Trouble with problem cars is that before we get to look at them they have often been looked at by everybody and his grandma before we get to sort them out, and of course they all know much more about cars than us. Then when the fault is found they stand back muttering "I knew it was that all along." And the diagnostic process is made more difficult because alongside of the existing fault there are sometimes fresh faults or false leads introduced during the attempted repair. So when the Astra came in to the workshops with a problem of intermittent cutting out at speed and a list of items as long as your arm replaced already we didn't rule out the areas that had replacement parts fitted previously - we've been caught out like that before. The car was an carburettor model fitted with a strange ignition system. This involves two ECU's (Electronic control units) together with a few sensors an Ignition coil and a distributor to make a spark to go to the spark plugs at the right time. To think that just a few years ago we had to rely on a set of points costing a pound or two that have now been replaced by this lot. Anyway our first job was to clean out the carburettor - cutting out faults are commonly caused by dirt in the carburettor. Drew a blank on this one though so out on roadtest with some datalogging equipment on board. When the fault eventually occurred it was found to be due to loss of sparks, but we then had to roadtest the car again to find which part of the ignition system was failing. Found the fault to be caused by a new ECU fitted previously - but the ECU was a 2nd hand unit with the same fault as the first. "I thought it was that all along," said the owner when he came to collect the car. For more info on ECU testing click here.

  The more you work with faults on cars the least knowledgeable you appear when a customer phones up with a problem on his car and asks what is the matter with it. He has probably had opinions on it from people like his next door neighbour, milkman, and invariably a local DIY person or local garage and possibly his dog, all of whom have told him most emphatically exactly what the cause is. But they all give diferent opinions. So when the customer phones me up and asks for my expert opinion on what I think and gets the reply "I don't know", he really isn't super impressed. However after I explain we don't know because any one fault could be caused by maybe 20 different reasons so if you ask 20 people you could get as many different replies we generally get the job. Intermittent non starting faults from a cold start are perhaps the worse to both diagnose and cure since once that you have cured the obvious reasons there may still be another lurking in the background that will re-appear later because this fault is an intermittent fault superimposed over the obvious one. The car in question was a Cavalier Injection with a history of bad intermittent cold starting and was towed in because it had finally refused to start. Normally we like them like this since as soon as the cause of the problem is solved the car starts. In this case we cured the obvious fault due to lack of enough sparks reaching the spark plugs, whereupon the car instantly fired straight up. A tune to sort out the rest of the engine and out the car went. We were surprised therefore when the owner still reported poor intermittent cold starting and so we had the car back left overnight to check it again. We installed monitoring equipment on the engine before attempting to start it the next morning, and found the fault to be due to a fuel injection relay that worked fine when once the engine had started, but was a a bit reluctant to kick in sometimes under the low battery voltage conditions of a cold start. A new relay cured this fault. The message of this story is that for the best general diagnosis to the exact cause of a fault on your car is to ask your dog - "Ruff" is the most accurate you can get without some detailed examination of the problem.

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.