Installed the Vulcan kit, relocated the pump to the frame. Now here is where it gets interesting. The fuel pressure will drop while idling, but go up with throttle. I know, exactly opposite of what I think it should do.

For example, the pressure at idle can be 6 to 15, greatly varies. I can hear the pump, sounds a lot like it is grinding. When the pump goes quite, the pressure rises to 14 to 15 momentarily, then the pump grinds and the pressure drops. Now...driving down the road, if the truck is under throttle it will maintain about 13 psi pressure. Even under moderate throttle it stays around 13 psi. I have no clue as to why. The pump is 11 months old, less than 8k miles on it. The place I bought it from said it only had a 6 month warranty. However the truck is under warranty but I will not take it in for the retrofit in tank it. This is the second pump in under 40k miles. Any ideas?

 

I also recently installed the vulcan big line pusher pump kit and am having the same type of fuel pressure readings. It did not do that at first. It kept the guauge pegged most of the time now it wants to run at about 13 psi and when I let off the throtte it drops down to 9 psi. I thought that the pressure had messed up the gauge. I tried bleeding the line from the port to the isolator but that did not seem to make any difference. The gauge (15 lb) does not seen to move the indicator as smoothly as it did. I hope some one has some idea on this.

 

how did you wire the relocated pump? did you use a full 12 volts with a relay. is it wired off of the factory harness?with less than 12 volts the pump may not be turning fast enough to maintain full pressure

 

It may be that you're noticing the fp drop when the fuel grids cycle on cold starts. Lights dim and fp drops with every cycle.

 

I'm guessing a 0-30 would fix it Has you replaced your FF recently?

 

I've had my last two Lift Pumps act that way as they were going bad.

Pressure drop at idle, the as soon as the rpms go above idle, 15 psi.

 

Fuel filter just changed. It doesnt happen under the cold start cycle, it happens all the time.

The length of the wire harness may be something...BUT...it is not as consistant as that. When the truck is idling and the pump is not grinding I have up to 15 psi pressure. Although it is worth a try so I will make a new harness run through a relay and see what happens. I plan on adding ring terminals anyway so I can use the generic Carter P4601 pump. Before the pump was relocated, the pressure was more steady and only dropped below 8 psi on an occasional WOT run. Now this is strictly speculation and I know DODGE says different, but I am assuming that because of the larger lines now installed, it would take more volume to fill the larger lines and therefore if the pump flowed the same, I would see less pressure due to the necessary volume. I know dodge says 0 psi at WOT with the intank setup is ok, because 0 psi doesn't mean less flow...go figure that out...lol

I did notice that the pump sits a little slanted, meaning not exactly parallel with the ground, but I can't imagine it was any different mounted to the engine. When I changed the filter it took a couple lift pump run cycles to fill it up, but it seemed fine and the truck started as it did with every other fuel filter change. So I know I am getting fuel where it needs to be, and the pressures are ok when pulling a load so I am not worried about the injection pump starving, I just would like to figure out what in the heck is going on.

Does anyone have any idea which color wire to use as the trigger wire for the relay?

 

I had the exact same problem when I relocated my lp. At first it would only act up occasionally, but after a couple of months it was staying around 5 psi unless I tapped the throttle, then right back down to 5 psi. I finally got tired of having to worry about it everytime I drove the truck.

I now have a Holley Blue and see around 15.5 idle and 12 WOT.

Basically, I think your lp is going south.

Brad

 

Agreed.

 

Well...geee...thanks for the encouragement that I gotta spend another $150...dang it.

I guess maybe the pump had just gotten weak in its stock location and then moving it didnt improve because it was already weak. I am going to try to take it off, empty it out and check the filter screen. Just maybe it will get better. Like I said before, its not dead and the pressures are fine when towing...and I have the original pump under the seat that I kept from the first swap. I may just have 2 spares now.

 

Mine was $200 at Napa, but w/ a 1 year warrenty.

 

I am not sure why this solved the problem with the strange fuel pressure reading that I was getting but I went and bought a new lift pump (only $69.76 thanks to info on this board) with plans to put it on this weekend and even though it is still in the box my fuel pressure readings have been normal ever since. Maybe it is the same syndrome as the engine running perfectly when you take your truck to a mechanic even though it was missing as you drove to the mechanic. I guess time will tell. But if the lift pump goes out I am prepared.

 

Mine lift pump made that noise also, but I added some cork gasket material behind the bracket the the frame and the noise went away. I also individually protected each metal fuel line with some rubber fuel lines.

Have you checked the electrical connector on both sides of the pigtail? It may be dirty or maybe some condensation inside it.

Hopefully your lift pump isn't dead, but if it is, better that than the vp.....


Joe

 

That's not a strange Lift Pump problem, that's the way they go out.


Merrick

 

I thought about isolating it from the frame....but that isnt why I am hearing the noise. I let the pump bracket hang free from the rail, not touching, and the pump grinding is just as noticable. I am going to take it completely off, let it drain and see if its just possibly some debris of some sort was causing it. I checked the electrical connections on both ends and they are fine. I am however going to wire a relay up as soon as I have time and at that time I am installing standard ring terminals so I can use the P4601 carter pump.

I asked before, but I will ask again...what is the color of the power wire for the factory harness. I assume one side to be power and the other to be ground. I need to trigger the relay, and while we are on relay wiring..what would be the suggested wire gauge ( I am guessing 14) to the pump and about what rating fuse ( I am thinking 10 amp). As usual, thanks for the info.