I've got one of those fuel pressure lights on the dash. What I notice, usually only at night, is that the light blinks a little when I press part throttle. Now, if I push hard on the throttle to accelerate or go up a hill the light goes out. If I coast no light. Only blinks when I just slightly press the pedal. Probably about 45 to 50mph on a straight grade.

Any ideas, what is going on here? Does the injection pump open some kind of valve that drops pressure a little bit a certain point? Possibly returning fuel to tank? Then when I accelerate the pump closes this valve and pressure remains steady. Truck still runs just fine, no loss of power. The light indicates normal when power is off...full bright indicating no pressure. Turn ignition on...light goes out.

 

I would say your going too have too get a gauge on there too really see what numbers your pulling. You may or may not have a dieing lift pump

 

Mine did not do that when I first installed the warning light. Later it began to flicker at part throttle but go out on acceleration. About 4 days after it started flickering it stayed on steady. I lost the LP. Had to limp it home about 3 miles. Then I got me an Airdog and a mechanical gauge. All is well.

Check your connections, but I bet the LP is dying. Sorry.

Josh

 

Spend $50 and put a mechanical guage on there - it will be the best money that youve spent on your truck.

 

I have a mechanical gauge, and a low pressure light. My light flickers too, and the gauge says I have above 10 psi at all times. The light fllickers more when it's cold, and when giving it throttle. Mine is mounted on the IP, and I think it's the vibration making the switch partially make contact.

 

It might be the pressure switch itself is going out. Electronics are 50/50 about lasting a long time or failing quickly. They're designed to be normally closed at 0psi, and open up their contacts internally at or above +/-5psi. Or you may have some air in the line causing cavitation and when you accelerate hard it clears up?

The relief valve is the banjo bolt on your return line coming off the IP. If you look at the exposed end, maybe with a mirror, you will see a steel ball in the center of it and let you know it's more than just a simple banjo bolt. It is mechanically activated, nothing electrical. There is a spring inside that opens at around 15psi to let flow back down to the tank, anything below that and pressure stays upstream of it and inside your IP. There is also a very small peep hole next to the larger controlled ones that lets a very small amount flow back full time, but not enough to drop pressure. If the spring is weak, it will open prematurely and dump fuel out of the pump and that would cause a pressure loss.

But in your case, I don't think it's your relief valve. Might want to check continuity between the pressure switch body itself and ground to be sure it's grounded properly. And as others have suggested a FP gauge will be a better monitoring tool. Nothing wrong with the light kit, I like mine as it's nice and bright and stands out to warn me if I'm not paying attention to the gauge.

 

Hey tanker what you are saying is my truck to a tee. I have a low pressure light installed by a local Cummin's shop and at night my light will flicker at a bit of a pull or on a hill at the speed you say. I had my pressure checked at the time the light was installed and it was between 10 & 14 psi. I drove the truck for a couple years and thought maybe it was time to replace the lift pump. The same tech. that installed the light said to stay away from the in-tank pump that Dodge was doing and that they ( Cummin's ) had an upgraded replacement pump. He didn't think I needed to replace the pump but the truck was going on 7 years old but only 35000 miles and I thought better safe than sorry.. Well the new pump acts the same as the old exactly. I think he told me the pressure switch will turn the light on at 5psi or less but will blink at psi's under 10. I guess its still better that not having any protection at all. Hope this helps..

 

When the pressure dies the light will stay on. I have had that happen too.