Engine diagnosis

Engine diagnosis overview and evaluating automotive engine problems. Text to follow and view a short video about cylinder damage and how to repair it at the bottom.

Once you run a compression test, cylinder leakage, vacuum, oil pressure and power balance tests a do it yourself auto mechanic is ready to evaluate the engine's overall condition.

As an example an engine with decent compression readings, but high cylinder leakage past the rings is a typical sign of a worn engine from high mileage. In addition an engine with high mileage may show these symptoms as well. Excessive blow by from the valve cover vent, lack of power, or engine smoking and reduced fuel economy.

Engine problems diagnosis

If this is the case you can try treating the engine with a combustion chamber cleaner, engine oil treatment, or performing an engine flush. This will only solve piston ring problems caused by carbon buildup in the piston ring lands.

If this fails to correct the problem you may be looking at a complete engine overhaul. It is worth trying these engine oil additives, but in most cases they are not effective. But the reviews on the Tufoil product on the right are amazing.

A cylinder that has poor compression but very little leakage indicates a possible valve train problem. In this instance, a valve might not be opening at the right time, might not be opening enough, or might not be opening at all.

You can verify this condition on automotive engines with push rod type designs by pulling the rocker cover and watching the valves operate while the engine is turned over manually or with a remote starter switch, while the ignition and fuel systems are disabled.

If one or more valves failed to move, either the lifters are collapsed or the cam lobes or worn. If all the cylinders have low compression with minimal leakage, the most likely cause is incorrect valve timing.

A timing belt or even a chain can slip and open the valves at the wrong time. This will give you a very low compression reading and extremely poor driveability in the form of rough running and lack of power.

More engine diagnosis results

If compression and leakage are both good, but the power balance test reveals weak cylinders, the cause of the engine problem is outside the combustion chamber.

The first thing to verify is that there are no ignition or fuel problems, which would be the most common.

But hard parts like broken valve train components, or Collapsed lifters can cause engine problems that show up on a balance test.

When performing engine diagnosis for weak cylinders a leaking intake manifold or excessive clearance in the valve guides can also cause imbalance.

Also note that if the valve guides are shot and you squirt some oil on them and then start the engine safely blue smoke will be seen from the exhaust system.

Blue smoke is a sign of engine oil being burnt, where as gray or white exhaust indicates either a fuel system problem or in the case of heavy white smoke possible coolant leaks into the combustion chamber.

I have details for you on how to perform each individual engine diagnosis procedure mentioned above. This next link takes you from engine diagnosis to automotive engine testing



If you would like to talk to a mechanic about your automobile engine problems you can do so on my page about car repair help



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If you plan on taking apart the engine on your own vehicle I highly recommend you get a manual for it. This next page has a video of the online factory car repair manuals I use.



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