1. Verify Water Presence:
* Drain the Water Separator: This is the most crucial first step. Locate the fuel water separator (usually near the fuel filter housing). It should have a drain valve at the bottom. Carefully open it (have a container ready!), and drain out any water. The amount of water will indicate the severity of the problem. A little water is normal, but a significant amount points to a leak somewhere. After draining, tighten the valve securely.
* Check Fuel Filter: If you have a lot of water, change the fuel filter. Water can clog the filter, leading to false readings or actual engine problems.
2. Inspect for Leaks:
* Fuel Tank: Check for cracks or rust around the fuel tank. A hole, even a small one, can let water in.
* Fuel Lines: Inspect all fuel lines for cracks, damage, or loose connections. Water can enter through any leak.
* Fuel Cap: Ensure the fuel cap is sealing properly. A loose or damaged cap can allow water to enter.
3. Water in Fuel Sensor (WIFS):
* Location: The WIFS is usually located in or near the fuel water separator.
* Testing: This is trickier. You'll need a multimeter to test the sensor's resistance. The exact resistance values vary, so consult a Ford repair manual or online resources specific to your 1999 Powerstroke's WIFS. A faulty sensor will give a false reading, even if the fuel is dry. If the sensor is bad, it needs replacement.
* Cleaning: Sometimes, the WIFS gets clogged with debris or contaminated fuel, causing a false reading. Try carefully cleaning the sensor (if possible). Refer to a repair manual to avoid damage.
4. Other Possibilities:
* Wiring: Check the wiring to the WIFS for any damage, shorts, or corrosion. A broken wire can cause the light to stay on.
* PCM (Powertrain Control Module): In rare cases, a faulty PCM could be misinterpreting the WIFS signal. This is usually a last resort diagnosis that requires professional attention.
Important Notes:
* Safety First: Diesel fuel is flammable. Work in a well-ventilated area, away from open flames or sparks. Wear safety glasses and gloves.
* Repair Manual: A 1999 Ford Powerstroke repair manual (Haynes or Chilton) will be invaluable for detailed diagrams, specifications, and procedures.
* Professional Help: If you're not comfortable working on your fuel system, take your truck to a qualified mechanic. Improper repairs can lead to engine damage.
Troubleshooting Steps Summary:
1. Drain water separator.
2. Change fuel filter (if necessary).
3. Check for fuel leaks.
4. Inspect/clean/replace WIFS.
5. Check WIFS wiring.
6. Consider PCM as a last resort.
By systematically checking these areas, you'll likely identify the cause of the persistent "water in fuel" light and get it resolved. Remember to always consult a repair manual for specific instructions relevant to your truck's model.
