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peacockandpurvey.com |
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[ECU testing] |
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Seaton Automotive Commercial & Car Leasing and Finance 
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Intermittent engine faults are the bane of all our lives in the garage trade. The customer comes in with a fault that occurs for perhaps a few seconds every few days and asks that you sort out his car while he waits for it. The customer has been programmed by the manufacturer to believe that all we have to do is to plug the car into a Star Wars type R2D2 machine and the cause will be instantly revealed. Volkswagen started this particular ball rolling with Tv advertising , presumably to allay consumer fears that high tech equipment was difficult to repair. We though have inherited the legacy and have to convince the customer that finding this fault is unlikely to be that easy, and that no cost can be given for finding it or repairing it. Main Dealers come under more attack than independents in this area as they are often the first port of call for the customer. By the time that us independents get the car the customer is discovering that the reality of this sort of problem is the garage versus Darth Vader. If the customer is still not convinced of the scale of the problem then I find that producing the wiring diagram for his car works well. No-one could make a living out of solving truly elusive intermittent faults, we find that the full cost of finding them cannot be charged out to the customer. The experience gained though enables a swings and roundabouts balance to be achieved with other easier faults. The first starting point for an intermittent fault is always to quiz the customer. This can save a lot of time. Does the fault happen with a hot engine, cold engine, in wet weather, hot weather, cold weather? With a full or empty petrol tank, at what engine temperature, after how long, how long for?. Does the engine cut completely or only partly, at what throttle opening, at what engine speed, at what road speed, after going over bumps? . Does the management light come on, any noises, any smells?. Even where it happens could be important (if external radio interference is a cause).Ask about any recent work done on the car in case the problem stems from this. First check with any car so equipped is the fault code reading system. Not because it is that brilliant at it’s job with some intermittent faults, but because it is so quick to do that makes the occasion that it gets it right first time all worthwhile. Next do a complete engine tune to be sure that the basics are right, and go around the wiring to all suspect components and their controllers wiggling to check for poor connections and wiring faults. Then the car needs to be rigged up with monitoring equipment ready for road testing. How much equipment is needed depends on the frequency of the fault, a fairly frequent fault, say once every 5 minutes, can easily be done using several area tests. Each area test narrows down the possible cause . First monitor petrol pressure at the fuel rail and ignition at the spark plugs. If neither fails then it looks like an injector area system fault. Then pick the now suspect area and put all measuring equipment at key points in that area. If this fails to identify the cause then the area will have to be split into sub areas for more road testing. Working in this manner though for faults happening only every day or so is going to take a long time, unfortunately the only way to reduce this is to get more sophisticated (For sophisticated read expensive) test gear to monitor more signals together. Before spending a lot of time on rarely occurring faults it makes economic sense to replace relatively cheap items on suspicion only, since their cost of replacement is dwarfed by the likely cost of finding them guilty. For instance some cars are prone to fuel pump relay problems, the cost of these is often about ½ hour in labour and so are best replaced on this principle. If you do have to go the whole hog in monitoring then you are going to need some serious test gear. For petrol pressure monitoring, a transducer in the petrol line is better than a gauge as often there are problems getting a petrol hose from under the bonnet to the car. Also the transducer can be connected to a multimeter with a min / max record function making it unnecessary to watch the pressure readings. For monitoring any electrical signals a breakout box is essential, it’s difficult enough finding the fault without creating more of your own with poor test equipment connection problems. For actuated components (injectors, idle air valves etc.) a mini breakout box at the actuator is best since otherwise a wiring system fault between Ecu and actuator could be missed, but for the same reason sensor wiring problems and Ecu operational live feeds and earths the breakout box need to be monitored at the management Ecu. Multimeter(s) with a max / min recording function are essential for monitoring live feeds and earths and for slow changing signals such as temperature senders. For faster changing signals or for picking up glitches more equipment is needed. Autodiagnos makes a diagnostic system for a large range of management systems that monitors the pins on an Ecu by use of a breakout box in parallel with the Ecu multi-plug. Any out of programmed value automatically generates a fault code. While the system is a more intelligent than fault code systems it also may not record as a fault something that is giving a wrong signal provided that the signal is within it’s normal operating range (For instance a water temperature sensor that goes through a period of giving a cold output when the engine is hot)
However the Autodiagnos system does allow a single suspect value to be recorded on a graphical display to detect this type of fault
. Later model cars can be connected to the Autodiagnos system by a serial link from the Ecu that can show even more information. A digital storage scope with a recording capability is essential for fast changing signals, the more channels the better. Bosch make a good 2 channel digital scope well suited for this purpose. To be in with a decent chance of catching your intermittent fault the first time that it occurs more than 2 channel monitoring is needed though. Top of the shop for this is a scope recorder. Yokogawa supply Car Manufacturers and Formula 1 race teams with theirs – this can monitor up to 16 channels at a time, and give print outs with an inbuilt printer . And another useful extra - may the force be with you. ext1] -- |
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