Low Fuel Pressure A Myth?

[JAP]

Air pocket. That makes me laugh. Where does this magical air pocket come from? When you have liquid in a sealed system air doesn't just happen. It would have to get I the sealed system through a hole in the sytem. or picked up by either end of the sealed system, meaning your tank would have to be empty. If air was getting in somewhere else then that would mean a hole in the sealed system an thus fuel would be leaking. I would think people would notice a leak.

Anyone have a clue how a piston pump work?

So is rusted injectors caused by low fuel pressure?

Never once did I ask the question if lower fuel pressure will cause power loss. I know that answer. I asked if low fuel pressure will damage injectors. I also don't disagree that Ford says it does, but that doesn't make it fact. It just means they have another excuse to not warranty injectors when they have a problem. Ford also says that you can't remove the spacer from the back of the crank. It is in all the manuals, yet I have done it several times many years ago with no ill effects and I know many others who have also. I have also converted 2wd trannys to 4wd with only a simple part swap and never removing one single part from the inside of the tranny. Yet everyone seems to still says that is impossible. Not to mention how many 6.4 trucks I have running around the country with a duramax cp3 pump on them that everyone says doesn't work.

I'm not sure if this has been started over here, but I just want to know if anyone has any insight?

To me, it SEEMS obvious... But I'd like to know why Lubeowner thinks that low fuel pressure is OK?

Cavitation and liquid dynamics seem to say that cavitation can happen at any time during a major pressure differential...

Lubeowner goes on to say "Where does this magical air pocket come from?"

Umm... Seriously?

I'm just mainly curious if he's fking around on PSN or if he really doesn't understand?

 

[faster6.0]

curious how many 6.4s are running a cp3 too lol

 

[Charles]

The "air" entrained into fuel in a system where the pump inlet is kept fully submersed in the fluid is actually the fluid itself in gaseous state.

If/when the temperature is high enough, and the pressure low enough, the fuel actually vaporizes and turns into a gas. We see the bubbles and call it "air".

This most often happens before the pump where pressure is sub-ambient, and vaporization is most likely to occur for any given fuel temperature. This is also why a clogged pre-pump filter will cause reduced pump outflow, it's causing excessive pressure drop, resulting in substantial vaporization of the fuel coming into the pump. If it reaches a high enough level, the pump may not be able to maintain prime with such a high percentage of vapor, and we call it vapor locked.

 

[Mdub707]

I get what Jeremy was getting at, he was asking why we think 20psi would damage an injector. His original question was in regards to the 55psi everyone says we need, and why 45psi is the min cut-off, but he seems to be ignoring a few things. He's thinking statically and not dynamically, it seems pressure would need to increase as RPM's increased.

He did mention that there is a power loss associated with this lower pressure, but his question in which he asked for proof of damage from running lower than 45psi... I'm not sure who's going to ruin a set of injectors to answer that, but I'm sure not going to.

I was really scratching my head on some of that... I couldn't tell if he was joking for some of it or seriously asking!?

 

[alwil]

Some of the things that he types makes me sit back and wonder how he keeps any customers at all.

 

[JAP]

The "air" entrained into fuel in a system where the pump inlet is kept fully submersed in the fluid is actually the fluid itself in gaseous state.

If/when the temperature is high enough, and the pressure low enough, the fuel actually vaporizes and turns into a gas. We see the bubbles and call it "air".

This most often happens before the pump where pressure is sub-ambient, and vaporization is most likely to occur for any given fuel temperature. This is also why a clogged pre-pump filter will cause reduced pump outflow, it's causing excessive pressure drop, resulting in substantial vaporization of the fuel coming into the pump. If it reaches a high enough level, the pump may not be able to maintain prime with such a high percentage of vapor, and we call it vapor locked.

Thanks Chuck...

I was thinking the main point of cavitation would be the orifice where the fuel is sucked into the barrel?

That's why I always assumed our pressures were so high compared to others.

 

[golfer]

Thanks Chuck...

I was thinking the main point of cavitation would be the orifice where the fuel is sucked into the barrel?

That's why I always assumed our pressures were so high compared to others.

