Truck died and will not start. Checked fuel pressure, 10 psi.  Decided to change fuel pump to Airdog FRRP-100.  Now with Airdog FRRP-100 pressure is at 10 psi (which I believe is low for priming pressure) with Airdog pressure screw all the way increase via screw.  Cracked VP44 return line banjo bleed than tried to bleed at 1,3,5 but pressure was low very little flow. 

What would cause the pressure to be so low?  There seems to be air still in the lines and can't seem to get it out- think be cause the pressure is so low. 

I did change the VP44 out in December & fuel pump (Airtek) ~year ago

 

any suggestions?

 

 

 

Several questions come to mind. Are trying to crank the engine or just pump it up to the injectors with the lift pump? Have checked for DTC's? 10 psi is low for a running pressure but will still get fuel up into the system. 18 to 20 psi would be a lot better. The FRRP should be able to reach that unless something is wrong with it. More info on the truck would be helpful also. You can fill out your signature on your profile page with that info and it will appear on all of your posts.

No problem codes-  1999 Dodge 24v 5.6L diesel 110000 miles autotrans.  I'll fill out the signature page.  The pressure now is <5 psi will bumping the starter.  Did try cracking a few times for ~20-30 seconds.   I've most likely bumped it 20 times  trying to get the air out. 

 

To bleed all air you will likely need to crank for 3-5 minutes to get her to fire if it was run dry.

Cranking it is the only way to get the last of the air out it. i replaced my AD pump about a year ago and I primed and cranked on that thing for hour or more before started. Never had that much trouble on any other occasion. You say that you now have less than 5 psi on your lift pump. Loosen up the supply going to the VP and see if you have any flow there. The return will let a little fuel thru but you cant tell how much.

 

Okay let me try cranking 3-5 times after I get the bump starter (priming) pressure to ~10

No luck cranked 6 times with couple bump in between.  The pressure was never above 12 psi.  It almost started once.  The was fuel coming into the VP44; cracked the banjo going into the VP44 and fuel was going in.

 

if it tried to start once your getting there. like I said before I spent a long time priming and cranking on mine after swapping the pump before it started.

Okay let me keep trying.  I've at the bleeding air, trying to start for about 1hr.  Still stuck on the pressure being so low, but will keep trying.  Should I keep bump it and bleeding, than crack 3-5 times or is there a point to just try cracking only?

 

Don't crank for 3-5 times crank for 3-5 minutes.  

No luck - did again try to start when pressure was psi.  The pressure never gets above 10psi and is usually at 5-7 psi.   There is fuel getting to the VP44.  The old pump was around 10 psi also that's why I changed it.  Thought it had gone bad but this Airdog is at the same pressure.   Guess I let the pumps cool down and try again.

Okay let me try again for 3-5 minutes.  How many times?

So, I cranked on it for about 1 minute and it started but then the pressure would slowly drop even as giving gas than die. 

It keeps doing this:

Crank for ~minute, pressure slowly rises, hits ~15psi starts, pressure continues to rise to about 20 psi, runs for about 10 seconds, pressure slowly drops even as I give it gas and truck dies.  It's done this ~5 times now and will not stay running.

Ideas?

 

No ran problem codes again - no problem codes

Still doing:

Crank for ~minute, pressure slowly rises, hits ~15psi and starts, pressure continues to rise to about 20 psi, runs for about 10 seconds, pressure slowly drops even as I give it gas and truck dies.  Will not stay running.

Ideas?

Tried again - same issue- will not stay started as pressure drops

Edited June 4, 20168 yr by Scuba64
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IIRC even just 5 psi is enough to fully supply the injection system with fuel (recommended 15 psi). But point is that even if the lift pump was failing, the injection pump would start pulling from the tank (but usually is prone to skipping, missing, or bucking under this condition). I think you may have other issues. Injection pump, injectors...

It's still hard to start and then dies as the pressure drops.  No DTC codes.  Don't see any white smoke. 

No sure what causes a pressure drop other than a leak.  Would the VP44 cause this type of issue or is it more likely something else?

Edited June 4, 20168 yr by Scuba64
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Where are you measuring fuel pressure from, before fuel filter, or after or at vp, just wondering if you have flow problems .

Mine has a two taps on the top of the fuel filter canister.  I measured it from both of those tap ports.  I did crack open the banjo fitting at the inlet to the VP44 and had fuel coming out of it spraying everywhere.

I have to crank it for about 45-60 seconds and the pressure slowly builds up then the truck starts (pressure 15-20 psi) then slowly decrease ~10 psi and dies.  Runs for about 10-15 seconds.  The batteries are dead now, currently charging.  It did run rough for about a minute once and it was a rough idle with pressure fluctuating around 12-14 psi- then pressure decreased and it died.

 

I would check the overflow valve on the vp44. Maybe stuck open? I still stand firm that it should have no issue running at 10 psi. My truck was running with 5 psi before upgrading to aftermarket pump. Overflow valve on return side of vp44 control low pressure fuel flow. Thats all I can think of other than a fuel leak somewhere whether it be internal (head at connecting tubes) or external.

Is the overflow valve the one on the return line of the VP44 attached to the banjo bolt?

Yes. That is just a suggestion. But if you are having hard starts, I would not try just cranking for longer than 30 second intervals and hope for the best. You have an issue and need to test things or you will burn up your starter. Hard starts mean the system is not primed or there is a leak. If there are absolutely no visual leaks (return banjo bolt behind head, tee fitting by firewall, injection pump banjos, or by fuel tank somewhere), maybe air is entering supply. Try teeing a clear tube to banjo on supply side of injection pump and post-filter to see if air is entering system causing your issue. I have done this many times to check for air bubbles.

Edited June 5, 20168 yr by Cumminz

Sometimes there is a suction leak. Which in turn never leaks out. So with those kind of leaks you have to prime the system best you can and pressurize the fuel tank with compressed air (1-3 PSI). Now with a buddy crawling around under the truck you should be able to spot a dripping leak on a suction line maybe.

 

Okay let me try those Cummiz & Mopar1973man.  I did pull out the injector pump return & it was stuck open( blew into it and air came out the large hole with the weep hole covered, stuck a small screwdriver down it and moved it around & no air coming out when blowing in it- will replace it).  See if that helps when the batteries are charged. 

Edited June 5, 20168 yr by Scuba64
grammer

I would suggest just replacing the overflow valve if the spring is weak or failing. There is a test for the overflow valve..

 

 

Thanks for the write up!