Jim Grant's Tech Tips
Ford F150, Phantom Problems
have an '87 Ford F150 that has started to give me a problem. About once
every two weeks the spark plugs foul out from a rich condition. I've tried
timing, sensors, plug wires, cap, rotor, fuel pressure is normal, compression
is normal. I have taken it to two shops and had no luck. This problem
started all at once. Any suggestions would be very helpful!
condition you're describing could be caused by a failing fuel pressure
regulator. What we have seen with Ford has been a pressure regulator that
randomly sticks. When the pressure regulator sticks, fuel pressure sky
rockets. The high fuel pressure easily doubles the amount of fuel being
delivered to the engine, resulting in stalling and gas fouled spark plugs.
The problem with this type of failure is you have to catch the fuel pressure
regulator in the act of failing. This usually requires adapting a fuel
pressure gauge to the fuel injection system to monitor fuel pressure.
We had one Ford van that ran great, but for no apparent reason the engine
would randomly stall. When re-starting the engine it acted as if it was
flooded with gas. The cause was a defective fuel pressure regulator with
a mind of its own. The tough part was catching and proving the failure
of the fuel pressure regulator. The easy part was changing it.