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2017 Fiat 124 Spider Classica, Grigio Moda
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Discussion Starter · #1 ·
Hi all,

I own a 2017 Fiat 124 spider Classica 1.4L Multiair. Since October the car has had a C3 misfire 5 times! The garage have checked oil, changed spark plugs, swapped fuel injectors, and changed the coil packs to the Bosch set (which I found recommended on here as a fix for the misfire problem).

Does anyone have any other ideas or have had the same problem and managed to fix it?

Thanks!!
 

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Compression check?
 
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Are these weighted moving counts or current drive cycle? 5 current drive cycle misfires is nothing to worry about.
 

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2018 Abarth 124 Spider, Mare Blue / Nero Abarth Leather, Brembo's, Record Monza, Automatic
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While it is extremely difficult to diagnose something like this from far away, there are some things that would be standard procedure to check - and, as you say this has happened several times over several months, I am assuming this is an intermittent misfire. Compression and Leak Down checks could reveal an intermittent issue such as a sticky valve (due to carbon buildup, lack of proper oil/oil changes, etc.) though it is quite unlikely unless you repeated these tests many times. Other things you might check are electrical connections - say, check female terminal tension at coils and injectors. Check ECM connectors for water intrusion and corrosion - Be Careful if you do a pin tension test here, terminals are very small and easily damaged! Also look for corrosion or fretting of the terminals. Also poor grounds may cause intermittent issues - so check & clean ground points. Some auto manufacturers recommend applying Stabilant 22a to electrical connections after cleaning and making sure contacts are good. Whereas you live on one of the Channel Islands corrosion of electrical contact points is a distinct possibility. Also, small amounts of water in the fuel could cause an intermittent issue, although if you have ethanol content in your fuel, as we do here, that is more unlikely. If you do not have alcohol content, a container of dry gas may help. Water droplets do not easily pass through injectors due to surface tension (I will admit this is more likely to affect all cylinders and not just #3). A leaking intake gasket could cause this (and could be intermittent depending on engine temp), or other vacuum leak (possibly due to pwm control that would be intermittent). The list goes on & on, but I hope this helps. Good Luck! Best, s
 

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Discussion Starter · #6 ·
Are these weighted moving counts or current drive cycle? 5 current drive cycle misfires is nothing to worry about.
The misfires are 5 separate single events. The car fails, is taken to the main dealer and runs fine for a period of time before misfiring again
 

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Discussion Starter · #7 ·
While it is extremely difficult to diagnose something like this from far away, there are some things that would be standard procedure to check - and, as you say this has happened several times over several months, I am assuming this is an intermittent misfire. Compression and Leak Down checks could reveal an intermittent issue such as a sticky valve (due to carbon buildup, lack of proper oil/oil changes, etc.) though it is quite unlikely unless you repeated these tests many times. Other things you might check are electrical connections - say, check female terminal tension at coils and injectors. Check ECM connectors for water intrusion and corrosion - Be Careful if you do a pin tension test here, terminals are very small and easily damaged! Also look for corrosion or fretting of the terminals. Also poor grounds may cause intermittent issues - so check & clean ground points. Some auto manufacturers recommend applying Stabilant 22a to electrical connections after cleaning and making sure contacts are good. Whereas you live on one of the Channel Islands corrosion of electrical contact points is a distinct possibility. Also, small amounts of water in the fuel could cause an intermittent issue, although if you have ethanol content in your fuel, as we do here, that is more unlikely. If you do not have alcohol content, a container of dry gas may help. Water droplets do not easily pass through injectors due to surface tension (I will admit this is more likely to affect all cylinders and not just #3). A leaking intake gasket could cause this (and could be intermittent depending on engine temp), or other vacuum leak (possibly due to pwm control that would be intermittent). The list goes on & on, but I hope this helps. Good Luck! Best, s
Yes it’s an intermittent misfire. Intially, it was every 10 days or so. On every occasion the spark plug is fouled and needs cleaned, and after resetting the fault codes it runs fine. Most recently though, it has only lasted 3 days before failing. It is back with the main Fiat dealer now but they seem to have run out if ideas.

Every time the fault codes are read the code says it is a misfire on C3. So far we’ve changed replaced 4 spark plugs, 1 fuel injector and 4 coil packs.
 

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2018 Abarth 124 Spider, Mare Blue / Nero Abarth Leather, Brembo's, Record Monza, Automatic
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I would start by looking for a poor (intermittent) electrical connection to the coil, both power and ground sides. Many other possibilities, such as ECM driver, chaffed/ shorted wire . . . Again, on and on, but that's where I'd start. Good Luck, s
 

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Discussion Starter · #9 ·
I would start by looking for a poor (intermittent) electrical connection to the coil, both power and ground sides. Many other possibilities, such as ECM driver, chaffed/ shorted wire . . . Again, on and on, but that's where I'd start. Good Luck, s
Thanks for the advice Steve! I’ll give the dealer a call tomorrow and let you know how we get on.

Thanks again!
 

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Kool, no problem - that's what we are here for. You might ask them to check resistance in the coil circuitry too. s.
 

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Discussion Starter · #14 ·
When does the misfire occur?
Under load, idle, all the time, etc?
The misfire occurs while driving. The sequence tends to go as follows:
Stop at a junction, roundabout, traffic lights etc
Pull away and the car feels like it wants to stall
Car continues to run fine for about 100 yards but slightly fluttery
Drive becomes lumpy, C3 stops and the misfire occurs, engine warning light comes on and flashes then stays on permanently
 

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If you just let the car idle after startup - does it misfire?
 

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Could be a problem with the MultiAir.
 

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I feel like faulty MultiAir units usually throw a code almost immediately. I’ve been battling a misfire issue for awhile now and it’s possible I fixed it. Unlike you OP, I was having misfires only at WOT, mostly in cyl4 but sometimes in 1.

Do another compression check just be to sure, and make sure you do each cylinder. Check ignition harness for obvious issues like mentioned above and do a smoke test and boost leak test just to be sure. If you have a leak somewhere or perhaps a crack in the intake manifold near cylinder 3, that could cause issues.
 

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I too was thinking possibly an intake leak until it was revealed that the spark plug is fouled each time. A leaking intake (either caused by a crack, poor gasket sealing, or whatever) would result in a lean condition that would cause excessive plug wear, but not fouling. Worn, broken, sticking piston rings might be at play here, so compression / leak down tests may reveal this issue if cyl. #3 results are compared to the other good cylinders, as would a sticking valve - though that may take many / multiple tests to figure out. The tech may have to employ a bore scope to look for cylinder wall scoring or other damage, the tops of valves may need inspecting for carbon buildup, maybe a valve guide issue, is there excessive oil consumption ? This stuff isn't easy, techs and customers often become quite frustrated. It takes patience, and in the case of the tech some smarts and savvy to figure this stuff out. s
 

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Could be a burnt valve.
 
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