No voltage to new o2 heater and sensor

[Halsupramk3]

I have searched and checked to try to diagnose this problem.

I have a 90T which is throwing a code 21. On the 89+ ecus if the o2 heater does not work it will throw a code 21 as well so if the sensor itself is bad. I bought the MDC o2 sensor and spliced it into the original oem o2 sensor plug with snap connectors which i then plugged into the wiring harness at the engine. In other words the o2 sensor wires are in two parts. One section is the mdc o2 wires and the other section is the oem wires to which both sets of wires are connected to each other with snap connectors so i can keep reusing the oem plug with multiple mdc o2 sensors as needed. I can not plug the o2 wire into the heater wires accidently. Each matches up to the correct wires.

The oem plug is not sturdy but i checked the voltage coming out and when the o2 snaps are not plugged into the original plug snaps i get 11+ volts coming out of the engine harness and oem o2 wires. But when i snap the mdc wires into the oem plug wires the 11 volts stops. Of course this is when the engine is running or if the key switch is in the on position. When the engine is running i get 5 volts out of the o2 sensor wire.

Why would i get voltage when the mdc o2 sensor is not plugged up but no voltage when the o2 sensor is plugged into the power source from the oem plug?

Would my ecu be bad?

The oem o2 heater has a resistance of 3 to 3.6 ohms. The mdc o2 sensor heater has a resistance of over 6 ohms. Does the ecu not like this and throws a code? When i plug all the wires together i get about 8 ohms thru the o2 heater wires and plugs.

Whats the deal?

 

[Bishop92t]

It's possible the MDC O2 sensor can't be driven by the stock heater. Try plugging in only the signal wire for the MDC sensor and leaving the heater circuit disconnected. Verify the MDC is putting out a good 0-1v signal and see if the ECU code goes away. I'm not sure about 89+, but I know on the 87-88 you don't need the heater circuit and it won't throw any codes.

 

[Halsupramk3]

Thanks bishop.

i will try that but it think i may have already. The 89+ does have a code for broken/absent O2 heaters. I am afraid when i do this it will throw a code. I have also tried to similate the stock heater by using (3) 1 ohm resitors to get to the 3 ohm of resistance the stock heater produces. Sometimes that works and sometimes not.

 

[Bishop92t]

Why are you trying this aftermarket O2 instead of the stock one?

 

[Halsupramk3]

I didnt want to spend the money for a new oem one but i would like to borrow a stock one to see if i still throw a code. It may be my ecu.

 

[gixxer750]

is that engine broke in yet Hal?

 

[Halsupramk3]

just 500 miles
It sure does want to go tho. I havent boosted it yet. I think i will drive atleast 1000 miles on it and i need to do some compression checks on it too.
I guess your rod knock was a false alarm.

 

[gixxer750]

still not sure. gonna check the torque on my balancer bolt tommorow. It comes and goes, but my oil pressure remains constant.