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Old 16-11-2016   #1
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Unhappy Fiat 500 1.2 Misfire.. EM light at high speeds.

Hi guys!

At my wits end with my 1.2 69bhp 63 plate 500S. I'll try to make a long story short.. it has an intermittent misfire. Also, when driving it at high speeds (70mph+), sometimes the engine management light will come on and the car starts chugging as if I'm running out of petrol. When the engine is switched off and back on, the EM light goes off and car runs as normal once again (still with the intermittent misfire but minus the chugging). When plugged into the diagnostic, the fault code reads as misfire cylinder 3 along with a few others. However, everything that the codes refer to I've had replaced. Replaced coil, spark plugs, lambada sensor etc etc with genuine parts.. it's also recently had a software re-flash for a problem with it being underpowered.

Does anyone have any experience of this? Helpppp!
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Last edited by sarahlouiseslj; 16-11-2016 at 16:50.
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Old 16-11-2016   #2
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

Ecu?
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Old 16-11-2016   #3
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

Thanks for replying typecastboy .. I'll ask my mechanic to check it out!
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Old 16-11-2016   #4
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

Have you replaced the spark plug leads? Ours suffered no.4 failure, you could see and hear the spark jumping across .
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Old 16-11-2016   #5
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

Quote Originally Posted by sarahlouiseslj View Post
Thanks for replying typecastboy .. I'll ask my mechanic to check it out!
Hi,
does this mean it's outside of the FIAT dealer network..??
far from an issue here .. BUT you may not be using the best diagnostic equipment for the 500.

some error codes generated are so general it can cover many components..
sound familiar..
Fiat / Alfa specific software should be more accurate


Charlie - Oxford
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Old 16-11-2016   #6
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

In my experience with the euro 6 engined 500 the ecu's are a bit prone to intermittent faults. I had one with a very intermittent missfire. Ruled out all the obvious so fitted the ecu to one of our courtesy cars and after quite a few miles of road testing the fault appeared on the courtesy car. Fitted a new ecu and all was good after that. If it's that be prepared for a very expensive repair. Where are you in the country?
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Old 16-11-2016   #7
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

Quote Originally Posted by John202020 View Post
Have you replaced the spark plug leads? Ours suffered no.4 failure, you could see and hear the spark jumping across .
Yes these have all been replaced thanks for your reply though!
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Old 16-11-2016   #8
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

Quote Originally Posted by varesecrazy View Post
Hi,
does this mean it's outside of the FIAT dealer network..??
far from an issue here .. BUT you may not be using the best diagnostic equipment for the 500.

some error codes generated are so general it can cover many components..
sound familiar..
Fiat / Alfa specific software should be more accurate


Charlie - Oxford
Hey, thanks for your reply. Yes it's been to Fiat, and my mechanic also has the Fiat software.. nobody seems to be able to come up with any solutions! I seem to be reading a lot about misfiring issues with 500's :/
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Last edited by sarahlouiseslj; 16-11-2016 at 21:41.
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Old 16-11-2016   #9
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

Quote Originally Posted by burrowsdeano View Post
In my experience with the euro 6 engined 500 the ecu's are a bit prone to intermittent faults. I had one with a very intermittent missfire. Ruled out all the obvious so fitted the ecu to one of our courtesy cars and after quite a few miles of road testing the fault appeared on the courtesy car. Fitted a new ecu and all was good after that. If it's that be prepared for a very expensive repair. Where are you in the country?
Hello, thanks for your reply .. I'll definitely look into this! It's driving me mad. I'm around half an hour from Cardiff, more Newport way.
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Old 16-11-2016   #10
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

Quote Originally Posted by varesecrazy View Post
Hi,
does this mean it's outside of the FIAT dealer network..??
far from an issue here .. BUT you may not be using the best diagnostic equipment for the 500.

some error codes generated are so general it can cover many components..
sound familiar..
Fiat / Alfa specific software should be more accurate


Charlie - Oxford
Absolutely. MultiECUScan gave me an error which led me to change the throttle pedal and the throttle body. The fault codes were cleared and they just came straight back again. Took it to my trusted independent and although they worked on it on and off for nearly 4 weeks, their software traced it to a voltage problem within the ECU. One volt higher than it should be which triggered the fault. MultiECUScan would never pick that up. I had to get a new ECU but it had to go to the garage for that.
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Old 16-11-2016   #11
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

It's odd that it misfires at high revs normally it would be at idle and low speed and pulling away does the EML light flash when it comes on then steady ? Of course a misfire is not just the spark, could also be injectors and valves.
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Old 16-11-2016   #12
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

Quote Originally Posted by John202020 View Post
It's odd that it misfires at high revs normally it would be at idle and low speed and pulling away does the EML light flash when it comes on then steady ? Of course a misfire is not just the spark, could also be injectors and valves.
The misfire has happened at both low and high revs, but seems more prominent at higher revs/speeds. The EML has only ever come on when going 70mph and flashes, never stays on steady. EML light then disappears when engine is turned off and back on again. Injectors have been taken out, tested, cleaned, replaced etc etc.. I can't keep up with the amount of things we've tried and tested to be honest! I've also tried fuel treatment and a gas treatment.. My brain hurts!
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Old 17-11-2016   #13
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

Wow you've certainly replaced and checked a lot, some parts like the Lambda were probably fine, next would suggest hooking up to a laptop/data logger whilst driving to see just what the ECU is doing? sounds too obvious but the connections to the ECU are good, and clean? Do you get 3 flashes then pause?
Do you know what the other codes were by chance?
Not sure but a secondhand ecu may be the way to go, only when its confirmed faulty.
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Old 17-11-2016   #14
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

I bought a secondhand ECU and it has to be virginised before it would work but sorted out my problem.
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Old 17-11-2016   #15
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Re: Fiat 500 1.2 Misfire.. EM light at high speeds.

Quote Originally Posted by burrowsdeano View Post
In my experience with the euro 6 engined 500 the ecu's are a bit prone to intermittent faults. I had one with a very intermittent missfire. Ruled out all the obvious so fitted the ecu to one of our courtesy cars and after quite a few miles of road testing the fault appeared on the courtesy car. Fitted a new ecu and all was good after that. If it's that be prepared for a very expensive repair. Where are you in the country?
sounds promising ,

big question here is wether @sarahlouiseslj has still enough warranty left for a Fix through FIAT dealership network..,

Charlie
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