LBZ low boost? 18psi.

thunder550

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Apr 2, 2013
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I can check a LMM here in a bit basically it's same ecm arrangement= Baro sensor on the ECM. Check your 5v supply to Map the sensor to if it's low the MAP sensor will also read low.
I only have 4.5 volts on the MAP sensor circuit. I checked from +5v to MAP ground, and from +5v to chassis ground, both engine on and engine off. It's consistent across all of those scenarios. Is that low enough to cause a problem? What would cause low voltage on that circuit?
 

thunder550

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I'm browsing through a stock LBZ tune file right now, and it looks like I'm right on the edge of setting off the P0106 MAP sensor code. Trigger would be 2psi difference between MAP and Barometer for 10 seconds...I'm at 1.9 psi difference most of the time. Looking at C0808 and C0809 values.
 

JoshH

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I would guess your scan tool is giving you incorrect data. Do you have a V2 you can use to get a datalog? I would trust EFILive a whole lot more than a phone app.
 

thunder550

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I would guess your scan tool is giving you incorrect data. Do you have a V2 you can use to get a datalog? I would trust EFILive a whole lot more than a phone app.
I don't have anything else anymore. Used to have EFILive but let it go with my LML when I sold it back in 2015.

For S&G I just plugged my bluetooth dongle into my wife's car...it's a different make, and the Torque Pro app reads Baro and MAP both at 13.8 psi with engine off. They are SAE pids (i.e. not GM-specific), so I would assume it's an OBD2 standard across all makes and models. I know that's not definitive by any means, but it indicates to me that it's being read and displayed correctly in the phone app.
 

rcr1978

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Another thing that affects boost you can check are intake air temp, if it's around 68-111F you should be good anything above or below it's taking boost away. All the LBZ's I ever messed with always had hot intake air temps, I was thinking it should be cold now but you being in Phoenix it might be a different story.
 

thunder550

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Josh is right your scan tool is a turd most likely.
I'll have to find a way to validate but since it reads correctly on my wife's car I'm thinking it's something else. The 4.5 volts on the MAP sensor circuit bothers me...not sure what the tolerance is though.

Thanks for checking the LMM, that helps a lot to know they *should* be matching with the engine off.
 

thunder550

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Sae/generic map reads shit on my end and map2/gm enhanced matches the baro pretty close.
OHHHHH I just saw the GM MAP vs the SAE MAP you're talking about...so your SAE MAP reads low too. I see. So you guys are right, if I want to see something meaningful I need to be reading the GM PID, not the SAE PID that my crap scan tool is reporting. Derp.

The 12kpa difference between the two on your screenshot is 1.75 psi....close enough to 2 that I think that's the issue. I've been on a wild goose chase, lol.

Thank you!!!
 

thunder550

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I found another crappy scan app that looks like it uses the GM MAP PID...it shows that the barometer and MAP values match with engine off. That one shows that I'm hitting 22-23psi peak boost, which is right about where I've read I should be.

I hope I can return the new MAP sensor I bought today 🤣🤣

Thanks everyone for the help today, I really appreciate the responses and assistance!
 

JoshH

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Glad to see you got it figured out, and thank you for filling us in after you did. Maybe it will save someone else in the future.
 
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