6.4 pump installed, fuel pressure still drops?

Dieseljunkie · Jan 20, 2014

Well I got the 6.4 lift pump and sump installed today and fuel pressure is much better now. Before cruising at 70 I could roll into it and drop the fp down to 48-50psi. Now it only goes down about 3 psi from where it is set at about 66-68 psi.
But WOT still drops to around 45-40psi until the torque converter locks up. Then it rises back up. Since my stock 6.0 hfcm has around 126,669 miles on it would it be a good idea just to replace the pump on it? Not the whole assembly but just the pump? And the 6.4 pump I got had around 70,xxx miles on it but it works fine. What do yall think? Filters were changed 7-9k ago.

Dieseljunkie · Jan 20, 2014

Anyone know?

webb06 · Jan 20, 2014

6.4 pumps only supply like a max of 8-10 psi to 6.4's. how does this one supply 50?

Dieseljunkie · Jan 21, 2014

I have the 6.4 feeding the stock 6.0 hfcm

webb06 · Jan 21, 2014

Dieseljunkie said:
I have the 6.4 feeding the stock 6.0 hfcm

Gotcha

weekendwarriorfsw32 · Jan 21, 2014

Can you even just get a stock pump motor?

Dieseljunkie · Jan 21, 2014

weekendwarriorfsw32 said:
Can you even just get a stock pump motor?

Apparently so lol.

http://www.ebay.com/itm/NEW-6-0L-Fo...Parts_Accessories&hash=item1e84b69f2b&vxp=mtr

Mdub707 · Jan 21, 2014

Have you ever cleaned your HFCM out? I know they can gum up at times. I've been wanting to try the stock 6.4 feeding the stock 6.0 setup too. What regulated return are you running? I'm shocked it doesn't hold with that setup? Are you on stock sticks too?

Dieseljunkie · Jan 21, 2014

Mdub707 said:
Have you ever cleaned your HFCM out? I know they can gum up at times. I've been wanting to try the stock 6.4 feeding the stock 6.0 setup too. What regulated return are you running? I'm shocked it doesn't hold with that setup? Are you on stock sticks too?

No I have not, may need to though. And Im running the sinister diesel RR. Stock sticks with spd tune.

04cr450 · Jan 21, 2014

responded to your thread on the org.. I would replace the 6.0 hfcm.. I had to replace mine at 167k miles.. I also have the 6.4 pump in front of the 6.0 hfcm with NO RR and my fuel pressure only drops a couple psi with 175/75's at wot.

Dieseljunkie · Jan 23, 2014

04cr450 said:
responded to your thread on the org.. I would replace the 6.0 hfcm.. I had to replace mine at 167k miles.. I also have the 6.4 pump in front of the 6.0 hfcm with NO RR and my fuel pressure only drops a couple psi with 175/75's at wot.

Oh ok, well I will give that a try and see what happens from there. Thank you, I appreciate it!

Mdub707 · Jan 24, 2014

A little off topic, but anyone have any pictures on how they hooked their 6.4 pump up? I might be doing this.

09stroker · Jan 24, 2014

Are you guys just leaving the filter out of the 6.4 pump?

MrOneEyedBoh · Jan 24, 2014

No the filter remains in the 6.4 along with the 6.0's normal filters.

09stroker · Jan 24, 2014

So you're buying two sets of filters now?

Strictly Diesel · Jan 24, 2014

Before you replace the pump, you need to figure out if that's where your problem lies.

Locate the FLEXIBLE RUBBER section of the RETURN HOSE going back to the tank. Using a pair of soft jaw pliers, or some vice grips with the jaws taped or a good shop rag covering them (something to prevent damaging the hose), crimp the hose partially/mostly closed. This is going to raise your base fuel pressure, just don't crimp the hose closed so much that the pressure goes above about 80-85psi (you can start lower and work up if needed). This is a SHORT TERM test, you don't want to leave it this way for long.

Then go drive the truck and see what the pressure does.

If the pressure holds more steady than before, if it stays up near the base fuel pressure setting under WOT, the problem is in the RR fuel system.

If the pressure still drops way off (20+psi like you are getting now), you need to replace the 6.0L HFCM or at least figure out why it's not moving enough fuel (dirty filter, inlet line restriction, etc).

This is not a perfectly foolproof test because the device managing the pressure (the clamp on the hose) can't "adjust" to the changing demand...but since you made the pliers the new regulator, and located it after all the rest of the regulators in the system, it helps to tell you where your problem is. It might take performing this test a few times at different levels of base pressure to see what is happening...up to possibly almost clamping the hose shut. The interpretation of the results is always the same, if you clamp the hose shut and you can hold more CONSISTENT pressure (little to no pressure drop at WOT) than when the system is being managed by your RR kit, your RR kit is the problem...not your pump.

Good luck...if it's the RR kit I hope they have figured out enough about them to be able to help you fix it. It doesn't take any knowledge to copy something...it takes lots of knowledge and experience to help a customer fix a problem like this without spending more money on "bandaid" fixes.

And people wonder why our kits are more expensive...