Jim Grant's Tech Tips
Mazda B2600 4x4, Engine Ping
Q: I have a '91 Mazda B2600i 4x4 P.U. that pings
very hard when the outside temperature is above 60 degrees. It doesn't
ping at all during the cold winter months. All the usual tune-up specifications
have been checked and double checked. I have also tried high octane fuel.
Cylinder compression and fuel pressure are normal. Vacuum is 14",
which I have been told is low. No leaks could be found to account for
low vacuum. This problem renders this truck virtually undriveable in the
have to fix the air pump first. What air pump you ask? The engine in a
vehicle is basically an air pump. To operate correctly an engine must
have the ability to breathe, draw in, compress, and then exhaust air.
A simple check of an engine's ability to breathe is done with a vacuum
gauge. Measuring the vacuum created by an engine allows us to determine
if the engine has the ability to breathe correctly. At idle, a good running
engine will produce approximately 18" of vacuum. 14" vacuum
is, without question, unacceptable, clearly there's problems. Low vacuum
reading can be caused by failed gaskets, vacuum hoses or defective emission
controls. Also, be aware that engine mechanical problems will also create
low vacuum readings. A good compression reading doesn't mean the engine
is right. Have your technician focus on the low vacuum problem. It could
very well provide the answer to the engine ping.