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Technical Misfire when hot

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Technical Misfire when hot

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Kodama

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Jun 6, 2012
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Location
Bristol
Dear All

Recently my Fiat 500 TA seems to misfire when I put my foot down, whilst coming onto a motorway for example, and my dealer has had it now 5 times for the same reason and they can't seem to work out what's wrong.

It only happens when hot. Only happens out of eco mode. The fault that comes back is that it needs a new coil pack b, but this has been replaced now 4 times, so obviously something is putting pressure on the packs to make them fail.

I spoke with the mechanic yesterday on the phone and was a little shocked at what he said. They hadn't even looked at the spark plug yet. Fiat have had it a total of 6 days for a misfire issue and hadn't looked at the plugs. Is this normal? It makes me angry as this is what I said for them to look at on the first visit. So today, they're going to change the plugs and the oil.

I was asked if it had been serviced recently and perhaps the oil used was incorrect. This could lead to problems. I gave him the grade of oil, and thankfully, it was the correct grade. He then came back to me and told me that perhaps the quality wasn't high enough and that ONLY Fiat have the correct oil for the Twin Air.

Now, I'm not expert, but can someone tell me what the oil has to do with spark plugs and misfires?

They're test driving it again this morning, I hope this fixes the issue, but a little miffed about the plugs and feel like I'm being fobbed off and lied to about the oil. I've had issues with other garages spinning lies before about cars and parts to make money, and this feels like another one.

I hope someone can explain and put me at ease.

Thanks for your time
 
Sounds like it could be spark plugs to me too.
Re the oil.. It has to be a specific 'thickness' in order to control the hydraulic multi air valve technology. A different grade of oil may cause these to act differently to normal but I doubt that this is causing your misfire as even if you have the 'wrong' oil, it's the correct grade.
The recommended oil is Selenia K Pure Energy.
I hope they manage to sort it for you this time : )
 
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Kodama said:
Dear All

Recently my Fiat 500 TA seems to misfire when I put my foot down, whilst coming onto a motorway for example, and my dealer has had it now 5 times for the same reason and they can't seem to work out what's wrong.

It only happens when hot. Only happens out of eco mode. The fault that comes back is that it needs a new coil pack b, but this has been replaced now 4 times, so obviously something is putting pressure on the packs to make them fail.

I spoke with the mechanic yesterday on the phone and was a little shocked at what he said. They hadn't even looked at the spark plug yet. Fiat have had it a total of 6 days for a misfire issue and hadn't looked at the plugs. Is this normal? It makes me angry as this is what I said for them to look at on the first visit. So today, they're going to change the plugs and the oil.

I was asked if it had been serviced recently and perhaps the oil used was incorrect. This could lead to problems. I gave him the grade of oil, and thankfully, it was the correct grade. He then came back to me and told me that perhaps the quality wasn't high enough and that ONLY Fiat have the correct oil for the Twin Air.

Now, I'm not expert, but can someone tell me what the oil has to do with spark plugs and misfires?

They're test driving it again this morning, I hope this fixes the issue, but a little miffed about the plugs and feel like I'm being fobbed off and lied to about the oil. I've had issues with other garages spinning lies before about cars and parts to make money, and this feels like another one.

I hope someone can explain and put me at ease.

Thanks for your time
Click to expand...

Can't see how the oil and the backfiring problem is related. Here is a list of oils (Click here) that can be used on the Twin Air or any petrol 500 with the exception of the A500.
If the coil packs have been replaced as pointed out by The Twins Spark plugs should be replaced.
How many miles has the TA done since the Spark plug service ?
What kind of damage can one expect from back firing - will it shorten the life of the CAT ?
 
loveshandbags said:
What kind of damage can one expect from back firing - will it shorten the life of the CAT ?
Click to expand...

There are two ways it could be damaged; the overpressure from the backfire could damage it mechanically, and the unburnt fuel from the misfire could poison the catalyst.

I once had an exhaust system completely destroyed by a backfire - the centre box was quite literally ripped apart at the seams.

A rattling from the exhaust when going over rough ground (like a speed bump) could be a sign that something has come loose internally.

Getting FIAT to do anything about potential cat damage will be challenging. If it has been compromised, you'll likely only find out when you take the car for an MOT, by which time it'll be out of warranty & not FIAT's problem.

Not replacing the plugs after a coil pack failure is to me almost beyond belief. If the following three further coil pack replacements could have been avoided by changing the plugs at the outset, it's a 'lose-lose' situation for both FIAT & the customer.
 
