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You are driving down the street and then have a feeling you instantly recognize, but just as quickly overlook.  The engine stumbles for a moment then regains its pace.  Just as soon as the engine settles down, the misfire reappears, and you’re stuck with the sinking feeling that accompanies all automotive problems, “Oh No!  I don’t have the time or the capital to spend on a car patch up!”  

There are many items that can cause the motor to miss or run roughly. The primary culprits are basic: spark or fuel.  These mostly manifest in spark plugs, plug wires, the coil(s), or the fuel-delivery system.   To determine which of these is causing your trouble you should start your examination with an under hood checkup.

Damaged ignition wires, blocked injectors, or motor mechanical malfunctions are all possible.  Begin your investigation with an under the hood examination. Look for mangled or cracked vacuum hoses. Examine the spark plug wires for chafing or signs of arching to the motor block. If the vehicle is due for routine service, this should be done before to spending too much time on an identification of problem. A complete tune-up including spark plugs, spark plug wires, distributor cap and rotor (if so equipped), fuel filter, and air filter will go a long way in patching up the most common problems. If a misfire is still present after a complete tune-up is completed, then a diagnosis of motor mechanical problems may be necessary.

A vacuum test using a vacuum gauge should be done. An engine should draw at least 15 pounds of vacuum at idle when connected to a vacuum hose that is connected to the intake manifold. The vacuum should be smooth and not fluctuating. A severely fluctuating vacuum gauge is an indication that there is a valve train defect, such as a damaged valve or slipped timing belt. Retarded ignition timing can cause particularly low engine vacuum. A compression check should be done on the motor to determine if lower than prevalent compression is present in any cylinder.

Refer to a manufacturer’s specific service manual for compression specifications. As a general rule, the compression should be above 120 PSI and the lowest cylinder should be at least 80% of the highest cylinder. If the above tests do not indicate a failure, a diagnosis of the fuel and ignition system must be done.  There are other more unfortunate causes: computer or wiring problems, breakage in the rotating mass (pistons, rods, and crank bearings), valves and the heads can fail or distort.

Cooling stress might permit overheating, and any number of gaskets could have pushed. Most are rare and were most likely caused by your failure to attend to simpler problems in the ignition or injection.  

If you are unqualified to enact the tests requisite to recognize the prevailing maker of the misfire it is without doubt most desirable to check with a prominent car repair shop and have them check out your wheels.  

Guessing at the issue and throwing parts at it will only serve to run up your expense and possibly make it more difficult to determine the true cause of the problem with your car.  Save yourself time and cash by performing maintenance according to manufacturer’s recommendations and take it to your nearest Auto Service Experts repair facility for a free diagnostic whenever you have any truck performance problems.

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