Hello,
The specs: 1993 F150 , 2wd , long bed , E4OD auto, 194000 miles. Gas milage about 14-15 highway.
The spark knock problem started at 20,000 miles. Heavy pinging under hard accellaration or FULL throttle. Also pings under at low RPM's ( nothing terrible but still more than normal.). Otherwise the truck runs fine.
It really hasn't been much of a problem all these years ( more of a minor annoyance ) because I usually drive with a very light foot and those situations where I MUST use hard throttle are rare. I can even use 87 octane.
The real problem is when towing. There is absolutely no way to avoid the pinging when towing. Usually I will have to slow to 20mph or so on the highway grades to keep the engine from blowing itself apart. Even using 93 octane doesn't help when towing. So therefore, I must get those problem diagnosed.
Heres what I've done so far:
1.Checked trouble codes : None 2.Replaced plugs and wires : I saved the old plugs. 3.Changed cooling system : I've ruled this out because pinging occurs even before the engine is fully warmed up.- Exhaust system is fine.
- Timing is right on the money.
In effect, I'm stumped...
The engine is in good shape, doesn't burn a drop of oil. The old plugs looked a little light in colour perhaps suggesting a lean condition but I'm not certain what is a normal colour plug for this engine. The plugs are also even in colour ( no plug looks any different from the other). The truck used to get 20 mpg when new. It dropped to 14-15 when the pinging started at
20,000 miles and hasn't changed.Any ideas ?