Miata Engine Mix and Match

Short version:  The misfire was the cam sensor.

Long version:  The misfire was not consistent and tended to happen between 3500-4000RPM, usually under heavy load but sometimes if I was driving at light load in that RPM range.  It would occasionally happen at other RPMs but not very often.  It was repeatable enough that it would show up at least once within a couple of blocks of driving. I double checked the air gap as Keith suggested, but it was where I had set it--.035" (I pick that size because fattest feeler gauge in the set I like to use for Miatas and it's within spec of .5-1.5 mm). When the tach was dropping with the misfire, my feeling is it was the whole ignition cutting out, not just an individual cylinder misfiring, so I went to the cam sensor.  I had my running 1999 and running 2000 Miatas nearby, so I pulled the cam sensor out of the 1999.  The misfire was worse and all over the RPM range.  I put it back in the 1999, which once again ran fine.  Then I took the one out of the 2000 and this car barely ran.  Back in the 2000, all was good.  The 1999 and 2000 have the sensor at the front of the cam (like this car did before the VVT) and maybe the gap is a little closer than on the VVT at the back of the cam, and/or maybe the sensors don't put out quite as strong a signal when they're 20 years old.  Anyway, a brand new sensor solved the problem.  I thought it would be worth posting this for the next guy who may have a similar issue. 

Glad you found it! A lot of people don't realize you have to check that air gap, so it's a common failure point.

The cam sensors are almost a consumable on NB engines, I should have thought of that first.

It's funny, I've gotten my share of Miatas in the shop with the air gap problem with the crank sensor so that's usually the first place I go.  I've known the cam sensors are pretty consumable, but I can't remember ever changing one on an NB before this. A lot of the Miatas up here in Michigan are low enough mileage that nothing ever breaks. 

Your '99 head/intake/fuel rail is worth a decent chunk of change.  There's always lots of people looking for them to update their NAs.

Bringing this back, how did this turn out for you?

Did you get vvt controlled with OEM ECU, or standalone? 

Was it worth the time, other than the 99 motor being crankcase ventilated via block hole, compared to just doing another 99 engine?

I'm intrigued by a vvt swap with vics manifold, variable things are fun. Can ms3 control it all?

In reply to engiekev :

MS3 can natively control VVT

In reply to engiekev :

I noticed this popped back up, but I've been slow to reply. Sorry about that. The car has been back burnered, so no progress on the VVT. I still autocross it every now again--it's only competitive in STR locally--and my sons have used it on some track days. I need to figure out what I want its next iteration is since it's not competitive in STR and then decide what to do. I'd like to make the VVT work for the learning experience if nothing else (and of course it may turn into a story in GRM).

I used the head from the original engine to replace a damaged head on another Miata in the fleet.

That's the update...pretty boring. 

Hey, it’s something. 

We had a local guy putting an LNF GM 2.0 turbo engine in an early Miata - he didn't finish it as far as I know but I wondered how much torque/power a stock driveline can take. He'd have been around 350 bhp with a mild turbo swap and I figured that the trans and diff would mutiny......

In reply to wspohn :

I would expect that you would use a Solstice trans rather than trying to adapt to Mazda.