I have a 98 cummins 24v just turned 92000 miles, stock as far as i know. It sis come with 2 gauges, boost and fuel pressure, though itès only 15psi. It used to bury the needle just after startup. But recently, on a fifth wheel trip to the southeast, it started at about 9 psi and slowly rose to about 14 psi. It was shortly after a fiilup so i thought it might be bad fuel, so i added some diesel kleen in the white bottle and things seem to improve somewhat. I continued on to cold Canada, where i am cuurently at a friends place and the fifth wheel is sitting in a public parking lot (with permission, of course).

Yesterday I started it up and it was at 6 psi, and rose slowly to 12. I changed the fuel filter, but it didn't help.This morning I had to move the truck and it was even lower at about 4 psi. The truck has run ok all along, no hard start, no white smoke, no loss of power. However, at about the same time the tailpipe began making a rattling noise at idle. Don't know if that's related or not.

Does anyone have any ideas or suggestion? I'll appreciate any help i can get.

Electronic gauge or mechanical. Need to verify fuel pressure. Most likely the lift pump is going bad

I'm thinking it could be the pump, too but idon't want to spend time and money on a fuel pumpI I don't need, like i did with the fuel filter.

 

The gauge says "auto meter pro comp ultra lite must be used with isolator". Can't see a nodel numberThere is a rubber hose going into a red, fairly flat, cylinder (the isolator?), and from there into a braided stainless hose that goes into the dash. So, mechanical, i'm guessing?

Spend $50 or so on a mechanical tester gauge. Screw onto the schrader valve and watch pressure there.

I agree with either buying or renting a mechanical gauge. At this point, it could be the Lift pump going bad, your gauge is bad, the isolator could be causing problems, etc. Double check with a straight mechanical gauge before you do anything and that will point you in the right area.

I had a rubber hose between my snubber and injection pump and the pressure would slowly rise. Found out the hose was collapsing causing the problem. Eliminated it and pressure was instant. So if you do test, test right at the injection pump

I appreciate all of the quick replies. I called the parts store where i bought the filter and they suggested a shop close by that could do a fuel pressure test. They connected up to the hose at the isolator and read 20 psi at idle, while the gauge read 6 psi. So the problem is probably in the isolator. Nice guys, too, and they didn't charge me. A big load off my mind. Thank you again for all the prompt response.

Glad you were able to get that pressure checked. I have heard tons of stories of isolators not working correctly. They are a good concept but I wouldnt trust one. Just my personal preference of course.

I recently had to take my dash out and in order to do that I had to take the piller pod off and disconnect all my gauges when I hooked them back up my fuel pressure is very slow to come up. I did not change anything just disconnected it and hooked it back up. it is a mechanical gauge with a needel valve and a snubber. any one have any ideas. 

Pinched or kinked line maybe.

I guess it could be i will have to do some digging around that -4 line is a real pain to deal with.

If you are using plastic nylon tubing for the fuel pressure gauge, double check your compression fittings. Sometimes the ferrals can get crooked when you go to tighten the nut down. That would act like a kink but you would never find it unless you back the nut off again.