Misfire after flat battery...
Discussion
Just wondering if anyone has any ideas what the problem could be. The car's going in to a garage soon for something unrelated (waiting for parts to come in) and will get it looked at properly then, but would be good to have at least an idea of what's wrong. 
The car (2006 MX5 1.8) was driving fine prior to this, but I then left it parked up for four days and left the interior light on and came back to find the battery was completely, utterly dead.
Long story short, after jump starting the car and trying to drive off, it stalled (i.e. died whilst driving, rather than just poor clutch control) and had to be jumped again. After starting it again and letting it run for a bit longer before driving, it ran fine. A bit rough (owing to the ECU resetting itself probably) but otherwise fine.
Well, fine except for it's now developed a misfire under certain conditions. It's difficult to reproduce, but it seems to mostly happen when cruising at high RPM in fifth gear (let's leave the exact speed out of it...
). Simply revving the engine to a high RPM doesn't seem to do it (i.e. working through the gears), so if it is RPM related rather than speed (more likely?) then it's probably only under sustained high RPM.
When it happens, it feels like it's running on three cylinders. There's a noticeable loss of power, then shortly after that the car starts shuddering and the check engine light starts flashing. Obviously when this happens I get off the power. The light stays flashing until I've slowed down to below a certain speed, at which point the car feels fine. Back on 4 cylinders, no shuddering, no loss of power etc.
However, since this has happened I've tried reproducing it and found it...difficult. Sometimes it will cruise at high speed without any problems, then the next day start misfiring again.
This has gone on for about a week (although the car isn't driven daily), but now it seems to have gotten worse. Now there is an elusive 'flat spot' in the rev range when accelerating hard, although this has only happened once. At 4k~ RPM it just felt like I'd hit the rev limiter (though the revs were slowly increasing). No shuddering, no engine light, etc.
Any ideas what could be the problem?
The flat battery it the only event I can think of between the car working properly and now being a bit of a pig...
The car (2006 MX5 1.8) was driving fine prior to this, but I then left it parked up for four days and left the interior light on and came back to find the battery was completely, utterly dead.
Long story short, after jump starting the car and trying to drive off, it stalled (i.e. died whilst driving, rather than just poor clutch control) and had to be jumped again. After starting it again and letting it run for a bit longer before driving, it ran fine. A bit rough (owing to the ECU resetting itself probably) but otherwise fine.
Well, fine except for it's now developed a misfire under certain conditions. It's difficult to reproduce, but it seems to mostly happen when cruising at high RPM in fifth gear (let's leave the exact speed out of it...
). Simply revving the engine to a high RPM doesn't seem to do it (i.e. working through the gears), so if it is RPM related rather than speed (more likely?) then it's probably only under sustained high RPM.When it happens, it feels like it's running on three cylinders. There's a noticeable loss of power, then shortly after that the car starts shuddering and the check engine light starts flashing. Obviously when this happens I get off the power. The light stays flashing until I've slowed down to below a certain speed, at which point the car feels fine. Back on 4 cylinders, no shuddering, no loss of power etc.
However, since this has happened I've tried reproducing it and found it...difficult. Sometimes it will cruise at high speed without any problems, then the next day start misfiring again.
This has gone on for about a week (although the car isn't driven daily), but now it seems to have gotten worse. Now there is an elusive 'flat spot' in the rev range when accelerating hard, although this has only happened once. At 4k~ RPM it just felt like I'd hit the rev limiter (though the revs were slowly increasing). No shuddering, no engine light, etc.
Any ideas what could be the problem?
The flat battery it the only event I can think of between the car working properly and now being a bit of a pig...
MangledMetal said:
It's more than likely down to the battery.
I would suggest this too. I reckon the battery doesn't have enough power stored at high rpm/high load. Does it get worse if you turn the headlights on? Do the headlights get brighter if you rev the car when stationary?I'd put the battery on a trickle charger
Jump starting cars nowadays can be fraut with subsequent ECU and other problems. Could be fuel flow with greater flow required at high speed. Or could well be the ECU or other component has not resumed settings. The days of guessing car misfires went as all the electronic gadgets came in. A suitable laptop analyser should narrow the field. Good luck.
Begin by fully recharging the battery with a battery charger then see what happens. Don't expect the alternator to fully recharge the battery in a short distance, it won't.
How did you jump start the vehicle? If off another vehicle then, depending how you did it, you MAY have caused damage to the electronics.
How did you jump start the vehicle? If off another vehicle then, depending how you did it, you MAY have caused damage to the electronics.
Not sure how to check re the unburnt fuel. If there was unburnt fuel then I'm guessing there'd be a fair bit of smoke on startup? As far as I can remember there was nothing like this.
Regarding the battery, I don't have a spare. The car did a fairly long journey after jump starting it (150 miles~) so I would have thought it would be charged up to a decent amount again. There's been no problems starting the car since. Or do you mean that once run down to empty, the battery may just be knackered?
As for the ECU: I'm just about to buy a cheap OBDII reader and see if there are any error codes.
Some other details that may help:
After jump starting the car the second time, the guy from the AA connected something (Ammeter?) to the battery and said it all looked fine.
