Electrical issues... need help....

[Doppelgänger]

Went to install my rear o2 sensor. It was disconnected because i had a track exhaust on the car. So i grabbed the o2 that had been sitting around and went to work. Got under the car and everything went in fine.

Then i jumped in the car and turned the car but the car started, sputtered and died. Figuring the o2 was the last thing, i disconnected it. This time the car started right up. But here is where things get interesting....

The battery light is on. I had the battery and alt. checked and they are good. The battery light stays on when driving, but when i go into boost the bettery light TURNS OFF. As soon as i let off the gas/get into vacuum , the batt. light returns. Also, at part throttle boost, the car hesitates bad, but not at full throttle. And my idle was running ~1800rpm. I turned the idle screw down and with it as low as it can go, idle is still at ~1200rpm.

I also ran the CEL codes, wiped them and then as soon as i turned the car on, the CEL was back on and here are the codes...

PO108---- Barometric pressure sensor circuit high voltage
PO113---- Intake air tempature (AIT) sensor circuit high input
PO118---- Electronic coolant tempature (ECT) sensor circuit high input
PO123---- In range Throttle posistion sensor (TPS) circuit high input
P1141 HO2S Bank 1 Sensor 2 Heater Circuit Low Input *** my rear o2 is disconnected at the moment***



I bought a replacement ECU, plugged it up and the symptoms are still the same. I also disconnected all of the sensors and started the engine and i still had the batt. light on. This is leading me to something wrong with a wire/ground somewhere. Where are the grounds on a 99?? I can't for the life of me find them. Im looking for ground location G115(S?) at "right front of engine"... but exactly where is that?

Also, what makes the ECU throw a battery light? Is it any sensor/group of sensors with a bad signal input?

And the common wire that all the sensors share starts at pin 2B and runs through the sensors and returns to the ECU at pin 3F.

Oh yeah, car is near impossible to start when cold.

Here is a wiring diagram for the engine harness.... its HUGE but you can see all the details, i have notes written on the bottom of what is happening. The blue highlighted wire is the common wire to the sensors throwing codes.

http://i99.photobucket.com/albums/l2...G/ca2c2b40.jpg




*****Reward to the person who can come over and fix it lol... free laptop computer. no sh!t.

[mr.koupe]

what kind of car is it ? lol

[Doppelgänger]

99 Miata

[mr.koupe]

hmmm gimme a minute lol i need some reps haha ill let u know something

[mr.koupe]

do you have access to alldata ?

[Doppelgänger]

no

[MIKE.P]

i do..what do you need??

[Doppelgänger]

Alrighty,

Got some much needed help lastnight from a member on another forum. Turns out that all 4 of those sensors were getting a 5v regulated signal from both the input and output wires! Basically like this 5v-----> sensor<------5v , when it should be more like 5v----> sensor------>output of less then 5v. This caused the ECU to throw a voltage code and run completely on limp mode. It took about 20min to figure out what the problem was and another 5hrs to find a solution lol. Turns out that the jumper box i have (its a ECU harness extension made for tapping/adding piggybacks), had a short in it somehow or another. Considering the construction of the box, i dont know how it happened, but it did. So now the car runs like a champ...yay. I'd probably type more, but i didn't get to bed until 3:30 and was up at 7:30....

[Z U L8R]

i bet there's an issue with the sensors' 12volt circuit. for example. on nissans the o2 sensor, the tps sensor, and other sensors the ecu uses for determining fuel trim pretty much get power from the same source. haven't taken the time to examine the power and ground distribution on miata, but verify that these sensors are getting the ignition power to them etc. if not, trace the circuit, it could be a short in the power wire, or it could just be a blown fuse. the o2 sensor you tried reinstalling could have a short in it and that could have been what popped the fuse. gl man
Dave =]

OOPS
Just read the post above this, glad u fixed it, gj man =]