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I have been fighting a ping and detonation spark knock on my 1990 pickup 5.7L TBI. It will only do it under even the slightest load going up hills etc. Whats strange is I took my dog to vet and truck was fine. When I left it started ping and knocks and has been doing so ever since.

Here is what I have done:

Repaired Knock sensor circuit
Checked Fuel Pressure to make sure it was not running lean (12 Lbs)
Checked IAC
Checked Throttle Position Sensor
Cleaned throttle body
Checked static timing
New plugs, Cap Rotor and AC delco factory wires
factory thermostat and no overheating
Great Oil pressure
Seafoamed engine and added fuel additives
Checked Temp Sensor
Checked MAP sensor with hand vacuum pump - perfect
Tried going to highest octane fuel - no difference

I did check the Oxygen sensor and it seems to not be acting quite right. It stays at a low voltage which should make the engine run rich Which is what it is since I can smell too much gas in exhaust.

Now what fixes it. I can retard timing a few degrees and it almost stops. If I pull computer timing control wire to place truck in limp mode. Absolutely no pinging at all but of course it runs like crap.

What have I missed? Could it be something in spark control module advancing timing too much? If so how could I check it? Is a ECM problem? Any experts that can help me with this beast?

I have put too much money into this old beater truck and I am thinking about painting deer pictures on the side and taking it over to a ******* hunting camp.
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