We do promote ourselves as specialising in sNorting out Piggy cars to the Motor Trade as well as to the General Public, this works out OK mostly as we do get some faults taking a bit more time than others, but they usually balance themselves out. Not this one though, it was a swine. A Volvo 440 running rough with a suspect ECU (Electronic Control Unit) fault. The car came from a garage with a good reputation for fixing this sort of fault so we knew it wasn't going to be easy - this diagnosis at least was correct. First off a check of all the basic engine parameters such as compressions, valve timing etc. before diving into checking the engine management system. The basic settings for the engine panned out OK, and so onto the engine management system. Apart from a few minor settings being incorrect and some wiring that needed tidying up all OK here as well. We would have been surprised if the fault had been uncovered during these checks as the previous garage should have done the same checks. However we've been led down the garden path, into the pigsty, and been squashed by Piggy cars rolling over before by assuming things to be right instead of spending the time to double check.

 Anyway at this stage we suspected the ECU as well, but these units are expensive so we arrange a test for the ECU on a dedicated ECU tester. It fails the test miserably. The ECU concerned is an unusual specification and no one has one at a reasonable price. The Volvo dealer wants loads of money so we get a cheaper exchange unit and this fixed the fault. For more info on ECU testing click here.

VOLVOS CAN BE AS TROUBLESOME AS THE NEXT CAR WHEN IT COMES TO SORTING OUT FAULTS AND THE VOLVO WE HAD IN FOR SORTING OUT A PROBLEM WITH HESITATING NOW AND AGAIN WAS NO EXCEPTION. AS WITH MOST INTERMITTENT FAULTS ALL CHECKED OUT OK ON ROUTINE TUNING FAULT CHECKS BUT THE FAULT STILL REMAINED. IT WAS FOUND TO BE CAUSED IN THE END BY THE MANAGEMENT SYSTEMARGUING WITH ITSELF, BUT TO FIND THIS FAULT TOOK  A BIT MORE TIME THAN JUST AN ENGINE TUNE. TUNING SORTED OUT POOR GENERAL RUNNING PROBLEMS ON THE CAR, BUT DID NOT UNCOVER ANYTHING THAT COULD CAUSE THIS SORT OF FAULT. AFTER TUNING WE INSTALLED MONITORING EQUIPMENT BETWEEN THE ENGINE MANAGEMENT ECU (ELECTRONIC CONTROL UNIT) AND THE CAR'S WIRING PLUS A FUEL PRESSURE MONITORING INTO THE FUEL INJECTOR SUPPLY AND WENT DRIVE ABOUT FOR 10 MILES UNTIL THE FAULT OCCURRED. WE FOUND THAT THE OUTPUT FROM THE OXYGEN SENSOR IN THE EXHAUST WAS POOR - THIS TELLS THE ECU HOW MUCH OXYGEN IS IN THE EXHAUST. THE ECU THEN USES THIS INFORMATION TO ADJUST THE FUELLING, WHICH THE OXYGEN SENSOR THEN DETECTS THIS CHANGE AND RE-ADJUSTS THE FUELLING AGAIN. UNFORTUNATELY BETWEEN THEM THE TWO TWO SOMETIMES COULDN'T AGREE ON WHAT TO DO AND WHEN THEY SAT THERE ARGUING WITH EACH OTHER OVER WHAT EACH THOUGHT THE FUELLING SHOULD BE THE ENGINE HESITATED. A NEW OXYGEN SENSOR WAS FITTED, ANOTHER 10 MILE ROADTEST TO BE SURE THAT THE PROBLEM WAS CURED, AND A VOLVO BACK ON THE ROAD AT HARMONY WITH ITSELF ONCE MORE.

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 here.