My 2003 1.2 8V Punto is now running on 3 cylinders. Problem started soon (5 miles or so) after refilling a very nearly empty fuel tank - misfiring and the engine warning light first flashing then staying on) so my initial thoughts were dirty fuel but, with all the rain and flooding on the roads that day, I didn't want to add 2 + 2 and get 5 so I borrowed a scanner to see what the fault codes were.

Got the following: P0302 misfire on No. 2, P0202 injector No. 2 circuit malfunction, P0445 evaporative emission control system - purge control valve circuit, and a couple of unidentified ones U1600 & U1601. After poking around a bit, checking that HT leads etc were secure, I ran another scan and got all of the above again plus a new one: P0352 ignition coil primary/secondary circuit.

I started by looking at the spark plugs - all looked the right colour (no unburnt fuel in No. 2). Then I tried swapping the coils around but the problem stayed at No. 2 cylinder (another scan - same fault codes) so I thought that the ignition system is probably OK and started on the fuel system. Thought I was getting close when I removed the plug from No. 2 injector when engine was running and it made no difference at all - same lumpy idle. Doing the same with any of others caused the engine to stall.

Then I tested the resistance of all 4 injectors - all were about 15 ohms so seemed OK. Then, with ignition on, I measured voltage across terminals of each injector plug - 1,3, & 4 were just under 2V, No. 2 was only 0.6V. I traced +ve wire from No. 2 injector back to connector at ECU (goes to the plug on the driver's side), cut wire just before plug and checked voltage again - no change from 0.6V so wiring harness is probably OK up to plug. Lots of WD40 plus refitting/wiggling of the plug didn't change things. Couldn't test if connection in plug itself was OK because the probes on my meter leads are too big.

Now thinking dark thoughts about it being the ECU or possibly the multipin connector - both bad news.

Please can anybody offer some wise advice on what to do next, before I have to start throwing money (that I don't have) at the problem?

welcome to the forum
have you done these checks in this guide https://www.fiatforum.com/punto-guides/52068-punto-coil-ecu-checks.html

Thanks Dave - I'm still finding my way around the site. There is a lot of good info and expertise to get through!

I'll do the coil/ECU checks in the morning and see what that that throws up. Is it possible that the ECU cuts the fuelling to a cylinder if a dodgy coil sends the emissions sky high?

Had another go at ignition system - it seems to be firing OK on all 4 cylinders. Swapping coils over doesn't move problem away from No. 2 cylinder. Also, using one of those yellow test light things that fits between HT lead and spark plug, all four cylinders were showed strong, regular flashing.

I suspect that ECU might not be sending a 'squirt' signal to No 2 injector. Engine runs exactly the same with or without this injector plug connected.

Anyone know how to test the signal at the injector plugs? Also, why is there a small voltage (2V) on the injectors with ignition on?

Update:

Swapped injectors between No.1 and No. 2 cylinders but problem didn't move from No. 2 to No. 1 so injectors themselves seem to be OK.

Now it's running on only two cylinders! Injector No. 2 and now No. 4 as well don't seem to be 'firing'. I can pull the wiring harness plugs off 2 and 4 with no change in engine note.

With engine stopped but ignition on, I'm still getting 2V across the wiring harness plug contacts for the good injectors 1 and 3 but less than 0.5V for 2 and 4. This is telling me something but I don't know what.....

Just been out and plugged the scanner in again to see what had changed - got all the fault codes I had before plus a full set of injector circuit malfunctions - all 4 cylinders showing errors.

Help!!!!

Ecu

Hi Chris,

If ECU is fried, is it likely to be because of an underlying ignition system problem (coil maybe?) despite all 4 plugs apparently sparking OK?

Fred in a shed said:

Also, why is there a small voltage (2V) on the injectors with ignition on?

Click to expand...

It's because it's not a constant current. You'll have to use oscilloscope to see the real voltage.

New ECU sorted it. Fitted new coils as well just in case they were something to do with the original failure.

Glad you solved it, make sure the correct plugs are in there too!