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
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
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.
4. Exhaust system is fine.
5.Fuel filter . Fuel pressure tested normal.
6.Cleaned out throttle body.
7.Replaced PCV valve, filter and air filter.
8. 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 ?
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