Xander Hugh

Cylinders misfire, seems to be related to electrical drain. Possible alternator issue?


3 months ago I was getting one and two cylinders misfiring which would appear when under electrical load, ie if the lights and heater were on, the misfires would randomly begin, and would only clear if I pulled over, turned the engine off and started up again. The cylinders would then fire normally, but would return again if under heavy electrical load. Occasionally just pressing the breaks would be enough to cause the problem, presumably because the rear break lights adding to the electrical load. Sometimes it would be one cylinder, other times definitely two, possibly three.

It began to appear around a week after I had to do a jump start from a dead battery due to leaving the internal light on. My first thought was that I might have knackered the battery, so I bought a new one and everything was fine for a month or so, then the same problem returned.



The voltage meter on the dash is a good 14v.

More recently the problem would not clear after turning off and restarting, however if I left the engine to run for a short period, perhaps a minute or two with no heaters, lights etc, then switch off and restart the problem is again cleared.

I rarely drive long distance, I generally use for town driving less than 10 miles a week.



If the voltage meter in the dash is reading the correct voltage, could it still be an issue with the alternator? Can cylinders refusing to fire even be cause by low electrical power, and if so why would they not fire up again if, say, I turned off the headlights and heater without switching her off and restarting? Why do I have to restart to clear it?

She seems to turn over just fine, it doesn’t sound like the battery is struggling.

I’m guessing it’s the alternator, but it just doesn’t seem consistent with what you’d expect a lack of electrical power to do. I see no brightening of the headlights if I rev the engine, the voltage meter is a nice stable 14v.



Has anyone else experienced these symptoms before?

Xander Hugh

Bump

CK_32

iTrader: (1)

It's possible.

Low power, low spark. Not enough spark no boom.

Process of elimination. See if you or a shop can try a new alternator, new battery.

I'm sure the shop can test the alternator if you don't mind spending $60

Xander Hugh

I just don't understand why nothing else is being effected, not even so much as a sluggish crank or dimming lights. Many of the issues related to low power I've read online seem to suggest that the dash will start to go haywire, air bag lights come on and then eventually fail to start, but I've got none of that and kicking out 14.3v. Maybe the voltage regulator is screwed and not giving a stable output.

CK_32

iTrader: (1)

Have you checked your coil packs? Your spark plugs?

Bad gas? Bad fuel pump? The list goes on.

Follow the trail. Gas from start to finish. Electrical from start to finish.

Then look for vaccum leaks.

Air-spark-fuel

Xander Hugh

Plugs are less than 18 months old, I only drive around 1500-2000 miles a year. I am attempting to isolate the problem of missfires with apparent low battery when there is no other evidence whatsoever of a lack of electrical power.

How might that effect the items you've detailed? I'm reluctant to continue throwing money at things which may or may not be a definitive cause, I had assumed that it would be symptoms of a specific issue, rather than having to start replacing all things electrical. One key piece of info as I mentioned is that it started almost immediately after having to jump her from a flat battery a few months ago. I don't see how that would effect the fuel pump or spark plugs. It was most probably the battery having failed, but as I said I've replaced that and a matter of weeks later the problem returned.

What else could a flat battery trigger? A problem with the ECU?

To be clear, a full battery charge will resolve the problem temporarily as if I'm using a battery that isn't holding charge, yet it's a new battery bought because I assumed the old battery was causing the problem. Daytime driving will resolve it temporarily.
As soon as I begin using things like headlights, heater, demisting etc for any extended period the problem returns.

Incidentally, as I've mentioned before if the issue is present it will not clear itself no matter how far I drive or what electrical load I place on her, however if I have driven a short period and take a guess that the battery has gotten some charge, I can then pull over, turn the engine off and back on again and the problem is again resolved.
However, let's say I start her up with the issue present, don't drive anywhere but then immediately turn the engine off and back on again, the problem is still there. It behaves as if it is a battery not holding charge.

So if I take action that one would if they knew their battery was almost flat (letting her run a bit before driving off for example) then the problem goes away. If I'm doing a lot of day driving and not putting the battery under load the problem doesn't surface. Aside from the 1 and 2 cylinder misfires there are no other outward signs of electrical issues.

CK_32

iTrader: (1)

Just because you get power to the meter/inerior power doesn't mean you don't have a weak connection or short else where.

It could or couldn't be it. It could also be a lot of other things. You're the one that stated it seems to be power related. So you must have some idea if you made that assumption. I'm just guessing going off of the info you gave.

It could be a thousand different things. Fact of the matter is you have the car in your hands I don't. I'm just telling you what common misfire problems are and the issues I've experienced with my own and or cars I've worked on in the last 15 years with similar issues.

Xander Hugh

I wonder if the alternator's voltage regulator is spiking/dipping enough to miss a single stroke, trip the ECU in to thinking there is a more serious firing problem than there actually is, then intentionally retard any further firing of that cylinder until the vehicle is restarted when it can assess again and decide it's fine until I start putting more load on to the electrical systems and start the cycle again.

She's behaving and reacting as if there is insufficient electrical power to spark, yet everything else says the electrical power is fine and available in abundance.

I'll try resetting the ECU tomorrow, and if that doesn't work I'll get the alternator replaced next and report back, clearly it's not a typical problem with a straight forward solution.

Xander Hugh

For the benefit of anyone else who may find this post in the future, I can confirm that an alternator replacement has resolved the issue. My voltage meter now hovers around 15v instead of 13v-14v.