Questions and Answers

Chevy Scottsdale Pinging Problem Q. Vince, I have a 1981 Chevy Scottsdale Pickup C10 with a 5.0 liter engine, automatic transmission, A/C, carbureted and 88,000 miles on it. It has been pinging for a number of years. The pinging does not occur during starting on during heavy acceleration. It seems to occur at partial throttle. If I press down hard on the accelerator pedal, the pinging goes away. If I let up on the throttle, the pinging goes away.

My first thought was the EGR valve. Is the EGR Valve located on the exhaust manifold? I found what looks like a valve on the exhaust manifold. I checked the valve and was able to open it by hand. There is vacuum at the module that appears to operate this valve. The valve itself seems to move up and down freely. How do I test this EGR valve? And did I locate the EGR valve? Would it be worth replacing this EGR valve to see if this is the root cause of the problem?

My second thought was timing. The timing was set at 8° BTDC. I change the timing to 10° BTDC. The vacuum advance seems to be working properly.

My third thought was carbon build up. I put Seafoam Cleaner through the carburetor until it stalled and let it set for 5 minutes before firing it back up. I did this three times. Is there a better method to clean carbon from the pistons and cylinder heads without pulling the heads? I hesitate to believe that the problem is carbon build up, as I drove the vehicle from Chicago to Mountain Home Arkansas on the open roads about 6 months ago. Would that not have cleared any carbon build up? It did ping during the ride down.

I then added premium fuel. The pinging seemed to stop, but as I continued to drive it, the pinging could be still heard although not as loud as before. I probably should not have done the timing, carbon cleaning, and adding premium fuel all at once.

I also read an article about an ESC System being used on the 1981 Chevy Pickup. They seemed to have used a higher compression ratio, 9.2:1. Can I assume I do not have this higher compression ratio engine, as they indicated that this system had a four barrel carburetor and my engine has a two barrel carburetor. Do you know how I could identify the “ESC” System or was the ESC System only on the 5.7 liter engine? Mine is a 5.0 liter.

Could it be carburetion, perhaps running lean during partial throttle?

Any direction would be greatly appreciated. My father was the original owner, it came to me upon his death. I will never part with it, it is in good shape. Excellent paint, solid rust free body, sprayed in bed liner, everything stock except the steering wheel and a slider rear cab window. I plan on passing it to one of my children, or grandchildren.

Best regards,
Gary

A. It sounds like an EGR problem. The valve you are describing is not the EGR valve. That valve closes off that side of exhaust to get the fuel to evaporate faster in cold weather. The EGR should be just to the rear of the carburetor on the passenger side of the intake manifold.

I'm not sure if there is a solenoid between the vacuum source or not. It could have a temperature switch threaded into the intake manifold near the thermostat. When the temperature gets up the switch opens and allows vacuum to pass to the EGR. You need to check the switch and the EGR. My bet would be the EGR diaphragm is ruptured or the passageway under it is clogged. Let me know!