Fuel Supply Pressure Spiking - Long

[FosterW]

Two days ago I filled my tank up and was heading down to PA. Ever since I owned my truck and began modifying it, I have used Power Service for ULSD at every fill up. My bottle was empty so I said, dang it I'll get some later, and went on my merry way. I stopped at a rest stop to leak and notcied my truck was idling funny, or just different than normal. I associated the noise with the lack of supplement. I went inside and they had no Power Service so I instead bought Howe's Lubricator. Shortly after driving again my pressure was jumping all over the gauge (0-40 Electronic Isspro). Its always been at 18 and now it was jumping to 28, 30, sometimes 34, then back down to the normal 18 for a few seconds and back up again. This stopped after a bit so I just wrote it off. While in PA and on my return trip I started noticing again that it would peg the gauge at 40 for up to 30 seconds or more and then jump back down to 18 or just slowly creep down to the mid 20's. I also noticed that when it was at 40, if I mashed the pedal, it would immediately go back down to 18. I thought maybe the return line was kinked somehow and that it would straighten from the extra return flow upon mashing. This was not the case. Is there a problem with the return spring in the pump? or the fuel pump itself? Could the one time non-use of supplement done harm? I kept trying to convince myself that high pressure is better than no pressure but I know better that 40psi is much too much for the ol' VP..

TIA,
Wes

 

[2Tone12V]

Two days ago I filled my tank up and was heading down to PA. Ever since I owned my truck and began modifying it, I have used Power Service for ULSD at every fill up. My bottle was empty so I said, dang it I'll get some later, and went on my merry way. I stopped at a rest stop to leak and notcied my truck was idling funny, or just different than normal. I associated the noise with the lack of supplement. I went inside and they had no Power Service so I instead bought Howe's Lubricator. Shortly after driving again my pressure was jumping all over the gauge (0-40 Electronic Isspro). Its always been at 18 and now it was jumping to 28, 30, sometimes 34, then back down to the normal 18 for a few seconds and back up again. This stopped after a bit so I just wrote it off. While in PA and on my return trip I started noticing again that it would peg the gauge at 40 for up to 30 seconds or more and then jump back down to 18 or just slowly creep down to the mid 20's. I also noticed that when it was at 40, if I mashed the pedal, it would immediately go back down to 18. I thought maybe the return line was kinked somehow and that it would straighten from the extra return flow upon mashing. This was not the case. Is there a problem with the return spring in the pump? or the fuel pump itself? Could the one time non-use of supplement done harm? I kept trying to convince myself that high pressure is better than no pressure but I know better that 40psi is much too much for the ol' VP..

TIA,
Wes

Do the pressures act up at idel? Hopefully so. It will help us check some stuff. Take the return line off at the tank. Get a big bucket for it to free flow in. Kick the pump on and see if there are any changes. Pressure goes back to normal take a look at its restriction going into the tank. Also try taking the fill cap off.

If nothing changes. Remove the spring and ball from the return side. Inspect it to make sure all is normal. Blow the return line completely out to ensure nothing is caught in the lines by chances. Install the ball then the spring back in the pump. Connect your line. Check pressure with return running into the bucket again. If you have any questions feel free to give me a call. 573-694-5155 Thanks

 

[FosterW]

Thanks for the reply. Today though, I drove to work and back (about 8 miles) and it never spiked. I have just over 1/8th tank.
I will add that, when I installed the AD about a year ago, the supply pressure was a bit lower than I would have liked, so I ever so slightly streched the return spring to get the current 16-18psi.