Complete loss of fuel pressure

[Yachtcare]

The facts.......

DS4 replaced with DB2829 4646 J code from '88 vintage 6.2. Only mods to IP are inlet replaced with 3/8" fitting to go with the FFM FTB mod. And the delivery screw turned up 1/3 of a turn.

Cummins hfp953 lift pump. Verified will push 17-18 psi with glow shift electric, and a mechanical pressure gauge located between FFM and IP inlet. Using the FASS regulator I started at 7.5 psi, and have gone all the way to 17psi max flow that's coming thru the regulator. Engine always starts with a bit of a stumble and whitish greyish smoke when cold(heavy, but clears quickly, about 10-15 seconds)and idles nicely. Once warm can start easily with a quick turn of the starter. Whatever the pressure is set, truck will idle there. Push the throttle to 1000 rpm and pressure goes to zero. Will recover about 50% if pressure was at upper end. No recovery if pressure was at 7.5 psi. Cannot adjust regulator to get any gain with engine running. Shut down, and pressure will recover all the way to where it was set when restarted. Then repeats the same process. The pump is still required to be advanced all the way to the driver side, less pressure did not make a difference in that department.

I replaced both filters, at the FFM and the Racor 10 micron before the lift today. No difference. There is return fuel from the regulator that can be heard at the fill pipe. There is a check valve in the return line that is tee'd into the tank fill vent.

Any ideas on what gives?

 

[Twisted Steel Performance]

Are you sure the IP is good???

Is the LP a constant pumping unit or does it quit pumping when it reaches a given psi??

Is there fuel coming out the IP return line at the front of the motor with the motor running??

Sounds like the LP isn't staying powered...

 

[Yachtcare]

Lift pumps constantly. It's loud enough to hear it over the engine at idle. Never had a problem with this lift pump when it was coupled to the DS4. The lift is bypassed from the vehicle's system completely. Wired to a switch at the dash. I turn it on before turning the key for the glow cycle.

The IP always ran good on the 6.2 I pulled it from. But it had sat unused for the last four years, and hadn't been fiddled with in terms of turning up the fuel, and was running the 1/4" inlet. I turned fuel up thru the plate on the side, didn't mess with the governor springs and such in the top. Beginning to suspect it might be fubar.

Will verify fuel at IP return tomorrow afternoon.

Also going to try restricting the return line from bottom of regulator a bit. Zip tie pulled tight on the rubber line ought to do it. Want to see if the system is bypassing all the pressure to the return at throttle.

 

[Paveltolz]

Trying to get my head around this and may be way off so forgive me for chiming in if I'm so very wrong in my thought processes here...my intentions are at least good.:twak:
It's a reading comprehension thing with me...need pictures and line drawings. At least I'm on topic.


Set up is, from back to front:
Fuel Tank w/ sender (tank sock?), Racor Pre-LP Filter (new), Cummins hfp953 lift pump, FASS pressure regulator, FFM new filter, fuel pressure sender, DB2 IP w/ FTB.
LP is running via command power rather than PCM.

Situation:
Truck ran fine with the HFP953 LP and DS4.

Idles fine after harder than desired cold starts with white/grey smoke (which clears up shortly).

Fuel Pressure drops to zero at 1000 rpm but will recover 50% if the FASS is set to Max (Does the truck still run after reaching 1000rpm the throttle is lifted regardless of FASS setting?).

Shut down and return to key on and the pressure returns to 100% regardless of where the FASS is set (7.5 to 17 psi).

Hopefully I've got this all correct.

Questions in the wrong order I'm sure but...

Is it possible for an IP to route that much fuel back to the tank through a 5/16th hose when there's upwards of 17 PSI at the inlet via a 3/8" hose? Seems the line reduction and IP internals alone would keep some pressure registered at pre-IP gauge sender. If not, then I would eliminate any pre IP issues before condemning the DB-2.

Was the FASS part of the DS4 set up?

What happens with the FASS eliminated from the set up? I know from some Stanadyne write ups that DS4 IP shouldn't be getting much more than 9psi (and I don't know what max inlet PSI is for the DB2) but it would be telling in the short term to see what the fuel pressure does without it.

Shots in the dark:

How did the old Racor filter look (Tank Sock mucked up)? Yeah, long shot as the symptoms are too consistent with the fuel pressure drop off at 1000 but I had to ask.

Fuel lines pre-LP twisted or collapsing at just the right/wrong time (Perfect Storm)?

Ok, I've shown my ignorance but I hope it may somehow help you or others.

 

[Twisted Steel Performance]

What model "FASS reg" do you have.. my return from the regulator goes directly to the stock return line on/at the frame just 'T'ed" in... there is no way it pressurizes the return system unless it's plugged, the return side is open all the way..

All the pumped fuel doesn't go towards the IP, it is bleed off at the reg with unwanted psi....

And 6-7 psi at idle is all you want for a DB2...

