Well I am still learnin about the CTD and my truck. But can someone please explain fuel pressure? I don't get it, my brother tells me that it shouldn't fluctuate and that it is a constant. And there is no need for a guage unless you can set and change it. He says that it should not go down with the use of throttle or be any different when at idle. Now he does have the gasser mentality, and does not know about the CTD. I know diesels are different from gassers in tons of ways. So why would the diesel be different with the fuel pressure than a gasser? I'm lost. Please help me out guys. Thanks

Nate

 

tell him that it's totally different than a gasser....read in the repair manual...it give the specs at idle and WOT...there different....

 

the gassers dont have the high preasure injector pump either.............

 

Your brother is actually partially right- in an ideal world the fuel pressure would remain a constnt 15psi all the time with the engine running regardless of load.
But since the real world fuel supply system on these trucks is known to be insufficient and prone to fail it's good to monitor the pressure- because if it fails and you go on driving you are shopping for a new injection pump.

HTH

AlpineRAM

 

BDR,

Our injector pump (VP44) needs alot of fuel to fire the engine as well as for its own lubrication and cooling.

As Alpine points out, these fuel systems are alittle weak (lift pump) and fail regularly. You need the gauge to keep an eye on it.

 

Or you will be buying a LP AND Injector Pump

 

If nothing else do it just to save money in the long run and to psss your brother off for free. But seriously you NEED to know that you have fuel pressure.

 

Here's the "why":

The injection pump serves as a restriction to fuel flow, but the AMOUNT of restriction changes depending on how much pedal you are giving it.

Don't be confused about pressure and flow. Think of a garden hose with your thumb over the end. NO thumb= max flow, no "pressure". Put your thumb over it, and you'll have less flow and MORE pressure. A pressure reading is resistance to flow.

The reason people get confused is that they don't separate static pressure and dynamic pressure. Static pressure is like an air tank with a gauge on it and there's no flow. Dynamic is when there's flow happening, like you're using an air tool connected to that air tank.

Imagine that you have a hose with a "Y" fitting on the end. Turn on the hose with both ends of the "Y" open. You'll see equal flow. But as you close off one side of the "Y", you'll notice that the flow is now coming out the other side.

Your fuel pressure guage is plumbed like that "Y"-- in parallel. So when there's restriction on one side of the Y (idle), the guage tap will see more pressure as the fuel is allowed to "pile up" in the plumbing. When you bury the skinny pedal, there's a lot less restriction posed by the injection system and the pressure won't "pile up" so your FP gauge reading will be lower.

The amount of FP variance is related to the VOLUME of fuel that the delivery pump is capable of pumping. The more "reserve capacity", the less variance you will see.

Justin

 

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Actually it's not to much different from the gassers...... Take a walk through the pits at a race track a tell me how many cars dont have a FP gauge. FP is a priority on any engine. For a gasser if your FP cant keep up, you start to lean out.... on your diesel truck since there is a return line from your IP back to the tank, when the lift pump(fuel pump) loses its ability to keep up the pressure needed to supply the engine and have extra to return for IP lubrication.
When you lose the return flow you are removing large cash from your wallet since the IP no longer is being lubed or cooled

 

Everyone is right. Your fuel pressure will fluctuate with fuel demand but the only other thing I can think is MAYBE your brother was possibly thinking of is the fuel pressure coming from the injection pump itself. Now thats totally different. There we're talking fuel pressure that is measured in the THOUSANDS OF POUNDS PSI!!! I dont know how much it fluctuates during driving if it does at all. The fuel pressure we are watching is really just how much fuel pressure the injection pump is getting from the transfer pump (aka. Lift Pump).

 

Thanks guys, I will have him read these posts after his finals. I keep tellin him that it's a diesel, totally different. But I never had an reason to back it up. His mentality is if it's a gasser or a diesel, it's still and engine. But thanks again for the help, this makes more sense now.

 

not to hi-jack a post here but...........I have 170,000 on mine and no f/p gauge, which is less expensive at the moment, new pump or gauge? how much fuel press should I see on mine?

thanks in adv!

 

You've got a 12 valve, it's a totally different system. The P7100 pump on your truck is cooled and lubed with engine oil, and the lift pump is mechanical. It's dang near bulletproof, no need for a gauge. I think FP is in the 25 psi range.

 

The 12v are a lot more mech than elec like the new CTDs, wish they used the 12v pump in the 24v engine.