4.0 OHV pinging under load
 

I have a '98 Ranger, it's nearing in on the 200K mark. A little over a year ago, I changed out the head gaskets and put on rebuilt heads. Other than a bit of oil consumption (even though it never used any before the heads....), the truck was running good. Beginning of winter, I noticed when I got the truck out on the highway, it would ping under load. Now that the weather has gotten warmer, it will always ping under load. It sounds pretty bad....

I've tried running injector cleaner and 93 Octane. There might have been a little bit of difference with 93 Octane, but it was minimal improvement.

Any ideas on what this could be? Should I try some Seafoam?

I have somewhat of the same problem. It isnt near as bad with the new coil pack though. Only really does it under hard acceleration. I did Seafoam and it made it run better but didnt help with the ping. Hopefully someone will chime in with more of an answer.

I would first see if any lean codes are stored in the PCM.
Check for any vacuum leaks that would cause it to run lean.Especially where the intake manifold meets the heads.
Flush the cooling system and replace the thermostat to 180 degree.
Replace the o2 sensors . You may have original ones that are running out of range.
Check/adjust the Throttle Position Sensor.

there is a TSB for pinging on OHV 4.0 motors, go to your Ford dealer, order PM-3 carburetor cleaner, use it like seafoam. use it 3 times in a row and then change the oil and it will be cured

SERVICE PROCEDURE

Use Motorcraft Carburetor Tune-up Cleaner PM-3.
Carbon removal:
Disconnect canister purge line from throttle body.
Attach a vacuum line to the canister purge port.
At hot engine idle, allow the engine to ingest 1/2 to 2/3 of a can of Motorcraft Carburetor Tune-up Cleaner. Use caution not to ingest too quickly due to potential hydro-lock issues.
Shut engine off and allow it to soak for one hour.
Start engine, allow engine to ingest the remainder of the Motorcraft Carburetor Tune-up Cleaner.
Remove vacuum line and re-install canister purge line.
Road test vehicle at 3500 RPM for 2-3 miles.
Repeat above procedure two times for a total of three times.
Change oil and filter.
Review the customers' driving habits. The recommended drive cycle should include daily periods of engine operation above 3,000 RPM, such as a brisk acceleration from a stop position. This will break/burn the carbon off the piston head.
Use regular unleaded fuel, 87 Octane. Mid-grade and Premium fuels may increase the probability of carbon buildup, leading to a knock noise.

when i do this ^^ i dont use 3 whole bottles like it tells you to, i add 5 ounces and let it sit for 15 minutes, run it at 2500-3000 rpm and repeat

If those recommendations don't work, clean your MAF. My friend's '94 Ranger w/4.0L OHV was doing the same thing. None of the additives cured it. He has 240K mi. on his engine.

I removed the sensor from the MAF (you will need a tamper-resistant torx driver) and the front of the sensor wires were dirty which was fooling the ECM. We cleaned it with carb cleaner and compressed air (I did not physically touch the sensor wires) till the brown film was gone and presto! It used to ping on 92 octane and now he's back to 87 with no pinging. My friend is ecstatic. Maybe that will work for you also, good luck.