Renault Megane 1.6l 81kw - P300 Random cylinder misfire - 3uga

Hi!

Random/multiple cylinder misfire is detected on this engine. The problem is intermitent and apears usualy when engine is warmed up. When it apears the engine starts vibrating and check engine light flashes, accelerating makes the whole car vibrate.

I'm thinking of water contaminated fuel.

Any ideeas on what might be the problem ?

Thank you!

Edited by 3uga on 02/02/2017 at 09:33

Renault Megane 1.6l 81kw - P300 Random cylinder misfire - RobJP

Absolutely impossible to tell.

Yes, it could be water in the fuel.

It could just as easily be a spark plug (or more than one), a coil pack (or more than one), a cable frayed, an ECU fault, a clogged air filter or any one of a number of other things.

The best solution is to get a PROPER diagnostic carried out. That should point you in the correct direction

Renault Megane 1.6l 81kw - P300 Random cylinder misfire - Railroad.

A flashing MIL indicates that the ECM is detecting a misfire. It knows due to irregular information from the O2 sensor B1S1. A random misfire is exactly that - random. Because of no particular pattern the ECM cannot be more specific, hence the P0300 code. The cause could be anything.

Renault Megane 1.6l 81kw - P300 Random cylinder misfire - Railroad.

Thinking about it again, the cause could be a failed ignition coil. These have pencil coils, one per cylinder, but they're wired in series pairs for cylinders 1 & 4, and cylinders 2 & 3. They're common failures, and if for example the coil on number 1 cylinder failed it would also have an effect on number 4 cylinder. This could result in the ECM setting a 'Random Misfire' fault code P0300, because a misfire on two cylinders, particularly if it's intermittent, may be sufficient for the ECM to be unable to track down. As I said, the ECM only knows the engine is misfiring because it receives an irregular pattern of information from the O2 sensor, and whilst this is enough for it to determine that the engine is misfiring, it may not be accurate enough for it to identify on which cylinder the problem lies.

Renault Megane 1.6l 81kw - P300 Random cylinder misfire - madf

Failing crankshaft sensor would give the same symptoms- but on all cylinders..

Renault Megane 1.6l 81kw - P300 Random cylinder misfire - hardway

Had one of these in with identical symptoms and code.

I ran a drop/load test on the battery and it failed the test.

New battery fixed the fault.

Renault Megane 1.6l 81kw - P300 Random cylinder misfire - 3uga

I checked out the coils and they're good.

Found another problem, coil packs form cylinder 2,3 and 4 have rust on them and found water in the inside ons sparkplugs 2 and 3 between sparkplugs and coils. Engine has humidity on it but cant see any on intake galery wich is mounted higher. Windashield wi per liquid sistem is in good shape and cant seem to find any humid parts to indicate that water pased through.

Should i be looking at a cracked sylinder head?

Renault Megane 1.6l 81kw - P300 Random cylinder misfire - RobJP

You've been given advice already.

Have you followed it ?

Renault Megane 1.6l 81kw - P300 Random cylinder misfire - 3uga

I usualy take care of my cars at home. Its cheaper.

Problem was the water vetween sparkplug and coil. Eectric discharge was going into cilinder head instead of sparkplug. Put half a liter of isopropilic alcohol in gas tank just to get rid of any water if there's any.

Problem solved. Thank you very much !

 

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