Fuel pressure dropping

[EMD_DRIVER]

I got my regulated return installed in the 99, but I am now chasing down a fuel pressure drop. I have my FP gauge sending unit installed with the return line, before it goes into the regulator. When I did my regulated return, I used 1/4" steel line.

Once the truck warms up, my fuel pressure will drop from 60PSI and go down to 30PSI under moderate throttle. If I hold it at WOT, I can make it drop to 10PSI. If I do that, it's only for a second. I do not want to starve my injectors. I thought maybe my OEM pump may have just been having trouble keeping up with demand, so I plumbed-in my in-bed tank to the factory fuel system. My in-bed tank has a Holley blue mounted to the side of it and I am now pumping fuel into the intake side of the factory pump. My pressure drop has not changed, with this setup.


The FP gauge I am using, isn't the most expensive one I could find, but seems to work well. I am almost tempted to try running a mechanical gauge to the cowl, so I can see what it would say. It's not the easiest thing to do and something I would do if I had to.

Worked on it for a while today... I found a kink in the line that goes up the front of the block.. Ended up having to replace the line, from the fuel pump to the fuel bowl. No change in fuel pressure performance. Took the truck, to pick my son up from soccer practice and fuel pressure was bouncing from 0-65PSI.. I had no idea what was going on..

Got it home (Barely) and commenced to re-wire the fuel pump. It is no longer controlled by the PCM (Hope it doesn't throw any codes) but is now controlled by a dedicated fuel pump relay, getting power directly from the battery. When I turned the key on, I noticed the pressure needle bouncing.. Without the engine even running. I listened to the fuel pump and it was making all kinds of noise. It would build pressure and then let most of it off, it would then build and drop pressure... It just kept doing that.

I checked for leaks and found none. I also checked the regulator and it's also working fine. I'm assuming that the fuel pump I just put on two weeks ago, is also bad. I have another used one and will install it in the morning.. We'll see what happens then!

 

[EMD_DRIVER]

Worked on the truck again today and I'm at even more of a loss... For right now, I am still getting fuel from the tank in the bed. It has ports for both supply and return. It also has a Holley Blue pump mounted to it. I am drawing fuel from the tank with the Holley pump, pushing it through a filter and then to the factory pump. Everything between the tank and the fuel bowl has been replaced. I also replaced the used pump, with a new one from Autozone.

Since I have a filter after the Holley pump, I decided to try removing the factory filter. Once out, I removed the standpipe and fuel heater. Tried another test drive and didn't even make it to the bottom of the driveway.


Since I have a new JDM adjustable FPR, I decided to try it.

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The regulator came as pictured... Gauge mounted to one side and barbed fittings on both the bottom and other side. The other regulator I was using, had the gauge T'd off the bottom, with my compression fitting on the other side of the tee. The barbed fitting on one side, was the output of the regulator. When I tried pressurizing the system with the new regulator, I could build no more than 10PSI.. I guess I need to put the input to the bottom of it and output on one side, with a plug in the other side.

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I know they aren't the best quality regulators on the market, but they are all I can afford right now.

This thing has me so frustrated, that I had to come inside and take a break.. I am about ready to part this truck out and cut my losses...

 

[EMD_DRIVER]

Ok....

I tried running both fuel pumps together, to see what kind of return I was getting to the tank. With the regulator screw backed all the way out, I had no fuel at the return line. I had been getting myself way too involved with the auxiliary tank and extra pump thing... I checked the pickup tube in the aux tank. What I found, was a clear tube, shoved over a single barb. There's no way, for it to be air tight. I decided to just return to the stock configuration and use the factory tank. I figured if it was the pump, this would show it.

I configured my new regulator the same way the old one was and set the pressure. Went for a test drive and was pleasantly surprised. In the stock tune, the pressure dropped to around 40PSI at WOT. In the 60HP towing tune, the pressure dropped even more and went down to 28-30PSI.


I cannot wait for my OEM pumps to get here... I noticed that the inlet and outlet tubes on the Airtex pump, have smaller inside diameters. The walls of the tubes are heavier than the OEM pump's tubes...

 

[Double-S-Diesel]

do you have a filter before the pump, sounds like there is air getting in the line , or the regulator is bad.
the airtex pump is capapble of supplying fuel had the same pump on the 96, same on the 99 and same is on my 03.

does it loose pressure cold or only when warm?

 

[EMD_DRIVER]

do you have a filter before the pump, sounds like there is air getting in the line , or the regulator is bad.
the airtex pump is capapble of supplying fuel had the same pump on the 96, same on the 99 and same is on my 03.

does it loose pressure cold or only when warm?

No Pre-pump filter... I did replace the hose from the pickup tube, to the steel line. My goal was to eliminate any possibility of air. I learned something about the regulator though... It is a 1:1 boost referenced regulator. There is a barbed fitting on the side of it, that is supposed to hook to the MAP sensor line. I stopped at Lowes this evening and got what I needed, to hook it up. After getting it done, it makes a huge difference. The regulator is set at 70PSI. At highway speeds, the pressure drops to 60PSI. When I get on the throttle, the pressure still drops, but will only go down to 49PSI... It was going below 20PSI before I hooked it to the MAP line.

One strange thing about the regulator... When I first start the truck (Hot, or cold) the pressure will go to 100PSI. It drops to 70PSI, within 2-3 minutes. I've never seen a regulator do that. For now, it's doing well enough, that I can live with it until I can afford a good one.