I noticed a couple of days later that the lid of the battery compartment hadn't been fitted back on securely and may have been rattling about a bit. Not completely disconnected, but potentially could have been moving the battery leads about.
Similar to above, I noticed one of the leads coming from the negative battery terminal (it splits in two) wasn't secured properly. It's supposed to clip to the engine cover, but wasn't. Not sure how long it's been like that but it's reattached now. Probably not much in itself, but again it meant the cable had a much wider range of movement than it should have had.
ETA:
Paintman:
The car was jump started twice. I waved down a passerby who happened to have jump leads and we used his car to get it started. After it stalled I managed to catch him again.
Honestly, details are a little thin as I was pretty tired by this point... AA arrived just after I'd got the car started the second time. They checked the battery and then left.
Regarding the battery, I don't have a spare. The car did a fairly long journey after jump starting it (150 miles~) so I would have thought it would be charged up to a decent amount again. There's been no problems starting the car since. Or do you mean that once run down to empty, the battery may just be knackered?
As for the ECU: I'm just about to buy a cheap OBDII reader and see if there are any error codes.
Some other details that may help:
After jump starting the car the second time, the guy from the AA connected something (Ammeter?) to the battery and said it all looked fine.
I noticed a couple of days later that the lid of the battery compartment hadn't been fitted back on securely and may have been rattling about a bit. Not completely disconnected, but potentially could have been moving the battery leads about.
Similar to above, I noticed one of the leads coming from the negative battery terminal (it splits in two) wasn't secured properly. It's supposed to clip to the engine cover, but wasn't. Not sure how long it's been like that but it's reattached now. Probably not much in itself, but again it meant the cable had a much wider range of movement than it should have had.
ETA:
Paintman:
The car was jump started twice. I waved down a passerby who happened to have jump leads and we used his car to get it started. After it stalled I managed to catch him again.
Honestly, details are a little thin as I was pretty tired by this point... AA arrived just after I'd got the car started the second time. They checked the battery and then left.
Edited by mx5tom on Saturday 12th October 18:04
t. Certain revs had no power and was extremely random. Battery disconnected over night and put back on fully fixed it.The MX-5 does run (like most modern cars) what is known as a KAM(keep alive memory) this allows the PCM to adapt it's base settings for things like the throttle body, long term fuel trim etc.. as engine wear occurs naturally through the vehicles life
When the battery is disconnected, this is wiped, and they take a while to relearn the required values to allow stable idle etc, and there is a drive mode that can completed to assist the PCM in relearning them, but; you say the battery was flat, not disconnected, and as long as the battery could still supply a small amount of current to the module, it shouldn't have been wiped
It still might be worth carrying out the drive mode to see if it makes a difference, although as you say you did a longish journey immediately after getting it started, it is unlikely to make a difference
As others have said, it could be a battery issue - the one installed on the MX-5 NC isn't the biggest, and even on newish cars, they can struggle to stay charged if the car is left for more than few weeks - if the battery is the original, the it's 7 years old, and is unlikely to be at it's best now anyway.
When the battery is disconnected, this is wiped, and they take a while to relearn the required values to allow stable idle etc, and there is a drive mode that can completed to assist the PCM in relearning them, but; you say the battery was flat, not disconnected, and as long as the battery could still supply a small amount of current to the module, it shouldn't have been wiped
It still might be worth carrying out the drive mode to see if it makes a difference, although as you say you did a longish journey immediately after getting it started, it is unlikely to make a difference
As others have said, it could be a battery issue - the one installed on the MX-5 NC isn't the biggest, and even on newish cars, they can struggle to stay charged if the car is left for more than few weeks - if the battery is the original, the it's 7 years old, and is unlikely to be at it's best now anyway.
It's not the original battery. Unfortunately, not my first time killing a battery... 
This one's less than a year old, so not new but hardly ancient.
Usually after a flat battery, it's run a little rough (especially on idle) for a couple of days and then sorted itself out, but never misfired or anything like that.
I'll try disconnecting the battery and see if the ECU sorts itself out. Probably the easiest and quickest thing to check. It would be a lot easier to check if the misfire wasn't so inconsistent though!
This one's less than a year old, so not new but hardly ancient.Usually after a flat battery, it's run a little rough (especially on idle) for a couple of days and then sorted itself out, but never misfired or anything like that.
I'll try disconnecting the battery and see if the ECU sorts itself out. Probably the easiest and quickest thing to check. It would be a lot easier to check if the misfire wasn't so inconsistent though!
Always the problem with intermittent faults! They often refuse to play when on diagnostics as well
Got the 'T'-shirt!
Disconnecting the leads with both engines running when jump starting can create a spike which can damage electrics.
IIRC a figure of at least 500 miles has been quoted to put anything like a worthwhile charge back into a flat battery.
Got the 'T'-shirt!Disconnecting the leads with both engines running when jump starting can create a spike which can damage electrics.
IIRC a figure of at least 500 miles has been quoted to put anything like a worthwhile charge back into a flat battery.
mx5tom said:
It's not the original battery. Unfortunately, not my first time killing a battery... This one's less than a year old, so not new but hardly ancient.
