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7 Seat Sports Car · Dec 27th, 2023, 09:55

I used to get around 400 miles per tank of fuel then that dropped to 300-350 tops. Plugs are sooty, O² sensors are sooty, the end of the tail pipe is sooty, the exhaust smells acrid and when in closed loop the fuel trims zoom off to the max and rear O² reads 0.8-0.9V. I'd like to think I'm not barking up the wrong tree here and all the symptoms are for running rich or somehow detecting false lean and over compensating.

The car ran sweet before the cat was fitted (old one was nicked) then I was plagued with a cat efficiency code ever since. After a year of this I got fed up and started to look at what I could do as I thought "it's a new cat, it can't be wrong". A rear sensor spacer didn't work so I went to remove it and that's when I suddenly started to get front O² codes! I'd get P0134 sometimes and P0135 most of the time. Battery was disconnected every time I swapped sensors. Randomly the ECU will not find any fault and go closed loop and hoof fuel in like no tomorrow.

The Bosch sensor part number is etched alongside the correct Volvo part number according to Vida, my vin says it's MY99. MAF is a part number match with the one that was factory fitted. And Bosch. After I replaced both newish O² sensors with other new ones it didn't change anything. Either I've bought duds from autodoc or it's not that.

ECU is a clone of my existing original ECU but immobilizer is switched off, not remapped. Is it likely the programming is corrupt and I've copied this fault to the clone.

If it's electrical I feel I should be able to prove it one way or another. If it's mechanical e.g. engine health then how do I isolate this as the problem without lobbiing money at it.

Incidentally, I've got a block tester for identifying bad head gaskets, no gas gets up to the reservoir and the pump on it cavitates as I'm using it. Fluid stays blue. Crankcase breather is only a few years old and I've just cleaned it out when I took the intake manifold off the other day.

Usability wise it starts first time, idles at solid 850 and it goes like a stabbed cat. However on occasion its lumpier than school custard and can watch rpms drop while trying to accelerate. On one occasion I managed to get my obd2 dongle on when this fault was on and the fuel trims were max negative! I'm proper lost.

Cheers, Drew

Dec 27th, 2023, 09:55	#5
7 Seat Sports Car Member Last Online: May 9th, 2024 21:04 Join Date: Oct 2010 Location: Newark	I used to get around 400 miles per tank of fuel then that dropped to 300-350 tops. Plugs are sooty, O² sensors are sooty, the end of the tail pipe is sooty, the exhaust smells acrid and when in closed loop the fuel trims zoom off to the max and rear O² reads 0.8-0.9V. I'd like to think I'm not barking up the wrong tree here and all the symptoms are for running rich or somehow detecting false lean and over compensating. The car ran sweet before the cat was fitted (old one was nicked) then I was plagued with a cat efficiency code ever since. After a year of this I got fed up and started to look at what I could do as I thought "it's a new cat, it can't be wrong". A rear sensor spacer didn't work so I went to remove it and that's when I suddenly started to get front O² codes! I'd get P0134 sometimes and P0135 most of the time. Battery was disconnected every time I swapped sensors. Randomly the ECU will not find any fault and go closed loop and hoof fuel in like no tomorrow. The Bosch sensor part number is etched alongside the correct Volvo part number according to Vida, my vin says it's MY99. MAF is a part number match with the one that was factory fitted. And Bosch. After I replaced both newish O² sensors with other new ones it didn't change anything. Either I've bought duds from autodoc or it's not that. ECU is a clone of my existing original ECU but immobilizer is switched off, not remapped. Is it likely the programming is corrupt and I've copied this fault to the clone. If it's electrical I feel I should be able to prove it one way or another. If it's mechanical e.g. engine health then how do I isolate this as the problem without lobbiing money at it. Incidentally, I've got a block tester for identifying bad head gaskets, no gas gets up to the reservoir and the pump on it cavitates as I'm using it. Fluid stays blue. Crankcase breather is only a few years old and I've just cleaned it out when I took the intake manifold off the other day. Usability wise it starts first time, idles at solid 850 and it goes like a stabbed cat. However on occasion its lumpier than school custard and can watch rpms drop while trying to accelerate. On one occasion I managed to get my obd2 dongle on when this fault was on and the fuel trims were max negative! I'm proper lost. Cheers, Drew __________________ '99 S’ V70 T5 SE - Gone but not forgotten 😔 ‘88 F’ 240 GLT - Hector '11' C30 diseasel - Dave Last edited by 7 Seat Sports Car; Dec 27th, 2023 at 10:07.