 

[Yachtcare]

Set up is, from back to front:
Fuel Tank w/ sender (tank sock?), Racor Pre-LP Filter (new), Cummins hfp953 lift pump, FASS pressure regulator, FFM new filter, fuel pressure sender, DB2 IP w/ FTB.
LP is running via command power rather than PCM.Correct, but there is no tank sock

Situation:
Truck ran fine with the HFP953 LP and DS4.yes

Idles fine after harder than desired cold starts with white/grey smoke (which clears up shortly).yes

Fuel Pressure drops to zero at 1000 rpm but will recover 50% if the FASS is set to Max (Does the truck still run after reaching 1000rpm the throttle is lifted regardless of FASS setting?).Truck runs if throttle lifted, if more throttle is given truck will stall. It will start again almost immediately as pressure returns. Tells me the pump is drawing a vacuum?

Shut down and return to key on and the pressure returns to 100% regardless of where the FASS is set (7.5 to 17 psi).correct

Hopefully I've got this all correct.

Questions in the wrong order I'm sure but...

Is it possible for an IP to route that much fuel back to the tank through a 5/16th hose when there's upwards of 17 PSI at the inlet via a 3/8" hose? Seems the line reduction and IP internals alone would keep some pressure registered at pre-IP gauge sender. If not, then I would eliminate any pre IP issues before condemning the DB-2.

Was the FASS part of the DS4 set up?NO. When I installed the DB2, it had to be advanced all the way to the driver side of the engine. The consensus was that too much pressure from the Cummins lift was causing the problem. Hence the install of a regulator. The FASS instructions expressly mentioned that plumbing the return fuel from the regulator to the vehicle's existing return system was not to be done. So I ran the new return line ands tee'd to the vent pipe at the tank filler neck.

What happens with the FASS eliminated from the set up? I know from some Stanadyne write ups that DS4 IP shouldn't be getting much more than 9psi (and I don't know what max inlet PSI is for the DB2) but it would be telling in the short term to see what the fuel pressure does without it.Havent tried eliminating the regulator from the setup yet, but have opened it all the way up. Will try restricting the regulator return line, and then perhaps just clamping it closed with some vice grips on the rubber section of line right ahead of the check valve.

Shots in the dark:

How did the old Racor filter look (Tank Sock mucked up)? Yeah, long shot as the symptoms are too consistent with the fuel pressure drop off at 1000 but I had to ask.Only a few months of use on both of the old filters, but wanted to eliminate them as a possible problem so put new ones in

Fuel lines pre-LP twisted or collapsing at just the right/wrong time (Perfect Storm)?With install of the DB2, I reworked the entire fuel system. The lines that aren't new are the Viton section I put in that comes up along the firewall several years ago. Other than that everything new, and most of it was replaced with 3/8" steel line. The lines at the sending unit on the tank are the only rubber lines I have never replaced since buying the truck 1/08. So I suppose it's possible, but don't deem it likely.

Ok, I've shown my ignorance but I hope it may somehow help you or others.

I appreciate any and all help and thoughts

 

[Yachtcare]

What model "FASS reg" do you have.. my return from the regulator goes directly to the stock return line on/at the frame just 'T'ed" in... there is no way it pressurizes the return system unless it's plugged, the return side is open all the way.

AFAIK, the only FASS regulator they make. FPR1001

FASS tech support says deadheading the return will give the effect of eliminating the regulator from the system, but also reminded me not to tee into the existing return system.

Their typical install is on vehicles that are utilizing pressurized fuel rails. That's why your method of teeing into the existing return is starting to make sense to me. By splitting the return, perhaps too much volume is being diverted away from the IP? By adding that volume back into the existing return further downstream equalizes what is supposed to be there coming out of the IP return? I cant say, I'm not a fluid engineer, or whatever the proper title may be.

I'll try to get a few pics posted up tomorrow as well, they are no doubt worth more than a thousand words in this instance.

If deadheading the regulator return gets no result, teeing the return back to the existing (factory) line may be the next thing to try.

 

[Paveltolz]

Well it was worth a try. I appreciate your answers to the questions and such. My only fluid dynamics experience mirrors that of electricity...follows the path of least resistance (that and water damage in a house). I saw a posting today about max fuel pressure to a DB-2 was 7-8 psi so yeah, 17 is going to upset things.

I do know that the LP drawing from the Tank creates the vacuum necessary for the return fuel to get drawn back in (which the vented fuel cap is supposed to keep at a minimum. I doubt the FASS' return line direct to the tank would create a positive pressure sufficient to stop anything though as my AirDog's return is run pretty much the same way and I've no issues. Certainly wouldn't hurt the LP's drawing fuel either. That all said, I think you and SCTrailrider are on the right track with changing the return line's routing as these aren't the fuel rails FASS thinks we have, To me, there isn't much else left to do except:
Try moving the pressure gauge sender to a pre FASS location to see if pressure is dropping prior to getting to it.
Run a lower pressure LP sans FASS
Condemn the IP.
Hang tough and best wishes

Hang in there