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You are driving down the avenue and then feel a sensation you instantly recognize, but just as quickly brush off.  The motor 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 dough to spend on a jalopy recondition!”  

There are many items that can cause the motor to miss or run roughly. The central culprits are basic: spark or fuel.  These commonly manifest in spark plugs, plug wires, the coil(s), or the fuel-delivery system.   To determine which of these is instigating your quandary you should start your diagnosis with an under hood check. Flawed ignition wires, restricted injectors, or motor mechanical malfunctions are all possible.  Launch your analysis with an under the hood investigation. Look for broken or cracked vacuum hoses.

Check out the spark plug wires for chafing or signs of arching to the engine block. If the vehicle is due for routine service, this should be done prior to spending too much time on a diagnosis. 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 prevalent problems.

If a misfire is still present after a complete tune-up is executed, then an analysis of motor mechanical problems may be imperative. A vacuum test using a vacuum gauge should be completed. 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 sign that there is a valve train failure, such as a not working valve or slipped timing belt. Retarded ignition timing can cause exceptionally bad motor vacuum. A compression check should be executed on the motor to determine if lower than usual 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, an examination of the fuel and ignition system must be done.  There are other more terrible causes: computer or wiring problems, deterioration in the rotating mass (pistons, rods, and crank bearings), valves and the heads can fail or distort. Cooling difficulty might permit overheating, and any number of gaskets could have pushed. Most are rare and were probably caused by your failure to take care of simpler problems in the ignition or injection.  

If you are unqualified to perform the tests necessary to home in on the prevailing incitement of the misfire it is undeniably most desirable to approach a fair vehicle repair shop and have them check out your wheels.  Guessing at the complication 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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