NB8A - possible coilpack issue?

samx5 · Postby **samx5** » Mon Feb 20, 2012 10:54 am

Lately my NB8A has occasionally started on less than 4 cylinders. Most of the time it will run rough for a couple of seconds, then it will go smooth. Occasionally it will not pick up the dead cylinder(s) at all, & I have to shut it down. Ususally after a short wait it will then re-start on all 4 cylinders and all is well again. Yesterday it started fine and was dríven for about 7km, then switched off for about 1.5 hours. When I went to restart it would turn over but not start at all. It was definitely pumping fuel (you could smell it) but wouldn't fire. Left it for about 10 minutes and tried again, and it stumbled slightly & started on all 4 cylinders. Once it is running on all four, it never loses a cylinder under load and can be dríven indefinitely with no problem. It started fine this morning.
Plugs were changed about 6 months ago, as were the leads. I thought I was losing one coilpack when the car wouldn't run on all 4 cylinders, but when it didn't start at all yesterday I was thinking it may be something else........either that, or I'm really unlucky and have two stuffed coilpacks!! Any simple checks I can do before going to the workshop?

hks_kansei · Postby **hks_kansei** » Mon Feb 20, 2012 11:04 am

Take out the plugs and check each one (even better if it's just after the misfiring)

see if you can work out which cylinder/s aren't firing (plug will likely be damp with fuel)

If it's a coilpack on the way out, it will likely be two cylinders not firing (I think they're paired 1-4 and 2-3)

I'd be replacing the spark plugs again anyway (they're dirt cheap, may as well)
And also I'd be checking they are the correct plugs, I accidentally ran plugs for an NA6 in my NB8A and it misfired horribly after a few days.

Out of curiousity, what brand leads were used?

My OEM ones died, so I used some Top-Gun leads, they were utter sh*t and were worse than the ancient OEM leads.

I then put on a set of Magnecor leasd and all was well again.

Oddly enough, when I tested them using a multimeter all were within OEM acceptable specs according to the manual.
Yet sure enough, only the Magnecors worked when on the car.

Insurgence · Postby **Insurgence** » Mon Feb 20, 2012 9:12 pm

i used to have a similar problem, but wouldn't start if engine was warm (cold was fine).

my fix was to slightly pull out one of the plugs on the coil end and it'd start sparking again...

this is a known NB8A issue..
not sure what state you are but mx5factory (baked enamel) was able to give me a good deal rather than going to the dealer for the coil packs.
yes ~600 is expensive, but hey i haven't had any problems for the last 4ish years.

93_Clubman · Postby **93_Clubman** » Tue Feb 21, 2012 2:45 pm

samx5 wrote:Any simple checks I can do before going to the workshop?

Mike, if you can temporarily swap in a known good coilpack.

samx5 · Postby **samx5** » Tue Feb 21, 2012 6:44 pm

Its a bit random at the moment, hasn't done it today at all. May have to do the resistance test, although it may not be guaranteed. The leads are OEM so hopefully not the problem, but worth checking them. The price from Mania for coilpacks is bearable, so I'll get it checked out & go from there. You can bet your bottom dollar that it will run fine when its at the mechanics workshop!
Thanks all,

hks_kansei · Postby **hks_kansei** » Tue Feb 21, 2012 6:53 pm

The resistance test on the leads won't really tell you much.

As I said, the Top Gun leads caused misfiring on mine, yet they tested fine.

The Magnecors had similar resistance to the Top Gun, and work perfectly.

sailaholic · Postby **sailaholic** » Tue Feb 21, 2012 7:24 pm

Cheaper to go coil on plug than replace the coil packs if your happy to do some soldering.

Sent from my GT-I9100 using Tapatalk

monte5 · Postby **monte5** » Wed Feb 22, 2012 10:01 pm

There are a number of variables at play here, but for what its worth I had a similar problem (and hopefully have just fixed it - touch wood!)

