Need help on MAP readings
Thread Starter
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Senior User
Joined: Aug 2014
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Need help on MAP readings
Hi all,
Sorry, but I already posted a thread about this but I am not getting anywhere. I could really do with a bit of forum expertise here.
Basically, what is happening, when the engine is working hard (or just floored) the MAP sensor reading rises to 38.0 and than drops suddenly to under 5.0. At the same time, Baro reads 14.5 steady, EBP rises to 50.0, steady and PSI to 28.0 solid.
Over a short period performance is unaffected and no codes are thrownbut in the case of a 20+ mile haul over the mountains the boost gauge on the dash flickers up and down and a CEL comes on and performance becomes erratic but it still pulls well although a bit up and down. If I back off, it resumes to normal but MAP still shows the sub 5.0 reading.
If anyone can help, it would be very much appreciated. I hope I have explained clearly....
Thanks in advance
Sorry, but I already posted a thread about this but I am not getting anywhere. I could really do with a bit of forum expertise here.
Basically, what is happening, when the engine is working hard (or just floored) the MAP sensor reading rises to 38.0 and than drops suddenly to under 5.0. At the same time, Baro reads 14.5 steady, EBP rises to 50.0, steady and PSI to 28.0 solid.
Over a short period performance is unaffected and no codes are thrownbut in the case of a 20+ mile haul over the mountains the boost gauge on the dash flickers up and down and a CEL comes on and performance becomes erratic but it still pulls well although a bit up and down. If I back off, it resumes to normal but MAP still shows the sub 5.0 reading.
If anyone can help, it would be very much appreciated. I hope I have explained clearly....
Thanks in advance
Lead Driver
Joined: Sep 2012
Posts: 7,825
Likes: 96
From: Manteca,Ca
all the CAC boots in good shape? some are kind of hard to see the little splits, also the Map hose look for cracks and splits , have you cleaned up the MAP nipple to Intake that little hole gets clogged along with the IAT2 sensor.
Thread Starter
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Senior User
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Everything appears to be fine and boost holds up at 28 PSI, solid. It's the MAP readings that go off the wall. Somebody said that PSI was just MAP less Baro, then surely PSI should go off at the same time? It doesn't.... a real brainteaser....
I'm at a real loss on this one. It would indicate that MAP and boost receive their signals from different sources?
Thanks
I'm at a real loss on this one. It would indicate that MAP and boost receive their signals from different sources?
Thanks
Lead Driver
Joined: Sep 2012
Posts: 7,825
Likes: 96
From: Manteca,Ca
yes but the altitude will very for my notes , I was leaning more towards cleaning them up, as far as the MAF use only Maf cleaner for that, IAT2 you can use carb cleaner .
Oh and ware your safety glasses
that stuff burns like
Oh and ware your safety glasses
that stuff burns like
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Senior User
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Ah, got you. I have been meaning to clean the IAT2 for a bit. I shall give them a go. MAF cleaner in Spain? I have carb cleaner, contact cleaner....
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Lead Driver
Joined: Sep 2012
Posts: 7,825
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From: Manteca,Ca
Need to be careful with the Maf and other cleaners very sensitive. may also pull the MAP nipple to Intake and clean that aswell.
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Senior User
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If these sensors would affect MAP readings, wouldn't they affect PSI readings too? Where does PSI get it's reading from? I would like to understand more, as I said, MAP reaches 38 and then disappears to less than 5 whilst PSI remains solid and constant. At the time MAP reading disappears, in reality it hasn't as the truck is unaffected and is still pulling hard until after a more sustained period when, I am assuming, due to an odd reading, the computer kicks in and panics
Fleet Mechanic
Joined: Aug 2012
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If these sensors would affect MAP readings, wouldn't they affect PSI readings too? Where does PSI get it's reading from? I would like to understand more, as I said, MAP reaches 38 and then disappears to less than 5 whilst PSI remains solid and constant. At the time MAP reading disappears, in reality it hasn't as the truck is unaffected and is still pulling hard until after a more sustained period when, I am assuming, due to an odd reading, the computer kicks in and panics
Did you check for codes? If the CEL light came on there should be something.
.