MAP sensor readings

[BigCarl64]

I am getting some strange readings from the MAP sensor. I hooked up a diagnostic tool for some troubleshooting and the MAP sensor reading is showing 60 inHg with engine off and at idle. I then drove the truck down the road with tool still on, and the readings went as high as 75 inHg, but no higher no matter what the boost gauge was showing. My boost gauge appears to working ok.



I did hook the same scan tool up to my Dad's 2001 Ford Powerstroke and it showed his MAP sensor reading at 30 inHg, which is exactly what I would expect here in Texas.



Wondering if anyone else has seen this and also what type of readings are other people getting from their diagnostic scan tools(i. e. Palm Quickcheck or other tools available).



Also, has anyone seen or know what a P1688 code is?



Any help would be appreciated.

 

[big barney]

Big Carl I have a 1999 service manuel and it says a

P1688 code is: internal fuel injection pump controller failure



internal problem within the fuel injector pump. low power, engine derated , or engine stops

 

[icarus33]

Carl,



I'm using the same software, rev 1. 01. and I too get flakey MAP readings. Most of the time there is no data displayed in the data column. Sometimes stopping and resending the request will get it to work. Otherwise, sometimes the reading will be displayed below the cells box when that line is highlighted. If you hit the stat tab on the right side, there is also min, max and avg. data. I just looked at it again and the average data will update even though there is no data displayed in the cell block.



My reading engine off or idle is 30. 5 inHg and I'm at 5300ft.



ic

 

[thepitts]

Code 1688

I have an 2001 Manual and it said the same as Big Barney's

 

[Little Bill]

The MAP sensor was changed on 2001. It is now calibrated for 1 volt per atmosphere(absolute). At sea level the 'key on' output is 1 volt. Fuel derating starts at 2. 5 volts(23 psi).