heated o2 sensor wiring

[mmigacz]

I've read that its common (or recommended) to run the fuel injectors, ECM and ignition off a 30 amp relay. If I am adding a heated O2 sensor, should the power to the heater be ran on its own dedicated relay?

Or simply combine it with the fuel injectors, ECM, ignition relay?

[Six_Shooter]

Yes!


Really, it won't matter.

[billygraves]

..............

[Six_Shooter]

The current from most heated O2s is 18 watts. In your case, with a boat, I would do as you plan and keep the O2 heater on at all times. If it was a vehicle, I would try to set up a simple circuit to turn off the heaters after a few minutes. The O2's heaters are turned off with the GM PCM 02-08. The engine calibrators say they will burn out quicker if powered up all times. But the thought might be the 200,000 mile bogie sought after by GM.
I used the heater O2 grd switched by the ECM in my truck and the ECM circuit I used was the AIR pump. Just set up the cals to do so. ON another car I used a Rear Defog relay and set it up to have the starter sol wire trigger the rear defog relay On. They have a 5 to 10 min time out. Fused it with a 7.5 amp. They all work and Im sure you can find a better way.

The earlier heated O2 sensors were powered full time and last a very long time, so I don't think he needs to go about complicating the circuit by adding timers. If you really wanted to turn the heater(s) off, you wouldn't really want it to be timer based anyway, you'd want it to be more load/RPM/VSS dependent, due to under what conditions an O2 is likely to cool to off.

[steveo]

I always group fuses by failure groups, with a mindset of "what happens if it blows".

for example a shorted heater circuit still allows engine to run, but if you fuse it with the pcm or ign power to sensors or coil, it's a failure mode.

so i'd fuse it seperately from pcm power, coil power, etc.

it's a 'just in case' thing that can also aid in diagnostic

also size your fuses with an ammeter.... go for actual operating draw *1.5 or something

[steveo]

also use of a relay depends on how beefy your ign. switch is, more than anything, but a relay is rarely a bad idea if in doubt, the less load on your 'master switch' contacts the better

[EagleMark]

Pretty cool ideas but really not necessary with as long as a heated O2 sensor lasts.

When I build a harness I do tend to over complicate with fuses and relays into separate circuits like fuel injector, fuel pump, ECM/PCM, Heated O2, 2 fans, etc... But I do have one that turns them all on, that way I only need one wire from the car to turn on EFI system.

[steveo]

come on, overcomplicating things is half the fun of diy car stuff!

hell my fuel pump runs on a 60a milspec relay with 0/0 welding cable as a main feed, anl fuse block at the front and heat breaker between pump and relay

maybe I should stop doing stuff like that, but at least if it dies, I know its not a wiring problem

[mmigacz]

Thanks for the tips!

[progdrums]

The current from most heated O2s is 18 watts. In your case, with a boat, I would do as you plan and keep the O2 heater on at all times. If it was a vehicle, I would try to set up a simple circuit to turn off the heaters after a few minutes. The O2's heaters are turned off with the GM PCM 02-08. The engine calibrators say they will burn out quicker if powered up all times. But the thought might be the 200,000 mile bogie sought after by GM.
I used the heater O2 grd switched by the ECM in my truck and the ECM circuit I used was the AIR pump. Just set up the cals to do so. ON another car I used a Rear Defog relay and set it up to have the starter sol wire trigger the rear defog relay On. They have a 5 to 10 min time out. Fused it with a 7.5 amp. They all work and Im sure you can find a better way.

Hi,
I am a noob currently installing a 92 5.7 TBI in a 1978 Camaro Z28. I have headers. My current harness has 1 O2 sensor connection. Could you please recommend the right part # for the O2 and is it possible to wire-in 2 O2 sensors? What is the best way configure them on the harness/ECM?
Any help would be greatly appreciated.

[fastacton]

AC Delco part number AFS21 is the standard one wire O2 sensor and should work for you unless you have a harness with a heated O2. The TBI ECM only looks for one O2 sensor, so there's nowhere to send that data if a second one was hooked up. TBI doesn't control fueling separately for each bank, so a second O2 isn't helpful anyway.

[lionelhutz]

If the O2 is in the collector then you need a heated O2 sensor. Personally, I would use a 4-wire sensor since they cost about the same as a 3-wire. There is a Tan wire from the PCM that is grounded to the back intake bolt on TBI systems and I would hook the negative sensor output to this wire. That way, the sensor wires both go directly to the PCM and you can't get some strange O2 result due to a grounding issue.

The 4-wire sensors are all about the same. Get one for a 95 V8 Camaro or a 97-04 Corvette would work too. Both have the common 4 terminal inline plug.

I can't tell you the colors but the wiring pattern is like this for all GM 4-wire O2 sensors.
2 wires the same color are the heater. It doesn't matter how you connect them.
The other darker wire is the sensor positive output - typically goes to a purple wire to the PCM.
The other ligher wire is the sensor negative output - typically goes to a tan wire to the PCM.