Pulled the motor on my NB2 for a simple rebuild and refresh this winter, as it was leaking at every seal, and after finally reassembling it and getting it back in the car I'm blown away that it won't start.

Cranks smoothly, just doesn't want to catch.

Has fuel on the plugs (injectors were tested/cleaned before install), good spark at every plug (new plugs/wires) and engine timing has been triple checked.

Swapped the timing plate from the mazdaspeed one back to stock, double checked orientation, flipped it just in case once too, checked gap. Still nothing. Swapped coils, wiring, plugs, no luck. Checked all the grounds somewhere in there too.

Hook up the OBD2 reader and no codes showing, sensors all reading correctly, showing rpm during cranking.

Out comes the ether! Gets a slight stumble but nothing resembling it wanting to fire up.

So now I'm at a loss, is there something on these NB's I'm missing? Feel like such an idiot not being able to get a stock miata running lol

 

Main relay?

 

Have you checked compression? I would just to rule out some major issue with engine assembly like the rings or clearances. Also, a major issue with cam phasing should produce low compression results.

How about VVT operation? Did you have the cam phaser apart during the rebuild? You could try unhooking the VVT solenoid, just in case it is trying to advance the cam. (However, since it takes oil pressure to advance the cam, I would think the engine would at least fire before the cam moved enough to stall the engine.)

Since you did get a sputter running on ether, it sounds like a timing issue to me. Have you looked at the live engine data using an OBDII reader/app, while you are cranking? That would allow you to verify that it is getting a good RPM signal from the crank sensor (look for 250+rpm and that the tach doesn't drop in/out). If the crank signal checks out, that leaves the camshaft position sensor. An OBDII reader/app which shows camshaft angle would be helpful, but that may require a reader/app with the Mazda specific OBDII PID's.

Good luck with the car. Let us know what you figure out.

 

I'd check the following...
-If there is fuel on the plugs but no fire, take the plugs out spin it without the main relay to make sure it's not flooded etc
-Grounding Straps - 3 on the motor and 1 on the ppf iirc.
-Main relay as stated above
-engine fuse in cabin
-CAS (known issue for vvt, fail without much warning or symptoms)
-crank sensor (absolute last thing i'd check)


I assume you've pulled the plugs out and turned it over to see if the plugs are firing (don't forget to rest the metal shoulder on the valve cover to ground them while you do)

 

Compression is good, 180 across the board. VVt wont function while cranking..

Rpm signal is solid as previously stated during cranking, tach shows nothing though.

Cam sensor has been swapped with my BP4W, not sure if its a known good sensor either though since it isnt used in the other chassis.

 

Spark at the plugs and fuel on them yes.
Yup all grounds are connected.
Main relay has continuity
Cabin engine fuse is good
RPM signal via obd2 port tells me CKP/CMP should be working right?

I'm thinking I must have got injector wiring wrong some how.. Maybe fuel is getting sprayed at a closed valve?

 

It would still run with the injector timing not matched with the valve opening. Think about Batch fire type port injection setups or carbs for that matter.

Are you are on the OEM ECU? You should see some RPM on the tach while cranking.

It takes compression /air, fuel, spark, and timing for an IC to run... You are missing one of those items!

 

Oem everything, no rpm on the tach but showing rpm via obd2 tool, whats that tell us?

 

If the crank and cam sensors don't coincide as the computer is anticipating then it won't fire sometimes. If it was a MS you could log the events and determine if they are off, or if one isn't being read at all.

Check the sensor signals with a multimeter while cranking to see if both are signalling, maybe?

 

Multimeter isnt sensitive enough for CMP/CKP

If I disconnect either I lose rpm signal on the scan tool, so both must be working fine.

 

https://www.youtube.com/watch?v=LRAo...ature=youtu.be

Solid spark, but plugs are soaked when pulled.

 

put an inductive timing light on one of the plug wires, see if there is any output during cranking. my guess is you don't have ignition under load (Weak spark). because the plugs are wet, if you had ignition, no matter when, its going to pop or back fire, it would ignite the fuel at some point.

 

Put a call into one of my Mazda tech friends, after him confirming its not some goofy NB special electrical issue holding me back I went out and double checked the basics.

Cam timing was good if you look at the gears, pulled the v/c off for a second look, exhaust cam was way out..

Compression tester is a lying ***** apparently (harbour freight equivalent)

Fired right up and runs great. Now its off to the exhaust shop then onto the corner scales, race next weekend!