I need some help with this guys. Just bought a 1993 RX7 several months ago and it recently decided not to start. Could not hear the fuel pump so I immediately checked the fuel pump relay and circuit opening relay. Fuel pump relay tested fine but the circuit opening relay was done. Replaced ciruit opening relay and car still won't start. Checked continuity between relay location and terminal 1T and all is good. Next I removed the relay and bridged terminals A & B (relay coil) and C & D (relay switch) and the car starts and runs fine. After further testing I have concluded that the ECU is not closing the circuit to the coil. The 12V source to the relay coil is good during start up. Has anybody run across this problem? Also, the ECU displays no codes.

 

Have you tried manualy grounding 1T? If the car runs then I can only think of two scenarios, one the ecu is not reciving a proper signal from the crank angle sensor and B the ecu is the problem. Be advised if the ecu is fryed, you'll need to check for a 12v short to the 1T terminal before trying a diffrent ecu.

Paul

 

Thanks Paul.
When this problem first came up I checked for computer codes and the crank angle sensor came back. I checked the resistance between 4E and 4H and found that the circuit was open (no signal from sensors). I pulled the sensors out and they both tested fine. I then checked the harness and found several poor wiring repairs; twisted wires, electrcal tape, exposed wire etc. Anyway, I fixed that and checked for continuity at the ECU plug again and now all is as it should be. Put it all back together and tried to fire up the car. No dice. I then pulled the circuit opening relay and bridged the terminals. Ignition on, I can hear the fuel pump, and the car fires right up. I then shut it down and checked for codes. None reported. I think it's the ECU. Any last idea? Oh yeah, If I manually ground the 1T terminal the car starts.

 

Paul, I have a degree in aerospace engineering and could probably help you with getting that glider hooked up to your car. Although, be aware, that this may qualify you for a new "you might be a redneck" joke.

 

So I think you sould revisit the CAS wiring. The ecu will only set a code if there is an open circuit or a short. But just continuity is not enough, the ECU needs a clean signal and other RF sources can cause strange problems. Shielded wire is used for the CAS to cut down on Interference.

Paul

 

All of the wire shield is intact from the CAS to the ECU.