Blinking Fuel Filter Light - Diesel Forum

ZX12R · 05-13-2007, 10:01 PM

Tonight when I started my truck,a night on the dash was flashing that read "Fuel Filter". The trck idled a lit rough for about in seconds and when I brought the idle up slightly,the light went off and the truck then idled as normally would and the light stayed off.I went home,shut the motor down and started it up about 5 minutes later.The same thing happened. So,I shut it down and channged the fuel filter,started it up and the light never came on.

My question is,why did the light flash like that.Was the filter packed with so much crap that it caused the light to flash? By the way,the sensor that connects to the bottom of the filter was not connected.

1989 F-350 242,000 miles

arthurgoboom · 05-13-2007, 11:28 PM

I'm pretty sure that is an indicator that the filter is clogged and you're getting low pressure/flow out of the filter, i.e. time to change it. Wish my 6.9 had one...

cdnsarguy · 05-13-2007, 11:33 PM

The light illuminates "fuel filter" when there is a vacuum in the fuel filter, 2 things can cause this a plugged filter (dirty) or a bad manual lift pump...... You could have a weak lift pump but with changing the filter it is passing enough fuel......

Do a pressure and flow test of the fuel pump at the Schrader valve on the filter header (FSS- fuel shutoff solenoid disconnected on IP). Remove the tire valve core and hook a hose and pressure guage on it should see 4-6 psi when cranking. Then do a fuel quantity test same place, should see 1/3 pint in 10 seconds of engine cranking, route fuel to a suitable container with a hose.

If there is a problem with the lift pump and you are changing it, ensure the new pump comes with instructions as to correct installation procedure if it is the newer model pump with the almost straight arm.

The wire on the base is for the "Water In Fuel" sensor/light.

ZX12R · 05-14-2007, 10:57 PM

When you talk about possibly having a bad "lift pump",you are talking about the fuel pump,correct?

cdnsarguy · 05-14-2007, 11:20 PM

That is correct.....

waterdude · 05-15-2007, 02:04 AM

The good news is that fuel pumps for our trucks are inexpensive and not hard to install. Be sure to use a fuel line wrench, also called flare nut wrenches. I bought a set, but you only need one of the correct size.

When my fuel light was lighting up, it was only at high RPM. I replaced the fuel filter, but also found some "sand" particles in the bottom the the fuel filter assembly. After I removed those sand particles, no more fuel light. I also installed a new lift pump, because my old one was 15+ years.

--Hugh

ZX12R · 05-22-2007, 10:21 PM

Thank you for the replies guys.Here's an update. As stated,last week,when the "fuel filter" light started flashing,I changed the fuel filter right away and the light stayed off until today. :-( It does not stay on all the time though. Usuallt,it comes on when I start the truck up,but,If I feather the gas for a second or two,the light goes off and does not come on again until I start the truck again.Is this a tell tale sign that the fuel pump(lift pump)is going bad?

Anyway,I checked my records and found that I last changed the fuel pump at 88,000 miles.The truck now has 244,000 miles .I ordered one from Ford today and it will be in tomorrow.

Phillipmc1268 · 05-24-2007, 04:23 PM

I think the lift pump will solve your problem. I may make starting easier too. Ditto on the line wrenches. My trucks previous owner had already rounded mine, so I had to use vise grips which were no fun.

cdnsarguy · 05-24-2007, 06:46 PM

I would check for a worn/shorting wire too, sounds too finicky to be just the lift pump or filter......... Diesel engine vibrations will wear exterior wire coatings away over time......

ZX12R · 05-24-2007, 11:13 PM

"I would check for a worn/shorting wire too, sounds too finicky to be just the lift pump or filter......... Diesel engine vibrations will wear exterior wire coatings away over time...... "

Interesting......I talked to a diesel mechanic at a shop yesterday .I told him whats happening.I also told him that the truck idles dead smoothe at all rpm's,and has not lost any power that I can notice.From that description,he thinks it may be a bad sensor. I am going to have him look at it tomorrow. A mechanic at the ford dealer also said it could be clogged screens in the gas tank but that is not likley. At any rate,I am changing the lift pump as it has 156,000 mles on it.

cdnsarguy · 05-24-2007, 11:26 PM

If the screens were clogged then the bypass valve would open. Just like it does when the fuel gells on the screen........

Good choice on the lift pump.......

ZX12R · 05-29-2007, 12:20 AM

Lift pump and the sensor was changed.Problem solved....the light does not come on anymore.Thank you again for all your replies!!!!!!!!!!!!!