WD40 - no problem in injectors as it is highly flammable and will burn off.
I had a similar sounding problem a couple of weeks ago on a 2001 mk2 Punto. You don't say what year, model of Punto, or which engine, but my car had the 1.2 8V petrol engine. I did the usual checks like you and concluded that only 2 cylinders were firing. I swapped the 2 ignition packs around to see if that made any difference. No, it was not either of them. I then replaced the ECU... and 'hey presto' after programming the replacement ECU everything is OK.
The ignition packs cost less then £30 to replace each, and a reconditioned ECU from Fiat will cost £352. A new one is over £500. Fiat will also charge about £200 to fit it, but it only takes 20 minutes to do - quite easy in fact.
If it is the ECU you will need to reprogram it. There is no need to buy new ignition switches or door locks or keys.
To program the ECU run the engine untill the electric cooling fan in the engine compartment comes on then over rev the engine a few times (3 or 4) and the flashing warning light will go out. It's that easy... programmed, without buying new keys, ignition switches door locks etc.
WotNotAgain
March 2009
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