E7 fuel lift pump

[Brandon 1]

Hi  we seem to be having fuel supply issues with a 98 model 454 

even though we have replaced the lift pump with a new PAI unit it seems to point back to this 

can anyone tell me what sort of pressure this should be generating , is there any adjustment inside the unit or is there a better pump that can be fitted

i have thought about adding an extra electric low pressure pump closer to the tank

thanks

[AZB755V8]

I have had a rash of fuel issues with my trucks. It may not be your lift pump at all. I don't know if your truck is mechanical but a gauge in the line between the lift pump and injection pump sure helps, Pressure should be 10-20 psi. Low pressure can be a bad return restrictor valve. Bad lines, crap in the tank, clogged filters can all restrict or block flow. It can even be sucking air through a bad hand primer.

[Brandon 1]

Thanks  it's a v Mac 2 half mechanical unit 

have eliminated fuel lines and filters by running a direct line straight into the tank and directly  to the lift pump just briefly to test and it still ran rough

when the filters are connected and it's running bad you can undo the supply filter and it can be half to three quater full

could be the hand primer but it's new

How would you test this

[theakerstwo]

wjhat is your fuel pressure?

[Brandon 1]

Will check and get back to you

[Brandon 1]

Hi fuel pressure ranges between around 10-35 psi so should be ok 

am thinking this could be an issue with electrical signal to the govener 

if the truck is shutdown with the key it works fine but about half the time when you let it idle down it'll run on 

[fjh]

Note what happens when u turn the key on! Doesn't the heater fan operate? If not you have a bad accessory relay.

[Brandon 1]

Yes the fan works with the key on ok 

ran a multimeter across the fuse box  there are two small posts that say serial link a and b  with a white wire connected to each they read approx 4 volts and 1 volt 

pretty much everything else at the fuse box is reading around 13 volts

can anyone tell me what these are and is this kind of voltage indicating an issue

thanks

[fjh]

Bud ! You really haven't provided enough info for us to help here! Give us some symptom  these fuel pumps were prone to quiting when warm  plug had issues Bla bla each have there own signature ,ECMs have been known to quit,Fuel starvation has its own symptom you didn't provide a symptom just an opinion!

[Brandon 1]

Ok  that's right 

the truck is running rough and is a little down on power sometimes better sometimes worse

if you completely bleed the fuel system it will run really smoothly until it needs fuel then will be bad rest of the day

if you idle up to around 1200-1400rpm you notice a distinct miss 

and as I said will run on only when shutdown by timer 

key off shutdown perfect every time 

thanks

[fjh]

So is it throwing up a check engine light!? Well it it runs good from a pail Correct? Did you check the tank vents I did all of the above once cause I was told to  and it ended up being tank vent! The  truck runs good for a bit then starts acting up sounds tank ventish to me! when something like this happens to got to start at the beginning  and the cheapest and easiest and  work to the expensive .