Negative boost under heavy throttle.... - Ford Powerstroke Diesel Forum
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Old 05-18-2011, 12:44 PM
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Negative boost under heavy throttle....

Its an 03 and i havent pulled anything lately with it so i havent noticed a problem but today while pulling an open car trailer (about 6k total) i noticed that the truck would build about 22 lbs boost going up hills when i had to get into the throttle then it would stop making power and my scanguage would start reading negative boost numbers around -10 to -15. It would also blow black smoke when it did this. I cant hear any boost blowing by the boots or anything when its doing this. Anyone have any suggestions? Thanks
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Old 05-18-2011, 02:25 PM
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Your gonna need to visually inspect the 4 boots, use a mirror to see the underside where you can't see, or remove each boot for visual inspection, usually it's the 45* boot that comes right off the turbo. Inspect the up-pipe and "Y" pipe bellows and clamp connections.

Page 5 has diagnostic procedure if you have a scan tool.
http://www.forddoctorsdts.com/articl...argerGuide.pdf
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Old 05-18-2011, 04:02 PM
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Which Xgauge code are you using for the boost? The following might help you get rid of the negative reading, it did on mine. You will notice the MAP and Boost are the same except once you enter MAP get reading first thing engine cold and see what it says. (14.? ) Then enter the same code except enter the last 4 digits of the MATH line with which ever FF?? corresponds the MAP reading.

Manifold Absolute Pressure
TXD: 07E0221440
RXF: 046285140640
RXD: 3010
MTH: 012203200000
NAM: MAP

Boost
TXD: 07E0221440
RXF: 046285140640
RXD: 3010
MTH: 01220320 (0000)<<<<these 4 would become FF?? from below.
NAM: BST

With a little tweaking you can adjust this to read boost as you said.

To do this, just plug in the MAP code - get a reading from it with the key in the on position but the engine off, then based on the reading changed the last 4 digits of the MTH to whatever corresponds to your reading on this table

14.0 -- FF74 (I USE THE "FF71" FOR MY AREA, IT WORKS GREAT)
14.1 -- FF73
14.2 -- FF72
14.3 -- FF71
14.4 -- FF70
14.5 -- FF6F
14.6 -- FF6E
14.7 -- FF6D
14.8 -- FF6C
14.9 -- FF6B
15.0 -- FF6A
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