No Lift Pump

[dorkweed]

For about 2-3 months now, my fuel pressure gauge has been real erratic. The needle not staying steady, bouncey and some times cutting out all together. I pulled the connections at the pump under the truck and cleaned the contacts and terminals. That seemed to help for a while. Then it started acting up a couple months ago. I bought a new Walbro pump off Ebay and a new wiring harness from GDP. Richard from GDP doesn't sell his Walbro system any longer, but he still had some leftover harnesses in stock. I've had this stuff for about 6 months now just in case. I keep meaning to take the harness and pump to a friend of mine and have him make it a bit more "weather tight" in the connections etc.

Well, anyhow, on my Saturday trip from Springfield, IL to Benton, KY the fuel pressure gauge is acting "hinky"!! It started that morning at about 25psi and as I drove and the temperature outside got hotter and hotter, the pressure about 200 miles into it, was reading 23psi. Not a solid 23psi though. The needle would bounce going over bumps and occasionally drop to 0 and then come back up. Then about 100 miles from Benton, KY, the needle goes to 0 and doesn't come back. I'm thinking.........Do I stop???? Do I drive on????? It's not a good feeling driving not knowing if it's the pump, gauge, fuse, relay etc.

I decided to drive on seeing that my rail pressure was still normal and the truck was driving fine. Getting off the interstate onto the KY state roads I got a scare though. If I let the truck go to idle at a stop, the RP was about 500-750psi lower than normal. Thank God that I didn't have but 2-3 stops before I got to where I was going. When I stopped there, I left the truck running and quickly jumped out and crawled under the truck to see if the LP was running............it wasn't.:cry: That leg of my trip was about 270 miles and I drove about 100 of it with no lift pump pressure. Good thing I bought the new pump and harness along.

The following morning, I tore into it. It's a real simple system. Ignition power to a relay......relay trips and then pulls 15amps of fused power down to the Walbro. I decided to check the easy stuff first. The fuse wasn't blown. Check relay..........I pulled the one that was in there and put in the one off the new harness...........still nothing. Checked the wires going into the base part of the relay........the power wire to the pump pulled out with almost no resistance!!!!!!!! I decided there to just swap in the new harness. About 25 minutes later, I had a solid 25psi of pressure and it stayed there all the way home!!!!!

The wire that pulled out from the relay base was corroded a bit and I'm guessing that the up and down of the gauge was just the harness moving a bit going over bumps etc. and effecting the electical flow. I still plan of making the new harness and pump more weather proof. When I find time!!!!! I don't think a VP44 would've made it that far without a LP!! The CP3 actually has low pressure pump on it. The early Duramax's had a similar CP3 set up and GM didn't use a LP with them. I just don't understand how the CP3 could pull fuel through a pump that wasn't running???? The real hot weather making the fuel thinner??????? Any ideas?????

[ISX]

Do you know of ANY writeups showing the CP3? A cutaway, description of everything in it, anything?

I have never looked the CP3 it up but want to know more about it now So what info you got?

--- Update to the previous post...

Alright found this for anyone else wondering. http://www.dieselplace.com/forum/showthread.php?t=187243

I'm guessing this has something to do with it. "DESCRIPTION

A radial, 3-piston pump, with a gearotor-type fuel lift pump attached to the back cover, is used as the high-pressure pump for common-rail fuel pressure generation - it is capable of pressures between 300-1600 bar (4351-23206 psi) ." I *think* that is all within the CP3.

--- Update to the previous post...

Ok read your thing again, so it has that pump in it, so I don't see why it even has another lift pump. Does it have an entirely separate one besides the one built into the CP3 from the factory? Therefore from the lot you would have 2 low pressure fuel pumps and then the 3 piston high pressure part?

[guesswho512]

A radial, 3-piston pump

isn't that what is a vp44 is? when i bought my truck the lift pump was on its way out. when i changed the fuel filter, i would bump start the truck to fill the canister...5 bumps later and the can was only half full. i got the truck at 128k and it was ~162k before i got the airdog, plus the previous owners miles before mine. these pumps will draw some fuel, just not good on them

[ISX]

isn't that what is a vp44 is? when i bought my truck the lift pump was on its way out. when i changed the fuel filter, i would bump start the truck to fill the canister...5 bumps later and the can was only half full. i got the truck at 128k and it was ~162k before i got the airdog, plus the previous owners miles before mine. these pumps will draw some fuel, just not good on them

No, I think the VP44 has one plunger and it just lines up with each injector line, rather than having 3 pistons. I am not sure though.

[AH64ID]

Yes be happy it was a CP3! Since it was the wiring that failed I would say thats why you could pull fuel thru the Walbro, because when its the pump I don't think thats an option. Did GM finally add a LP, I didn't they had one even in 2009. I am guessing that your RP dropped at idle due to the slower rpms of the CP3 not creation the suction needed. The ability of the CP3 to suck its own fuel is great when you look at getting stranded, especially if you spend a lot of time off the beaten path. One of the reason I want to go with a frame mounted LP is the quick ability to bypass the pump with a 1' piece of hose, and get home!Glad you back up and running.

[dorkweed]

Yes be happy it was a CP3! Since it was the wiring that failed I would say thats why you could pull fuel thru the Walbro, because when its the pump I don't think thats an option.

Good point, I didn't even consider that!!! Makes perfect sense though!!!! Thanks!!

--- Update to the previous post...

Did GM finally add a LP, I didn't they had one even in 2009. I am guessing that your RP dropped at idle due to the slower rpms of the CP3 not creation the suction needed.

I have no clue as to what GM is doing now. I know the Duramax bombers have added LP's to their fuel systems to ensure adequate fuel supply during heavy fueling. I was thinking the same thing about the RP at idle also.