Well I am glad I finally got this question out in the open so the MAP sensor is used for fueling. I have only set an SES light twice and that was after two hard pulls in 140 showing the chip off and it wasn't an over boost because it came on even after I shut the truck down and then put it in high idle. It never came on when I was defueling comming up a few hills pulling a heavy load and never came on when I was drag racing. So how come it would defuel and not throw a code?

Chris and Cory I like the idea of marking the position on it, I bought the best one I could find at Home Depot last year and it isn't a locking regulator. So I guess marking it would be the best way and reset it because at 22 PSI it seems awfully loose.

 

The following is pure speculation on my part but I think it's why I got vague nonresponsive answers concerning the defuel threshold and some other changes I wanted made to my PCM code. The PCM program basically consists of two parts. 1) Lines of code and 2) Data tables. There are many lines of code that are the instructions for how to calculate things, logic flow paths etc, and some of these instructions say go to various data tables, lookup some numbers, do a calculation, and take some action.

I think that after market chips, tuners, programmers, or whatever you want to call them typically only modify the reference data set that's accessed by the OEM's proprietary software code. If they actually changed this code it would be the same as me changing a few lines of code in say the Microsoft Excel spreadsheet program and then marketing that modified software code as my own product! You can imagine how long I'd stay in business doing that, or for that matter how long I'd stay out of jail!

So instead of changing the OEM instructions they fool them by overwriting the reference data that the instructions refer to with their own numbers. This approach can change a lot of the functionality of the PCM but it can't modify features where the instructions don't reference numbers in a lookup table. If for example there's a line of code that says if BP is greater than 22 psi then defuel, and the 22 psi is part of the code and not some number in a lookup table, then I think there's a definite liability issue if someone changes this line of code???

I think one of the reasons why live tuning gives better results is that it takes the guess work out of fueling at the top end when the BP is above the 22 psi limit and there's no BP data available to the PCM.

 

this is very interesting. we cannot make precise fueling after 22 psi because of the MAP sensor.. just seems there must be a better way to do this your self.

I dont know the requirments a diesel engine needs for enough fuel other than lack of EGTS. nor what it takes to be precise about it. so maybe if a guy could tap into the map sensor with an adjustable dial to tune enough fuel to keep EGTS down when really mashing on it but turn it down when you want economy...you would have to closely watch EGTS to first get an idea where you are at. if the tables create the fueling "acceleration" maybe this doesnt come into play. hard to say whats on my mind but im very interested.
subscribing.

 

is that feasable? a dial switch to change what the map sensor sends to the PCM? i may be off track here but i guess with out looking at exactly what comes into play (tables wise) i dont know enough about the fueling process to say much.. hope some one can tho!!! would be nice if you could get a dial that would throw more or less fuel into the equation for your specific mods and needs. a turbo that flows well over stock, shouldnt that change the "after 22PSI" threshold? more air to same amount of fuel or is there another way the fuel keeps up to the amount of air entering your engine? getting my DP back today WOOOT!!

 

before tuners didnt have way to change what map sensor is getting(need for a boost fooler), one of them does, and its able to modifie computer, to acommodate for it, what in detail it does im not sure, but you wont get the overboost code and truck wont defuel.

 

If thats the case wouldn't it be better for the tuner to do eliminate the boost limit instead of doing an OBA?

 

you wont need one , wrong choice of words on my part, there is no need for OBA with tuner adjusted for it. sorry....

 

I'm sure I am way off on this, but, if the map sensor is only seeing 22# boost with the OBA and the PCM is still pushing the fuel to the cylinders. Why am I wanting 40# boost? Is the boost over 22# necessary to make more power?

 

more boost needs more fuel, and the fueling program cant be very precise with a boost fooler obove 22 psi, but still has to fuel more. my question is how to controle fuel over the 22 psi mark accurately, or in case of more air, adiquately.

