Saab 900 that suffered from slight hesitation and misfiring once it had been running for a while.

    The car had already been serviced and tuned elsewhere, and all of the parts that could commonly cause such a problem had been replaced - Distributor cap, Ht leads, Rotor Arm, Spark plugs, contact breaker set, and condenser - yet the problem still persisted. Checking all the tuning settings revealed nothing amiss, and neither did stripping down the carburettors to inspect the condition of the needles, jets, and float levels. In the end the answer was found when removing the spark plugs for the umpteeth time to recheck something else - one of the new HT leads showed signs of tracking ( Leakage away of current that should go the spark plug.) This sort of fault is something that goes undetected by Tuning equipment since it can't differentiate between sparking at the spark plug and sparking between the spark plug boot and the cylinder head. In the Saab's case it was impossible to see either because the spark plugs are buried out of sight in the engine. A new HT lead and a final test drive for half an hour confirmed the fault was cured.

        The advance of semi-conductor electronics into the ignition system of All cars today has lead to far greater life and reliability of components but it has it's downside as well - like if they do need renewal they cost a lotmore than a set of plugs, and unless they fail completely it can be difficult to diagnose intermittently occurring faults. The Saab 900 we had in recently had an intermittently failing Ignition ECU that would only misfire after 1 mile from a cold start - and then wouldn't necessarily every time. After and before that 1 mile mark, and for the rest of the day it was fine. A new ECU unit cured it completely. For more info on ECU testing click on ECU.

Hessitation, power loss. This type of problem can be one of the most time consuming faults to find because the problem often is only slight and the fault only shows up when the car is being driven under load.

One of the most commen causes of this is fouled or sticking injectors that can be reconditioned at less than tenth the price of a new set. For more information on injector servicing click on injector.