riprodder

I have a 93 1.6L Miata five-speed running a Mitsu. 14B turbo, Voodoo fuel controller, stock injectors, LC-1.

This all started when I was trying to find out why my 91 was running rich, so I checked the O2 and coolant temp sensor readings at the computer on my 93 with my Fluke voltmeter by piercing the insulation on the wire. Then I compared the readings to the ones on the 91. They were different so I decided that maybe my readings were off because of the computer, so I made the stupid mistake of pulling the computer out of my 93 and put it in the 91. The 91's readings didn't change so I put the 93's computer back in the 93. Now it's screwed too. The only weird thing that happened was when I probed the O2 wire on the 93. It spiked to 9volts and the engine revved up. Then I pulled the probe and it went back to normal.

The problem I'm having with the 93 is that my car seems to be stuck in open loop. It reads 12:1 AFR when it's idling and randomly spikes up to 18:1 and almost dies. Then it goes back to 12:1. AFR does not swing like normal (13:1-15:1). It just stays mostly constant. Also, now I don't get any voltage from my O2 wire. I've put in a new O2 sensor, swapped in 2 other computers, switched my air flow meter, and I still get the same results. My coolant temp sensor still reads the same 2.5-2.8volts and I checked to see if there were any error codes. There were none. I also unplugged the Voodoo. No change. I even bypassed the O2 wire by connecting a jumper wire from the new sensor and ran it straight to the computer wiring harness just before the main connector on the CPU with a T-tap. I also checked for continuity from my T-tap and the metal connector itself in the plastic holder. It was good.

The 93 ran perfect before I started all this.

I don't know what else to check. Please Help.

riprodder

I fixed it !

After checking every sensor by itself and the voltage readings at the computer and finding nothing out of spec, I said screw it and took the car for a drive. I had backed the fuel pressure down to 35psi from 50psi where I had it set to get a little closer to stoich but it still steadily ran 13.5:1. But as I took it out on the highway I noticed the AFR going into the 14's, and then it touched 15. After that it started to swing; 13-15:1 like normal. Then I bumped my fuel pressure to 40 and then back to 50psi and it still was holding stoich. Then I knew it went back into closed loop .

In summery, when you unplug the battery (or computer as well in my case) the CPU forgets everything it learned and runs a base fuel map. It won't start looking normal until the car is driven and the engine is loaded up. Then it gathers real world data from its sensors and creates an optimal fuel mix. Thus stoich. I hope this helps anyone else avoid the same headache I just went through.