Sputter/hesitation @ low RPMs when cold NA6

tails · Postby **tails** » Wed Mar 02, 2016 2:16 pm

droo wrote:Have you atleast tried drying out the plug wells in the head?

Yep, did that 6 months ago shortly after I purchased the car as it started missing all the time (previous owner pressure washed the engine bay right before I picked it up).

tails · Postby **tails** » Fri Mar 04, 2016 10:20 am

Tested the coilpack with a multimeter.

Measuring the resistance between coils 1 to 4 and 2 to 3 I was getting 12.85kohms. Spec is meant to be about 8.7 to 12.35kohm, so it looks like the coilpack could be the culprit. They were also filthy.

93_Clubman · Postby **93_Clubman** » Fri Mar 04, 2016 2:00 pm

If you've not already, have a look inside tops of the 4 turrets/posts as they seem to get damaged from arcing &/or corrosion, at which point a Mazda specialist advised me to replace the coilpack on my old NA6 years ago.

tails · Postby **tails** » Fri Mar 04, 2016 3:10 pm

I had a look, and one pole of each coil is a gold at the bottom and relatively clean but the other two are a mottled corroded silver colour. All four poles were full of dust which I blew out.

It'll be frustrating if it isn't the coilpack as they're pretty expensive. Maybe I'll just grab one from a wreck and see if that works.

93_Clubman · Postby **93_Clubman** » Fri Mar 04, 2016 3:52 pm

Yeah, they're not cheap new - replacement for mine was about $200 15 or so years ago. Don't know if they're still available & how reliable, but there was an Australia ebayer selling them new for about $100 a few years ago. Bit of a lucky dip from a wrecker unless they're really cheap.

speed · Postby **speed** » Fri Mar 04, 2016 5:18 pm

tails wrote:I had a look, and one pole of each coil is a gold at the bottom and relatively clean but the other two are a mottled corroded silver colour. All four poles were full of dust which I blew out.

It'll be frustrating if it isn't the coilpack as they're pretty expensive. Maybe I'll just grab one from a wreck and see if that works.

Mine are also silver and gold. I just thought that's how they came? Work fine but I'll be changing to COPS as part of my FI build anyways ;)

tails · Postby **tails** » Fri Mar 11, 2016 12:33 pm

I had the coilpack replaced and it has for the most part eliminated the problem. It still feels a bit flat when shifting into third, but it's a lot better than what it was.

93_Clubman · Postby **93_Clubman** » Fri Mar 11, 2016 1:28 pm

Great to hear!
Especially given your cold & A/C idle issues, & deceleration clicking noise all since end 2015:
viewtopic.php?t=70834
viewtopic.php?f=29&t=70591

tails · Postby **tails** » Fri Mar 11, 2016 2:51 pm

Yep.

Virtually no strange noises/running problems now. They were all caused by different things too. Curing one issue simply uncovered something else.

Support and help from the community has been great. Advice, free help and even free working parts! I'm hoping to be able to pay it forward in the future.

93_Clubman · Postby **93_Clubman** » Sat Mar 12, 2016 11:42 am

Yeah a few issues for a 130k km broadly reliable car, but it's a 1992 & things do crop up, hence the value of baselining (to some extent as you've found you've had to) soon after you buy one.

tails · Postby **tails** » Thu Mar 17, 2016 11:42 am

Some of the issues stemmed from previous owners fiddling with it I guess too (like a dead end gasket blocking the ISC).

tails · Postby **tails** » Tue Sep 06, 2016 10:03 am

Looks like I was right in that a previous owners tampering was causing most of the running problems. My AFM had had the bypass screw bung removed and was wound all the way in (so full rich essentially). I replaced the AFM with an untampered unit and this seemed to have fixed all my cold running problems. No more misfire at idle, no more low RPM hesitation and my idle when warm seems to have steadied as well.

This was in combination with a number of other fixes that all seemed to have contributed somewhat, but replacing the PCV (and both breather hoses, including the little restrictor on the hot side), fixing a vacuum leak on the intake tube and replacing the AFM seemed to do the trick.

Just thought I'd update the thread with what actually fixed my problem as there's a million of these threads on a few different MX-5 forums and not many of them post the fix.