1993 F150 Spark knock

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.
  1. Exhaust system is fine.
5.Fuel filter . Fuel pressure tested normal. 6.Cleaned out throttle body. 7.Replaced PCV valve, filter and air filter.
  1. 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 ?

Reply to
gil
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|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. |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 ?

I have the same problem. I don't see where you list the engine size, but mine's a 1994 5.0 V8. Most of the time it runs great, but sometimes it pings a lot no matterhow I drive it. It gets better pretty quickly though, usually if I romp on it a time or two. I have just about narrowed my problem down to the TPS, which I note you have not changed. Rex in Fort Worth

Reply to
Rex B

Thanks rex. Unfortunately the TPS checks out fine. The engine is the 4.9 six cylinder.. John..

Reply to
gil

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