So same problem I've been having. Idle fuel pressure is 60 psi give the skinny pedal a little love and pressure drops. Every time i find a problem it resolves the issue for about a month then slowly returns. Usually find a different source each time. So started at the back droped the tank to check connections on top of tank and my compression fittings in the tank. I noticed what looked like metal flakes lightly spread through the tank. Tired it on its side.and didn't see anything nothing stuck to my magnet.




what I did find looks like rust oil algae? Truck doesnt burn oil or smoke topside filter looks clean noticed some sediment in my pre pump filter but nothing crazy.
any ideas?

 

15 years ago, I ELIMINATED any fuel pressure/supply/volume issues by doing this. Still running the same pump. Naysay it all you want, but it's the most effective way to supply fuel to your engine. It's much easier to push a fluid to it's destination than to pull it towards the fuel pump inlet and then try to deliver it.

 

You always get fuel from a good clean source? That almost looks like burnt oil. I've read that injectors can have some type of internal issue that allows combustion gasses back feed but can't say much more than that. Never actually heard from anyone that's had it happen.

Edit: Oh, and I too let my pump swim in the deep end. It can't suck air if it's in the drink.

 

What problems have you found and fixed?

Fuel pump has an internal screen that could be plugged.

Fuel Pressure Regulator might be an issue. Did you rebuild it including a new poppet valve?

Did you use injector hose clamps (like in Kwik’s photo)? If not then your system could be sucking air.

 

Hit up the questions from Jason with as much detail as you are able, then the community will steer you toward another fix action that will hopefully be the last.

Is the engine running OK despite the drop in fuel pressure on the gauge? You may have an air pocket in there before the gauge.

We have seen a time or two where the pump is faulty and will sustain 60 PSI at idle, but fall on its face when the accelerator is pressed. Let's look at the other possibilities first before spending money.

Are the slots in the bowl standpipe aligned properly?

 

https://youtube.com/shorts/eSy4tgLXT...ture=shareThis is a link to how my fuel pressure looked when i first bought the truck. Droped the tank found clogged filters cleaned it out and performed hutch mod. Truck ran alot better. It still had a pressure drop at wot but performed like it should so I left it alone. About a year or so later we had a nasty freeze and my pre pump filter geled up despite a healthy dose of stanadyne in my tank.

after replacing the truck was cackling alot and I noticed my fuel pump fitting was loose tightened and back to normal. For Xmas I got a new set off isspro guages.

And since then I've been able to monitor my fuel pressure constantly. Which is where my problems became more apparent. So I started looking for air leaks. Used double fuel injection clamps and each joint. Never got it perfect. But it got better. So I'm still troubleshooting and found that I had alot of trash in the bottom of my fuel bowl.
cleaned it up truck ran better , but still has a pressure drop at wot. Checked my pumps flow rate found it lacking and ordered a new bosch pump from clay. Finaly started to look good still had a small pressure drop at wot but only 5 psi from what I understand that is considered normal so I was content. A week later the problem started to slowly return. Getting to the point to where I had to be careful when getting on the freeway to not drop below 45 psi. So at this point frustration is kicking in and I began searching for all the knowledge I could find on trouble shooting our fuel systems. Bought a new inline filter hooked it to about 10ft of fuel line ran it in the tank then plugged it into my fuel pump. Ran down the road no change. Moved to the pressure side. Istuffed paper towels around my fuel bowl and valley then went for a ride. Found a few leaks at the fuel bowl so ordered a kit from clay rebuilt fuel bowl and were good again. Then same thing runs good for a week and then the pressure starts dropping under a load getting worse over time. At this point im scratching my head. I decided to inspect everything from back to front. And when I droped my tank and found it was coated in whatever that is it did not help my confusion. Here is a link to my pre filter mechanical guage on startup and hitting the gas.
this is post filter
https://youtube.com/shorts/TJ0QTa8_0vc?feature=share
As far as my fuel source. I buy from the truck stop by my house and murpheys if I'm close by a walmart.
Now for the fuel stand pipe i deleted the internals so to my knowledge i cant have the alignment issue? Im not an expert and learn new things every day so i could be wrong lol.

As far as the in tank pump relocation I don't think it's a bad ideal but I do plan on upgrading my sticks and turbo and was planning on doing a dual bosch setup once I work all of my bugs out. I don't like droping my tank anymore than I have to. I used my gave to catch a falling strap putting it back under he truck yesterday. Now I have a nice little scratch and what resembles a Neanderthal brow line. Lol
I have not replaced my fuel pressure regulator. It seems to be functioning as intended from what ive read. If I pinch my return line pressure is more than ample and doesn't show any change with my issue.

 

Ohh and as far as the internal pump filter I have not checked that. Do i just shine a light on the suction side?

 

With the factory pump design the way it is there really isn't a way to get a look at the internal filter screen. Maybe an inspection camera if it's small enough. I can't remember if the stock pump has the check valve in the discharge fitting or if it's in the housing, but if it could be bypassed you could attempt back flushing it. Another thought just occurred to me, you could try cycling it back and forth. With the pump full of fluid you can reverse the polarity and make the pump spin backwards effectively blowing whatever is inside out the suction port. Then hook it up to clean fuel source hook the wiring up correctly and refill the pump internals. Then rinse and repeat until your satisfied it's clean.

If and when you get around to the upgrades you mentioned, depending on your goals the dual pump setup likely isn't necessary. For probably less $$ and defiantly less hassle a Bosch 044 or 040 will provide enough fuel for 600-700 hp. The 044 can be mounted to the frame rail or in the tank and the 040 is in tank only.

 

I already have the extra pump thanks to a friend of mine. So really just 2 extra hoses needed and if one burns out I could go 044 and cap the 2 lines. I thought about swapping pumps but if it is a clogged filter I would want to find what's causing that issue before throwing another pump at it. I'm gonna pop the outlet side off and see if I'm getting air. I'm currently running the wix 33270 so I can't see through it. I'm running 4 14-16mm fuel injection at the sending unit 2 on both side of my filter and 3 at the pump. I'm put a nice thick coat of permetex #2 around the house ends tonight and I'm letting it cure hoping that will fix any air leaks.

 

Just slide the factory tube off and a 5/16 hose in it's place on the bowl drain valve. That way no breaking connections and you get to see exactly what's getting to the bowl and going to the injectors.

 

I agree with udsuth. Time for a flow test. What is is SSJ normally says? 1 quart on a key cycle? Pump will run about 20 seconds per key on.

 

This is what resulted with a 30 second test run back when I did it. One gallon jug in the picture. The "new" pump is the Bosch that I ended up putting in the tank at the bottom of the fuel pickup.

 

Got rained out this morning hoping tonight after work I can test it out. The permatex 2 helped out a little my mechanical guage isn't bouncing all over the place now. Figure I'm gonna see some air and hoping my pump isn't clogged up.

 

Okay so here what did unhooked my mechanical guage pre filter and used the hose to check for air and flow test I'm getting more than a pint per 20 sec. It takes me 3-4 for a full gallon. I did not get any air bubbles but now I'm wondering if the fitting is designed to stop air.
I was limited on time so didnt hook up right after the pump or at the drain valve may have to tey again there later. I also cramed a crapton of blue shop towels around my fuel bowl and fittings to check for leaks again
Either way here's the link.
https://youtube.com/shorts/-jgcQshY2Bg?feature=share

 

I'm pretty sure I read somewhere that the stock pumps are rated at around 35 gal/hr so that comes out to a little over half a gallon/minute. Sounds like you're in that ballpark at least.