressures read on both units are they 3 psi off into boost? if not then i would worry about the vac stuff reading two much different.


HTH

Well the MAP is in the stock location of the original and factory harness. I will check the voltage tonight as well.

So at 5v = 20 psi (for say), then 4v = 16psi

What is confusing me is why to objects with identical operation but not same in appearance, coming from the same source are reading differently. Could the voltage drain cause the MAP reading to drop 3in\hg?

 

[TurboDave]

There is no correction factor that i'm aware of in the power logger software to compensate for the voltage error.




HTH

Sure there is. On the F3 page, in the analog input settings area, there is an "adjust" button. Press it, and you'll see that you can either tweak the ECM reference voltage (not advisable) or each analog input has an offset adjustment that can be tweaked. But let's not mess with this just yet until he can get a good boost gauge on and do some comparisons.

 

[DavzGN]

Also altitude can cause a difference too. If the gauge resets to zero at key on while the map absolute pressure there can be a couple lb differences if you are at a couple thousand feet or higher. What does PL read key on engine off.

 

[SloGN]

I can tell you that if your using the factory location map sensor wiring then thats your problem. That 5v supply is coming from the factory boost gauge/tach assembly. That power supply is not regulated very well at all.

I went thru this a few yrs ago when i installed my FAST system and using the factory wiring to power the map sensor.

My advice to you is wire up the 5V and ground from the ECM or the power logger unit itself. I'm sure this is also make your tune a little fussy as well.


When checking the voltage check it with the key on engine off. Then check it with the engine running and last check it with the parking lights on. The voltage at the sensor will change on all three tests. Why the parking light/headlight on affects it i dunno but i have a feeling it has something to do with how it dims the guages for night time driving.

HTH



Dave

When making the adjustment in the scaler is that for the actual ecm or is that for just the datalogging ? Cause if one is using a Speed density set-up that really needs to be corrected for the ECM/chip calibrations to be correct.

 

[TurboDave]

Scaler adjustments?? The one's I'm referring to arent called scalers. There is "ECM Reference Volts". at the top of the adjustment window. I like to set that to what the ECM is seeing on it's 5v reference supply. The easiest place to see this is what the ECM is supplying to the TPS.
The rest of the adjustments are "Analog Offset Volts". These adjustments can be tweaked to compensate for various offsets in supply or ground that may affecct the accuracy of that particular analog inputs device.

 

[CGASTON]

Well I didn't get to checking out my gauges last night or the voltage. I started of replacing my header gaskets. I had reflex gaskets on my car and the #2 and #6 ports were blown out. I originally though it was just #6. When I loosened the bolts and pulled back the header, piece of the gasket fell from the top of both ports. This is where it was blown. Come on now, they say these gaskets were awesome.


So anyways, tonight I am going to finish up the header gaskets and then move over to the gauges. I will let you know as soon as I get it done.