Usually after a flat battery, it's run a little rough (especially on idle) for a couple of days and then sorted itself out, but never misfired or anything like that.
I'll try disconnecting the battery and see if the ECU sorts itself out. Probably the easiest and quickest thing to check. It would be a lot easier to check if the misfire wasn't so inconsistent though!
I feel your pain! I have exactly the same problem albeit on completely different type of car...very low mileage BMW 840Ci Sport...and that has TWO batteries. Same scenario though and I ended up replacing batteries and still to no avail. This one's less than a year old, so not new but hardly ancient.Usually after a flat battery, it's run a little rough (especially on idle) for a couple of days and then sorted itself out, but never misfired or anything like that.
I'll try disconnecting the battery and see if the ECU sorts itself out. Probably the easiest and quickest thing to check. It would be a lot easier to check if the misfire wasn't so inconsistent though!
Good luck!
Superhoop said:
Matt UK said:
Could be HT leads? Quite a cheap DIY trial to find out.
Not really sure what the cause is, but it 100% won't be this^^^^ A 2006 MX-5 is coil on plug
When I had a 1996 NA with a mis-fire, new HT leads were the answer. I didn't read the 2006 bit - my mistake.
So... a month later and an update.
I bought a cheap wifi fault reader off eBay to use with one of the free OBD iPhone apps. Wasn't expecting much but only cost around a tenner so worth a go. Anyway, it wasn't able to read any fault codes, but did give me the option to clear any codes...
I did that and the engine light immediately went out (not sure if I mentioned this, but it went from occasionally flashing to being on constantly).
Afterwards, I drove the car a few times and was unable to replicate the misfire. All sorted!
Or not, seeing as I'm back posting here.
A few days ago my exhaust destroyed itself... Well, the centre section anyway. I was driving at a steady 70mph, not accelerating and things suddenly got a LOT louder. I didn't notice any misfire or anything like that prior to this happening. Long story short I've replaced the centre section and the car has started misfiring again. I'm unsure if the two are linked; I don't drive the car very often so it's possible the problem was never fixed (well, that seems obvious now).
After it misfired, I got the fault code reader on it straight away and it said P0303 - Cylinder 3 misfire. That's a start, I guess. I cleared the code and immediately got a different code... 3430. Just that, no message or anything else. I've googled that and haven't found anything particularly useful (just a lot of manufacturer specific error codes, but none for Mazda).
I've cleared that too and it's been ok since but clearly something is amiss here...
I can't get my car to a garage until Tuesday, so until then has anyone got any ideas what's up?
Edit:
Only generic reference to '3430' I can find it for:
'P3430: Cylinder 4 Exhaust Valve Control Circuit/Open'
Not sure if I trust that though...
I bought a cheap wifi fault reader off eBay to use with one of the free OBD iPhone apps. Wasn't expecting much but only cost around a tenner so worth a go. Anyway, it wasn't able to read any fault codes, but did give me the option to clear any codes...
I did that and the engine light immediately went out (not sure if I mentioned this, but it went from occasionally flashing to being on constantly).Afterwards, I drove the car a few times and was unable to replicate the misfire. All sorted!
Or not, seeing as I'm back posting here.
A few days ago my exhaust destroyed itself... Well, the centre section anyway. I was driving at a steady 70mph, not accelerating and things suddenly got a LOT louder. I didn't notice any misfire or anything like that prior to this happening. Long story short I've replaced the centre section and the car has started misfiring again. I'm unsure if the two are linked; I don't drive the car very often so it's possible the problem was never fixed (well, that seems obvious now).
After it misfired, I got the fault code reader on it straight away and it said P0303 - Cylinder 3 misfire. That's a start, I guess. I cleared the code and immediately got a different code... 3430. Just that, no message or anything else. I've googled that and haven't found anything particularly useful (just a lot of manufacturer specific error codes, but none for Mazda).
I've cleared that too and it's been ok since but clearly something is amiss here...
I can't get my car to a garage until Tuesday, so until then has anyone got any ideas what's up?
Edit:
Only generic reference to '3430' I can find it for:
'P3430: Cylinder 4 Exhaust Valve Control Circuit/Open'
Not sure if I trust that though...
Edited by mx5tom on Saturday 9th November 18:00
If you are the DIY type you will need to test for voltage etc ranges across everything that could possibly be causing this, obviously having to hand the data which is not very difficult nowadays.
Since there is already a specific ref to Cyl 3 it could well be that the coil for that cylinder is on the way out, nothing extraordinary as far as it goes, coils (or rather coil, singular) were a common failure item in the old days, seemed to have been sorted in the recent past, but now placing them somewhere hot such as between camshafts does not seem to be doing them much good and we are back full circle.
Since there is already a specific ref to Cyl 3 it could well be that the coil for that cylinder is on the way out, nothing extraordinary as far as it goes, coils (or rather coil, singular) were a common failure item in the old days, seemed to have been sorted in the recent past, but now placing them somewhere hot such as between camshafts does not seem to be doing them much good and we are back full circle.
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