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They sound great with my xpipe and racepro mufflers from Pypes. But as you can imagine the ECM doesn’t even think about touching closed loop due to the o2 not getting hot enough from being that far back. (Bung is in the collector)
To remedy this I’m converting to a 3 wire heated sensor. I am using an ACDelco AFS74 o2 and the Michigan Motorsports adapter. I’ve read a lot on where and which wire to tap for power but I did not want to use either my fuel pump relay or my cooling fan relay. I will actually be putting in a new relay to provide steady power from the battery. Since the o2 uses less than 5 amps I have put an inline 7.5 amp fuse in between the battery and terminal. Everything is properly grounded. Now for the switching I’m not to sure where to connect for ignition on power. I have eliminated smog equipment and the EGR which left unplugged connectors, both of which provide a 12 volts keyed on. My question is, has anyone gone this route and what did you use (EGR solenoid or air diverter plug)?
I really want to go the relay route as this seems to be the cleanest and most factory way.
I installed long tubes on my 86 years ago I reused my stock O2’s and they are still working fine.
Reading through corvette forums I found out that some vettes need them after a header install and some don’t.
I had a feeling something was going on with mine when it was running way too rich. Hooking the laptop up indicated it wasn’t sending out the correct oscillating voltage of .1 to .9 once the car got warmed up. Actually reading consiteny around .1 indicating a lean mixture so the ecm composites by richening it. Thus the it runs rich.
I did put in another known working single wire sensor to rule a dead o2. It was doing the same thing.
The only possible issue is the sensor ground. I'm not sure how good the ground will be for the sensor body, since a 3-wire sensor still grounds itself via the sensor body for the O2 signal (the heater has it's own ground wire).
The "O2 sensor signal ground" coming out of the ECM is just tied to chassis/engine ground, so it's only an "inferred" ground reference since the single wire O2 grounds itself to the exhaust manifold. It's a recipe for a ground loop if the electrical path from the O2 sensor body to the main engine ground point for the ECM isn't the greatest.
If you're still seeing any running issues, you may need a 4-wire sensor, where the 4th wire is actually a ground for the sensor.
With my headers, I err'd on the side of caution and got a 4-wire (AFS-75). I tied that 4th ground wire back to the main engine ground point so that the ECM now has a true O2 sensor ground.
Using the pink wire on the EGR circuit to drive the O2 sensor relay should be ok. It's a constant 12V source.
That’s a good thought if the o2 is still having low voltage issues after warm up. I’ll double check tomorrow on whether it’s grounded well. I think it should be simce the headers are bolted to the block and I know the blocks grounding point is well grounded.
Thanks for the heads up on the EGR wire.
You can use the pink wire at the EGR solenoid To power the heaters directly. You don't need a relay. The heaters are Positive Temperature Coefficient (PTC) elements. When they reach a predetermined temperature, the current draw reduces to almost zero. So they don't draw current continuously, only while they heat up. You'll be fine without a relay. Parts left out cost nothing and can't cause problems in service.
Upgrading to Heated O2
