I just bought a 1991 mariner blue Miata two weeks ago, and I have been having a lot of fun fixing it up. It ran fine when I got it, but it had been sitting for somewhere between 3-6 years in a garage without being run at all. The ODO says 138k miles, but I have receipts that prove that a new engine was put in about 12k miles ago, so the engine SHOULD be almost new (though that was back in 2002 or so before it was garaged).
I replaced all of the fluids (brake fluid, clutch fluid, transmission oil, diff oil, engine oil/filter) the air filter, fixed the trunk and glovebox locks, replaced one tail light, took out a bunch of defunct aftermarket stereo and alarm system stuff, and it was still running great. After that, I replaced the stock cat/catback (which had some damage and was warped/rattling) with a JR High-flow cat and a less damaged stock catback that I bought on Craigslist. Both looked fine, doubt they could be related (I did read at least one post where a clogged cat-converter caused problems, but i don't THINK it's related).
Anyway, the problem at hand: I was driving it a very short distance to a friend's place to show it off, and I went over a fairly rough bump in the road (this MAY or may not be coincidental) and a few seconds later the engine was losing power until I just rolled to a stop. I turned it off thinking I had stalled but I heard it actually turn off, and then after that it wouldn't start. It alternates between just cranking away and whining with no vibration, and then vibrating the engine a lot like it's trying to catch but just NOT. I have observed exhaust gas coming out of the *intake* during this stage. This does not seem like a good thing to me!!!
I checked the diagnostic codes and it is throwing code 3 (No G Signal) which supposedly signals issues with the CAS. I checked the fuel pump by shorting GND and F/P, and I can hear it whining along. I verified that the camshaft does spin by taking off the oil cap and watching while a friend tried the ignition.
I did some testing of the CAS wiring as per these pages:
Our Friend CAS
I am getting 12v and +5/+5 with the key turned to ON, and the ground wire appears to give a good ground... I am not sure how I am supposed to test the voltages with it plugged in (and attempting to start the engine), since when I plug it in there is no way to get the voltmeter sensors to touch the wires. How do people normally test this? Anyway, I got a used CAS (supposedly working, though leaking a bit of oil) from a local contact, and swapped it out, with no effect. Still won't start, same exact symptoms.
The other advice I've been given is to check to see if the timing belt slipped, as possibly the rather large bump I hit could maybe have funked with the tensioner and caused it to slip a few teeth? I took the valve cover off to see if I could check the camshaft positions, but I ran out of time trying to figure out how to get piston 1 to TDC. I am going to give that another go tonight, but in the meantime, here is a pic of the engine with the valve cover off:
Is there any other advice you guys can give me? I did buy this as a project car, but I wasn't planning on having to do in-depth engine/electrical work quite yet (I was really hoping the engine would hold up until I worked my way up to a 1.8L swap)...
TLDR: engine won't start, code 3 "no g signal", sometimes seems to send exhaust out of the INTAKE while cranking :(