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killerbee
June 21st, 2010, 11:41 PM
Has anyone else an opinion on what the problem is here?

At or near seal level, MAP and Baro should be equal. I have noticed idle (no boost) MAP is around 12.0 psi, instead of the expected 14.x psi. Location error, or calibration issue?

This has been observed on multiple LMM's.
WeathermanShawn
June 21st, 2010, 11:46 PM
Has anyone else an opinion on what the problem is here?

At or near seal level, MAP and Baro should be equal. I have noticed idle (no boost) MAP is around 12.0 psi, instead of the expected 14.x psi. Location error, or calibration issue?

This has been observed on multiple LMM's.

Thats at Key-On, engine not running yet. At that point (before ignition) BARO and MAP would be equal at sea-level (perfect vacuum). At Idle, you have vacuum, so that correlation would not exist.

Is that what you are asking?
killerbee
June 21st, 2010, 11:51 PM
I don't see how it is even remotely possible to have 2 psi of vacuum at idle at that location, but I am willing to listen.

Thanks.
WeathermanShawn
June 22nd, 2010, 12:18 AM
I don't see how it is even remotely possible to have 2 psi of vacuum at idle at that location, but I am willing to listen.

Thanks.

Maybe I am not understanding your question/premise. BARO and MAP will be equal at Key-on at sea-level. Are you saying there is an issue with the Idle MAP?

My only point is that MAP and BARO are not equal at Idle..only at Key-on. If the Idle MAP is off..maybe I missed the premise of the question.:confused:

Edit: I am working off the premise of a 1 BAR system. If boosted, there may be some assumption I am missing. The only other condition to consider would be MAP Voltage. 0.0 Voltage does not always equate to 0 kPA ( I hit 0.0 at 14 kPa), but I am not sure what your MAP sensor Voltage maxes out at..

..So hopefully we are taking about the same issue here..if not perhaps someone can clarify..
joecar
June 22nd, 2010, 03:29 AM
The OP's asking about diesel system... no throttle blade so no vacuum due to throttle.
WeathermanShawn
June 22nd, 2010, 03:33 AM
The OP's asking about diesel system... no throttle blade so no vacuum due to throttle.

Yea, I have to give up ever answering another question that relates to diesel. OP, forgive my ignorance..I need to read up on diesel's for about a year..:grin:
killerbee
June 22nd, 2010, 04:04 AM
Actually, in the LMM there is an intake valve, used mainly for reducing oxygen/increasing EGT during dpf regeneration. But it does not appear to be the issue, as one of the trucks I logged has it removed.
killerbee
June 22nd, 2010, 08:22 AM
Is the MAP sensor only good to 37 psia?

That 37 psi cap on the log is a PIA. What happened to 3 Bar?

Thanks for the feedback guys.
bballer182
June 23rd, 2010, 11:39 AM
Is the MAP sensor only good to 37 psia?

That 37 psi cap on the log is a PIA. What happened to 3 Bar?

Thanks for the feedback guys.

LMM's only read to 37? I'm pretty sure i've seen my LBZ in the 40's.
JoshH
June 29th, 2010, 12:32 AM
Try using the Boost2_DMA PID. I have done a bunch of logging on my dad's LMM and his Baro matches perfectly with that PID, and it goes up to at least the mid 40s, probably higher.
L31Sleeper
July 1st, 2010, 07:16 PM
What is the factory LMM MAP capable of reading ??
L31Sleeper
July 6th, 2010, 07:39 AM
Anybody know what the MAX pressure the stock MAP is capable of reading ??
JoshH
July 6th, 2010, 02:27 PM
Should be 52ish PSIA.
L31Sleeper
July 6th, 2010, 07:37 PM
vs PSIG ??
bballer182
July 7th, 2010, 12:28 AM
I would think that PSIA and PSIG would be the same in this case.
JoshH
July 7th, 2010, 01:12 PM
vs PSIG ??Yes. The absolute highest reading is somewhere around 52, but that is including atmospheric pressure.


I would think that PSIA and PSIG would be the same in this case.Only if you are in space or somewhere else where there is a very high vacuum.
joecar
July 7th, 2010, 01:57 PM
I thought PSIA = PSIG + BARO


anywhere where BARO is zero will allow PSIA to equal PSIG.
L31Sleeper
July 7th, 2010, 03:19 PM
So what do you do if you want to run 80 PSIG ??
JoshH
July 7th, 2010, 03:45 PM
I thought PSIA = PSIG + BARO


anywhere where BARO is zero will allow PSIA to equal PSIG.
I'm not sure if this is directed at me or bballer, but a vacuum is a lack of atmospheric or barometric pressure.


So what do you do if you want to run 80 PSIG ??Get an aftermarket gauge. There have been a couple of people who have worked with replacement sensors that are good up to 100 PSIA and rescaling the sensor, but last I heard they were having problems with it. It was also on LB7 and LLY motors. I don't think LBZ and LMM motors have access to the boost sensor scaling in EFILive.
joecar
July 7th, 2010, 05:54 PM
I'm not sure if this is directed at me or bballer, but a vacuum is a lack of atmospheric or barometric pressure.I was questioning bballer and affirming your reference to space (PSIA = PSIG = BARO = 0).

:)

PSIA and PSIG are generally defined to be related by PSIA = PSIG + BARO

(nevermind me, I'm just sweeping thru all the threads)

So has anyone explained why MAP isn't equal to BARO at sea level (I'm curious to know)...?
bballer182
July 8th, 2010, 12:19 AM
I would think that PSIA and PSIG would be the same in this case.


I thought PSIA = PSIG + BARO


anywhere where BARO is zero will allow PSIA to equal PSIG.



Boy i was tired when i posted that... Duh PSIG = PSIA - BARO:doh2:

note to self... don't post when you wake up:bangin:
bballer182
July 8th, 2010, 12:24 AM
I would think that PSIA and PSIG would be the same in this case.


I was questioning bballer and affirming your reference to space (PSIA = PSIG = BARO = 0).

:)

PSIA and PSIG are generally defined to be related by PSIA = PSIG + BARO

(nevermind me, I'm just sweeping thru all the threads)

So has anyone explained why MAP isn't equal to BARO at sea level (I'm curious to know)...?


Isn't MAP (Manifold Absolute Pressure) supposed to be the same as BARO with zero boost and then as boost rises it reads PSIA? PSIG+BARO??
JoshH
July 8th, 2010, 01:21 AM
Isn't MAP (Manifold Absolute Pressure) supposed to be the same as BARO with zero boost and then as boost rises it reads PSIA? PSIG+BARO??

Yes it is. I haven't played with the MAP PID much, but I know the Boost2_DMA PID matches.
joecar
July 8th, 2010, 03:31 AM
See post #1:


Has anyone else an opinion on what the problem is here?

At or near seal level, MAP and Baro should be equal. I have noticed idle (no boost) MAP is around 12.0 psi, instead of the expected 14.x psi. Location error, or calibration issue?

This has been observed on multiple LMM's.
bballer182
July 8th, 2010, 12:17 PM
I was just saying that no matter what altitude MAP should equal BARO
L31Sleeper
July 8th, 2010, 01:02 PM
See post #1:


Has anyone else an opinion on what the problem is here?

At or near seal level, MAP and Baro should be equal. I have noticed idle (no boost) MAP is around 12.0 psi, instead of the expected 14.x psi. Location error, or calibration issue?

This has been observed on multiple LMM's.

It's simple there is a vacuum for some reason I don't know.
bballer182
July 8th, 2010, 01:08 PM
could it be that the intake butterfly is closed during this anomaly?