Hi
I have a question re my sons 2004 1.2 8v Punto, the issue started with an occasional misfire but has now progressed to a permanent one, it's missing on cylinders 1 & 4, I read plenty of posts about possible causes and so far have changed the plugs and leads, and done a compression test (all good), i've substituted another coil and swopped them round on the car, i've also checked/wiggled various wires/connectors to no effect, i'm thinking ECU but am slightly uncertain. I tried the coil/ecu test documented on the forum but found I was getting a very dim light on the test lamp on the suspect coil when the negative switched, I've also tried a set of spark plug testers ( the ones that fit between the plug and lead and light up) and these confirmed a good spark on 2 & 3 and what appears to be a very weak spark on 1 & 4, would an ECU failure show up like this or should I be getting nothing at all on the offending cylinders, I've seen adverts for plug and play ECU's on EBAY and I've seen an advert via a forum link to ECU Testing, if it's what the car needs then fine but I wanted to be sure before spending the money, does anybody have any ideas? Thanks Steve

Looks like you have done all The sensible things (-:

Worth checking the connections to the patchy coil..

Both the coil and ECU ends

Even a wriggle.test of the loom might show a change.. its all getting quite old now

Hi
I've disconnected the ECU plugs previously to check for water etc and all seemed ok, tried wiggling the coil connections and the ECU plugs while it was running but it made no difference. Thanks Steve

I would definitely investigate the ignition coil further.

I had a similar issue with my 16v and there was a tiny spec of corrosion on the terminal where the HT lead connects to the coil pack. It become progressively worse like the issue you describe with your son's car (assuming the corrosion became worse). I feel if it was an ECU issue, it would be quite binary. Either working correctly or not. Not gradually getting worse. The coil packs can degrade internally also and this cannot be observed by eye (obviously).

See here:

Haynes Fiat Punto Owners Workshop Manual said:

The ignition side of the system is of the static (distributorless) type, consisting of to twin-output ignition coils located on the left-hand side of the cylinder head. Each ignition coil supplies two cylinders (one coil supplies cylinders 1 and 4, and the other cylinders 2 and 3).

Note: On all engines, two ignition coils are used, with each coil supplying two cylinders. On SOCH (8-valve) engines, the coils can be removed individually, whereas on DOHC (16-valve) engines the coils are combined to form a single unit.

Click to expand...

The fact that you are getting your misfire on cylinders 1 and 4 suggests that one of the coil packs is bad to me.

I guess you could swap them round and see if the misfire moves to cylinders 2 and 3? The manual also details a test that you can perform with a multimeter (if you have one around) that I can post if you require it.

If you find it to be one of the coil packs, I would replace both as they will be of a similar age. Make sure you use a high quality replacement part. I would recommend this BOSH part (you will need 2). They're £15. Delphi also make decent parts (part number CE20058-12B1). The original FIAT part number for the coils on your engine is: 46548037. They are identical. See the picture I have attached for reference (ignition.PNG).

EDIT: I re-read your original post and it seems you have done this. I will leave this information in case someone stumbles across it via Google. I guess the ECU would be the next logical guess but for £30 maybe just swapping both coil packs is worth a go first. The fact that your bulb is lighting up on the negative shows that a trigger is coming through from the ECU. Check out Ziggy's response in this thread here to a very similar issue. He seems to agree with me on the coil pack replacement theory.

I've changed one coil pack and then swopped them over so had one been faulty I would have expected the fault to swop over but it didn't, I also have one new (Lucas) coil I tried previously ( I started again this week to try and keep everything logical), I will have a look at the coil connection, maybe try and get the plug apart or go back up the wire and test again. When I did the negative test at the coil plug I got similar results on both coils ie the test light was only very dim though it would not start with the 1/4 coil only connected so it only cranked, that could be down to the test light though. As I said previously I thought an ECU fault would have sent no signal but I do seem to have a very weak spark so not sure, I will also have to have a look at the wiring though for some reason my Haynes manual does not have an ECU wiring diagram, if the coil negative was wired straight to the ECU I wondered if I could substitute another wire outside the loom and just connect both ends to the respective plugs, I'll try the internet for a wiring diagram too. Thanks Steve

adamsdad said:

I've changed one coil pack and then swopped them over so had one been faulty I would have expected the fault to swop over but it didn't, I also have one new (Lucas) coil I tried previously ( I started again this week to try and keep everything logical), I will have a look at the coil connection, maybe try and get the plug apart or go back up the wire and test again. When I did the negative test at the coil plug I got similar results on both coils ie the test light was only very dim though it would not start with the 1/4 coil only connected so it only cranked, that could be down to the test light though. As I said previously I thought an ECU fault would have sent no signal but I do seem to have a very weak spark so not sure, I will also have to have a look at the wiring though for some reason my Haynes manual does not have an ECU wiring diagram, if the coil negative was wired straight to the ECU I wondered if I could substitute another wire outside the loom and just connect both ends to the respective plugs, I'll try the internet for a wiring diagram too. Thanks Steve

Click to expand...

