weird no-start problem
 

OK I have posited this elsewhere but I am not succeeding at present with getting it started, and I could use a little help. I want to get going with my other projects but I need to get this car running soon so I am getting a little impatient. Basically, I have no idea what to do at present.

I picked up this 1990 Miata cheap with a moderately damaged snc. I fixed it with loctite, replacing the timing belt and other things with new OEM parts. The prior owner was thinking about engine replacement so he did a few screwy things like unscrewing and thus wrecking the AFM, which I replaced. I also replaced the O2 sensor, plugs, wires, spruced up vacuum hoses, new catalytic converter, and other non-engine related things. After getting it running, I drove it a while and recently parked it in the drive. The weather was cold, and it snowed, and when I tried to start it 2 days after running fine and a 30 mile drive it won't go. I put it in the garage and warm made no difference.

I have even compression, about 150 dry. It holds vacuum at about 15 in Hg. The injector wiring lights up noid lights. The plugs spark on the valve cover. Fuel pressure is about 45 psi, although it is leaking gas around one or 2 injectors at present.

Most recently I swapped the CAS with a known good one to no improvement. Any suggestions where to go at this point?

Clean all engine grounds. Did you accidentally put the cas in 180 degrees off. Check the computer, and are you sure the afm is good.

No codes since the new O2 sensor. I believe the grounds are good, everything electrical works nominally, just no starting. I have not tried replacing the AFM again, although with this one in place, it ran fine. The weird thing is it ran well, I came home from a spirited drive on interstate and local roads, then it wouldn't start again. I even rechecked the valve timing to be sure there was no problem with that.

Is it possible to put the CAS in 180* off? That would suck. I thought it went in just one way. Hmmmm...

It's not possible for 90 out but to you can accidentally put it 180 out. And the 90-93 ecu doesnt really throw codes unless there is a huge problem. Did you jump the fp at the box for the pressure test, if you did did you keep it jumped while you were trying to start. Check the fuses under the hood

I replaced some fuses earlier as 1 or 2 were missing when I got the car. They seem to be intact now, and if not, I don't think I could have pump fuel or spark anyway. For that matter, if the old CAS were no good I don't think I'd have spark, correct me if I'm wrong. I did try the FP-GND jump when cranking. The only thing I can think of that I haven't done yet is recheck the AFM wiring. If that checks out, I can switch the CAS orientation. Thanks for the ideas, all input is appreciated! Fuel, air, spark...it all seems to be there but I must be missing something. Maybe the AFM.

you say there are no codes but did you jump ten and ground to see or just sit in the car.
heres a guide to codes on 90-93.

Oh yes, there have been codes before. As I said, none since I changed the oxygen sensor, which resulted in codes 15 and rarely 17 when I drove it fast. It ran better with a new sensor and stopped giving me 15. Those were the only codes ever shown, and none since I got it running well recently.

you need to confirm 3 things: spark, fuel, and timing. I don't really know a lot about the 1.6s, but I know on our cars if your CAS is out you will get neither spark nor fuel.

Anyways, spray some starter fluid in and see if it fires up. lastly, check the timing belt.

CAS/CPS are things to check also (not sure if you have either/both).

Starter fluid doesn't help really. Is there any other way to check spark and fuel? There is spark from the plugs, there is fuel pressure and as it is leaking a little, I see a small puddle form when I crank it. The valve timing is correct (last week I opened up the timing cover to check it) and, when it was running, before I swapped the CAS, the ignition was timed at 10-12* BTDC.

It must be the AFM, I can't think of anything else.

have you replace the fuel pressure regulator recently? check to make sure idle control valve is connected to the intake pipe. mine wouldnt start once and this was the problem. actually check all of the intake pipe for cracks. the other way to tell if its a vaccum problem is to hold the flappers on the afm open and crank if it starts something is cracked between the tb and afm.