Took the car for a run yesterday and after about 15 mins driving I stopped to take a photo. When I came to a stop I felt the engine wasnt running on all 8 straight away. Or felt like. Turned round to drive home, and it drives fine over 2500rpm. Drop under 2000 and its misfiring. Anyone got any ideas? I have tried a new coil pack (I have a spare) on each bank and it made no difference. The idle control valve looks ok (no idea if its working). Just about to pull the plugs but dont have the tool to get the wires off so need to have a think on that. Anyone had similar?
I have pulled the plugs. They look about due for replacement. I have ordered a set. If no joy will try fuel injector cleaner - always a bit worried about that sort of thing on a 355 engine.
A couple of things spring to mind. Misfuelling when the engine is in closed loop mode due to a duff lambda sensor which resolves when the engine goes into open loop with some revs on it. Plug in a code reader and look at the fuel trims. Alternator on the way out. Check voltage at idle.
OK both good suggestions cheers. Will a code reader work - I always thought it wasnt possible on the 355? Its a UK car.
It will on a 5.2 car. You need a Fiat/Lancia 3-pin to OBD2 adaptor, then plug into the Motronic diagnostic connector behind the driver's seat. I also soldered a cig lighter adaptor onto the relevant OBD2 pins to power the reader, as I have a cheap Autel one that takes its power from the car. On 2.7 cars, codes can be displayed on the dash by shorting two pins on the Motronic diagnostic connector.
Another quick way to check for spark on all 8 WHILE it is skipping @ idle. Connect a timing light to each spark plug wire and confirm secondary voltage, this at least gives you a good idea that your coils and primary ignition are functioning. Then you can suspect plugs or fuel system.
I would change the spark plugs first, the symptoms you are having are not uncommon when the spark intensity drops, either due to too old spark plugs leaking high tension, too old plug cables or due to ignition coil on the way out (which is not the cause in your case).
When cold the mixture is richer. Once it fully warms up it leans considerably, especially at idle. A lean mixture is harder to ignite and burn properly so exposes weaknesses in the ignition system, usually plugs or wires. It can also be exposing an injector issue. Dirty injectors have the most trouble at very low flow rates and are are dependent on good spray patterns to function well at idle.
Cheers all. I have a set of plugs on the way. The HT leads were replaced maybe 6 years ago ish - they seem in good nick so I think they are ok. I will defo be running some fuel cleaner through just because why not like you say. Then will look at getting a code reader too. Will report back if the plugs fix the issue. Fingers crossed.
<Farnsworth> Good news everyone... <f/> New plugs did the trick. Also acquired a tin of liqui moly injector cleaner which I will put in next time I fuel up. Sill researching OBD but will get one in the next couple of weeks. Cheers all.
Simon, I'm happy to hear that new spark plugs solved your problem. But do consider having your fuel injectors serviced and calibrated as Brian (Rifledriver) suggested. Barry
