Intermittent coilpack 1-4 no spark removing lead 2or3 fixes.

[RiccyHisto]

Hi guys, this is my first post but I have been lurking the forums for a while. Loads of useful information. I know the coilpack issue has been done to death but I cannot solve my issue.

I have a 99 Nb mx5 (with about 150 000 Kms)with an intermittent misfiring coilpack issue. Basically the car has very limited power, incredibly slow acceleration and very lumpy idle. The issue only occurs on startup, never mid-drive and it is only ever the 1-4 (drivers side) coil that ceases firing. It is usually after the car has been warmed up to operating temp and then allowed to cool back down for about 2 hrs however I have not been able to activate the fault deliberately. As a result the mechanic has told me he cannot diagnose it until he sees the fault in action.
The interesting thing is that when I removed lead 2 during a misfiring episode, coil 1-4 fired straight back up again. This has happened on two occasions so I am hoping some of you guys may know what is causing the coilpack to be misbehaving.

I replaced both coilpacks with new ones from mx5 mania about 2 months ago (5000 Kms or so) however it did not seem to affect the regularity of the faulting occurrence.
Other things I have replaced trying to solve the issue are:
Plugs
Leads
O2 sensor (passenger side, NOT the one beneath coilpack)
Removed, cleaned and checked connects CAS, crank and cam position sensors, MAF
Cleaned EGR (?) port, intake manifold and throttle body.
I have tried wiggling all the wiring in engine bay and beneath steering wheel to activate the fault.
The problem has been occurring intermittently for over a year however the frequency and duration have both increased. Originally the engine would right itself after a few seconds. Now it can take up to 20 minutes unless I remove lead from the functioning coilpack.
I have tried testing the 'failed' packs with a multimeter and the resistance readings I am getting are similar to those specified in the testing articles I have read so it is possible that the coils aren't actually failing but I'm not sure on this.

Does anybody have any ideas on what could be causing this issue or how I might be able to cause the problem to occur to show a mechanic?

Apologies for my poor descriptions of the problems and if I have left out any important information. I have limited mechanical knowledge so may have I accurately described some of the symptoms.

Any help would be greatly appreciated, I am completely out of ideas. All the solutions that I find online lead to replacing the coilpack, which I have already tried.

Thanks a lot



Ric

[Nevyn72]

The next step is to very carefully work your way along all the wiring in the engine bay looking for wear. This could result in some exposed wire leading to an intermittent short....

[93_Clubman]

You could also check the ECU for water damage, & check that all earthing points are secure.

But first, if you haven't already, specifically check the wiring immediately before the coilpack as there's a known weakness there that's not necessarilly visible to the eye. The wires inside the plastic insulation deteriorate where they deflect just prior to plugging into the coilpack. Apparently the combination of deflecting & not being well supported in this particular spot, probably compounded by alternating high & low temperatures, weakens the wires. It's not immediately apparent to the eye as the plastic insulation may appear intact, but if you move this part of the wiring loom around while the motor is running you'll get a response in terms of idle if the wires have deteriorated.

[manga_blue]

It's all pointing to weak 12V main supply voltage at both coils. 93_Clubman is pretty much on the money. Do everything he says, including all the earths.

I'd also be tempted to replace the engine loom. Otherwise you can mod it by adding a 30A relay drawing from a solid 12V power source just before each 12V side of the coilpack - a bit bandaidish though.

[RiccyHisto]

Thanks a lot guys, I really appreciate the help.

Yes I will follow the advice and check the grounds and ecu or wiring problem.

I don't know if I have the knowledge/skill to replace wiring harness but could be something to chat to the mech about.

My terminal tool arrived today. I have heard of problems with the coil pack connectors so I want to check those too but that problem doesn't really coincide with the quick fix of removing lead #2.

On a side note, a wiring harness from a wreckers, good idea or bad idea? I don't want to end up with a dodgy one...



Cheers

[manga_blue]

Not the wiring harness, just the engine loom. Or at least I thought it would be a good idea until I had a closer look at it. It's more complex and widespread than my NA8 loom. You'd need a patient forum member to get one out whole. A wrecker wouldn't have time to do it properly.

[RiccyHisto]

You could also check the ECU for water damage, & check that all earthing points are secure.

