90 w250 automatic

This morning when the grid was heating before starting my water in fuel warning light came on. It was not on last time I used it. I dont think water magically appeared in the fuel system. I have not used the truck for about three weeks, but it is almost full of fuel. With the recent rains here in the PNW, is it likely that the warning switch has failed? I could not find a test proceedure on the FAQ or searching previous posts. Any ideas before I start draining fuel and changing the filter?

TIA

 

Did the lite stay on or did it shut off after a few moments? Mine has always come on at startup ever since it was new but then shuts off after few moments.

 

I didn't start it. I had never had the warning light come on before. The light stayed on after the wait to start light went out. So I thought I would check it out before running it. Like I mentioned on my last post I suspect that the sensor may be malfunctioning since last time I ran the truck the light didn't come on and its just been parked on the driveway.

TIA
Simon

 

Since the sensor is made to detect water,the entire wiring harness for the sensor is also senstive to water/moisture. I have had the sensor go off on humid days with large temperature swings or after a wash.

Pull the wire harness 2pin connector at the sensor and then turn on the ignition. If the lite goes out then the sensor or the connection is at fault. If the lite stays on again then the harness has some moisture. The next connection is one of the plugs on the rear of the engine by the brake booster. Pull them apart and clean them out with WD40- or similar water dispersant. Reconnect and try the ignition again. If it still goes off then there is another 4 pin connector on the fender well near the firewall that contains the same color wires as the WIF sensor, IAT sensor and KSB control. This one may also be moist. Clean and try the ignition again.

Let us know how it turns out.

J-eh

 

I finally got out there this moring to look at the truck in the daylight. I unplugged the harness at the sensor and the light went out. While I had the plug undone I gave it a shot of wd40. I drained out some fuel and didn't get any water. So I started it up and it seemed to run fine. I purged a bit more fuel with it running. The light stayed on for about a half an hour before going out.

So I suppose that with all the rain we had a few weeks ago plus the cold snap had resulted in some condensation within the sensor. As soon as the engine warmed up the moisture was driven off and the light went out.

Thanks for the advice on where/what to check.

 

Good to hear...

Now that the connections are dry, go and apply some dielectric grease to the connectors and this should help to elliminate that as the cause of the lite next time. The next lite should be the real deal..

J-eh