Fuel pressure confusion

[aarolar]

I posted this on FSC but incase someone doesn't regularly visit I'm going to post it here as well.

99 K2500 Vortec 7400

I started with low fuel pressure and so far have done the fuel pump, fuel filter and fuel pressure regulator. The injectors were already done when I purchased the truck. The pump is a delphi and reguator a BWD, when I did the regulator I verified that the injectors were not leaking.

So with engine off key on it jumps to 62psi but as soon as the pump quits it drops immediately to nothing, crimping the return line makes no difference.

Engine on pressure hold steady as a rock at 49 psi and jumps to around 56-57 psi for a second then levels back out at 49, once againg crimping the return make no change.

I have been over it multiple times looking for leaks and don't see anything at all, I am completely at a loss as to what needs to be done next anyone ever seen anything like this or have any ideas of what to try now? I have a group of guys expecting this truck to take them from GA to AR on a duck hunt and I hate to let someone down.

 

[SAATR]

Have you pulled the injectors out, while still attached to the fuel rail, and verified that they aren't dripping from the nozzle?

 

[aarolar]

Is that something I couldn't have seen with the upper intake off and system pressurized?

 

[SAATR]

You could have seen it while looking down the intake ports, but if you weren't looking for it you may have missed it.

 

[aarolar]

You could have seen it while looking down the intake ports, but if you weren't looking for it you may have missed it.

I looked and felt around real good while I had it apart. The ports looked real consistant as well not like you would expect to see with a leaking injector.

 

[SAATR]

If the injectors aren't leaking, the lines and connections are good, and the regulator has been taken out of the equation, then you are only left with the pump leaking down. To eliminate all possibilities, I would pull the fuel filter off and connect directly to the fuel line coming from the pump. This is what you would call dead-head test, which will test the pumps maximum output pressure and will give you a definitive answer on whether or not the pump is holding pressure. You'll need a 3/8" female inverted flare fitting to adapt to the fuel line, and then whichever barbed or screw on fitting your fuel pressure tester requires. The Delphi FE0114 dead-heads between 75 and 100 psi, and I think that's what your pump assembly should use, so look for output in that range.

 

[aarolar]

If the injectors aren't leaking, the lines and connections are good, and the regulator has been taken out of the equation, then you are only left with the pump leaking down. To eliminate all possibilities, I would pull the fuel filter off and connect directly to the fuel line coming from the pump. This is what you would call dead-head test, which will test the pumps maximum output pressure and will give you a definitive answer on whether or not the pump is holding pressure. You'll need a 3/8" female inverted flare fitting to adapt to the fuel line, and then whichever barbed or screw on fitting your fuel pressure tester requires. The Delphi FE0114 dead-heads between 75 and 100 psi, and I think that's what your pump assembly should use, so look for output in that range.

I agree with this but to add more confusion this is the second pump. I started with an airtex and put the Delphi in because of this issue. I will probably test the pump as you say and if it checkes out throw a set of injectors at it.

Does anyone know which injectors are metal bodied with a blue ring on them?

 

[someotherguy]

Right off the bat I would be suspicious of the BWD regulator. Over many years I've become leery of any of their products. Even their sensors/senders kinda suck and I won't buy any of their ignition parts, either.

When I last did injectors/regulator/etc on a Vortec 7.4 I went with a regulator from Standard Motor Products, and the "yellow" Ford Mustang Bosch 4-hole style injectors from Five-O Motorsports. Have the part # around here somewhere...

Do you know what injectors were used on the replacement? Specific brand and part # ?

The big blocks operate at a little lower pressure than the small blocks; the "real" injector (8 individual units) setup doesn't require the higher pressure that the small block's crummy poppet valve setup needs. Case in point; a small block Vortec starts crapping out once pressure dips below the mid 50's and usually won't even start; a big block Vortec will start and run at even 30psi (and maybe lower) - it will fall on its face when you give it the pedal, but I yard-drove one like that many times until it was time to get started on the project and I replaced the pump.

With all that said, question is, how does your truck run? If it starts easily both cold and on warm re-starts after a little sitting (good test of injector leakdown), and has good power, then I say don't sweat it. If the somewhat low pressure bugs you I would start with dumping that BWD regulator.

Richard

 

[aarolar]

http://www.fiveomotorsport.com/product-search/?v=9470

These are the injectors I have in it now.

Richard, if the regulator were to blame wouldn't crimping the return line prove this out?

The only performance complaint I have is it takes an extended cranking time after it sits for over an hour or so I assume because it leaks down. I have pulled loads with no complaint and from a dead stop it'll burn both tires down all thru first gear.

 

[someotherguy]

Yeah, sorry, I must have overlooked where you said you did the return line crimp test - I see now that you did it.

Dunno man with two separate pumps giving you the same results I would almost start to question your gauge accuracy!

Also, being able to fry tires all the way through 1st gear I would seriously doubt you have a marginal pressure situation.

For it to momentarily jump up to 56-57 I wonder if that's your real pressure and the 49 is the gauge flaking out. Have you tried a different gauge? 58-62 is spec and I wouldn't sweat a couple psi shy of that, on the big block.

Richard