Diagnostics Doctor

I have a burble at idle in the exhaust and a popping and banging noise when letting off the accelerator of my 2005 Ford Streetka with the 1.6 Endura E engine. The car does not have a rough idle, no hesitation on acceleration or misfires and, according to my Foxwell NT301, there are no fault codes.

I have replaced the air filter, fuel filter, plugs, coil (I changed the coil leads at same time), engine temperature sensor and both Lambda sensors. I also replaced a fuel injector that was recording lower than others. I checked for air leaks by spraying carb cleaner and listening for changes in engine note and have cleaned the air intake carb. I also had a look at the ECU because I read about connections getting rusty, but can see no evidence of this and the pop rivet is still in place showing it has not been disturbed.

I have access to live data on my Foxwell NT301, but this means nothing as I have no stats to compare other than that it idles at 897rpm. When warm and no accelerator applied it can have a lumpy idle for a few seconds or struggle to catch on starting. When I bought the car, it did have a performance back box which I removed, thinking it would solve the popping and banging. I am now wondering whether my ECU had been programmed to use this, but how would I tell? I have checked the exhaust for leaks and it does not look like a performance system.

I have also noticed it gets very hot quickly and the fan cuts in and out regularly even on cool days, but I have changed the thermostat and have no leaks on the coolant side, so maybe this is a characteristic of the engine. I haven’t monitored the mpg, but I’m getting about 200 miles to the tank driving locally. I intended to try and clean the air flow monitor and idle control valve behind the inlet manifold, but I am not convinced this would resolve things. Colin Chadwick

The popping or burbling from the exhaust may be caused by an excess of unburned fuel entering the exhaust and being ignited on exit. The ECU may have been remapped to alter the ignition, which might account for the burbling and for the running temperature being higher than expected. It is difficult to check if an ECU has been remapped – some companies may leave a sticker on the ECU, but many don’t. The only way to be sure would be to take the vehicle to either a remapping company or a main dealer to get the ECU checked. It’s also possible a modified camshaft has been fitted, altering the valve timing.

Before checking about any tuning modifications, I would perform a cylinder compression check to ensure a burnt valve is not the source of the burbling, although if this was the case I would have expected a misfire to be present.