Brown smoke at WOT

[nobananas]

Not a Volvo but a customers Fiat coupe 20v turbo that I have had the displeasure of changing the engine in !. Second hand engine supplied, the engines not great in my opinion and when driven seems to lack power. When booted hard in 1st it will go and the turbo spools but I noticed a trail of brown exhaust smoke left behind. This could just be rust in the exhaust as it's been stood for 4 months but is brown smoke also a sign of detonation/weak mixture ? This would explain lack of power in the higher gears. The previous engine died when it burnt out several valves and I'm wondering if the cause of this is still present (faulty Maf ?).

[Biff]

Your problem is its a fiat mate! Lol Fix It Again Tomorrow?
I wouldn't say it would of got that rusty in 4 months, would take a fair bit of surface rust to do that.
I reckon your right but can't say I've ever seen brown smoke.