It is typical for an ECU coil output transister to fail so it only partially works. The ECU is controlling Earth. The coil is always battery positive.

If you connect a test light between the trigger wire and the battery positive supplied to the coil, it should flash brightly as you crank the engine - as brightly as the other coil does. Dimly flashing suggests the trigger wire is not pulling the other side of the bulb to earth. Unless the wiring is faulty that is a typical fault. The ECU cannot ground the coil sufficiently. But you need to check the positive and negative side of the coil for good electrical connection between ECU and battery.

Hi
If it's normal for it to have failed and only partially work then it looks like it's going to be the ECU, I will double check the positive feed and the negative switch again to be sure.
If it's the ECU does anyone have any recommendations/experience with any of the ECU people out there? I've seen them on ebay and places online but a recommendation is always worthwhile? Thanks Steve

adamsdad - it may be worth checking all your the earthing points on the car and cleaning them up too.

Regarding the ECU replacement, you can find examples on eBay that have been reset or virginised" that should be plug and play. That's as far as my knowledge extends though as I've not personally had to bother with a ECU based repair or replacement (yet).

I did some more checks this morning though I'm not sure it's helped any, I went round various earth points on the engine etc with a multimeter and get very similar results to across the battery, so that all seems OK, the earths were removed and cleaned a while ago to try and cure a power steering problem,
I still can't get a bright light using the negative switch through the ECU on either coil plug, both coils have battery voltage to the feed, however I tried connecting the meter across the disconnected coil plug and when you initially switch on I can get battery voltage for a couple of seconds then it drops to zero, i believe this is normal, when you crank the engine I only get about 9v across the coil plugs, the coil for 2/3 being very slightly better, i know the meter is not sensitive enough to show the current switching but if i can only get 9v this may explain why the test lamps dim? Is it possible that both circuits in the ECU are faulty and it's actually just limping along on the better one? I tried cleaning the ECU plugs and have continuity from the ECU plug to the coil, I did have some head scratching trying to work out whether the pictures on line where the ECU or the plugs (which was A/B) as everything seemed the wrong way round/upside down, however it seems I needed points 10 and 38 (allegedly on plug A), this turned out to be the left hand side of the left hand plug when looking from the front of the car, i've since removed the ECU and these pins are numbered so i must have got the right ones! Don't know if any of this is helpful but in the absence of anything else to try I may have to send the ECU off (at least to get it tested). I did some more research into the ECU issue and it seems the ones on Ebay are often a working 2nd hand unit that's been reset/virginised, but does not appear to have any more testing done, I'm waiting for a reply about any warranty but would be wary of this as the one we have was perfect a month ago then started failing. The ECU testing one is said to be fully tested/rebuilt with a lifetime warranty.

Did you get a solution on this ?

Hi,
Please let us know how you have solved this problem

adamsdad said:

I've changed one coil pack and then swopped them over so had one been faulty I would have expected the fault to swop over but it didn't, I also have one new (Lucas) coil I tried previously ( I started again this week to try and keep everything logical), I will have a look at the coil connection, maybe try and get the plug apart or go back up the wire and test again. When I did the negative test at the coil plug I got similar results on both coils ie the test light was only very dim though it would not start with the 1/4 coil only connected so it only cranked, that could be down to the test light though. As I said previously I thought an ECU fault would have sent no signal but I do seem to have a very weak spark so not sure, I will also have to have a look at the wiring though for some reason my Haynes manual does not have an ECU wiring diagram, if the coil negative was wired straight to the ECU I wondered if I could substitute another wire outside the loom and just connect both ends to the respective plugs, I'll try the internet for a wiring diagram too. Thanks Steve

Click to expand...

Any updates over the summer?

Hi
Apologies for not replying sooner, I tried all the checks but it was very difficult to narrow anything down as nothing seemed to have completely failed, in the end I sent the ECU off for testing and they confirmed it was faulty, repaired it and sent it back, fitted along with the previously fitted plugs/leads/coils etc and car runs perfect, can well recommend ECU testing, quite expensive but i felt worth the money. Thanks Steve