Low fuel pressure under load.

B

bd blk 12v

Fixen broken bulldogs
Joined
Sep 10, 2008
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241
Hello guys. I have the 94 in my signature. I have searched and looking for some help with low fuel pressure under load. The truck has a Vulcan dual feed line 1/2 feed line from filter to dual feed. I have an adjustable tork tec overflow valve. The truck at idle no load sees 32psi. The lift pump is a cummins with less than 5k miles on it. Revved up in neutral sees 40psi. I have deleted the fuel heater also. Driving the truck no boost 35psi of fuel pressure. When you floor the truck it drops to 0 psi. Let off the throttle and fuel pressure restores. Is there any other common air leak spots in the fuel system? I appreciate the help.
 
Not enough volume from pump for the demand. Walbro 225 is a relatively cheap pump.

Also does it run badly at 0 psi like no fuel would? Possible the gauge is not in a good spot.

I set them up with a regulator on the return side and no overflow valve 40-50ish psi is fine.
 
The gauge is hooked up on the tee fitting on the p pump supply. The Vulcan dual feed tee is tapped for 1/8 pipe. I have a needle valve and hose to a glycerine filled gauge. I did pinch the return at idle and jumped to 55 psi. On the walbro do you delete the factory lift pump or feed to it? It does seem soft like it is running out of fuel. It will only pull about 3300rpm and doesn't want any more. It will free rev to 4k. What regulator do you use in place of the overflow? Thanks
 
bd blk 12v said:
The gauge is hooked up on the tee fitting on the p pump supply. The Vulcan dual feed tee is tapped for 1/8 pipe. I have a needle valve and hose to a glycerine filled gauge. I did pinch the return at idle and jumped to 55 psi. On the walbro do you delete the factory lift pump or feed to it? It does seem soft like it is running out of fuel. It will only pull about 3300rpm and doesn't want any more. It will free rev to 4k. What regulator do you use in place of the overflow? Thanks
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Your overflow valve sounds like it needs a stiffer spring or just order a tork tech bolt way cheaper than sourcing regulator and fittings.. I would give that a try first and see if it helps.. I think you will still be needing more volume sounds like your pump able to keep up. I always eliminate the factory pump but alot of people tend to run through it..
 
Have you changed your filter and cleaned the pre filter screen in the factory LP setup?


I like to go fast
 
It is a fairly new napa fuel filter. I pulled and deleted the fuel heater. The pre screen I haven't ever touched while owing the truck since 06. When I deleted the heater I cleaned the screen and it was very clean considering the age of it. I'm sure it's loosing fuel. I have a Holley black I'm going to install on it and see it it helps. What tork tec bolt are you thinking?
 
Interested which bolt he is recommending too.
You replaced the lines from the tank? Common to suck air around those clips on the top of the tank.
 
95cummins5.9 no I haven't replaced the lines. I haven't looked at that. I was curious if there is any common places for leaks. Thanks for the idea. If I pressure up the fuel system through the fuel cap would I possibly see a leak if there is an issue there? Thanks
 
you could check for leaks,but I would think by looking at your sig your just running out of fuel with the delivery v/v's and injectors. duel feeding the pump with 1/2" but supplying it with 3/8" doesn't make any sense to me (If it's still stock). I would start by tearing out all the factory lines replace with 1/2" feed and 3/8'' return you said you deleted the heater but is the strainer still there? I just bypassed mine completely and installed a 3/8" inline filter. If the tank pick up lines are shot either a sump or a Draw straw. Testing it out afterwards if it's still too low a pusher pump as mentioned earlier or go electric only
 
The factory return line commonly leaks behind the filter housing where it turns to rubber for a couple feet and then transitions to metal again. However, this only creates problems with hard starts and fuel dripping down the block.

With 5x.016s and 191s I'd say the factory lift pump just can't keep up. You can make it slightly more efficient by running the pick up line straight into the lift pump and skipping the strainer/heater all together. Splice a 150 micron strainer into the line before the pump to keep trash out. It won't help much though. Best setup would be something like an aeromotive A1000 with 1/2" lines from the tank, through a remote screw on filter, to the p7100, out the other end to a fuel pressure regulator, and on back to the tank with a 1/2'' return line.
 
If I understand correctly the fuel strainer is below the fuel heater correct? If so yes it is still on the truck. I do have a beans sump not installed. I've been pondering on this fuel system for quite some time. I built the engine about 5 years ago had kids and haven't touched it since. I'm wanting to get her going. Will the sump 1/2 line to strainer filter a1000 pushing through like a cat fuel filter head to the p7100 delete the overflow valve 3/8 return a regulator back to the tank sound sufficient? Sorry for the run on sentence. I appreciate the help. I have searched a lot and just can't see how a stock lift pump could support 500hp or more. I would assume I'm close to there or possibly over. I'm hoping that with the correct fuel volume and pressure in the system I'm leaving hp on the table with my setup. Thanks
 
check out Will's junker thread on the fuel section of the build page number is probably in the teens ish. knock off holley black feeding the stocker supporting pretty good hp.

My opinion is buy once and cry once on most stuff.
So I am gonna run a magnafuel and regulator system

I have set them up with aeromotives and walbros or fass and airdogs. Whatever you choose just be sure it will support end goal hp.

If slightly modded is what you are after 500ish hp. rock the stocker and a pusher with a ofv and be done. its easy and cheap.
5x16 and a 66 tell me that you have the "itch" So I recommend spending a bit of dough and do it right. once.
 
Thanks jakerc69. I do have a Holley black knock off and haven't installed it. I'm the same way if it costs more I'm up for it. I like to do things once and be done. I do have the itch I'm not gonna lie. What would be the once and for all fuel setup? I'm not going to go bigger on injectors I believe these should suffice. Thanks.
 
I know you have the sump but...I would sell it, you really don't need it. Buy a draw straw for 50 bucks and run 3/8s. put in your pusher, and be done.
 
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