sudden missfire on V6 - more when warm - Alfa Romeo Forum
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(Post Link) post #1 of 5 Old 26-03-12 Thread Starter
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sudden missfire on V6 - more when warm

Hello all

I haven't had a chance to have a root around yet but wonder if anyone can point me in the right direction? Car normally idles ok - not super smooth, hunts very very slightly in a sort of rythmic way but maybe because it has a CDA and Alfaholics cat, centre section and Autodelta rear pipe?

Anyway it seems to have got slightly worse the last few days and stuttered a couple of times on pulling away with a missfire that would then seem to clear - then today seems to be missfiring all the time when its warm, so i took the wifes Vespa to work!

I'll check the 6 rubber inlet pipe things and the feed going into the plenum. Have cleaned the injector plugs (just the connections). Anything else worth a look before i try plugs and coil packs etc?

Many thanks!
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The MAF might be knacked. You can disconnect it and that may give you an improvement (though it won't be working as it should).. at least to prove that it's the problem.

If you recently oiled up your CDA that may have dumped a load of goo on the MAF... which may have done for it.

Failing that.. a lumpy idle could be the lambda sensor... (check it with a CO meter like the MoT place uses) though generally they only cause lumpiness at idle and at low rpm as they transition through the heater's on/off phase (around 1800 rpm).

Or it could be a sign that your TDC (crank position) sensor may be on the way out.. though these are usually fine when cold.. but get worse when hot.

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The "when warm" low revs hesistancy would point towards a lambda problem.
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(Post Link) post #4 of 5 Old 27-03-12 Thread Starter
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Thanks folks - i haven't touched the CDA and it's not long had a MAF. It did have a lambda before i bought it 6 months ago but who knows. It's due a service anyway so i might see what shows up on the diagnostic, i assume that might give an indication? At least my old Ducati started this morning so i'm mobile!
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Hunting as you describe is typical of a failing/failed lambda. The circuit goes into a default open loop where the ECU literally quizzes the lambda for data but is forced into a default map which is where you see the change in revs. It only does this once warmed up so cold idle is unaffected. Find and replace your faulty lambda and it will go away. I had the exact same problem on my V6.
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missfire , sudden , warm

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