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You are driving down the highway and then have a feeling 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 capital to spend on a van repair!”  

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

Inspect the spark plug wires for chafing or signs of arching to the engine block. If the automobile is due for routine service, this should be done prior to spending too much time on an investigation. 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 correcting the most familiar problems. If a misfire is still present after a complete tune-up is accomplished, then an examination of motor mechanical problems may be requisite. 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 sign that there is a valve train defect, such as a damaged valve or slipped timing belt. Retarded ignition timing can cause abnormally bad motor vacuum. A compression check should be completed on the engine to determine if lower than ordinary 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 executed.  There are other more dreadful 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 not able to enact the tests necessary to locate the prevailing cause of the misfire it is definitely best to get ahold of a high-principled automobile repair store and have them check out your vehicle.  

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 carrying out 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 automobile performance problems.


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