Mechanical Engine Misfires – What Are They – How To Find Them

Mechanical Engine Misfires - What Are They - How To Find Them
Mechanical Engine Misfires - What Are They - How To Find Them

Mechanical engine misfires, will not go away by themselves, and will only get worse over time.

So, mechanical engine misfires, can be serious enough to cause, noticeable vibrations or even engine backfires.

Unlike air to fuel balance misfires, these misfires will become more intense, as your engine gains speed.

As a result, Mechanical Engine Misfires, can cause expensive engine damage. When misfires occur, performance suffers along with fuel economy, emissions and idle quality. Generally, this type of misfire, has more of a “thumping” feel to it.

Broken Valve Spring Causing, Mechanical Engine Misfires
Broken Valve Spring

So, it is usually noticeable, regardless of engine speed. In fact, it may even intensify, as the engine speed increases. Most of the time, these types of repairs, are more costly and take longer to fix. At this point you will need to do, some engine mechanical testing.

There Are Many Different Reasons, For Mechanical Engine Misfires

Some Include:

  • Worn cylinder walls
  • Worn piston rings
  • A leaking head gasket
  • Damaged or broken rocker arms
  • Damaged valves or pistons
  • Leaking intake manifold gaskets
  • Bent or dislodged push rods
  • Worn camshaft lobes
  • Damaged fuel injectors
  • Worn or slipped cambelt/timing belt

Different Ways To Find, Mechanical Engine Misfires

Using A Vacuum Gauge

One good fast trick I like to use is, checking engine vacuum, with a hand held vacuum gauge. Most engines pull in upwards of, about 19 or 20 inches of vacuum nice and steady at idle.

Using A Vacuum Gauge, To Test The Condition Of Your Engine
Using A Vacuum Gauge, To Test The Condition Of Your Engine

If your engine has a misfire, due to a mechanical issue, the needle on the vacuum gauge, will bounce around. This could indicate, a mechanical failure, with the engine itself that will need to be fixed.

Using A Compression Tester

So, low compression is usually the most common cause. A simple compression test, will be able to verify, if a certain cylinder is low on compression. A compression test can tell you that your engine, isn’t developing sufficient compression.

Using A Compression Tester
Using A Compression Tester

As a result, causing a loss in power and in extreme cases, can keep the engine from running. If you find that a cylinder has low compression, the next thing you need to know is why.

Using A Cylinder Leak Down Tester, To Find Mechanical Engine Misfires

Doing a cylinder leak down test, will tell you how much air is leaking, and where it is leaking from.

Using A Cylinder Leak Down Tester
Using A Cylinder Leak Down Tester

Consequently, it could be the intake valve, exhaust valve, piston rings, cylinder head, or even the cylinder head gasket.

Using A Fuel System Cleaner

Carbon is going to form, but you can limit its creation, by using fuel that contains, a fuel system cleaner.

Carbon Buildup On The Back Of Valves, Causing Mechanical Engine Misfires
Carbon Buildup On The Back Of Valves

I would also limit idling time and cold starts. Also, use high quality oil, and keep the carburetor or fuel injection system tuned properly.


So, mechanical engine misfires, can also be a little more complicated. Also, check the vacuum lines connected to the intake manifold. Look for cracks and replace lines, if you find any problems.

Also, check the condition, of the intake manifold gaskets, especially around the throttle body. Take a timing light under the hood, to make sure the timing belt or chain, has not slipped or jumped. Finally, pop off a valve cover, and have a close look at the valve train for any obvious damage.