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cummins1984

Boost reading on startup

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Anyone ever get with their touch a negative boost pressure reading after starting their truck? I don’t get it all the time but sometimes it’ll read up to -2 psi on the touch.  

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I'm having the same issue,

my auto meter is reading normal but my smarty is going down to -12 ?

when I'm at 20psi on the gauge the smarty barely reads 3 psi

is my map possibly going bad?

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It very well could be your map sensor. The Smarty Touch reads the information it is provided so I would look the direction of the map sensor.

 

 

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I find if I start the truck before the touch has started up I never have it read into the negative at idle aside from an occasional 0.0something psi.  Its when the touch has been fully turned on then I start the truck, say waiting for grid heater warmup to finish, is when it tends to happen, not always though.  The only time I've ever seen the touch display a boost reading really far into the negatives at idle is if I apply an RT while driving under boost conditions.  It sets whatever boost it's reading at that time as the new zero boost reading so once I'm back at idle it will read negative whatever boost I happened to be at at the time of applying an RT.

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So I had it show negative 1.7 boost after start up and I noticed that when I was starting the truck the touch shut off and flashed the red led, booted back up and was showing the negative boost pressure.  Perhaps battery voltage dipping too low during startup causes it happen?

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Yes most definitely happens when the touch’s screen goes black during engine cranking, the red led flashes a couple times then restarts, boost reading is all screwed up at that point reading a couple psi in the negative and the touch has to “read” the micro sd as if you just put it in

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Boost isn't measured in terms of gauge pressure, it's calculated. 

 

The Touch calibrates it self during the startup to get 0.0 psi, if it's calibrated before cranking it may not drop that calibration when cranking and now you have more vacuum in the intake manifold that shows negative boost. 

 

I see boost errors when I start the truck at once elevation and make a drastic elevation change, such as 3-4K feet difference. 

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Issue I’d have is the touch doing a reboot instead of resuming during cranking, I’m thinking possibly batteries starting to get weak causing too much of a voltage drop.  After the truck has been ran for a little bit I can shut it off, wait for the touch to go into standby and restart the truck and everything is fine, it’ll resume instead of doing a full reboot

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I just installed my new MM3 last week and it's doing the same thing. It has shown -4 psi at idle all the way to -12 psi while driving. Seems worse if I switch tunes while driving. Switch again while stopped and it reads fine. Other than that it's great I'm very happy with the clean responsive tuning I got from calibrated power. Looking for a 12 valve tune now?

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I have run into this as well when applying RT Flashes.  It seems like the touch resets to zero at whatever boost it's reading when the flash happens.

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On 2/1/2018 at 4:23 PM, Rob D said:

I have run into this as well when applying RT Flashes.  It seems like the touch resets to zero at whatever boost it's reading when the flash happens.

 

Same.

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