Renault Megane Coupé, 2.0 16v IDE

Date: 06/11/2009

The customer bought the car to our attention after a breakdown late one night on their way home from work. The week prior to the actual breakdown the car had steadily been misbehaving more and more frequently which started out as an occasional but minor misfire when lifting off the throttle. Eventually, a few days later, the minor misfire grew into a major issue on the motorway leaving the owner stranded at the roadside as the vehicle refused to restart. Doing what any normal person would do the owner called their breakdown company who sent out a patrol and attempted to diagnose the problem at the roadside… apparently the issue was the transmission temperature sensor. They attempted to restart the car but it immediately cut-out after a few seconds and so towed it from the roadside back home.

The car had obviously had time to settle over night and all appeared to be fine as the car started normally. Diagnostic tools were connected and general ignition and engine sensor components were checked which revealed nothing looking or sounding out of the ordinary. The car performed flawlessly on the initial road test until we returned and left the car to idle where a slight audible misfire was noted so we attempted to drive the vehicle again with very little success - By now it was seriously misfiring, eventually cutting out and failed to restart. The diagnostic equipment was hooked up once again to find no obvious errors only this time when the vehicles fuel injection became the subject of investigation problems were instantly apparent: The fuel rail pressure was being mis-reported to the ECU which on this Renault IDE engine is a serious issue as it is a “direct injection” unit relying heavily upon a precisely controlled fuel pressure levels in order to run the car in a similar way that modern common rail diesel engines do. The problem? The “Fuel Pressure Sensor” located in the fuel rail was sending unreliable readings once it got warm and so needed to be replaced!

A main dealer only replacement part was sourced from Renault UK (Part No. 7700-113205) and fitted before taking the vehicle out on a second test drive. The misfire issues had now ceased however after driving for a few miles the engine once again bought up the MIL warning light and finally cut out refusing to restart at the roadside for a few minutes – Great, like anyone I hate being broken down to! Back to the diagnostics and the live data screen to see what was happening. The actual fuel pressure in the rail was now stable so the new sensor was obviously doing its job but the fuel pressure was increasing to well over the systems operating levels which the ECU detected as a dangerous level so, to stop it increasing even further and potentially causing damage to expensive engine components such as the fuel rail, injectors or even causing a high pressure fuel explosion the engine was electronically governed and forced to shut off. Initial thoughts, a blockage of some sort so the vehicle was allowed to cool down whilst the fuel lines and filter system were inspected for damage or blockages… but nothing! After 30 minutes of playing with fuel lines and fitting a new filter the fuel rail pressure had dropped enough to safely remove the electronic fuel pressure regulator which was also found to be suffering from heat soak due to the high engine bay temperatures causing it to stick – there’s the blockage!

The sensor was dismantled, inspected and reasembled after being thoroughly cleaned (See Guide) and refitted to see if it rectified the problem. The vehicle immediately started and instantly seemed far happier but I noted the fuel rail pressure continuing to rise so the sensors internals were unfortunatly still suffering. I also found that gently tapping the sensors body with an object such as an extension bar seemed to help free the moving parts as the fuel pressure reading would suddenly drop before steadily starting to climb again… tapping it again would repeat the cycle and cause it to fall again. The solution: A new fuel pressure regulator was sourced, again only available from Renault UK (Part No. 7700-113483) but on a one day special order.

Day 2 – Return visit to fit parts:

After a trip to the local Renault dealership to collect the new fuel pressure regulator it was installed before the vehicle was  started and run to allow it to achieve normal operating temperature. Diagnostic equipment was again connected and all indications looked encouraging with stable readings displayed on screen. The vehicle was finally taken out on to the roads for its final, extensive test drive: 20 miles of mixed driving styles - motorway speeds, urban and even sat in lunchtime city traffic which saw the fuel pressure remain stable when it needed to and react as it should under load without a single sign of rough idle, misfiring or the engine cutting out. The vehicle was returned to the happy customer later that day in full working order after 2 days (Due to the parts required being special order items from  the factory in Dieppe, France).

Another job well done with another happy customer - not only for keeping them informed at all stages but for also taking the time to explain the faults to them.

Renault Megane Coupé, 2.0 16v IDE