Technical Fiat Punto III P0351

[Redlight]

Hello,
I own a 2014 Fiat Punto III 1.4 57Kw BiFuel (factory LPG installation). For the past month, I've been struggling with a fault that I haven't been able to resolve yet. The vehicle reports misfire codes P0300, P0301, P0302, P0303, and P0304. Additionally, it shows error P0351 (Ignition Coil A Primary/Secondary Circuit Malfunction). The vehicle is not running on a rich mixture, and the lambda regulation is functioning correctly.


First, I replaced the spark plugs, then the ignition cables—without any change. I then measured the ignition coil pack (55200112) and consistently got a reading of 0.6 ohms on all four pins relative to the first pin. So the ignition coil pack should be fine as well.


The fault occurs both on LPG and gasoline, but only above 3500 RPM (around 120 km/h). For example, when driving in the city, the issue never appears. The vehicle also has an irregular idle—sometimes it stumbles briefly but then runs normally again.


I don't know where to proceed next, and I don't want to blindly replace working parts with new ones.

 

[GrandePunto PL]

Check this Polish forum, there is a lot of info about timing belt, VVT wheel and solenoid valve, valves lash/clearance, ignition system etc.
Study it for couple hours minimum (with Google Translate): https://fiatpunto.com.pl/forum37.html - then we can talk.
Your coils might be bad at this point (LPG is more demanding), your "check" is not enough (proves almost nothing).
As for lambda, you validate it by external check: obligatory inspection each year, exhaust gas analysis.
You DON'T judge the engine just by looking at Your lambdas, sensors (they can be spoiled and lie to you and ECU).
Primary coil circuit error is a bad connection somewhere (ECU failure, coil "driver" chip is possible but rare).

Possible combo in neglected/abused car:
- bad timing (old belt and/or bad tensioner), first "VVT1" position should be about 106 degrees (use FES or MES program to see this),
- dirt in the engine and VVT system (remove and inspect the solenoid valve), old oil, spoiled oil delivery to the VVT (valve cover o-rings),
- valve lash, clearance (shims) in 8V engines, never checked, never adjusted, probably went bad on LPG (typically cylinder 1 and 4),
- camshaft wear, lobes "polished" (0,1-0,3 missing lift), in 1,4 8V lobes have precisely 9,50 mm lift (you check it with a dial indicator),
- bad coils, "dwell", coil charge time rises to the max. (2,5 ms), while new strong coil should make sparks at 1,5 ms,
- old lambda(s), go to the inspection station/workshop and ask for exhaust check only (not full inspection),
- other things (intake and/or exhaust restrictions or leaks), old faulty sensors (MAP, coolant temperature), excessive oil consumption.