I have been working on the fuel system on my truck a bit, and am having some trouble. I put in a FP gauge, new fuel filter in the stock location, Tork Tek adjustable OFV, and a new pre-filter screen when I deleted the fuel heater Wednesday. The changes have smoothed out the motor some, but my fuel pressure is not right. Currently idling at 18 PSI, but when I free rev to 2500 RPMs the pressure goes down. 14-16 PSI is all I see with no load. I am seeing as low as 12 to 10 on the highway accelerating, and 5 PSI at full throttle. To test the lift pump, I looked for but was unable to find a rubber section of line to clamp off the return. I was able to find some stainless braided line coming down past the transmission though and clamped the smaller of the two lines off. Pressure readings did not increase. Is this a valid way of testing the lift pump, and have I correctly verified the lift pump as a major cause of my low pressure? There were no drips or spray of fuel from other areas when the line was clamped.
Thanks in advance for the advice.

 

The rubber line you want to clamp off runs behind the fuel filter to the back of the engine> http://dodgeram.info/tsb/1996/14-07-96.htm

 

Thanks.
Sounds like I need to go hunting again deeper into the engine bay. I was hoping that clamping the line further down would be adequate, since it is the same line. When I looked where the picture shows all I was able to find were wire looms so far.

 

Here you go, fuel filter looks different, but in the same location. And yea, pinching it off further down should do the same thing, likely time for a Lift Pump.

 

I went in through the fender well and was able to locate the lines Thursday night. Pressure did not spike at all when clamped so the lift pump was replaced. That helped pressure quite a bit, but it is still not where it is supposed to be. It was good enough to knock out 27.3 MPG going from Canton Ohio to Jacksonville North Carolina though. I am floored at the good mileage over the weekend. I am going to replace the fuel lines front to back this weekend. They show lots of rust and make me nervous. They almost have to be sucking air, and need replaced either way. Hopefully that will eliminate the rest of the low pressure issues. Thanks for the help so far.

 

Doubt the lines are causing low pressure problems but they should be replaced anyways.

Things that cause low FP:
bad lift pump
bad overflow valve
plugged main, pre or tank filters
kinked supply hose

#1 rule nowdays with so many Chinese parts is never trust that a part works just because it's new.

 

Thanks for the help. If the tank screen and hose don't turn anything up, I have heard there is a UV dye similar to what is used on AC systems that is ok for finding fuel system leaks. I may try that.

 

Have you considered that the fuel pressure gauge might not be reading correctly?

 

Yes, but I don't have a good way to prove it. The original install did not include an extended fuel line between the tapped snubber that replaced the banjo bolt and the pressure sender. I was seeing an exceptionally bouncy 25 to 35 PSI. I got a new pressure sender installed after the 1st one popped (autometer) and added a length of fuel line to further reduce pulses in the gauge. It now reads very steadily when driving. It fluctuates slightly while idling. I can double check that I was given the correct 100 PSI pressure sender. If it is the correct sender would it be worth threading in a cheap mechanical gauge to compare against?

 

I know that tor tek overflow valve is supposed tobe pre set but could it be that it needs adjusting? They sell several different ones might check and see if you got the right one.

 

I've had very bad luck with electrical fuel pressure senders lasting very long.
Unfortunately the way they fail sometimes is by lying to you so well that you'll never know unless you double check with another gauge.
I would use a cheap mechanical gauge to check.
You will need a gauge snubber or a needle valve barely cracked open in the line before the gauge or the needle will fly back and forth so fast that you won't be able to read it in the short time before the gauge self destructs.
That's probably what happened to your first sender and quite possibly your new one too.
A snubber is essential.

 

I restarted trying to make the truck right, and finally found the issue with the help of a professional mechanic. I checked the spring in the OFV and it looked ok, so I reinstalled it and tightened it down a good bit. A week later, I lost almost all fuel pressure. The mechanic and I went through every line, fitting etc. , even to the point of putting a dial indicator on the cam lobe to check for wear. It was fine after all. We got back to the OFV that I had checked as a last option, and found the spring utterly mangled in three or four pieces. Good to his word, the Tork Tek guy mailed me a new spring, ball, o-ring, and two sealing washers free of charge. I am thinking that the original spring was off a little or it would have been making good pressure all along. I now have a nice steady 20+ PSI. It only dips when going past 1/3 throttle under 2k RPM. Now that the fuel is there, it is time to grind my stock fuel plate to a "0" and go have more fun.