CF3 cat. removal - running issues - Alfa Romeo Forum
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CF3 cat. removal - running issues

I have a 2.0 CF3 GTV that has run perfectly for as long as I've had it.

I recently changed the three-cat front exhaust system for a CF2 manifold, matching downpipe, 300 cell sports cat and aftermarket flexi. Two lambda bosses tig'd into the new manifold and the third behind the cat as per original system. Essentially it's all the same as the Alfaholics CF3 aftermarket system here -

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It felt like a new engine for first 40-50 miles of the drive back from the workshop - well, it felt like the engine in my old 16V 155 anyway, lovely and crisp and freer at high revs compared to how it was. However for the last 5-10 miles it felt like it had lost a fair bit of power, and it's been the same ever since. Idles perfectly and drives alright on light to mid throttle, but is reluctant to rev and feels like it's missing power right across the rev range.

I took the system back off and internals of cat look as I'd expect; MultiECUscan suggests all three lambdas are working (or at least, it shows no errors with everything plugged in and then shows faults in turn as I disconnect each lambda.

Given that I've messed witth the exhaust on a car that ran perfectly that's the obvious place to look but I'm a bit stumped as all appears ok? Any ideas?

Thanks.

Last edited by Toby Unna; 28-09-16 at 13:07.
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Getting the primary lambda sensors properly angled into the downpipe is imperative to them working well. We had so much trouble with this when designing the Wizard exhaust manifold for the 2.0 TS CF3, they are very sensitive to lambda sensor position, angle, depth of penetration into the secondary pipe etc. Thats not a euphemism either!
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@Pud237: Out of curiosity - how would one diagnose that primary lambdas aren't properly positioned (angle/depth)?
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@Pud237: Out of curiosity - how would one diagnose that primary lambdas aren't properly positioned (angle/depth)?
If they're really badly positioned they will pop/splutter when up to temperature. If they're just slightly off, then the long-term fuel trims are affected and the car loses power over time (like in the OP's case although it may be something other than lambas causing it for him).
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Thanks Pud. I don't know much about the ECU system on this car but I did wonder about it being a fuel trim problem given that it ran fine to begin with.

Have you any thoughts about how I can verify this, short of getting the old system out of a scrap bin and putting it all back on (can I use multiECUscan or similar to reset any 'learned' fuel trim data?)

Thanks again.
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You can watch the lambdas operate in real time using MES. On my CF1 TS they switch from lean to rich every few seconds which I guess is correct because it always passes the MOT emissions test.
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Quote:
Originally Posted by Toby Unna View Post
I have a 2.0 CF3 GTV that has run perfectly for as long as I've had it.

I recently changed the three-cat front exhaust system for a CF2 manifold, matching downpipe, 300 cell sports cat and aftermarket flexi. Two lambda bosses tig'd into the new manifold and the third behind the cat as per original system.
I have a CF3 Twinnie as well. My original front pipe is now blowing from the flexi and I am looking at my options for a permanent fix rather than a yearly bodge for the MOT. This is one of the options that I have considered.

Where did you get the bosses and other bits from?
How much did the welding etc cost?
How did you decide where to put the lambdas?
Do you have any photos you could post?

With thanks
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Quote:
Originally Posted by Toby Unna View Post
Thanks Pud. I don't know much about the ECU system on this car but I did wonder about it being a fuel trim problem given that it ran fine to begin with.

Have you any thoughts about how I can verify this, short of getting the old system out of a scrap bin and putting it all back on (can I use multiECUscan or similar to reset any 'learned' fuel trim data?)

Thanks again.
You can reset the fuel trims using the diagnostic tool. If all your power comes back, then you know the ECU is adapting badly to the changes you have made to the exhaust system. Lambda positioning etc is difficult, you need an exhaust fabricator to look over it really and determine if the bosses have been correctly positioned.
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Personally, it sounds to me that the car was busy relearning it's values... I.e. crisp performance initialy would be over fueling, running rich. The values would have slowly started to correct/ rebalance thus starting to run lean before eventually settling at a relearned trim. I think you jumped the gun and had a knee jerk reaction to the learning process before it started to settle.
I've seen this many, many times over the years with simple installations of induction filters and performance exhausts. Pre fuel injection days it wasn't as dramatic an issue and tinkering with fueling/airflow was an art in itself but with immediate effects. More modern cars will resist everything you try in order to optimise their given fueling/ignition map then settle eventually to a happy medium.
Another alternative is a rolling road tune up with your new items installed for virtually instant results. Down side is this costs money but you'll get far better results than you will ever get with a factory map and just new items fitted.
Look at it this way, the money you will save in fuel economy over a year once it is all matched will pay for the tune up initially.
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