3.2 Busso rough idling at start-up, after decat - Alfa Romeo Forum
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(Post Link) post #1 of 11 Old 14-06-16 Thread Starter
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3.2 Busso rough idling at start-up, after decat

Hi,

I recently had the cats cut out of my exhaust manifolds of my 3.2 V6 GTV. The car now idles roughly and misfires on cold starts with an accompanying fuel smell. When the car is warm it behaves much better but the smell of fuel is still there. Is this normal for a decat system?

The exhaust manifolds are still CF3, just with the cat monolith removed.

I also didn't get the expected power gain after the removal of the cats. Is there some other problem that I may be looking at?

Cheers...
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Certainly sounds like a problem somewhere.

Get it on a code reader and make sure the lambda's are not throwing up any errrors.

For info, fitted an underbody decat to mine and it runs exactly the same as it did before only sounds a bit nicer.
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Knocking out the Cats in the CF3 you need to move the Lambda positions I think. They won't function properly with the void created by the cat removal.Running rich and rough idle would point to Lambda too.
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I don't know how the v6 is, but on the TS there is a sensor on the thermostat, it is a thermal sensor. but it is a "cold start" sensor as well, if it has one it maybe dead.
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My thermostat is brand new, the car heats up quite quickly though but the fuel smell remains. There was no ecu light until a few days ago on a bunt start (engine fired and died) but then it started up immidiately and performed normally again. The light went off a few starts later as I expected. I'll plug my ecuscan in and see if it registers anything abnormal.

In any case, would full cf2 manifolds make a difference?

Last edited by Ian Lusso; 08-08-16 at 13:21.
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I just had a thought, When you say "cats removed" did you mean that the cells where broken up and removed leaving a large empty chamber? I can imagine that would do no good for the running of the engine as the exhaust system pressure and gas flow through the manifolds would be ruined.

In that case, absolutely yes to fitting CF2 manifolds.
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Quote:
Originally Posted by ransoman View Post
I just had a thought, When you say "cats removed" did you mean that the cells where broken up and removed leaving a large empty chamber? I can imagine that would do no good for the running of the engine as the exhaust system pressure and gas flow through the manifolds would be ruined.

In that case, absolutely yes to fitting CF2 manifolds.
Surely a remap +\- lambda fakers would sort it?
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I think you removed the wrong cats.. manifold cats are the issue to performance and pud who makes the wizard exhaust has done a load of testing and says the main cats barley effect the performance.
and just knocking the cats out as above is a bad move. if you have welded pipes in get a set of cf2 or pud manifolds fitted.
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Wizard catless manifolds are of course straight fit, with lambda bosses already on them.

But if you are unwilling to pay that amount of money, I would suggest buying some second hand CF2 exhaust manifolds (from GTV), which you would have to combine with downpipes for CF2 manifolds as well. Rear CF2 GTV manifold already has lambba boss, so you would have to add one lambda boss to the longer downpipe (it is not a big job, it just has to be welded in properly). There are also equal lenght downpipes availabe for GTV models (check thread in the GTV section called Peco equal lenght downpipes), you would need CF2 type in that case of course, or CF3 if you get Wizard manifolds.

It might be a bit hard to get your hands on CF2 GTV exhaust manifolds.

Since you are smelling fuel, are you sure there isn't a leak somewhere, which would disturb the lambda sensors?
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Wizard manifolds also sound immense. Go for em!
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(Post Link) post #11 of 11 Old 21-06-16 Thread Starter
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Just for some feedback, my two faults discovered:

1. Exhaust leaking at both knuckle joints in front.
2. Massive tear in intake air hose at concertina joint.

Both of these would be very bad for engine performance. I have no idea how this engine still keeps going so well!
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