Hi Guys. I have an 88 cutlass supreme 307 and it has run fine since May; but now its pinging. I have to slow down for a turn on a country road and its a moderately steep upgrade and I am probably going 20-25 MPH and the engine is pinging. Not sure what to check. It has 38,000 miles and there is no check engine light on. Any help would be appreciated. Thanx Ed (old guy)

 

Did this suddenly start with a fuel fillup?

 

Eric. I changed the map sensor and tweaked the timing and its running fine now. There were other problems that I was ignoring and it all pointed to the map. I changed it first then reset the timing. All is ok now. Thanks for offering to help. Ed

 

The passages in the intake manifold for EGR get clogged. If the engine isn't breathing enough recirculated exhaust gas the combustion temperatures spike and you get pinging. The intake should be removed and the holes in the bottom of the plenum cleaned out. The EGR valve should be checked for proper operation or replaced.

 

^^^This.

The fuel map on the 307 is designed to take advantage of the EGR when it opens during part throttle. The primary side mixture is leaned out under those conditions. Any restriction in EGR flow or fault in the EGR valve or system causes part throttle pinging on these motors. This effect is compounded by ethanol-laced fuel, which is inherently leaner than pure gasoline. Couple that with colder, denser air during winter driving and you have the perfect storm.