Hi everybody !

First, please excuse my english, it's not my first langage !

My punto was ok, but, three month ago, sometimes, i had some misfires, and the engine warning light on for 200km. I thought it was the plugs, so, i changed it. As it was not a permanent problem, I thought it was ok, and my punto did not misfire for a while.

Another day, (i was going on holiday), my punto started to misfire a lot (with the orange warning light), and, it did not fire without problem since that day !

I search the internet, but i was not able to say if it was a misfire of one plug, or two. So i bought a ELM327 on dx.com, and had a P0351 diagnostic code. So, coil or ECU problem.

I follow the guide "Punto coil-ECU checks". I build a light probe with two LEDs and resistor.
When starting the engine, i saw that i have the +12V on one pin of the coil connector.
On the second, when i connect it to the negative probe, and the positive to the +12V it start flickering fast enought, i guess. So i change the coil. BUT it did not solve the problem Should i change the ECU ?

I try to use the old coil on the firing coil, it works. DO you have any idea ?

Thanks a lot for reading me !

po351 is the Coil pack error
http://www.permoveo.ltd.uk/tabid/122/OBD-Error-Code/P0351/Diagnostics/Fiat/Default.aspx

Each coil have a 12v feed - but its a switched negative feed that works it

You say you have 12v feed, and a consistant light probe signal, so i suspect the next thing in line been your HT's

If the Plugs are new - gapped and fitted nice then it unlikely to be them
The Coil was replaced and its intermitant - So next weakest is HT

Ziggy

Hello ! Thanks a lot for your quick reply !

What is the HT ? Is this the wire between the spark plug and coil ? (I'm learning motor vocabulary ). But i can't explain the problem : why a single wire could misfire in 2 cylinders ?

I thought it could also be a coil connector problem, so is this a HT ?

Maybe I was not clear enough, but, now, my car does not start without problem. I have the feeling that when i start the engine it's ok, and a quater of second later, it start misfiring on 2 cylinders. I mean there is a sightly difference between with the faulty coil pack disconnected, and with all coils connected.

Does the punto disconnect the coil when sensing a short on one spark plug wire ?

HT Stands for High Tension
HT leads are Yes connected from the Coil Pack to each spark plug

The Coil has a Low tension Side (the 2 pin connector) and the High tension where the HT leads connect

Its possible 2 HT leads have failed giving 2 different cylinders a misfire

BUT if the misfire is on
1 and 4
or
2 and 3
its most likely to be a coil pack issue

https://www.fiatforum.com/punto-guides/52068-punto-coil-ecu-checks.html
Is a handy guide to testing Coil packs

Ziggy

Yes i followed this guide, that's why i changed the coil ! And the 2 coils are ok, i'm sure of this !

It's like the ECU problem but i have the flickering on the connector. I will try to buy a kit of HT wire, it's "only" cost 20€ !

But after that, if it doesn't solve the problem, maybe the transistor in the ECU is dead, and the current is to low to fire correctly the spark through the coil. I build the probe, and the current used to light the LED is about 150mA. I read that punto coil are about 7.5Ohms => 1.5A current to drive it. So my light probe is perhaps to easy to drive ? Does a real light probe uses a lot of current ?

Thanks !

God Only Knows.

The obvious (simple, and cheap) way to test is to remove plugs, place on rocker cover, plug in HT lead, turn engine over). A spark is a spark is a spark.

So the coil was changed and now all 4 have a nice clean strong spark?

Ziggy

Ziggy : No, I changed the coil but i still have the misfire problem. I will change the HT lead to test, and hope it will solve the problem !

If not, i think i will try to change the ECU

Somewhere here there's a guide to testing that accursed ECU.

Generally easier -- and maybe cheaper, if the ECU is the problem -- to send it off to be repaired (no messing around with codeboxes, etc.)

fingers99 said:

Somewhere here there's a guide to testing that accursed ECU.

Generally easier -- and maybe cheaper, if the ECU is the problem -- to send it off to be repaired (no messing around with codeboxes, etc.)

Click to expand...

Yea for us UK lovers
But unfortunatly he is across the pond in France, so no idea what ECU repair companies are like over there

If the ""replaced"" coil is giving 2 dead sparks
Swap the working coil with the suspect dead one
It'll very quickly identify if the ECU is at fault

And the suspect dead one works it kinda a win win thing going on there on diagnostic

Ziggy

finger99 : Yes, i saw that it was possible to repair my ECU, in UK (ecu-testing.com, they ship in france !)

Ziggy : I swap the suspect "dead" coil with the working coil, and it was working. My problem is that according to the guide, my ECU should be OK, and the coil should be dead. But it's not ! With a new coil, my engine runs on 2 cylinders !

I hate electrical problems !

mgrenonville said:

finger99 : Yes, i saw that it was possible to repair my ECU, in UK (ecu-testing.com, they ship in france !)

Ziggy : I swap the suspect "dead" coil with the working coil, and it was working. My problem is that according to the guide, my ECU should be OK, and the coil should be dead. But it's not ! With a new coil, my engine runs on 2 cylinders !

I hate electrical problems !

Click to expand...

So with 2 coil swapped over
The suspect Dead one works in its new temporary position
And Was working now doesn't work in its new temporary position

So it does look like ECU potentially

Have you checked the wiring - make sure it aint been rubbing and snapped somewhere?

Ziggy

Ziggy122 said:

So with 2 coil swapped over
The suspect Dead one works in its new temporary position
And Was working now doesn't work in its new temporary position

So it does look like ECU potentially

Have you checked the wiring - make sure it aint been rubbing and snapped somewhere?

Ziggy

Click to expand...

Yes, when swapping coil, the engine works the same : bad ! I tried to move wires while engine was running and it did not change anything. Have you ever seen a faulty low voltage coil connector ?

What scares me is that the problem was intermittent at the beginning (maybe 10 times and 1000km) and becomes permanent. I've read that when a coil broke, it is sudden, am i true ?