NorCalVP

This problem is on my 84 Tercel Wagon, not my 4Runner, but I figured i'd ask here to see if anyone has any ideas.

My problem is when i am driving between 65-70MPH, I hear a sound that sounds like pinging, but it isn't pinging. This noise only happens under very specific circumstances. I must be doing between 65-70MPH, on a flat level road, I cannot coast, or put the engine under load. I have to give the engine just enough gas to maintain speed. Once i do this i hear a ratteling from the engine compartment. As soon as i give it a little more or less gas the noise goes away. it's starting to drive me nuts, and i can't just turn up the radio. I drive this car 100 miles per day and don't want to get stranded.


The noise sounds just like the HGLR Ping from a supercharged truck.
Steve

SloPoke

Streatched timing chain, worn timing chain guides??? Your probably hearing the chain slap the housing.

NorCalVP

I thought of that, but this has a timing belt... (I changed it about a year ago) Just a little more background info.

it's a 1.5L carbed 3A-C engine with a 5 speed tranny. it's got 140K on the clock (original miles)

Steve

arkieoscar

It probably is pinging. Sometimes the mixture/timing is only right for pre-ignition under certain conditions. I can fool the knock sensor in my 22re motor with a combination of load and rpm that will make it ping at 2500 rpm. It stops with more throttle. You may want to try a seafoam treatment to clean our some carbon and see if that changes anything.

NorCalVP

I'll give that a try to see if it helps, I'll post back with the results.

Steve

alltrac165

Another possibility is slight rod knock. That usually shows up under light load conditions, not accelleration or decelleration. Slightly deeper sound than pinging though...

Willcipher

Yet another possibility, the 3A and 4A distributor advance mechanism can freeze; causing the shaft to hang in one position. Remove the distributor cap and test the advance using a hand held vaccuum pump. If the nothing moves, it needs to be rebuilt or replaced. This would cause spark knock under certain conditions.