Bleeding Air Out Of Fuel Lines

[RJOL]

I've seen serveral posts that mention techniques to get the air out of the fuel lines, after a filter change, or after working with the fuel lines that go to the VP44 (I'm not talking about post VP44 lines that go to the injectors).



Several post advise to loosen one of the banjo bolts (i. e. the input line to the VP44), and turn the ignition to run (not bump the starter) to bleed out the air.



My question is this: Why would it be necessary to loosen a banjo bolt? If you just bump the starter (so the pump runs) a couple of tiimes, won't that flush out all the air, as this fuel is sent back to the tank, via the fuel return line?

 

[Alan Reagan]

You are exactly right. It's supposed to bleed itself. I did have a problem after one change where it didn't. I just took the cap off the Schrader valve on the rear of the pump and bled the air off there after I bumped the starter and got my 30 sec lift run from that. I pressed the valve till the bubbles stopped and fuel ran out and the truck fired right up.

 

[ralphr]

I must be doing something wrong?

every time I've change the fuel filter it has been a nightmare to get it started. I start iwth the filter, (filling it as full as I can and being very careful not to spill even a drop while replacing), I go through the following:



1. loosen the nuts on top of the filter, bump starter until fuel runs without bubles.



2. loosen banjo bolt at pump, do the bump starter, etc.



3. loosen one or two injector lines and bunp usually 3 or 4 times.



4. finnaly crank and crank and crank 30 to 45 secs at a time until it "catches", it will then run rough, (like only firing on 1 or 2 cylinders for a min or two it then smooths out and everything is fine until next filter change. (four filter changes so far since june 2000 when new).



If I do not follow these steps it will not fire ... anyone else having similar experiances, or should I worry about the lift pump or injector pump etc. ??

 

[Bigramguy]

ralphr



You may have a weak lift pump that doesn't want to prime after the filter change.

 

[Alan Reagan]

Ralphr, I don't think you finished. What is it you go through? If you fill the filter cannister and then bump the starter, the pump should cycle and run for about 30 sec. Then when you go to start, it should start right up.



Edit: Sorry, for some reason the steps were not showing up when I first read the thread. I agree with Steve post following. Sounds like a weak lift pump. Maybe you have volume but no real pressure.

 

[Steve St.Laurent]

Definately check your lift pump Ralphr - that is indicative of a bad lift pump!

 

[mikel]

Howdy,



I don't know if all of the trucks do this or not, and I haven't had a chance to test my '01 but on my '99 if you turned the key on and then back off within about 2 seconds the lift pump would run for about 30-40 seconds. No need to bump the starter at all.



Hope this helps,

Mike

 

[RJOL]

Bump the Starter

Mikel,



Don't know about the 99, but in the 2001 if you just turn the key to the on position, you get about a 3-5 second running of the lift pump. You only the the 20-30 running if you bump the starter.

 

[Royal]

RJOL:In response to your original question. Your lift pump cannot force the air thru your VP44 pump,as the return overflow valve is set to open and return fuel to the tank at 14psi plus. Your lift pump puts out 12psi at best. After you fill and bleed the filter and it won't start,it may be necessary to bleed the supply line to the VP44 at the banjo connection.

 

[RJOL]

Royal

Well I guess I just must be lucky, then, cause I've changed fuel filters, changed inlet banjo bolts, put two differendt fuel lines on the intake banjo bolts, for a FP sensor, and never had even a hickup when restarting the engine after just bumping the starter a couple of times. I guess I'd better change the way I'm doing things so I can have prolems like everyone else. LOL ... .

 

[Ron Bissett]

Re: I must be doing something wrong?

Originally posted by ralphr

every time I've change the fuel filter it has been a nightmare to get it started. I start iwth the filter, (filling it as full as I can and being very careful not to spill even a drop while replacing), I go through the following:



1. loosen the nuts on top of the filter, bump starter until fuel runs without bubles.



2. loosen banjo bolt at pump, do the bump starter, etc.



3. loosen one or two injector lines and bunp usually 3 or 4 times.



4. finnaly crank and crank and crank 30 to 45 secs at a time until it "catches", it will then run rough, (like only firing on 1 or 2 cylinders for a min or two it then smooths out and everything is fine until next filter change. (four filter changes so far since june 2000 when new).



If I do not follow these steps it will not fire ... anyone else having similar experiances, or should I worry about the lift pump or injector pump etc. ?? [/QUOTE Ralph I have a 99 3500 and I make sure that I only let out a small amount of fuel out to look for water ,then remove the filter can and dump out the remander , I think this keeps the lines full and air out , I replace the filter dry and crack the plug on top pre plug (right ) other after has line for guage , then turn key to run pump runs for a few seconds fills filter ,tighten plug . bump statrter two times pump runs for 25 sec each time . wait for a few seconds , try to start if no start wait for a 15 second rest try one more time , most time will start , some times it will take along time to start but it only a last resort for me to bleed lines , havent had to do yet . Hope this helps . Ron in Louisville KY

 

[D6Diesel]

For my first project, I'm planning on installing a couple of fuel pressure gauges. On the gauge line coming off the banjo at the VP44, I'm considering a "T" with a control valve so that I can bleed off air. One could route such a bleed line down to the plastic tube (or a longer one as per Big Saint) that comes off the bottom of the fuel filter. If the lift pump becomes marginal, than such a bleed option could be helpful? I'm not sure how necessary this would be but would be easy to build into the line.

 

[Vaughn MacKenzie]

I'm in RJOL's club, mine lights right off after a filter change. In fact on the last one I purposely left the canister only half full of fuel when I put the lid on. Bumped the starter for one cycle and waited 10 seconds, then it took right off. Only a couple cylinders stumbled but that was it.



Vaughn