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© 200438 3-3 System inspection with DAVIE XD UPEC DAVIE XD diagnostics manual 2 3.3 SPEED VARIATION CONTROL TEST One of the controls of the engine management system is the uniform operation of the engine via the speed variation control (this speed variation is recorded via the crankshaft sensor). Too large a variation in speed is prevented by correcting the quantity of injected fuel per cylinder. Due to a fault in the fuel system (bad injector, fuel leakage etc.) the fuel correction applied to a cylinder may have increased to such an extent that it falls outside the permitted specification. Note: Bear in mind the fact that a mechanical defect in a cylinder (compression loss) may affect the fuel correction for another cylinder that falls outside the permitted specification. Here the relation is as follows: In the "speed variation control" test the fuel correction of each cylinder is determined during a trip cycle (a trip cycle where a high engine load is required for a long period), on the basis of the total fuel consumption. The "speed variation control test" in DAVIE is one of the diagnostic tools that can be applied in case of complaints about fuel consumption and reduced engine power. Other tests are the acceleration test and plotting a boost pressure curve; in principle these have to be carried out before the "speed variation control test" is carried out. in case of compression loss of cylinder: 1 5 3 6 2 4 a positive fuel correction on cylinder: 3 6 2 4 1 5 |