I am a one owner of a 1996 fullsize bronco, 154,000 miles. Recently it has developed a pinging/knocking noise when I accelarate while cruising at 70 miles per hour or when I am climbing a step hill. I have recently had the rotor, distributor cap, spark plugs, ignition wires, fuel filter, and air filter replaced. The fuel system was cleaned and the fuel injectors serviced. Also, the differential was repaired/overhauled, and the transfer case serviced. Also, the oil is changed at regular intervals of 3-4,000 miles. Nevertheless, the pinging continues. I have always used 86 octane brand from the same gas station. When the pinging started, I switched brands, staying with the 86 octane, but the noise continued. So, what's up with the kocking? As the truck becomes older and more worn does it require a higher octane gasoline?

One other thing, why does the coolant resevoir always become empty after a day or two? There are no visible leaks, I put coolant/water in the radiator every two weeks, the mechanic pressure tested the system and found no leaks.

 

Your symptoms sound like an internal leak due to a bad head gasket, cracked block, or cracked head. The coolant is being burned by combustion and out the tailpipe. If it is very bad you will see a white, steam-like smoke coming out of the tailpipe - but they don't always do that if it's not so bad. This would also explain the pinging. If the motor is burning coolant as well as fuel, then the octane is lowered. And 86 octane is too low for your Bronco anyway. 87 is the minimum. I know that it costs more, but then so does a motor.

The mechanic should have investigated further once he learned that you're losing about 1/2 gallon every two days, and he found no leaks.

A shop can run a test on your car to determine if there is an internal leak. It is different from the pressure leak test. There is an adapter that clamps onto the radiator cap, and then the engine is run. The adapter has a clear sight glass, and if it detects coolant in the combustion chambers it will turn a different color inside the glass. I would suggest that as your next step.

 

Check spark plugs if your burning Antifreeze you will see or smell it on the plugs.
Did the coolent start dissaparing when the motor started to knock ?
Could be two different problems.
Could be a timing chain at 150k wouldnt surprise me.

 

Thanks for the help. I'll follow up on your suggestion.

VA

 

The coolant problem has been around for about a year. The pinging started a couple of months ago. I'll follow up and check those spark plugs.

Thanks,

VA

 

lol I had the same problem on my 98' f-150, 4.2. Water acted like a freakin david copperfiled act, just hmm where the hell's it going. Although in TX its not that bad, I really noticed it when I was in CO cause the bottle would be empty like every 4 days. Opposed to TX maybe once or twice a month I have to fill it.

 

Sometimes you can drive them like this indefietly, as long as you keep adding coolant. It may be getting worse though, hence the pinging I can't tell you for that that's the problem, but I would start there.

When my Bronco cracked an exhaust manifold, it pinged for a while afterwards - probably upset the computer somehow.

 

i had the pinging problem, just switched to midgrade and put ina bottle of slick 50..u might also wanna try sea foam, you could have carbon build up thats causeing detonation.