I have been reading numerous threads on installing a second or replacement pump on some of the third gen's. And there seems to be conflicting statements as to wether or not you can pump fuel through the stock fuel pump (Mounted on fuel filter).

So the question is:
Can you pump through the stock lift pump if it should fail with another inline pump?

 

yeah i thought about that to

 

Put a pressure\vacuum guage between the filter and the CP3 - idle the engine, noting the pressure - disconnect the lift pump, either by pulling the connector or the fuse - note the vacuum: CP3 can pull up to 20" vacuum thru the system and keep the engine running, so 2-5" would be normal for a 7-10 micron filter, 10" would be some problem, incl dirty filter, failed lift pump - 20" would be serious problem - engine will run over 10", but with increasing difficulty as rpm increases - it will still get you home, but at a slower speed

That is the only sure method of verifying a stopped flow-thru lift pump - you cannot damage the CP3 - it will self lubricate even if insufficient flow for injection, but the engine will stop

 

It all depends on how the pump fails. If the pump locks up...no... no flow. If the electrical part of the pump goes bad - i.e.- brushes, or loses power or ground to the pump, then yes...you would be able to flow fuel thru it.

 

You cannot pump through a bad stock lift pump (unlesss you have way more pressure than you should). The CP3 will not "suck" through it and a little in line pump will not push through it at reasonable presure.

I have a stock one sitting here that was still working and I could not blow throw it.

The type of failure does not matter and I think most fail because of the brushes. I tore mine apart and the brushes were worn badly after 10,000 miles.

When the cannister mount pump fails the truck stops and you must plumb around it and get it out of there.

It would be nice if there was an easy shortcut, but when they fail it's time for a Walbro or some other setup and you are just fooling yourself if you put a pusher pump in ahead of the stock one thinking you'll be fine.


John

 

Raspy - a good check would be to put a hose on the output, connect a hand vacuum pump\guage, such as a coolant system tester, and verify the break-over point where the valve begins porting - after sitting awhile the valve can stick, so the initial break will be higher than any successive breaks - Carter specs that to be flow-thru when fail, so it would be good to verify that, one way or another - 2"HG = 1psi - the output is spec'ed at ~15psi

 

I would agree ^ . The pump should at some point be able to spin , as long as the rotary vanes inside are not stuck and the motor is capable of moving.

 

You guys can theorize, speculate, and give advice all you want. Do all the tests you want. I hope you do and tell us the results.

But the bottom line is, if the lift pump quits, for whatever reason, the truck stops. Period. And it's a known problem that will very likely happen sooner or later.

If someone wants to add another pump they should get rid of the stock one and just simplify the whole weak stock setup. It makes no sense to guess what might be and advize based on that. The pump is not magically going to start spinning if it only failed because the brushes went out. Tell that to someone stranded in the middle of the night 500 miles from home.

It's a relatively simple modification to install a Walbro setup and be done with it. Or we could guess how the pump is designed and how it can be used even though it failed. No, just fix it right, before it fails and be done with it. Then run all your tests and analysis on the bench, at your leisure. When your done with your testing you can advize based on facts.

John

 

Never mind, Raspy - constructive contribution is not a requirement on any forum........

 

Raspy.......there is quite a difference between a "bad" lift pump, and one that has lost power or ground. If that were the case, the pump still has the ablility to spin, just wont because there is no electricity going to it. If the brushes fail, or for any reason the pump locks up, then agreed, you cannot pump fuel through it.

 

I have pumped through my stock lift pump, it worked fine for me. I was in a pinch and had to get the truck running again, while waiting for a filter housing adapter and expensive aftermarket pump, so I tried it and had the exact pressure that the cheap aftermarket pump I put on there was supposed to (ie no restriction). I have a fuel pressure gauge to verify this. I am assuming it was an electrical failure since I was able to do this.

 

Carter sez yes - some say yes - some flatly deny it, no factual reason or failure known or given - would be nice to get hands-on with about ten or so failures for some R&D - boneyards here want 50-100bucks for one, pump-ability unknown - would be good to determine exact failure and quantity of each mode -

- brushes\armature
- bearings
- regulator\bypass
- nylon coupling\vane\rotor
- inlet screen
- bad fuel\all above

Try to get some idea of why some trucks get up to 100kmi out of one pump, others get multiple failures out of 100kmi - other than those who powered-up the truck without addressing the entire system.

Just think of the hundreds of thousands of trucks made since '98 with that Carter pump, many of which are still out there, running with only normal electric-motor-powered pump failure at ~60-75kmi, some longer than that - you can still pop the hood on an oem '98^ and find a Carter pump on the filter housing

I, for one, have a desire to know why, with some good hard factual evidence as proof.

 

Yeah, well, mine went out today, and I have a Walbro 392 behind it... no love. The walbro would push just enough in the canister to run it for a minute, long enough for me to get it on the trailer, but it would shut off after that.

Hope I didn't ruin my CP3...

 

That, in and of itself, wont hurt the CP3 - the CP3 lubes itself even if there's not enuff fuel for injection, at which point the engine dies - it's nothing like the VP44 - the initial-issue '03-'04 CP3's had some problems with internal seal leakage, but those failures had nothing to do with fuel supply - symptoms included hard-starting, low rail pressure - subsequent issue CP3's were improved in all areas