I'll also add...(with regard to HEUI injs)

since our (7.3L & 6.0L) injectors are fired by HPOil...the piston & plunger WILL travel downward without any 'fuel' inside the barrel of the injector...

the internal (plunger) spring will cause the plunger and piston to go 'back up' to top-dead-center...or its' at-rest position...

this will create a siphoning of the fuel allll lthe way from the tank even without positive fuel pressure....I think this is where the confusion happens...

so..yes, a 7.3L &/or a 6.0L can/will run at low rpm without adequate fuel pressure...keep in mind that at idle...a 6.0L injector may only be flowing @ 20cc per 1000 shots...

another missing link in this scenario...is this 20psi a regulated pressure? like (example A) you have 14 pumps on the truck (plenty of available volume) and only have it regulated to 20psi?

orrrr (example B)...is the FP regulated to 60psi+/- but the thing can only maintain 20psi...

big difference, LOL.

at higher rpm...

the injection events happen MUCH more quickly..which also means there is much much LESS TIME to refill the plunger with fuel...to keep things lubricated...

so I don't see how it's hard to see why 20psi at idle is 'OK'...which could easily mean the thing is dropping to zero under a load (moving a bit more than 20cc's of fuel, LOL)...and that is not 'OK'...

or...giving someone the benefit of the doubt...and we're contemplating example A...as if the truck was HOLDING 20psi at WOT...the lack of refill rate (inside the injector) is going to cause the plunger to score, or not have adequate fuel to cushion the nozzle on it's return.

anytime there is a change in orifice diameter, there will be a pressure drop across that orifice...so just because you have 20psi at the fuel bowl (or wherever) does not mean you'll have 20psi at the plunger (inside the injector)...which is the guy that needs the fuel to keep itself lubricated.

this is the most ridiculous argument I've seen in a while...it's like trying to prove a negative.

 

[Mdub707]

I'll also add...(with regard to HEUI injs)

since our (7.3L & 6.0L) injectors are fired by HPOil...the piston & plunger WILL travel downward without any 'fuel' inside the barrel of the injector...

the internal (plunger) spring will cause the plunger and piston to go 'back up' to top-dead-center...or its' at-rest position...

this will create a siphoning of the fuel allll lthe way from the tank even without positive fuel pressure....I think this is where the confusion happens...

so..yes, a 7.3L &/or a 6.0L can/will run at low rpm without adequate fuel pressure...keep in mind that at idle...a 6.0L injector may only be flowing @ 20cc per 1000 shots...

another missing link in this scenario...is this 20psi a regulated pressure? like (example A) you have 14 pumps on the truck (plenty of available volume) and only have it regulated to 20psi?

orrrr (example B)...is the FP regulated to 60psi+/- but the thing can only maintain 20psi...

big difference, LOL.

at higher rpm...

the injection events happen MUCH more quickly..which also means there is much much LESS TIME to refill the plunger with fuel...to keep things lubricated...

so I don't see how it's hard to see why 20psi at idle is 'OK'...which could easily mean the thing is dropping to zero under a load (moving a bit more than 20cc's of fuel, LOL)...and that is not 'OK'...

or...giving someone the benefit of the doubt...and we're contemplating example A...as if the truck was HOLDING 20psi at WOT...the lack of refill rate (inside the injector) is going to cause the plunger to score, or not have adequate fuel to cushion the nozzle on it's return.

anytime there is a change in orifice diameter, there will be a pressure drop across that orifice...so just because you have 20psi at the fuel bowl (or wherever) does not mean you'll have 20psi at the plunger (inside the injector)...which is the guy that needs the fuel to keep itself lubricated.

this is the most ridiculous argument I've seen in a while...it's like trying to prove a negative.

That was his whole point though, where is the proof, and at what fuel pressure is it no longer safe. The question in itself is silly, but I get his point. The forums just say 45psi and lower is doing damage. It may or may not be, but I'm not going to try and find out. He might have well just asked what the meaning of life was, except with less background info.

From what I read, I think he meant holding 20psi across the board.

I have run my truck up and down the driveway with the fuel pump unplugged. Wondering why it was such a gutless pig. Idled surprisingly smooth for have 0 fuel pressure.

 

[lubeowner]

You know the internet forums are used for lots of things. I use them for my personal entertainment sometimes.

So everyone is like "you have to install this blue spring to save your injectors." Is this true? Now if we are talking about getting the best performance out of the injectors then that is a totally different discussion.

So for my personal entertainment, show me an injector that was damaged by low fuel pressure, not fuel contamination.

And whether or not the cp3 setups works on the 6.4 or not and how many people are running it, I guess you will just have to believe what you want. I don't care to change that opinion, this subject has lost all entertainment value to me.

 

[Extended Power]

When my FASS 150/180 quit when Keith and I were 2200 miles from home doing some recon work, I bought a Holley blue pump, and ran it all the way back home on only 11-15psi.
Nothing screwed up...

 

[Wayne]

I've torn down plenty of 6.0 injectors, and while capitation is minimal when I see it, a bigger problem seized components due to lack of cooling and lubrication (properties of fuel to be overly obvious). There is also a check valve inside which can actually crack in half if subjected long enough to a lack of pressure. This doesn't happen too often, but I have seen it a handful of times.