Car running weirdly

JBT · Postby **JBT** » Sat Mar 21, 2009 6:56 am

Sorry, I'm a bit confused by what you've last posted.

If the car is mis-firing and you pull a plug lead and the misfire remains unchanged, that lead/plug is dead or the coil is dead. If you can pull both leads from that particular coil and the misfire remains unchanged, you have a dead coil or two dead leads/plugs.

Maybe it's worth taking out the coil packs and thoroughly checking them over for damage and that all electrical connections to them are OK.

philz · Postby **philz** » Sat Mar 21, 2009 9:17 am

JBT wrote:Sorry, I'm a bit confused by what you've last posted.

If the car is mis-firing and you pull a plug lead and the misfire remains unchanged, that lead/plug is dead or the coil is dead. If you can pull both leads from that particular coil and the misfire remains unchanged, you have a dead coil or two dead leads/plugs.

Maybe it's worth taking out the coil packs and thoroughly checking them over for damage and that all electrical connections to them are OK.

Well it sounds like what you have just wrote here: "If you can pull both leads from that particular coil and the misfire remains unchanged, you have a dead coil or two dead leads/plugs."

But leads and plugs are new, so this leads to coilpack ?

ie/ The car is misfiring, I take out the leads at the coilpack, firstly removing number 2 or 3, there is no spark jumping, no spark at all.
Whereas, when I remove either 4 or 1, the spark jumps to the metal close by*, then I put the lead back on, and then the car idles normally.

* Picture example, when I take out lead number 4, while the car is misfiring, the spark is too quick and my lead has been pulled away too far, so it jumps to that metal, which I believe is 'ground', and I think this is what helps the other coils to fire. ( I may be wrong, but this is what seems to happen )

Hopefully that makes sense?

Postby **Okibi** » Sat Mar 21, 2009 1:13 pm

So what you're saying is that the coil needs a defibrillator style shock from its twin to kick it back to life?

philz · Postby **philz** » Sat Mar 21, 2009 1:26 pm

I think so... well that's what seems to be making it idle properly.

JBT · Postby **JBT** » Sat Mar 21, 2009 8:07 pm

Well that's really weird and doesn't make sense. Have you removed the coil pack and checked out the electrical connections/wiring?

Postby **Okibi** » Sat Mar 21, 2009 9:18 pm

Ok, here's a guess. I'm sure an engineer or mechanic can translate into the propper terms.

There must be some sort of electronic contact breaker inside the coil which releases the charge to the spark plug.

The coil isn't grounded so the "ground" path must be down the lead into the sparkplug.

If the coil is weak there's not enough power for the electronic breaker to ground itself down the ignition lead and induce the coil to fire off a its charge.

Finding the shorter path to the metal housing might be enough to kick this electronic breaker back into action.

JBT · Postby **JBT** » Sat Mar 21, 2009 9:22 pm

But coil 1/4 is apparently kicking coil 2/3 into life when the leads come off coil 1/4

philz · Postby **philz** » Sat Mar 21, 2009 9:59 pm

Rotary wrote:Try removing the Ignition leads 1 by 1 at the coil, and seeing if there is a constant spark jumping while car is running just after it starts missing.
(this test worked on mine as the metal bracket(earthed) is close enough to the coil mouth, Should be the same on yours, but my coils where changed before i bought the car, so not sure if anything was altered)

Well this even happened to Rotary, the spark jumped to the bracket as well.

Aside from trying to understand why 1/4 is powering up 2/3 (as it still boggles me as well, being an engineer at heart)

Wouldn't this still mean coil 2/3 are temperamental and on it's way out?

I haven't checked the coils yet, will try tomorrow.

EDIT: Searched on miata.net, and some similar problems, and the result is CAS...

http://forum.miata.net/vb/showthread.ph ... t=no+spark

http://forum.miata.net/vb/showthread.ph ... t=no+spark

http://forum.miata.net/vb/showthread.ph ... t=no+spark

BUT from these problems, their cars don't start or die out, which isn't a problem on mine.

And from what I have read, they say it's bad to remove the leads from the coilpack, as it may ground, causing it to blow the coilpack?

Also is it okay to swap leads around? instead of 4,1,2,3, I swap them 2,3, 4,1?

philz · Postby **philz** » Sat Mar 21, 2009 10:13 pm

Alright I'm gonna try and explain what I think is happening:

From the pic, we see that the screw threads on the spark plug and the side electrode are the ground, and the center being the ignitor.

The coilpack bracket is held onto the engine, which in turn is the ground.

So when the spark jumps from the coil to the bracket(ground), it travels all the way down to the spark plug ground, and I would assume that it would also jump to the ignitor/center electrode, which in turn would go up through the leads and into the 2/3 coil pack, firing it, hence causing it to keep firing, giving it the "defibrillator style shock"?

And this is what I think Okibi is saying.

I might have to put some cardboard in between the coil, blocking the bracket, and prevent the spark jumping.

JBT · Postby **JBT** » Sun Mar 22, 2009 6:47 am

is it okay to swap leads around? instead of 4,1,2,3, I swap them 2,3, 4,1?

Don't do that.

What I'd do:

Remove coil pack.
Swap coils over.
Carefully check all electrical connectors/wires to/from/at coils etc.
Replace coil pack.
Run engine and wait for the mis-fire to happen again.

If 2/3 still fails to fire it's a CAS/ECU/wiring problem. If 2/3 is now OK and 1/4 fails then it's the coil.

Surely someone in Sydney has a spare working coil for him to try?

philz · Postby **philz** » Mon Mar 23, 2009 10:50 am

Alright swapped coils over, the old 2/3 are now the 4/1 and vice versa.

No misfiring as yet, just a matter of waiting.

However I have noticed the idle has dipped lower down around 500rpm (clutch engaged, 1st gear) and there was a slight backfire from the exhaust, upon shifting around.

Richard from plus has given me a price on the coilpacks, so I'll see how we go with the next misfire.

edit: Oh and I checked the connections, nothing frayed or broken, connectors and everything all fine.

JBT · Postby **JBT** » Mon Mar 23, 2009 12:28 pm

Idle dip: Did you disconnect the battery? If so, you may need to reset the "base" idle speed.

philz · Postby **philz** » Mon Mar 23, 2009 12:31 pm

Yep disconnected battery.

How do I reset the base idle speed?

JBT · Postby **JBT** » Mon Mar 23, 2009 12:44 pm

Go to the diagnostics box, open it and run a bridging wire (paper clip will do) between the TEN and the GND terminals.

Start car. Adjust idle speed by turning the screw in the air intake to 800(ish) using the car tacho. Idle adjust for the NA 1.8 is as per the photos below. Not sure about NB8A.

When you have the speed set, remove the bridging wire - it should not change. Once done, close the diagnostics box and drive. :mrgreen: