Fuel pressure and the inner workings of a DB2

[dieseldummy]

I have been battling a low fuel pressure problem and have come up with a theory. First the problem: After mulitple transfer pumps fuel pressure reads a max of 7psi with engine idling. Add any rpms, or accelerate while driving and pressure goes to 0 instantly. Cruising at 55 mph provides a fairly constant 3.5psi if no hills are encountered. I got to reading the article on Oliver diesel.com about the DB-2 mechanical pumps and it seems that the pressure regulator could be stuck or the vent wire could be messed up inside the pump itself. I have had the cover off of this pump multiple times and after 140000 miles I figure it could just be getting tired. Anyone have thoughts on any of this? I would ask TDG on the "other" board, but I don't believe that I'm welcome there...
Thanks,
Justin

[gmctd]

More likely the sock filter in the fuel tank is plugged, or the line from the tank to the lift pump is blocked.

Remove the fuel line-in to the lift pump, tube it into an empty plastic milk jug, blow the tank with lp shop air - should get a healthy stream.
If not, back blow it with lp shop air, with fuel cap removed - this will, of course, dirty the fuel in the tank.

Or, pull the fuel pickup assembly out of the tank for closer inspection.

If that doesn't do it, ask tdg...........

How did you rate 'exclusion' from a forum of inner-light directed, outside-the-box, quantum-retard idiots (with notable exception of a few folks, incl some folks from here)?

(Sorry - social decorum and diplomatic protocol prevents me from being any more specific than that............) :rolleyes:

edited to not offend the scientific community

[ 02-25-2005, 08:52 AM: Message edited by: gmctd ]

[dieseldummy]

GMCTD, I have often considered the fuel pickup as a suspect, but I get healthy flow from the water drain at the filter housing... Might have to try your suggestion though using the compressed air.

All I can say about exclusion is I brought about the conclusion of the war room... Some of the pots seem to like to call the kettle black...

Thanks for the help

[gmctd]

Yeah - and they also call pots, switches.

Appears as tho I have been excluded over there, also, as my posting priveleges have been removed, occuring sometime after posting here last nite.

Would seem as tho we may have a rat, or two, over here........... :eek:

Ah, well - nobody kicks a dead Diesel tech, as they say.

And, I got friends in low places....... :cool:

[moondoggie]

Good Day!

I never was the brightest bulb on the tree :( but it's obvious there's another forum you folks are referring to; I don't want to know which one it might be. I have gone to another forum with a strikingly similar name to our beloved DP (forgive me father, for I have sinned

[gmctd]

Not to fear, Brian - underdog is here! ;)

And this is NOT any of the low places I was referring to.......... :cool:

[dieseldummy]

Back to the topic at hand, my pressure drop seems to be directly related to engine rpm's, the more rpm's the lower the pressure. Maybe Saturday will be sunny so I can try and blow through the fuel sock without messing up the garage.

One a side not however, isn't one of our more respected members over here a mod. over there... Sorry to hear about your "loss" JD, it did get pretty lively over there...

[gmctd]

Required engine fuel 'draw' exceeds pumped 'supply' - fuel line(s) or fittings must be plugged.

Also check return lines, including Inj Pump housing return, top front center.
Also check that hose fitting.

Also check filter-to-Inj Pump hose for crimp, plug, etc.
Pull fuel inlet fitting, see if it is plugged.

Engine Shut Off Solenoid may be sticking partially closed.

Check the tank-to-lift pump plumbing first, tho.

[dieseldummy]

I guess I should have clarified a little more, at a full standstill with the tranny in park if I slowly rev the engine up fuel pressure will eventually drop off to zero. I know a that an engine free reving can't require that much fuel because I only have to push the pedal in a tiny amount. In my mind that rules out crimped fittings and such. I did give the system a visual inspection and found everything to be as it should, no pinched hose, no crimped lines, and a steady flow of fuel from the water drain while the lift pump is running. Here is my theory, based off of a limited amount of comprehension of stanadyne pump, the vane pump in the IP is further pressurizing the fuel and is spinning at a rate that is directly related to rpms(IP runs off of camshaft). As vane pump spinns faster it moves more and more fuel until the lift pump can't keep up with it anymore and it eventually pulls a vaccum in the lines. I theorize this could happen if the pressure check valve inside the pump was gummed up and malfunctioning. For further knowledge: I have owned this pickup since 115000 miles, it now has 140000 on the odometer. In that time the engine has been out and overhauled twice due to inferior parts being reused... So the IP has been exposed for some period of time possibly to outside contaminents. I have religiously ran power service with every tank of fuel and have "slugged" the system a few times to make sure and keep things lubed up and clean.
Thanks for the help so far, keep it coming please
Justin

[BobND]

Drop the fuel tank and replace the "sock". Been there, done that, got the "T" shirt. Suburban runs MUCH better after the sock replacement.

[gmctd]

Ok - hook a hose from the water drain spigot into an empty plastic milk jug, so you can observe the fuel.

Start the engine, open the water drain, which is pre-filter element, observe flow as you increase engine rpm.

If flow slowly trickles down as rpm is increased, that's blockage pre filter assembly, probably pre lift pump.

If flow suddenly stops at some point, thats probably electrical - OPS, grounding, or some such.

If flow remains constant, then problem is inside filter cannister, or filtered output to Inj Pump, incl the rubber hose.

Wherever your pressure gage is, cause of pressure drop is pre gage-tap.

That lift pump is somewhere around 7psi at idle, 3-4psi at engine full power output, which means lift pump flow rate, at 15gal\hr, is greater than DB2-4911 Inj Pump demand at full power, which is ~60mm3\stroke x 4 strokes\rev x 3500rpm x 60min.
I think.......

'Nother way to think about it - 15gph at 60mph is 4mpg

[ 02-26-2005, 08:43 PM: Message edited by: gmctd ]

[dieseldummy]

Flow from drain is fairly constant. Pressure is measured at the drain as well. Just for kicks I pulled cover off injection pump and there were traces of rust on some parts, this rust wasn't there 6 months ago... It appears that I need to go through the whole system and clean. I was hoping to avoid getting a diesel fuel bath this week... Thanks for the help, and if ya got any more info let me know.
Justin