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Well spotted by MEP and JR on the misfire as opposed to backfire.(y)

What's a little ironic is that on the A500 engine it's relatively easy to get it to backfire a little by giving it the beans and then backing off on the throttle - not doing the CAT any favours :eek: but it can be fun giving it a bit of character :). On the new breed MA engines they're not designed for that.

Still for the OP if it's not misfiring when ECO is engaged it should be burning any of the excess fuel that's built up those minimising any after effects on the CAT.

Realise that the plugs are a little expensive on the TA but surprised at the penny pinching given that there's only 2 of them !
 
loveshandbags said:
Still for the OP if it's not misfiring when ECO is engaged it should be burning any of the excess fuel that's built up those minimising any after effects on the CAT.
Click to expand...

Its the buring off of the excess fuel in the exhaust system (specifically the CAT) which causes the damage to the CAT as it overheats.
 
loveshandbags said:
Well spotted by MEP and JR on the misfire as opposed to backfire.(y)

What's a little ironic is that on the A500 engine it's relatively easy to get it to backfire a little by giving it the beans and then backing off on the throttle - not doing the CAT any favours :eek: but it can be fun giving it a bit of character :). On the new breed MA engines they're not designed for that.

Still for the OP if it's not misfiring when ECO is engaged it should be burning any of the excess fuel that's built up those minimising any after effects on the CAT.

Realise that the plugs are a little expensive on the TA but surprised at the penny pinching given that there's only 2 of them !
Click to expand...
Sorry for sounding ridiculous, but is backfire like those flames that come out from racing cars on the downshifts?
 
Most Easterly Pandas said:
Its the buring off of the excess fuel in the exhaust system (specifically the CAT) which causes the damage to the CAT as it overheats.
Click to expand...

I once fitted Splitfire plugs to a MX5 and they caused it to misfire and then backfire. It was a Jap import model and IIRC it had a CAT. I didn't delay fittingit with standard NGK plugs & new leads. It still had the same CAT on it when I sold it but we didn't have MOT / NCTs at the time.

Seriously though - will the misfires have any measurable effect on the CAT life of the OPs TA - would it not be the subsequent owners that might be effected given that a number of 500s that seem to change after 3/4 years ?
 
ahmett said:
Sorry for sounding ridiculous, but is backfire like those flames that come out from racing cars on the downshifts?
Click to expand...

Yes. Works best on a dark night. The difficult bit is checking the rear view mirror and driving at the same time.:devil: It's more noticeable if I use the higher octane fuel which I can get at Maxol. We don't get the V-power. Still I've got a little sensible and don't it much anymore.
 
loveshandbags said:
Yes. Works best on a dark night. The difficult bit is checking the rear view mirror and driving at the same time.:devil: It's more noticeable if I use the higher octane fuel which I can get at Maxol. We don't get the V-power. Still I've got a little sensible and don't it much anymore.
Click to expand...

Must be fun!
 
A completely incorrect oil grade could cause misfires due to incorrect valve timing/duration - but the engine would generally run like a dog throughout the range.

You say 'misfire' when accelerating hard, but what actually happens? Describe the situation..
 
Doesn't sound exactly the same but I wonder if it's another case of the MultiAir unit failing. Been a couple of Punto Evo's suffer this on here, plus a MiTo 135 MultiAir and numerous MultiAir 170's in the Giulietta on AlfaOwner, too.

I agree about the spark plugs. Utterly ridiculous that they've not looked at them after so many visits and coil pack changes and I'd seriously consider using a different dealer. If it's the one I'm thinking of near Bristol then it won't be the first time they've been talked about on here, but it would be interesting to hear the outcome as the MultiAir unit failure does seem to be affecting a few other models at the moment, albeit no 500s yet.
 
was on the m way this morning when I got ss unavailable when I got home I read various po codes on mes
I cleared them as intermittent changed the sparks coil pack and leads


just been for a spin down the mway again got ss unavailable and engine light for 10 secs then it went off
got back and again intermittent po codes just not as many?


ive added pics hopefully they upload all ive done this week is change the crankshaft pulley, im wondering what the hell ive done!? could it be down to my new exhaust? any help please chaps
 

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Hi,

Does your crank position sensor generate signal from bumps on crank pulley?

On older models of 1.2 fire engine any time the crank position sensor or crank pulley were disturbed a phonic wheel relearn was required(phonic wheel=crank pulley)

I'm thinking misfire is related to replacement of crank pulley. Don't throw away old crank pulley just yet.

Check crank sensor too , maybe it was knocked/disturbed.

Best wishes

Jack
 
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