Cholmes

I installed an Airtex Fuel pump on my 02 today after the gauge I installed said 7 lbs fuel pressure. This is a new to me truck for about a month. Imagine my surprise when I realized someone had changed it to an in tank version. I am second owner and I know the guy I bought it from and he can't remember this being done. (he bought new) Anyway I decided to mount the new pump back in the stock location and just unplug the tank pump. Well good plan but... The new pump would not run the truck. She would run out of fuel in a few seconds. When I plugged the tank pump back in it would run but show 0 pressure. I assumed from this there must be a valve in the tank pump that will not allow fuel to pass through when not powered. So I wired up both pumps. I now have 28 lbs Fuel pressure at all times. Question, Is this too much or is there such a thing?

illEatUrDuramax

sounds like your getting a wrong reading from the fuel pressure gauge. thats way too much pressure on a vp. check the gauge

Cholmes

Well I believe it must be right I think if there is a pump in the tank pushing to it it would relieve all the work from the second pump. But will it harm the injection pump?

hawaiianbro

I've got the Airdog II and i'm bouncin between 17-19psi on idle. WOT it'll drop to about 13-14psi.

Junk Man

Fluid mechanics indicate that it is easier to push a fluid than pull it. Forum research indicates that engine vibration has negative effect on engine mounted electrical pump. Further research indicates that there are restrictions in the stock lines. Further research shows that many have had problems using 2 pumps in-line. FSM has minimum pressures listed. Over flow valve opens at 17# (confirm in FSM. I haven't looked since winter.) Prices of reman VPs start at $1,000. It appears that strategy is to mount pump closer to tank and install larger lines. Yes, topic has been beat to death and answer hasn't changed. It is your truck and your choice.

edit: yes, toomuch pressure will harm the VP.

johnh

any pressure over 15 psi goes back to the tank

Cholmes

well I hooked up both pumps, I have 28lbs at idle and can pull down to 23 if I step on it hard. So I called Cummins and talked to a tech guy and he said that is what they do all the time. He says 30lbs will not hurt the pump. He also said the worst that could happen is the truck may start a little hard from the pressure floating the valves in the VP. My truck starts fine so no problem. He told me Dodge changed the specs on the pump in the tank and changed them from PSI to flow. Probably to get away from changing them all the time.

totalloser

Read this post twice. Good info except the last part. Too much pressure will cause difficult starting.

I'll add; Relay for lift pump is in the ECM. I don't know if I could think of a worse place. Use a second relay to take the load off the weak ecm relay.

Banjo bolts can easily be drilled out for more than adequate flow, or aftermarket bolts or nipples can be purchased.

A vane type pump mounted above the tank can run dry on every startup if there is a small leak or the pressure return at the vp fails. STOOPID mounting location on the block.

Carter sells a nearly identical pump with a slick mount and nipples for about $100 (vs $240) which will live nearly forever mounted to your framerail. Your underhood relays work fine for control relays-just be careful where you put the hot to prevent a hot pin when off (look at the diagram on the relay and this will make more sense)

Hard starting problems with dual pumps (or high pressure singles) can easily be overcome by using a relay to kick them off during starter engagement. Fuel system cleaner made this problem go away on my truck. Dunno why.

Cholmes

Good info, someone has already added a second relay, probably for the in tank pump the dealer installed. I used same harness so the relay is wired in. I have no hard start issues at all. Starts immediately maybe sooner. When I step on it hard I can pull down to a bit less than 20#s FP. I plan on relocating to the rail but dred the job of pulling the tank. I was going to do some body work and pull the box so kind of hedging untill then. Truck is working great. I add conditioner every tank. (Amsoil)