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Soooooo..... ages ago my car started to misfire - I was running COPs without a problem for a month or two - i had been putting off install some/a cap for a while because the car was running fine. Anyway, this misfire would randomly happen under load, between 2000-3000RPM and if i was lucky to catch it and hold the same rpm, you could get it have a number of misfires (multiple misfires even ). Anyway, i thought i had solved the problem by add 2 4700 uF capacitors in parallel of the COPs wiring. I installed the caps, changed the dwell to 2.5 on my ecu (haltec e6x - museum edition) and went on my merry way...

Until last week i noticed whilst driving my car like a pissed off teenager, that i had a misfire at 5k under heavy (foot) load. hmmm.... so i propmtly ignored and started driving the car normally again - tried to test it out on the high way a few times but didnt have a problem - random. Sunday I went to the dirt sprints - didn't notice anything unusual until i was driving home sitting at 3500 i would have a random misfire every few hundred meters or so - seem to disappear after a while.

I got up yesterday morning, drove the car to work and had no issues. Driving home was another matter - pretty much when ever i put my foot down i would get a number of misfires and the car would struggle to pick up revs

Made it to the gym - did my thing - drove home, no issues

Drove to work this morning with no issues - car drove like sh*t driving home.

So, I just re installed the standard coil packs and spark plugs - changed the dwell to 4.5 - car was only just drivable. Changed the dwell to 5ms - still misfired

So, having done this, and it is still misfiring - i check all my plugs - they looked like this


blurry spark plug photo by plohl, on Flickr

That was cyl 1 iirc

I checked the plug gaps (roughly) and they all seem 1 - 1.1mm

Check the fuel injector resistance - all read from 15.5 - 15.8 - limits as per the service manual is 12-16ohm

getting a new fuel filter tomorrow - couldn't pick it up today.

Anyone got any other ideas? things i should look at? have thought about getting my injectors cleaned - but.... that's expensive and i am feeling exceptionally cheap atm.

The cops are wired as per http://www.miataturbo.net/showthread.php?t=12704

Car details:
NA6
BP engine
tighe cams - 804 iirc?
haltech e6x ecu

any help would be greatly appreciated.

So it doesnt happen just under load? And happens with stock ignition and with the cops?

It must be a wiring issue, earthing or something, if its not fuel related.

Dann

I can only get it to happen under load - reving the car in neutral is ok.

The stock coils were heaps worse than the cops. That's why i was thinking it was fuel.

If i didnt have to run the stupid maf i would install the stock ecu and test that out - why hook the fuel up to the maf mazda? why?

I am hoping it is a fuel issue - i don't feel like chasing stupid wiring faults - plus i was pretty pedantic when i did the wiring, so i can't think where the issue would be.

Hard to tell from the photo. A white deposit on the plugs can mean burning oil - worn rings and/or valve guides. They could be getting enough deposit to cause a misfire. It can also be caused by lean mixture and/or or too much advance.

yeah - it was a pretty consistent white - some of the stuff on the internet said too hot or normal so i was a little lost.

I just got reminded i have another set of plugs in the NA6 so i might throw those in and see how i go.

It burns a little oil ~1L/5000km so nothing that i was super concerned about. I did an oil change on saturday and put royal purple in it - car seem to run a little better. The old stuff was in there just <5000km

Unsure on the AFR - the tune was done by Brisbane tuning and dyno when the previous owners put the cams in - seems pretty rich/fairly conservative.

Check the haltech unit's MAP vacuum tubing to ensure it is leak free - I assume if it doesn't use the stock MAF it must be getting manifold pressure from one of the T's off the intake, and then a vacuum hose is going to where the ECU is located. Check that hose to ensure it is leak free and hasn't worn through on a sharp bend (firewall) or just fallen off the ecu.

Timing could be the issue too, did you do any work near the CAS or is it not tight and can you move it with your hand? If so, you'll need someone with the ECU controller to fix the timing whilst you reset it back to a know base - normally 10 or 15 deg advance on the pulley. As you have a non-stock ECU you wont be able to use the GND-TEN to check the timing at 10 because that is a stock ECU feature - unless the Haltech emulates that feature (which I doubt).

G

i had the laptop hooked up last night logging some data and the MAP seemed fine. I'll check it at the ecu to be sure.

The cas hasnt been touched since i bough the wreck (it was running at the time - though i never got to drive it as speed). The timing is set up stock as per the service manual - might get the timing light out tonight.

Those plug deposits wont stop a set of cops from firing, not under 20PSI anyways.

Im betting fueling or wiring. Or cas is stuffed.

Dann

I had the same miss in my car for a while. It was lean mixture occurring at certain rpm and certain throttle positions.

I use an OEM ECU which I attacked with a soldering iron so I can remap fuel and timing. At one stage I swapped in a larger Nissan MAF which had a slightly different output signal curve. I did a really quick and dirty fuel tune on it by doing a few runs to achieve AFR 12.3 from 1000 to 7000rpm at WOT. Then I cascaded those fueling values down the table so that I had the WOT settings from 100% throttle to 50% throttle. Below 50% throttle I just filled the whole table with default values for AFR 14.7. The result was the car was great at WOT or close to it but an absolute pig in some instances of part throttle. For example, at about 10% at 4000 and again about 25% at 2500 I was getting the same sorts of things you describe: rolling miss, occasional cut-outs and uneven power.

I've swapped the MAF back out until I have time to tune it properly. What I need to do in order to get a streetable tune is a full series of runs at 10%, 20%, 30%, etc throttle and build a proper fuel table for it.

As a general rule it's almost impossible to diagnose transient fueling problems from spark plugs. You have a bit of a chance if you do an ignition cut as the condition occurs. It's much more productive to log AFR instead.

Sounds like someone should invest in a wideband.. :grin:.. I'd loan you mine but it's a pain to get out and I'm not keen on removing anything at this point!

So yah, and get a wideband then ill drive it around while you stare at the computer. :grin: no need to thank me for doing the sh*t job..

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I'd say spark plug leads, but I know I'm wrong.

It had the same misfire on cops.

Dann

Despite the fact that I said you can't trust plug readings it does look like yours are too hot. i.e lean mixture, too much advance or too hot a plug

I just noticed.
It's an NA6 with a BP engine.


are the plugs the correct ones?
When I accidentally put a set of plugs for an NA6 into my NB they came out looking exactly the same.

You haven't accidentally used the plugs from the B6 have you?

Nah, they were brand new installed by the previous owner when i was looking at it. The are a ngk bkr611* iirc. I looked up the heat range last night and i think they're ok for a bp.

*that part number could be wrong - but there is 6 in it.

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