I was looking at turbos at Gillette diesels site and noticed a relief spring for $20.00 there. They say it is of a better material than stock. But get this, it set the pressure at 95psi. I have always been told that 75psi was the highest you go. I have tested mine up to 130psi where the pump stalls. It ran its best, no joke at 100psi. Anybody else try this?? I have never seen any springs that claim this pressure is a good thing. I know mine ran great up there. I need some other imput here.

 

The stock pump won't do more than 70psi from what i understand.100psi?
High performance systems run around 65psi. Ford specs around 50psi.
Nut

 

I've never run it above 65 psi. I'd be worried about seals on the fuel filter bowl blowing out at pressures near 100 psi.

 

I guess my question would be, what pressure is optimum for the injectors? Are they designed to operate within a pressure range or is more better/worse. I know gassers use O-2 sensors to adjust the mixture for optimum burn. I haven't got a clue how this is handled in a PSD or if it will simply dump additional fuel into the cylinders. I would like to know.

 

With no O2 sensor, they basically just dump more fuel. The injector itself actually pressurizes the fuel to something like 20,000 psi, inside of the acutal injector. Raising the fuel pressure via the regulator will make it easier for the injector to fill itself with fuel.

 

So but there must be some sort of algorhythm that the truck uses between the HPOP and the injector duty cycle in conjunction with fuel pressure in order to meter the fuel flow. If not, and this is a mechanical thing, I sense a state of inefficiency. How does the PCM control this with no O-2 sensor or MAF?

 

Remember a diesel regulates it's RPMs with fuel, so instead of an O2 sensor to determine the mixture it uses the tach and throttle position to determine if it needs more or less fuel at any given time.

 

I gotta get off of this gasser thing I guess. I do recall reading that a diesel regulates rpms with fuel. I can get my arms around that concept. I suppose I need to get comfortable with the idea that it just works, like FM radio, F'ing Magic. So using this analogy, I assume I could play with fuel pressure and drive the truck to the point where I get excessive black smoke at which point I have reached the point of maximum efficiency, then back off?

 

Well, you've bypassed my ability to answer all of those questions. I wish I knew the answer. To my knowledge, the truck does not have a pressure sensor for the low pressure fuel. I do know that there is an Injection Pressure Regulator sensor in the high pressure oil lines, but don't know for sure how that plays into the equation of metering fuel. The injectors will meter different amounts of fuel based on their duty cycle. Changing the duty cycle of the injector is how the chips and tuners are getting more power out of the engine. It is computer controlled and not mechanical, but I don't know all of the exact details.

The diesel doesn't need an O2 or MAF sensor because the amount of fuel going in is not determined by the amount of airflow. Rather, it's the other way around. The airflow is determined by the amount of fuel injected into the cylinder. That's why diesels have no throttle body. You can keep dumping in more fuel to make more power, until you hit your EGT limit. Then you need to increase the airflow, with intake, exhaust, and bigger turbos to bring the EGTs back into check.

My guess is that the amount of metered fuel is pre-determined from the factory. Injector size and high pressure oil both play a role in that too.

 

I'm not a Ford tech but just a guy who can't leave anything alone. The way I understand it is the HPOP system push's the injector open. The ICP sende tells the PCM what the rail pressure is where as the PCM controls the IPR to keep the rail pressure no higher than 3000psi. Now the fuel pressure from the tank to the fuel rail is controlled by the fuel return to tank line via a spring and valve. By raising this on my truck it gave me a quieter running and quicker responding engine. Depending on throttle position and boost the PCM will adj. the pulse length for correct fuel delivery. I think!!