I have a 1990 Miata and it will not start,I got the car from an person that pulled the motor out and done some repairs and replaced it, and it would not start, I checked it and it had no
Fire at the plugs or the injectors and the fuel pump would run all the time, I replaced the motor with another that came out of the same year model and replaced every sensor from that car to mine, even the ECM, tried to start and it will not, still no fire at the injectors and fuel pump is still running, if any one can help please, I need it. Thanks

. Check all under-dash and under-hood fuses with a test light or multimeter:

https://www.askmehelpdesk.com/cars-t...tml#post252145

. See if you have a Constant Control Relay Module (CCRM), located near the battery. It may be bad. If you don't have a CCRM, you need to gain an understanding what controls power to the fuel injectors and fuel pump.

. Test the Ignition Control Module and coil. AutoZone can do this for free.

. Test for codes.

. Start testing for power with your DMM; e.g. distributor, ECM, main wiring harness, etc.

. Ensure all grounds are good, especially to the ECM.

. Try to determine if the Crankshaft Position Sensor (CKP) and ECM are good. This may involve intensive analysis of your electrical system, in order to understand exactly how it functions--this is imperative and may take several weeks of intensive study to put it all together. Analyze what is the key sensor (e.g. CKP) on your car and determine what reference voltages the ECM should provide. Test for these voltages with your DMM. Start establishing a "known-good baseline." This will help you zero-in on exactly where the problem is. Get all of the wiring diagrams on your Miata and make this your project for the next several weeks. Be patient and keep a positive mental attitude. The reward, when it starts, will make it all worthwhile.

. Does the Check Engine Light stay on?

Well,I went back and looked at the fuel wiring digram and found that one wire from the fuel pump relay went to the Mass Air Flow, so when I unpluged it the fuel pump quiet pumping all the time, so I tested for spark in the coil and injector pulse I had it all, the car cranked up and run, I have never seen a bad mass flow cause a no fire problem, but now I will not forget this and hope this helps someone else Thanks for the help

There's the possibility that you are not through with this yet. I'm concerned that disconnecting the wire and everything working is a sign of intermittent ECM failure. I'm fairly certain you have a deeper-seated problem that will resurface. Sorry, but that's my experience.

MAF Sensors have replaced MAP Sensors on most cars. What you observed makes perfect sense to me, because MAF Sensors control timing (similar to the old vacuum advance on distributors) and air/fuel mixture, depending upon air mass changes. Like any transducer, it converts energy from one form to another. Here, it converts air mass changes into fluctuating electrical current signals to the ECM. If this sensor does not receive the proper voltage from the ECM, you may experience catastrophic ignition and fuel system failure. Therefore, test the reference voltage between the ECM and the MAF Sensor connector at various times. My hypothesis is that your ECM is failing and is at the heart of your problem.

Another possibility is that the MAF Sensor is dirty (use special cleaner) or needs replacing. Keep us posted with any new developments--this is an interesting one.