Thread: Engine 'sneeze', what causes it?

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Why does an otherwise properly running engine to 'sneeze' every now and then when cold starting?
Did the engine just diesel and run backwards? is the fuel burning so slow that it is kinda retarded? What do you guys think is going on?
Thanks, oj

What's your static timing? If you're too far advanced it might not have enough inertia to overcome the cylinder pressure, especially if it's maybe cranking a little slow?

This is speaking in general terms, not just a particular engine. But the 'cranking a little slow' is probably dead on, i hadn't thought about that. Good observation!

A leaky needle and seat that allows gas into a hot chamber after you shut off the ignition will diesel until the gas is gone.

Never heard that term before, but I sure have see it happen... engine sneeze. That's the perfect description of that event... nice!

Originally Posted by ojh

Why does an engine 'sneeze' every now and then? Thanks, oj

HMmmmm... hay fever??


(sorry, couldn't help myself!?!?!? )

Originally Posted by 34_40

HMmmmm... hay fever??


(sorry, couldn't help myself!?!?!? )

Jeez, you just ain't right!

Usually a combination of slow cranking and too much timing. Easily cured with an MSD box that automatically pulls the timing back on start up, or a toggle switch to shut off power to the ignition. With the ignition power switch off, crank the engine over with the start switch, when it's spinning good, turn on the ignition.... Old timey fix from back in the days of high compression engines and trying to get them to crank when they're still warm and it's time to get up to the line for the next round........

Originally Posted by Dave Severson

Usually a combination of slow cranking and too much timing. Easily cured with an MSD box that automatically pulls the timing back on start up, or a toggle switch to shut off power to the ignition. With the ignition power switch off, crank the engine over with the start switch, when it's spinning good, turn on the ignition.... Old timey fix from back in the days of high compression engines and trying to get them to crank when they're still warm and it's time to get up to the line for the next round........

Great approach, but be sure that your starter's not "tired", or your battery voltage is not a tad low due to age? Check your system voltage at the terminals before you crank, and while cranking. Should be up in the 12.5 range static, and not drop below ~10 cranking. I changed out my two year old starter a couple of weeks back, and was amazed how much faster my engine cranked.

Originally Posted by ojh

Jeez, you just ain't right!

That's been said before!

NAHHhhhh.. just in a silly mood, Gotta have a sense of humor sometimes, right?

Sorry to stress yours!