Engine knocking noise

My 2005 Freelander Td4 Sport has developed a diesel knock under load that only occurs once it gets up to temperature.

It’s just gone through its MOT and the emissions were all fine. It was chipped some years ago but has been fine – the knocking only seems to have started since I put a bottle of ARCHOIL additive in the fuel tank.

I put a full bottle in with £30 worth of diesel and unbeknown to me, my partner had also put a bottle of Redex in the tank the day before. I asked her to pick up a bottle when she collected some parts for me, and she thought she’d put it in because that’s what I wanted.

Could this in some way enrich the fuel too much? I have now got just under a quarter tank. I’m trying to use it all before refilling it – or would you recommend putting in another £30 worth to weaken the additive. I know I can remove injectors

(try to remove!) and check the spray pattern of each one. My scanner isn’t showing any faults, so isn't pinpointing which injector could be at fault.

As usual, Steve, your advice is very much appreciated.

Steve Haywood

It is possible that using the two different fuel additives has increased the volatility of the fuel and this may be enough to cause the knocking you now have under load.

With only a quarter of a tank of fuel now in the vehicle I would be inclined to fill the tank, which should even out the acceptable level of additive to fuel.

Hopefully this will remedy the situation; but if the knocking continues, further measures may have to be considered.