L322 4.2 S/C has lost 60 horses and very fumey...please help :(

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84
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Greenock, Scotland
Hi all... going to go into a bit of a spiel here so that anyone with any technical knowledge can have an overview of all the facts - I apologise in advance!

I purchased the above car back in July, a 56 plate (MY07) with 94k on the clock. I knew it had a slightly different rear section on the exhaust, as it sounded a bit "fruitier" than the OEM system - and also, given the tiny stainless rear backbox and different shaped oval tips, it was quite obvious it wasn't stock. I didn't realise until I had driven it from Devon back to Glasgow however, that it had clearly been remapped aswell... got a rather surprising shock downshifting close to home when it crackled and banged like a supercar, after such a peaceful and quiet cruise up the motorway from England. The next day was a surprisingly nice day in Scotland, so I thought I'd take my new car out for a spin and rather than "waste all that fuel" running the aircon pump, I got the windows down and the sunroof open... at which point I nearly passed out from exhaust fumes. It seems that opening the windows draws an overpowering stench of fumes into the cabin like a venturi!

The car has a BRC gas system, with donut in the boot floor - so I inspected this to see if there were any holes that might be letting exhaust fumes in. There were a couple, so I siliconed them up but this had no noticeable effect. I also checked the exhaust over myself and had my usual workshop check it too - his comments were that he could find no leaks, but that he liked the "decat" system (he said this rather sarcastically...) To be honest, the car appears to have cats in the place I would assume them to be, but perhaps they are dummies or something, I'm not sure. Maybe he was judging this by the strong fumes smell.

The next chapter of the story is that I took it to Ecotune in Hillington, a highly respected tuning shop with 4wd dyno. I thought that by getting it dyno'd I would at least have a basepoint to start from to get the car running less rich/fumey. The dyno result is that the car is only producing 330hp at the engine, and 380lbft of torque. The manufacturer figures are in the 390hp region, and 420lbft of torque, confirmed by a fellow 56 plate S/C owner there at the dyno day, who said his was stock and dyno'd at 401hp.

So basically, where should I start? The issues I want to address are specifically the fumes in the cabin/trying to attach a trailer, it is genuinely so fumey that you can't stand behind it without wanting to hold your breath or turn it off. It's clearly running far too rich but has no warning lights on and generally runs very smoothly. Note that running on petrol is worse than on LPG, but still fumey on LPG just not to the same extent.

Where could the fumes be entering the cabin, and could the revised position of the exhaust have an effect, as they are now located more centrally than the OEM peashooters would be?
Secondly, what should I do about finding where this 60hp has got to...do I need to do some mechanical investigation, such as find out if I'm getting a slight misfire or something that I can't detect due to the other 7 cylinders working fine? Or should I get it remapped by someone first to stop it being so rich.

Any advice appreciated as I would really like to be able to put my windows down by the end of the year!
 

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Maybe get it put back to standard and go from there. For fumes to get into the cabin, I would have thought that there would be an exhaust leak towards the front. Is it still bad inside with the windows shut?
You would never notice the difference in fuel consumption with aircon off or on.
 
You can't smell the fumes at all with the windows closed, whether you have the blower and a/c on or not. It seems to only be with the windows down which makes me think it's being drawn forward in the cabin up from the exhaust tips. It has been up on the ramp getting investigated at the front as it made me wonder if the manifold gaskets could be leaking, but Craig my mechanic said it seems fine to him.
 
You can't smell the fumes at all with the windows closed, whether you have the blower and a/c on or not. It seems to only be with the windows down which makes me think it's being drawn forward in the cabin up from the exhaust tips. It has been up on the ramp getting investigated at the front as it made me wonder if the manifold gaskets could be leaking, but Craig my mechanic said it seems fine to him.
When I say windows down, I mean whilst the car is doing 15mph+. Stationary it's not so bad as there is no airflow to cause a vacuum effect by having the window down.
 
You can't smell the fumes at all with the windows closed, whether you have the blower and a/c on or not. It seems to only be with the windows down which makes me think it's being drawn forward in the cabin up from the exhaust tips. It has been up on the ramp getting investigated at the front as it made me wonder if the manifold gaskets could be leaking, but Craig my mechanic said it seems fine to him.
If it's OK with the windows closed, you are right, it's being drawn forward. Better keep the windows closed and use the aircon as posh RR drivers are supposed to.
 
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Lol, I have no qualms using the aircon - my quotes on the aircon comment were because why would you care when you have a rich running car that can only manage about 14mpg, yet some people genuinely care about this haha!

No but seriously, I would like to open my windows :)
 
You could get your mate to plug it in to the emissions tester to see what is coming out, plug it in to diagnostics to see what is going on at the other end.
The stock exhausts don’t exit past the end of the vehicle so that could be dragging in your bad emissions if you have them
 
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