Technical P0300 P0302 1.4 8v Punto

[Aether]

Hi all,
Getting the P0300 & P0302 along with the possibly unrelated stop start not working. At the current moment here are the steps I’ve taken:

Service Oil/Filter & Air filter & Fuel additive injector clean.
Replace spark plugs with NGK plugs
Inspect HV leads, resistance test consistent amongst all leads. Haven’t checked Coil pack since it’s all grouped together and the tutorial seemed slightly complicated.
Crankcase breather?? hose (small one) snapped off airbox, blanked the airbox hole and hose just venting to atmosphere at present.

From what I’ve been reading on the forums this is possible it’s throwing off fake codes, I’ve seen a couple of ideas but I can’t feel the misfire, engine light only sometimes comes on now but is fixed by restarting car (used to be on constantly) however codes are still present and return when driving. Before I take it to a mechanic for the vacuum test and a more thorough electrical inspection is there any other gremlins I should be looking at (without just straight part swapping)? I’ve heard evaporation solenoid might be going bad, ground wires, low voltage, leaks in hoses and etc but that’s been on different car models. Hoping someone has dealt with this before thx.

 

[GrandePunto PL]

1. First rookie mistake: you just swapped the sparkplugs. You should document how the old ones looked like.
You can judge condition of the engine by sparkplug appearance.

2. Coils. Get FES os MES program and check "dwell" (coil charge time). Brand new strong one works at 1,5-1,6 ms (average is 2,0 ms, maximum 2,5 ms). Then other electronic stuff (sensors, if readings make sense according to current weather and so on).

3. Get emissions test and show us the result (print). Gas analysis is as basic as compression test and oil pressure, fuel pressure, etc.

4. Misfire can be caused by fuel system. Remove and check visually the injectors. Change places (and see if the error code goes with the injector from cylinder 2). Check fuel pressure (3,5 bar nominal).

5. Some major leaks, exhaust (spoiling the lambdas), then intake and other stuff. Remove and check the EVAP solenoid (it can be stuck open sometimes).

6. Basic electrical: alternator, battery, main ground (corrosion).

7. Small breather hose terminal never breaks itself. Most people cannot remove the airbox properly. You remove the hose first, then jerk the filter box. Most do it in the opposite order, damaging the plastic nipple. Because official training material from 2004 says so.

 

[Aether]

1. First rookie mistake: you just swapped the sparkplugs. You should document how the old ones looked like.
You can judge condition of the engine by sparkplug appearance.

2. Coils. Get FES os MES program and check "dwell" (coil charge time). Brand new strong one works at 1,5-1,6 ms (average is 2,0 ms, maximum 2,5 ms). Then other electronic stuff (sensors, if readings make sense according to current weather and so on).

3. Get emissions test and show us the result (print). Gas analysis is as basic as compression test and oil pressure, fuel pressure, etc.

4. Misfire can be caused by fuel system. Remove and check visually the injectors. Change places (and see if the error code goes with the injector from cylinder 2). Check fuel pressure (3,5 bar nominal).

5. Some major leaks, exhaust (spoiling the lambdas), then intake and other stuff. Remove and check the EVAP solenoid (it can be stuck open sometimes).

6. Basic electrical: alternator, battery, main ground (corrosion).

7. Small breather hose terminal never breaks itself. Most people cannot remove the airbox properly. You remove the hose first, then jerk the filter box. Most do it in the opposite order, damaging the plastic nipple. Because official training material from 2004 says so.
View attachment 457500

Thanks for the help.
I’m more of a diesel guy never worked on petrols and this is the misses car so I will note that for the future.

I’ll get to the checking and swapping the injectors along with checking the evap solenoid along with a basic look over and then I’ll take it in for an mes scan. I’ll be sure to come back with the results so thanks for the help.

As for the small breather, is that a crankcase vent? Hypothetical if you lived in say Afghanistan (where the car is definitely driven) and didn’t have strict environmental laws, could you maybe put off not reattaching it for a little bit? It had a steering column issue and we’ve had like 10 garages look through the cars electrics so one of them would have broken it off and they’ll probably just break it off again next visit.