2004 NB cranks but won't start
 

I have had a few hard starting issues at track events this year. The first was at an Autocross. The car became hard to start. After it started, it ran strong. Ultimately, I cut the day short as it would not re-start in grid for the second run group. Later, it started and ran. I loaded it into the trailer, checked the basics; fuel, spark... then road tested it before going to a trackday roadcourse event. It also became hard to start after the first session. It did eventually start, and ran well during each of the 20 min run sessions. However, there is clearly a problem. It is now to the point where it will only start on a sporadic basis. Complicating this is that I now have a new MS that I want to install, but I hesitate to install a new ECU when the car is "questionable".

What I have checked:
1) The fuel pump cycles on with the key. I have just under 100# rail pressure.
2) The spark plugs are grey/tan and the electrodes are undamaged. They are not wet after cranking. Pulling #1 demonstrates no-spark when cranking; but then will occasionally spark and the engine will fire up on the other 3 clds.
3) I have replaced the crank position sensor and re-set the gap to .050.
4) I have replaced the cam position sensor.
5) I had one instance when an error light came on in the top right part of the dash. It looked like a key... perhaps a security system prompt? This got me wondering if I had a problem with the immobilizer??

The car is a 2004 MSM used for track days.

Pertinent car mods: Garrett 2860, bigger intake/intercooler/exhaust, flattop, mini alternator.

Pertinent wiring mods: BEGI re-flash, egr delete, vtcs delete, PD alternator delete, airbag/radio/ect. delete, prior trouble with melted heat/wires near MAF; now repaired. (there are now lots of unused connectors hanging). Added master kill, transponder, wideband O2, EGT.

100psi of fuel pressure on a stock NB system indicates something being exceptionally broken.

e: Just re-read. If the immobilizer light blinked, I would also look at that system.

Yes. I suspect that my test gauge is old... I'll pick up a new one today to confirm. Mostly, I just wanted to confirm that I was getting fuel pressure to the rail.

I do remember disturbing the immobilizer location when I welded in the knee bar of the cage. I think I just zip tied it to a nearby wire loom. I guess it's cause for concern if it's been touched.

I looked into the immobilizer circuit. It looks like it has an antenna that reads the rf signal in the key, then powers up the pcm. My diagram is only a partial and labels this wire "17" red/blue. I hope I can find it at the PCM din-plug to see if it's hot when the key is switched on and cranking.


https://www.miataturbo.net/attachmen...ine=1459201075

After reviewing the service manual, it looks like that since 2000 the imobilizer would cut not only spark and fuel; but also would cut cranking. Mine cranks but no spark or fuel. Thank goodness its not the immobilizer as it appears to be a daisy chain of continually randomized comunication with few places
for diagnosis... way over my head programming. So, where to go next? The dealer doesn't want me as the car is not stock. Beig (who reflashed the ecu)? is many States away. My local friend is a honda tech... not much into mazdas, but has helped me in the past. I have a source in Portland, but I don't want to bring them a basket case. Do i install the megasquirt and hope for the best? Or, will this just piss off my new friend braineak?
...so many bad choices.

So I test what I can in the din plug, then I plug in the stock-begi ecu and it starts right up. WTF? I didn't do anything... and at starts right up! I am so ready to trade this in for something with a carb and a distributor....

Fuel pressure 65lbs at idle with new gauge. Weather is nice. Since i've been upside down beneath the steering wheel I've taken off the hard top for the first time in a long while... maybe I'll drive roadster around with the top down awhile and try to remember why I loved this car so much.

If the immobilizer system is broken it will still crank. Sorry to say but I wouldn't rule out the immobilizer yet. Do you have a spare key?

On the 2001+, the immobilizer cuts out the starter via relay right next to the immobilizer if there's a problem, so that's not it.

Ah sorry. Disregard my comment then.

car starts and runs fine; three days in a row. It must have been a loose pin connector in the din plug. Now, off to plug in and tune with the Megasquirt!!