Firstly, low compression can be caused by a number of different issues resulting in engine misfires.
Secondly, let’s say you have ruled out ignition and fuel delivery, as the cause of the engine misfire.
Consequently, that leaves low compression as the underlying cause of the engine misfire. However, there are many reasons, why low compression might exist in your engine.
Sometimes, there will be low compression, in just one cylinder. And, other times there will be low compression, in all cylinders. You just have to understand the main possible causes and then, fix or replace whatever is damaged. Now we are looking for mechanical engine misfires.
Consequently, one of the best ways to prevent engine misfires from occurring, is to perform proper car maintenance.
When You Have An Engine Misfire, Usually The First Thing To Happen Is, A (CEL) And (DTC)s Spring Up
A flashing (CEL) and a P0300 to P0312 (DTC) is a surefire indication, that one or more cylinders are misfiring. Occasional misfires may pass unnoticed, but a steady misfire is hard to miss. The engine usually feels rough, lacks power and uses more fuel than usual. Sometimes a misfire may feel like a vibration. Above all, a misfire also will cause a huge increase, in hydrocarbon (HC) emissions. And, that can cause a vehicle, to fail an emissions test.
Misfires that turn on the Check Engine Light (CEL) and log a cylinder-specific fault code, are the easiest to diagnose. The OBD-II system will identify the cylinder(s) that are not contributing to their normal dose of power. As a result, setting a code, that corresponds to the firing order. So, a P0303 code, for example, would tell you that the No. 3 cylinder is misfiring. To figure which cylinder is No. 3, refer to a diagram of the engine’s firing order.
This Kind Of Failure Is Easy To Check, Using A Compression Tester
So, If No Compression Is Present, In Any One Or More Cylinders, It Means A Mechanical Malfunction Has Occurred.
Engine Mechanical Testing, is another great way to pin point problems.
Consequently, misfires that turn on the check engine light and log a cylinder-specific fault code, are the easiest to diagnose. The OBD-II system will identify the cylinder(s), that are not contributing to their normal dose of power and set a code.
Causes Of, Low Compression, In One Cylinder:
Carbon Deposits On Intake Valves/Valve Seats
So, carbon build-up can hamper the performance of any engine. Don’t let this build-up result in, misfires causing check engine lights, loss of power, or loss of fuel economy.
Broken Valve Spring
So, if you’re currently having misfire, compression loss, or strange ticking or tapping noises, you may be in trouble. Broken valve springs can cause, obvious performance and efficiency issues. When a spring breaks, it may collapse just enough, to allow the valve to drop into the cylinder. And, in an interference engine, the piston may strike the valve. In addition, the valve stem locks or keepers may release the valve and allow it to drop into the cylinder. Resulting in severe damage to the piston, cylinder head, and other nearby parts.
Bent Push Rod
A bent pushrod can cause several symptoms in an overhead valve engine. Including poor engine performance, reduced fuel economy, rough idling, misfiring, increased emissions, and a failed compression test. The pushrod is an important part of the overhead valve engine. Push rods are used in (OHV) engines, because they are simple and reliable. Finally, the pushrod actuates the rocker arm, which in turn opens and closes the valves.
Dropped Valve Seat
Usually dropped valve seats, is a coolant system issue. For some reason the engine, has experienced extreme heat. Aluminum and steel expand at different temperature rates. So, the aluminum cylinder head over expands and then, the steel valve seat press in fit is lost.
Other Issues May Include:
- Cracked Cylinder Wall
- Gasket Issues
- Holes in Piston
- Damaged Timing Belt
- Valve Problems
- Worn Pistons or Piston Rings
A leak-down test or cranking compression test, can be used to see if the cylinder, is holding or pumping up normal pressure. As a rule, most engines should have, 140 to 160 lbs. of cranking compression, with no more than 10% difference, between any of the cylinders.
Causes Of, Low Compression, In All Cylinders:
Broken Camshaft
Broken Timing Belt or Chain
Fuel Washed Cylinders
There is a condition that adds to many failures of rebuilt or re-rung engines, generally referred to as “fuel wash”. It is caused by engine flooding at initial startup or in early operation, of a newly rebuilt engine. This phenomenon can cause very serious damage, to the cylinder bores, pistons, and piston rings. And, can result in misfires.
Blown Head Gasket
Other Issues May Include:
- Worn Piston Rings
- Bad Intake or Exhaust Valves
- Flat Camshaft Lobes
- Broken Piston Rings
Fouled Spark Plugs From Carbon And Oil Deposits
So, if you have any of the above causes, the cylinder head will have to be removed. Another reason for removing the cylinder head, is if you find spark plugs that are, heavily fouled with oily deposits. Oil leaking past worn valve guides or seals, is usually the culprit.
Installing new spark plugs will cure the symptom, but not the cause. Consequently, the permanent fix, is to replace the valve guides and install new, valve guide seals. However, not the fix, for low compression.
A spark plug that shows heavy whitish to brown deposits, may be a coolant leak. And, may be either past the head gasket or through a crack, in the combustion chamber. This type of problem, will only get worse and may soon lead to even greater problems.
Also, a cylinder will not fire normally, if the valves are not opening and closing properly, due to a weak or broken valve spring or a rounded off cam lobe.
Conclusion
So, when compression gets below 90 pounds, the cylinder could misfire. You may need to do some, mechanical testing.
TIP: You can also do, a A running (dynamic) compression test.
Consequently, if you find that there’s low compression, you need to check all possible areas, where the problem may be. Including, the gasket, valves, pistons, and cylinder. As a result, any type of damage in these parts, can add to your problem.
Thank You !