 

I did a series of posts on this general topic on the Diesel Garage forum but they were all destroyed by a hacker last Dec so I can't link to them. I've still got my notes and if there's interest here I could reconstruct them on FTE. The titles of the 3 part series were...

Air Flow+Fuel Flow=Combustion+HP+ Exhaust Flow...

Diesel Engine "Black Box" Equations...

A step by step derivation of the "Black Box" HP equation...

I used data from my CAT C7 to plug into the equations to show how they work, but my 300 FWHP at 28 psi BP C7 numbers are probably comparable to those for a mildly tuned PSD.

 

ernesteugene; I'm thinking that since we ford map peoples use frequency for our map sensors there is a limit to how far the stock sensor will take the HZ changes. one of the PCM code checks is to look at ambient pre start hz, and decide if it is within a band of (i think) 96-102 hz after checking with the baro for sea level corrections. otherwise it discards the data and proceeds to calc fuel in a limp mode and may or may not set a SES light. fuel injection per RPM is old school and easy to do, but inefficient.

the 2 difficulties arise: a wider band map sensor electronics starting at the low end and modifying the upper protion, and a code mod in the pcm if there are high limits for pressure map signals. I am guessing that tuners do modify the look up table, and since they also "know" the rpm the truck is turning, add fuel in a calculated way based upon max map and rpm. "tuning" gives them vehicle specifics for fuel flow and HP so they can modify the "slope" batter.

Therefore I am not sure that you can really go above the 22-25 psi the PCM/stock MAP is set for. Better way is to flash the program into a new naked PCM. Should be able to download the program out of BIOS, out the OBD port, but handshake protocol is foriegn to me. Or however ford reflashes the new bios.

 

a system could be devised to use your max boost reading (derived from each time you start/drive the truck) to put as the max PSI threshold, and just stretch the fuel map out to those given values,and make those values be incorporated into the pcm one way or another. possibly by just having the sensor's last max boost reading as the max signal to be sent to a stck PCM.
i dont know if anyone will follow me here just my thoughts im curious how accurate even some of the better tunes are with that part of the equation not being there? they most certainly help dont get me wrong just curious

 

IMO, the only way other than live tuning to get the most out of fuel mapping for anything above the 22psi mark, (assuming the stock map sensor is for a specific range-lets say 0-30psi for ex.)would be if some made a map sensor that was designed to read a much broader range of psi and to have a pcm that was flashed to work with this new sensor in all the same manners as it would factory, OR a tune that would be compatable with this sensor that would base the fuel mapping from it instead of "guestimating" what it would be as they do now. If the tune was to be used with a pcm that was not flashed for use with this sensor, the tune would need to include programming to eliminate defueling and the SES light for over boost.
Now assuming the factory MAP sensor has the range capability of a broader range( ie. 0-100 or whatever it may be). The tunes such like I have and others that do not require a boost fooler, may actually be using the true BP over 22psi to calculate fuel mapping. If this is the way they are doing it, that would get you the same accuracy as far as live tuning is concerned, However that would only be for the boost part of the equation. You will still get better performance out of live tuning for several reasons
-EACH truck and engine is different
-Different mods
-temperature
-elevation
These type of things are part of the rest of the equation that can be fine tuned only by live tuning and not by Calculating or esimating. These factors cannot all be determined and compensated for in fuel mapping IMO b/c diesels do not have a "feed back" type fuel mapping system programming like gas motors do.

Just thought I would throw that Idea out there.

 

Thats along the lines of what i was thinking, seems a module could be made to do these things automatically, finding peak boost and setting that as the max value(voltage) would be set at roughly that psi maybe stored. so at least these values could be incorperated into the rest of the fueling tables some how. yeah live tuning is good but it would be nice if these motors had a on the fly way to adjust it or have it tune itself a little more closely with the new modual sensor or whatever. wonder if the guys like jody have looked into this wouldnt this help on fuel economy? it may not be a big part setting those tables correctly but if it helps at all some one should make it