low rail pressure

[1dyer9]

My 6.4 mini maxx, all deletes, and intake. Keeps throwing low rail pressure code. Even when im just casually driving. I researched some and was wondering if a lift pump would help this but don't understand why some of them bypass the factory lift pump.

 

[Amyers]

Mine did the exact same thing. Your HPFP is going out bud.

 

[1dyer9]

ah **** how much is one of those roughly.

 

[Sysx]

It's a cab off job.

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[jdgleason]

It's a cab off job.

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Not necessarily... pain, but you can do it cab on.

HPFP is around a grand new from ford.

 

[Sysx]

Not necessarily... pain, but you can do it cab on.

HPFP is around a grand new from ford.

That's good to know.

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[jdgleason]

Some guys that have done it a few times and are good can probably do it in 3-4 hours

 

[Tree Trimmer]

or if your cab has been up recently for some work, where your bolts aren't 5 years frozen makes it easier to.

 

[Dzchey21]

you need to trouble shoot it a little further imho to make sure you aren't just throwing parts at it.

You need to get something that can monitor rail pressure to start off and then report back

WOT should be around 24k psi
idle should be around 5k, and crusing should steadily raise rail pressure as you give it throttle, if it does not, or comes up and then drops off then you either have a harness issue or a pump issue. If you have a pump fail you need to be sure there isn't a bunch of metal in the system

pull the fuel filter and look in the bottom of the bowl as well as the filter itself for metal

 

[1dyer9]

ok can the mini maxx monitor it? We did the turbos with cab on? If it needs replaced should we go with stock or bigger? I don't have head studs on it so thinking I should stay with stock.

 

[sootie]

No one makes a reliable pump so stick with a stock one.

What is the build date on your truck? Some of the job 1 trucks had issues with the hpfp harness chaffing thru.

 

[Dzchey21]

no mini max wont do it
stock injection pump new from ford
yes once the turbos are out the pump is easy

 

[1dyer9]

believe its a job 1 im not around it to look sorry. So have to have the turbos out to remove it?

 

[madman1234509]

My minimax monitors rail pressure...

Or at least Im pretty sure its actual rail pressure, and not like desired rail pressure or something.

Also, how can we say its not the lpfp going. My buddies job1 had the same symptoms and his stock lpfp ended up going out. Downside is there is no code that i know of to tell if that pump is bad, and we dont have a low pressure system gauge on our available tuning devices. You can measure the ohms or whatever to diagnose a bad pump but Im not sure on specifics. Id look into that as wel because if you hpfp isnt supplied with enough fuel youll get low rail pressure.

 

[Dzchey21]

Good point

There is a fuel valve on the fuel cooler. Check pressure there you should have 2-5 psi all the time

 

[B585Ford]

Good point

There is a fuel valve on the fuel cooler. Check pressure there you should have 2-5 psi all the time

Do you happen to know the size fitting needed?

 

[B585Ford]

Good point

There is a fuel valve on the fuel cooler. Check pressure there you should have 2-5 psi all the time

What can you use to measure the pressure on the cooler?

 

[Tree Trimmer]

if its a schrader valve, couldnt you just use a low pressure tire guage??

 

[B585Ford]

if its a schrader valve, couldnt you just use a low pressure tire guage??

I guess if you pulled the needle from the gauge that would give you "real time" readings...I never thought of that.

 

[Morgan@Midwest Diesel & Auto]

A billet fuel pressure cap with a hose connected to gauge ran into the cab and take it out and floor it. If I goes to 0psi the lpfp is junk. If it stays at 1psi or above you probably need a hpfp. The lpfp goes you may be able to replace it and fix the situation. But the hpfp may already be damaged and you'll end up replacing them both.