I have a 2004 F-250. I just towed a ~7500# Travel Trailer from SC to NY. I noticed that when I had to really get on it, once boost got to about 22#, it would show a -14.7 to a -13.6#, essentially a perfect vacuum. The truck felt like it was still pulling when this happened and there wasn't any noticeable smoke from the exhaust. Has anyone else seen this and if so, any ideas on how to fix it?

 

which type of gauge are you using?

and can you please clarify, 22 psi or -14???

14.7psi is atmospheric pressure at sea level, so I am guessing a faulty gauge.

 

What monitor are you seeing this on?

 

Scan Gage II. I am assuming that the PCM is also seeing this value.
It reads up to about 22# on the Scan Gage II and then dives to -14.7#. The highest I saw was 22.2# before diving to a pure vacuum. The BARO reads about 29.8 to 30.0 inches of Hg, normal for the location.
I'm assuming the MAP is bad, but wondering if there could be something else.

 

More likely the SCII programing of the PID. MAP and BARO should be the same at KOEO.

 

This is the stock MAP from the Scan Gage II. I'll try the manually input one and see what happens.

 

I'd change BARO also, psia instead of Hg.... so they all read in PSI and easily compared.

 

I noticed my 07 was doing showing the same on my SGII while towing. so you all are saying I need to change something on the SGII to read boost more accurately?

 

the factory boost setting in the scan gauge does that. if you input the correct one from the website it will act right again.

 

Baro 07E0221127 046285110627 3008 003100500000 BAR PSI
Baro 07E0221127 046285110627 3008 000A00080000 BAR Inches of Mercury
EBP 07E0221445 046285140645 3010 001D00500000 EBP PSI
EPV 07E02216AE 0462451606AE 3010 000100800000 EBPV EBP Volts
BST 07E0221440 046285140640 3010 01220320???? PSI/BST MAP Modified signal PLUG IN VALUE FROM TABLE FROM YOUR MAP
MAP 07E0221440 046285140640 3010 012203200000 MAP EXTENDED RANGE

14.0 -- FF74
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

 

Thanks for the help. I'll find out how well it works on Sunday when I head back to SC and oppressive heat.

 

I put the manual code in and it didn't go negative. Thanks.

 

no problem. it took me a minute to figure that one out too when I first got my SGII.

 

I'm gonna jump in here......no intent to hijack, same problem with an added question. My bst does the same thing (goes negative) and I did enter the new bst numbers with the four digit/letter sequence from the chart but mine still does it? however I haven't entered this yet:
MAP 07E0221440 046285140640 3010 012203200000 MAP EXTENDED RANGE

Do I also need this to make this work right? Thanks in advance for the help and sorry to the OP for tagging on here.

 

I'm to remember exactly what the MAP extended range reads and why it's different, I'm thinking it's just an adjustment so it will correlate with Baro at KOEO.

One question, Alan. Do you have two BST values in your SGII and are you sure you're reading the one you plugged in, or did you have to change the existing?