could someone please explain the technical aspects of what you refer to as defueling are? how it relates to boost and any other things which contribute to it? and what is needed to help the situation. what do upgrades like injectors, programmers ect. have on it. i guess i just am looking for information, i have been a mechanic for years, started out on diesels, but that was 25 years ago, things were a bit different then. thanks in advance steve

 

Welcome to the wonderful world of computer controlled engines. The computer, thanks to a lot of smog controls and other non-sense, will actually begine to cut the fuel back at certain points as programmed into the computer. Basically like letting off the hammer somewhat. Not to technical there but that is basically what happens.

 

That is correct. Diesels are different from gassers in controlling the rpm's in that diesels take in all the air it can and the rpm's or torque is controlled by limiting the fuel or "defueling". It will actually decrease the fuel to the point of no fuel when the rpm's get too much over the max programed rpm range, just like taking your foot off the go fast pedal. Then when the rpm's get back into the range it will increase the fuel to maintain the rpm you command from the go faster pedal. Computers have a program to control all those parameters and the old school versions have a governor that will pull the fuel rail back to cut off the fuel above the rpm it is set at.I think the p7100's have an all speed governor. That means that the governor controls the fuel rate at all speeds and when you push the go faster pedal all you control is the rpm range you want the eng to run at, the governor will add as much fuel as it can to get you to that speed then cut the fuel back to maintain speed and you don't have to adjust the go fast pedal to level off on speed. The fords and chevys use a DB2 roosamaster pump that has idle governing and limiting speed governing. Then you have full control of fueling above idle to limiting speed before it "defuels". Hope this helps

 

so what will the effects be if i limit my wastegate to build more boost? will it just throw a code? are there any advantages/disadvantages?

 

without a 'boost fooler' it will throw a code and defuel at ~20psi boost. you have to do two things for more boost:
1) mechanically allow the wastegate to stay closed longer with boost elbow (man trans) or spring/turnbuckle auto trans)
2) fool the ECM into NOT defueling past the factory limit. there are standalone boost foolers and most fueling boxes have that function built in.
max efficiency for the stock turbos is ~32psi for the hy35 in an automatic truck and ~35psi for the hx35 in manual truck

 

why do you want more boost?

more boost does nothing if you do not have any more fuel to burn with it.


Pat

 

i dont know, hence the ???s i like making informed decisions, and am not afraid to ask for help. wanted to know about defueling and its reactions so i can figure out what to do with my truck, so i have learned i need to get injectors before adding boost, and a way to stop the code from being thrown. the other question would be, does Marco's ECM provide for more boost/ or do i still need a boost fooler?

 

your best bet is to decide where you want to end up. you probably won't stick to it 100%, but that will help you decide WHAT parts you need, and in what order.
are you shooting for 400hp? 500hp? single turbo? twins? nitrous? etc, etc
you can add fuel and boost fooling with a box. comp (or tst, blue chip, DDUFM) is a great first step because it's adjustable, adds ~100hp on max setting and will grow with your system. the MAD ECM is great for low end response and fueling, doesn't add much hp at the top end. it does the boost fooling, it adds fuel and makes driveability a BLAST!

 

and BTW, our stock trucks HAVE enough fuel to build more boost. by adding JUST a boost fooler (comp turned off) and elbow, i could get 30psi from my truck and 30hp. the EGTs are lower under towing load, the HP is higher, the driveability is better, what's the downside? once you pass the threshhold for a given turbo you'll start to create more heat and less power, but that's not at the stock injector's fueling.

 

Are you sure about that??
I didn't pay any attention to that aspect when looking at the MAD ECM, cause I had a boost fooler, but I don't remember hearing this.

RJ