The CP3 is a mechanical pump and has no internal operations that can or will turn it off to so to speak. But it through the rail pressure sensor via the pressure it produces through to the ECM can and will turn off the fuel flow via the FCA if a low fuel pressure is detected on the Rail.

Remember this happens almost instantly.

When the fuel pressure on the HP fuel rail drops below the specific parameters (measured by the rail pressure gauge) and then the speed of the engine, axle speed, tranny speed and the throttle position sensor all are out of spec for the pressures, the ECM detects this and then sends a signal to the FCA to shut the fuel supply off to the engine to reduce the RPM of the engine, alternatly the Injectors are also effected so as to slow the engine speed down and limit the amount of power allowed by the lack of proper fuel supply. AKA limp mode

As for your the dumb idea of disconnecting and running the engine on purpose with out the LP. Get real. HA HA your funny..I almost fell out of chair laughing.

Bottom line is if the CP3 can maintain a min pressure with in specs it will stay running. THAT is a fact. If it gets a complete blockage then it will not run that is another fact.

The CP3's output is controlled by the FCA via the ECM that is another fact. The rail pressure sensor sends the signal to the ECM to tell the ECM when to open and close the FCA that is a fact.

Further to this the there are many ECM differences between the early 03 to mid 03 models and then between the mid 03's to the early 04's. All have their own trials and errors.

The problem with this persons original question is that his lift pump is already going bad. I would change this pump ASAP. Can it damage your CP3 Technically no but there is a chance that yes it will. The engine should shut down before it has a fuel starvation situation. Do you want to temp fate?

Have you thrown any codes as of yet. Ie low rail fuel pressure.

I would recommend if you are keeping your truck stock then have a factory fuel pump put into the tank. They have so far worked well. Good luck and keep us posted as to your finale outcome.

Guys I think we can agree to let this go unless some one has actual technicle data to share.

 

Just out of curiousity, since you are obviously an expert on the subject, how low does the pressure have to go before it shuts down??? And yes, I do have data that I have collected while BETA testing to support my statements.

Not to mention, fooling the ECM with low rail pressure numbers is how pressure boxes work. They don't shut the engine down either.

Either way, as I quote you in your last rambling, you admitted I was right.

"The engine should shut down before it has fuel starvation." So should means it is possible it won't and if it doesn't it will starve, just as I said. No point in arguing.

 

I wouldn't call that a "rambling",...... sounded well worded and thought out to me?

 

I would call it rambling. From the sounds of it he must be the one that invented the cp3...

 

It'd help your case if YOU would present some technical data

Can you post some of your data?

But even you're not sure, are you? ( "?" )

... or at least the InterNet

 

I don't really want to dive into this debate. I just want to add that my truck will run fine with the FASS disconnected. Found this out by accident!! It will start fine with no delay. Much quieter too!!! Of course, I didn't go out and hammer on it either. Don't know about this.

 

I personally have never seen one run with out the LP! But what do i know i only work on them for a living

 

You've never seen the filter-mounted LP, the in-tank LP, or both run without the LP running?

There's quite a difference, as these type of fluid pumps push much better than they SUCK (Freudian slip, there... )

My truck will run w/o the LP, but I wouldn't want to drive out a whole tank that way!

 

So far you guys have at least 4 trucks in here mentioned that they ran without a lift pump supplying fuel to them. Now, over the years I have spoke to quite a few pumps shops and people that work on these for a living (pump specialists) not dealer mechanics and they all say the same thing. You do not want to operate a cp3 under a vacuum condition when there is a pump in line to restrict the flow.

 

As far as I know... my LP is fine. I have a fuel pressure gauge though, just in case. At what pressure should I drive home and do something (like replace a filter or the LP) and at what pressure should I shut down and get towed to a shop?

ps - I see 7.5psi at idle and 4 psi at WOT with some load, just driving unloaded I see 5-6 psi.

 

That's right - but it sometimes happens due to ignorance or necessity...

 

Dave that is about what I see on mine for comparison sake. However lately for the past 500 miles or so........mine has been reading about 1 to 1.5 psi higher for some UNKNOWN reason. I have not changed my fuel filter.

 

Must be the ULSD

 

Thats it you guys are going to make me go unplug my LP just to see

 

Here is a question towards the CP3 and its functions. thrown out to anyone.

How does the engine shut itself off?
How does the engine vary the amount of pressure from the CP3?
How does the internal bypass, HP and LP work inside of the CP3?
What parameters must be meet in order for the engine to run,
then what are they for WOT?
What does a pressure box effect and how does it do it?

Just a couple of questions now that I have no idea as to how the components work together. If there is anyone that actually knows these answers please post and post referances and such.

Cheers.