But first, if you haven't already, specifically check the wiring immediately before the coilpack as there's a known weakness there that's not necessarilly visible to the eye. The wires inside the plastic insulation deteriorate where they deflect just prior to plugging into the coilpack. Apparently the combination of deflecting & not being well supported in this particular spot, probably compounded by alternating high & low temperatures, weakens the wires. It's not immediately apparent to the eye as the plastic insulation may appear intact, but if you move this part of the wiring loom around while the motor is running you'll get a response in terms of idle if the wires have deteriorated.

I'm sure this info is on the forum somewhere but I cannot locate it. Do all the electrical circuits ground back to the battery area in the boot or are there multiple grounding points in the engine bay? Anybody know if where I can find this information?

Thanks again.

[93_Clubman]

Do all the electrical circuits ground back to the battery area in the boot or are there multiple grounding points in the engine bay?

There are multiple grounding points throughout the vehicle, with a major one in the engine bay as well as some minor ones. Manga_Blue has posted the most info ref earthing points, but don't think they're all listed in one post on here.

[manga_blue]

Just going from memory here from my NA8. Ithink NB8A is much the same.

In order of importance for engine grounding they are:
- coil/injector loom to rear of inlet manifold
- misc bits to bracket below front of inlet manifold
- engine block to chassis from near dipstick to firewall ledge
- PPF to chassis near rear axle

Also check all connections to alternator are clean and sound, especially the white.

[RiccyHisto]

Thanks guys, I found three earthing points in engine bay and one near rear axle. All looked good but I cleaned and reinstalled anyway. The one below car had a bit of wear on it so I sanded it back and reinstalled it.

I pulled back the carpet in passenger side footwell to get at the ECU and it was quite damp around the middle section. I am drying that out as we speak and this could definitely be causing the problems.

My soft top leaks near the windscreen/window junction. Is there a way to adjust the latches to increase tension in soft top which could give me a better seal? (I will give this a crack this afternoon but if somebody has done it, help is always appreciated).
The rubber appears to be in good condition at this point so it may just require adjusting.

Regarding the ECU, will a relocation help with this problem if it takes me a while to fix the leaks? There is a reasonable amount of cable so I am thinking of sticking the ecu in the glovebox and rerouting the cables in from behind.
Does anybody know of this being done successfully? I have found a few turbo conversions on American miatas but they create custom wiring.

Thanks all for the help.

[93_Clubman]

My soft top leaks near the windscreen/window junction. Is there a way to adjust the latches to increase tension in soft top which could give me a better seal?

Re soft top latch adjustment:
http://www.miata.net/garage/garagetops.html

If you haven't already, then also clean all the water drain points to ensure that water isn't getting into the car by overflowing from blocked drains:
viewtopic.php?f=28&t=35601
http://www.mx5oc.co.uk/forum/forums/p/270/439.aspx#439

Regarding the ECU, will a relocation help with this problem if it takes me a while to fix the leaks? Does anybody know of this being done successfully?

Don't know for sure if you could relocate the ECU to the glove box on an ADM NB, but there might be enough flexibility in the loom to do it.
For info, the ECU in the USDM NA was behind the driver's seat (LHD). This location may have carried over to the NB. The immediate consideration that comes to mind from the NA would be that you could need an additional earth strap for the ECU given it won't be mounted to metal via metal brackets as per factory.

[manga_blue]

Once again speaking only for NA8 ECU location, I just velcro'd mine into the glovebox. No earth issues, cables long enough.

[RiccyHisto]

I managed to relocate it to beneath the glovebox and attached it to what looks like an air on filter box.
Unfortunately this didn't fix the intermittent spark problem so I don't think it is a moisture related ECU problem.
The only thing I haven't tried yet is the alternator wiring inspection however I am thinking I will book the car in with an auto electrician and see if they can locate the gremlins.
Thanks all for the help and will update this post when after I have it looked at professionally incase anybody has a similar issue.

[93_Clubman]

I pulled back the carpet in passenger side footwell to get at the ECU and it was quite damp around the middle section.

I managed to relocate it to beneath the glovebox
Unfortunately this didn't fix the intermittent spark problem

If the ECU got wet then unfortunately the damage has already been done - try swapping in a known good NB8A ECU.