Hello all, just looking at a 2005 UK model Accent LC 1.3 SOHC 12V.
Initial symptoms:
Initial very occasional single miss / brief hesitation, not enough to light the check engine light. Possibly intermittent loss of power. Developed into a very obvious heavy multiple misfire, with fault codes for multiple misfire and cyls 1, 2, 3 misfire. (P0300, P0301, P0302, P0303). Car runs (just) but undriveable. No other fault codes. Possible small amount of coolant loss.
Actions taken and further symptoms:
Initial inspection (not much more than poking around to look for anything obvious), checked plug leads for condition and arcing and cleaned plugs. Engine then ran cleanly for around 15 miles then reverted to heavy misfire. Car then left overnight.
Plugs were in poor condition so replaced with NGK BKR5E-11 (per NGK parts lookup). No change, started with heavy multiple misfire.
Testing appeared to show No 2 & 3 coil might be faulty so replaced the coil pack. Car left for a week before fitting coil pack (holiday!). Coil pack fitted, engine ran cleanly for around 5 minutes and restarted OK three or four times, then reverted to a heavy misfire after having been driven round the block. Car left overnight.
Plugs removed and checked; no obvious fouling, damage, or differences in colour / residues. Regapped to 0.035" and tried again, no difference.
After 3 hours or so started car again, started cleanly and ran smoothly for around 5 minutes then reverted to heavy misfire which sounded like a single cylinder misfire, but I couldn't narrow it down to one particular cylinder.
When the car does misfire I can't narrow it down by either plug lead removal or injector lead removal, though removing the lead from No. 4 appeared to make the misfire worse.
Injectors all appear to be working electrically though of course that doesn't mean they're not clogged or dirty.
Though there is a suggestion of coolant loss, there is no obvious sign of head gasket failure.
There's no sign of vacuum building in the fuel tank.
Thoughts:
Assuming the misfire detection is accurate it's interesting there's apparently no misfire on No. 4.
That makes me think the problem is less likely to be something that you'd expect to affect all four cylinders equally such as air flow sensor, fuel pump, fuel filter, knock sensor or position sensors, though I'm not ruling these out.
I'm inclined to think that a head gasket failure significant enough to cause a multiple cylinder misfire would be showing some obvious signs, though I haven't ruled it out and will test for it.
I'm also inclined to think that head gasket or inlet manifold gasket failure would tend to get worse rather than being intermittent.
It's interesting that on several occasions the misfire has disappeared when the car has been left, only to reappear after several minutes running. That makes me think either a part is getting hot and breaking down, or the misfire is masked by the operation of the cold start loop, or there is some other thermal or time effect playing a part.
I'm struggling to find test data or technical information, which doesn't help - and I've got a stinking cold which isn't making systematic testing any easier!
Going to keep plugging on, but if anyone has any thoughts I'd be glad to hear them.
Initial symptoms:
Initial very occasional single miss / brief hesitation, not enough to light the check engine light. Possibly intermittent loss of power. Developed into a very obvious heavy multiple misfire, with fault codes for multiple misfire and cyls 1, 2, 3 misfire. (P0300, P0301, P0302, P0303). Car runs (just) but undriveable. No other fault codes. Possible small amount of coolant loss.
Actions taken and further symptoms:
Initial inspection (not much more than poking around to look for anything obvious), checked plug leads for condition and arcing and cleaned plugs. Engine then ran cleanly for around 15 miles then reverted to heavy misfire. Car then left overnight.
Plugs were in poor condition so replaced with NGK BKR5E-11 (per NGK parts lookup). No change, started with heavy multiple misfire.
Testing appeared to show No 2 & 3 coil might be faulty so replaced the coil pack. Car left for a week before fitting coil pack (holiday!). Coil pack fitted, engine ran cleanly for around 5 minutes and restarted OK three or four times, then reverted to a heavy misfire after having been driven round the block. Car left overnight.
Plugs removed and checked; no obvious fouling, damage, or differences in colour / residues. Regapped to 0.035" and tried again, no difference.
After 3 hours or so started car again, started cleanly and ran smoothly for around 5 minutes then reverted to heavy misfire which sounded like a single cylinder misfire, but I couldn't narrow it down to one particular cylinder.
When the car does misfire I can't narrow it down by either plug lead removal or injector lead removal, though removing the lead from No. 4 appeared to make the misfire worse.
Injectors all appear to be working electrically though of course that doesn't mean they're not clogged or dirty.
Though there is a suggestion of coolant loss, there is no obvious sign of head gasket failure.
There's no sign of vacuum building in the fuel tank.
Thoughts:
Assuming the misfire detection is accurate it's interesting there's apparently no misfire on No. 4.
That makes me think the problem is less likely to be something that you'd expect to affect all four cylinders equally such as air flow sensor, fuel pump, fuel filter, knock sensor or position sensors, though I'm not ruling these out.
I'm inclined to think that a head gasket failure significant enough to cause a multiple cylinder misfire would be showing some obvious signs, though I haven't ruled it out and will test for it.
I'm also inclined to think that head gasket or inlet manifold gasket failure would tend to get worse rather than being intermittent.
It's interesting that on several occasions the misfire has disappeared when the car has been left, only to reappear after several minutes running. That makes me think either a part is getting hot and breaking down, or the misfire is masked by the operation of the cold start loop, or there is some other thermal or time effect playing a part.
I'm struggling to find test data or technical information, which doesn't help - and I've got a stinking cold which isn't making systematic testing any easier!
Going to keep plugging on, but if anyone has any thoughts I'd be glad to hear them.