Car would start fine then after it had heated up the car would drop to 2 cylinders. You could turn it off and some times after say 5 min's it would be fine, sometimes not. Replaced plug leads, cam sensor and crank sensor and still it occured (infrequently). Then replaced the coil pack (ordered a new one via eBay for about $220) and it didn't miss a beat for about a week, then it started to play up again.

During the misfire we found that cylinders 2 &3 had no spark at all. Given that it was a new coil pack we started to trace what was left to cause the problem. There isn't a lot to this part of the system - the ECU, the power leads, the coilpack, the plug leads and the plugs.

Whilst it was misfiring we swapped the leads that feed the power to the coil pack and the plug leads and we were able to transfer the problem to cylinders 1 and 4. So we then knew the wiring was Ok, but that the new coilpack was stuffed on one coil.

The only thing left we felt was that the ECU was sending a bad signal to one side of the coil because it was the same 2 cylinders with both old and new coils and this bad signal (perhaps an earth issue) was frying the coil. Took the good half out of the old coilpack and used it to replace the bad half of the new coil pack and have replaced the ECU & so far all good, but holding my breath.

good luck - hope your problem isn't the ECU, but if it is not firing on 2 cylinders then I suggest the coilpack is a place to start.

93_Clubman · Postby **93_Clubman** » Wed Feb 22, 2012 11:48 pm

monte5 wrote:The only thing left we felt was that the ECU was sending a bad signal to one side of the coil because it was the same 2 cylinders with both old and new coils and this bad signal (perhaps an earth issue) was frying the coil.

Interesting - a few NA ECUs have been troublesome. Hopefully Patty reads this - his was another NB8A with issues!

samx5 · Postby **samx5** » Thu Feb 23, 2012 3:09 pm

Very interesting Monte5, thanks for the info. My car is doing the opposite of yours, it will sometimes start on 2 cylinders, sometimes when cold and sometimes after a short drive (or not start at all, as it did on Saturday), but once its running on all 4 cylinders it never drops a cylinder from then on, no matter how it is dríven. I checked the plugs 2 nights ago, took all the leads off the coilpacks, gave them a bit of a clean (for what its worth) and refitted. Haven't had the problem yet, so we'll see. I'm not going to buy coilpacks until it starts to play up semi-regularly again. At the moment I can't replicate the problem at will.

samx5 · Postby **samx5** » Fri Mar 23, 2012 2:48 pm

An update for what its worth......car was serviced recently & I asked for the intermittent problem to be investigated. The leads & coilpacks were electrically tested (resistance??? I'm NO electrician!!!), all electrical systems were given the once over and all reported to be in good health. The car was faultless at the workshop all day. The next day it started on 2 cylinders again!!! Did it twice, then has been OK for the last 2 weeks. Until it gets worse (or misbehaves at the workshop), I can't really do anything. The car is running as sweet as ever at the moment, so no point throwing money at it. Think its time for a nice Adelaide Hills drive!!!

93_Clubman · Postby **93_Clubman** » Sat Mar 24, 2012 1:30 pm

Mike, Patty's thread covers a fair bit of ground, so might be of use if not already seen:
viewtopic.php?f=29&t=47266

samx5 · Postby **samx5** » Tue Mar 27, 2012 1:56 pm

Thanks Paul, his symptoms are different to mine. Mine runs perfectly once it's on 4 cylinders no matter how hot it gets. Its just at start-up that it sometimes doesn't fire on all 4. Is running very smooth and strong after the service. His is a very worthwhile thread, though.

Guran · Postby **Guran** » Tue Mar 27, 2012 5:17 pm

Asked a bloke here at work ... he suggested leaky injectors? If one or two are leaking fuel into the cylinder, it'd struggle to fire on those cylinders. But then after it warms up, they'd start to fire OK.

Diagnostic: with a cold engine, remove the plugs, then look inside with a torch OR have a sniff of each cylinder (maybe use a hose). Turn the crank over by hand to make sure there's no fuel behind the valves too. If you see a few ccs of fuel on the piston, it could be a leaky injector on that cylinder.