Misfire and hesitancy
Discussion
Last week my MX5 (supercharged mk2.5) ground to a halt with a blown coilpack. I drove it a couple of miles with it running on only 2 cylinders until I found somewhere safe to stop, and by then the cat was literally glowing red hot.
I've since replaced both coilpacks and all plugs, and it was running fine for a few days, but now it's started misfiring again once it gets warm to the point that it sounds like an impreza with a loud exhaust :S
It'll intermittently idle okay, and sometimes pulls fine as if she's clearing her throat, but more often than not, it's misfire city.
Would a ruined/clogged cat cause such symptoms?
As the cat on the MK2.5 is integral to the center section, I'm not keen on replacing it unless I'm sure the fault lies there. I'm tempted to gut the cat in the meantime anyway, if only to eliminate it from the fault finding process, but I'm wondering if I'm missing something obvious.
I've since replaced both coilpacks and all plugs, and it was running fine for a few days, but now it's started misfiring again once it gets warm to the point that it sounds like an impreza with a loud exhaust :S
It'll intermittently idle okay, and sometimes pulls fine as if she's clearing her throat, but more often than not, it's misfire city.
Would a ruined/clogged cat cause such symptoms?
As the cat on the MK2.5 is integral to the center section, I'm not keen on replacing it unless I'm sure the fault lies there. I'm tempted to gut the cat in the meantime anyway, if only to eliminate it from the fault finding process, but I'm wondering if I'm missing something obvious.
Just been out for another run. Higher revs with a wider throttle opening initiates a bit of a misfire, but I can keep her running clean if I cruise around at around 3000 rpm. Idle's fine until, for example, stuck in traffic or getting hot when it starts to get lumpy, but generally, keeping on the go in a gentle manner seems to avoid the symptoms. Just when the foot goes down and the revs exceed around 4500 that the misfire reappears.
Not sure about the cat causing an issue OP but sounds exactly like my own coilpack issues. Fine at cruising speed. Let it get too warm sitting in traffic or putting the hammer down and it misfires. Does it struggle to start if you turn if off too until it cools down? If so it may be worthwhile to check those coilpacks again... I changed mine and it was grand.
Best of luck getting it sorted!
edit to add, you mentioned coilpack and plugs. Did you switch out the HT leads too?
Best of luck getting it sorted!
edit to add, you mentioned coilpack and plugs. Did you switch out the HT leads too?
Edited by Pandaboy on Sunday 28th June 17:11
I've been doing some digging and tweaking today.
I did a plug chop and found them all to be equally sooty. One of the other things I've done recently was refit the crank sensor and trigger wheel, so I doublechecked my settings for the ignition timing reference offset. It 'appears' that it's been running with a bit too much retard. This also matches the symptoms as the ECU has a 5 degree advance on starting which reduces as the engine warms, and so it quite possibly have been starting with the igntion around the right point and then ending up retarded.
I've experimented with the ignition reference offset and have it running much better, the misfire is almost gone, but it feels strangled and underpowered t higher revs, with an occasional misfire. That, in my mind, would also fit with a partial blockage of a knackered cat.
The plug leads are incredibly short on this model (it's effectively coil-on-plug for two of them, and for the remaining two, one is about an inch and a half long, and the other is no more than the run from cylinder 1-4.)
So, the sequence of events seems to have been...
- refit crank sensor and trigger wheel. Set ignition reference point a little bit out, but enough that the advance on starting compensated.
- Drive it short journeys for a week so it wasn't run for long enough for the advance to be completely removed, hence masking the retard.
- Coincidentally on the first longer journey, a coil-pack failed, dumping unburnt fuel from two cylinders into the cat resulting in it glowing red hot
- replace both coilpacks and all plugs and all is fine for a couple of days, but now doing some longer journeys. I noticed a little hesitancy at higher revs but wasn't too fussed as I am planning on getting a remap in the next month or so, so was going to live with it till then.
- Hesitancy gets gradually worse till it's a full on misfire, but again, it seemed better when the engine was cold.
till today...
So in a nutshell, I think the current state is that the cat is partially blocked or damaged from the coilpack failure (dumping neat fuel into it from two cylinders for several miles). The plugs are fouled (I'll chop them out and clean them properly again tomorrow) and I've adjusted the ignition reference offset so it's running better generally.
I might gut the cat rather than replace it for now. That should at least remove any restrictions and allow me to verify whether or not that was the issue, rather than replace with a new cat and end up potentially knackering that one too if the issue is elsewhere
I did a plug chop and found them all to be equally sooty. One of the other things I've done recently was refit the crank sensor and trigger wheel, so I doublechecked my settings for the ignition timing reference offset. It 'appears' that it's been running with a bit too much retard. This also matches the symptoms as the ECU has a 5 degree advance on starting which reduces as the engine warms, and so it quite possibly have been starting with the igntion around the right point and then ending up retarded.
I've experimented with the ignition reference offset and have it running much better, the misfire is almost gone, but it feels strangled and underpowered t higher revs, with an occasional misfire. That, in my mind, would also fit with a partial blockage of a knackered cat.
The plug leads are incredibly short on this model (it's effectively coil-on-plug for two of them, and for the remaining two, one is about an inch and a half long, and the other is no more than the run from cylinder 1-4.)
So, the sequence of events seems to have been...
- refit crank sensor and trigger wheel. Set ignition reference point a little bit out, but enough that the advance on starting compensated.
- Drive it short journeys for a week so it wasn't run for long enough for the advance to be completely removed, hence masking the retard.
- Coincidentally on the first longer journey, a coil-pack failed, dumping unburnt fuel from two cylinders into the cat resulting in it glowing red hot
- replace both coilpacks and all plugs and all is fine for a couple of days, but now doing some longer journeys. I noticed a little hesitancy at higher revs but wasn't too fussed as I am planning on getting a remap in the next month or so, so was going to live with it till then.
- Hesitancy gets gradually worse till it's a full on misfire, but again, it seemed better when the engine was cold.
till today...
So in a nutshell, I think the current state is that the cat is partially blocked or damaged from the coilpack failure (dumping neat fuel into it from two cylinders for several miles). The plugs are fouled (I'll chop them out and clean them properly again tomorrow) and I've adjusted the ignition reference offset so it's running better generally.
I might gut the cat rather than replace it for now. That should at least remove any restrictions and allow me to verify whether or not that was the issue, rather than replace with a new cat and end up potentially knackering that one too if the issue is elsewhere
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