fuel filter light on at idle

[miles1400]

hello everyone, tonight i filled up my truck with diesel and put in diesel kleen additive. i started the truck and the fuel filter light flickers/flashes/blinks but only at idle, part throttle to WOT the light is out. the engine runs good, good throttle response so i don't think it is the filter but i could be wrong. it is a one piece filter that has about 7K miles on it, i know it is recommended to change fuel filters every 10K.
i looked at other threads on here and some people say that its the lift pump going bad, my truck has 195K on it and i believe the lift pump is original so that might be it but i'm not sure. most important thing right now to me, is the light coming on trying to tell me there is a serious problem and i shouldn't drive the truck far from my house or is it just a dummy light

 

[BeastMaster]

You apparently have low fuel pressure and your IP is trying to suck fuel.

Not good.

Your IP needs to be supplied with more than enough fuel. It will take what it needs, and send the rest back to the tank. It's not just fuel... The diesel is also being used as a coolant, flushant, and lubricant.

If you start pulling vacuum at your IP, it won't get the known pressure it was designed for, the timing will be off, lubrication, heat dissipation, fuel filtering functions will be compromised, and the sucking will leave you vulnerable to air intrusion, or even sucking air backwards via the fuel return.

My advice... Get a pressure gauge on your IP inlet, find out why. If you ignore this I almost guarantee you will experience a bout of air intrusion, which will happen at the most inconvenient time, as well as premature aging of the expensive IP.

 

[miles1400]

thank you for the reply, so low fuel pressure would mean that the mechanical lift pump is getting weak and its going to die soon, and that i should either replace the mechanical pump or upgrade to electric, right?
i'm not too worried about the ip and injectors, the ip has 120k on it, i have paper work that says ip was replaced at 75k, not sure why. injectors i believe are original, (195k) i was planing on replacing them both next year anyway cause i have heard they have a "lifespan" on 125k then they get weak and don't work right

 

[IDIBRONCO]

so low fuel pressure would mean that the mechanical lift pump is getting weak and its going to die soon, and that i should either replace the mechanical pump or upgrade to electric, right?

It sounds close, but to be completely accurate, "would" needs to say "could".

 

[miles1400]

i drove the truck again today and the light turned off, so i dont know if its just being dumb or if it fixed itself

 

[miles1400]

ok so my truck was fine the past couple of days but then tonight the light starting blinking very dimly at stoplights. do you guys think fuel tank/system cleaner would clear up the issue? there might be junk in the tank pickups or fsv or mechanical LP,. i am looking into getting a bottle or 2 of Diesel Kleen clear diesel fuel and tank cleaner, but i dont want to spend the money if it wont change anything.

 

[MtnHaul]

It might be worth cleaning the connection for the vac sensor on the filter header. FWIW mine was coming on with high RPM but after cleaning it the light only comes on if I turn off my e-pump and the IP is doing all the work. Of course I don't actually know if the sensor is functioning properly.