I don't think one HO2 sensor draws that much, maybe the entire set of 4 for Vortec 96+ do?I put a 5 amp fuse in the fuseholder for my O2 heater; I better check to see if it popped.
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I don't think one HO2 sensor draws that much, maybe the entire set of 4 for Vortec 96+ do?I put a 5 amp fuse in the fuseholder for my O2 heater; I better check to see if it popped.
Obvious test is to connect an ammeter in series between battery negative post and negative cable. Measure the current (amperage) drain. Anything over 1/2 ampere (500 miliamps) is probably excessive. (Older cars had ZERO drain; or a pulsed, low-amperage drain if they had an electro-mechanical clock.)I wired my heated 02 sensor to the fuel pump fuse wire on my 91 after installing shorty headers and o/r y pipe.
Still have a mysterious battery drain so was hoping that I didn't wire something wrong.
If I don't run the truck for at least 30 minutes everyday, battery goes complety dead within 24-48 hrs.
did you check to see if the fuse is hot even with key off? i have seen the fuel pump fuse on battery voltages. I splice into the NC side of the fuel pump relay. this way the heated O2 ONLY gets power when the vehicle is RUNNING. On the '92 gmc I just did, this was the grey wire off the relay. the fuel pump fuse did not have battery voltage in this instance.I wired my heated 02 sensor to the fuel pump fuse wire on my 91 after installing shorty headers and o/r y pipe.
Still have a mysterious battery drain so was hoping that I didn't wire something wrong.
If I don't run the truck for at least 30 minutes everyday, battery goes complety dead within 24-48 hrs.
Looking at the Haynes manual page for 1996 and onwards 5.0, 5.7. 7.4l fuse ENG 1 is rated at 20A and supplies EVAP, cam sensor, crank psn sensor, EGR valve, VCM, 4 x O2 sensors and MAF sensor and is 'hot in run or start' so it seems that as long as the key is turned the heaters are live.The "circuit"--meaning the fuse--will almost certainly stay live as long as the key is turned to "Run" or "Crank".
Haynes shows all O2 heaters to be directly - not via PCM - grounded. Again, this points to that as long as the key is turned the heaters are live.I believe that the computer controls the ground on the heater in the O2 sensor. So the computer could turn the heater on and off as required--which means the heater likely wouldn't be operational with the engine not running. The service manual might have more insight.
I'm more concerned about accidentally flattening the battery. Kind of gotten used to it being safe to leave it 'key on' without the engine running since electronics became common place.This also means that I'm a little concerned about the heater life in the O2 sensor I just installed. That heater will be active as long as the engine runs, not turned on and off based on sensor temperature. But what do I know?
Five heaters (including the MAF sensor) running in parallel. I'll take a guess that the currents can't be that high and, as you observed, the thinness of the wiring suggests this.I don't think either of us will have a problem; I have the sense that the heater doesn't draw much power.
I'm sure that's true with 3-wire heated O2 sensors. I'm not sure that's true with 4-wire sensors. And I happened to have a spare 4-wire sensor, which is why I used that instead of buying the recommended 3-wire plus the easier-to-install 3-wire adapter harness.Haynes shows all O2 heaters to be directly - not via PCM - grounded. Again, this points to that as long as the key is turned the heaters are live.
There's another thread where a guy has a faulty oil pressure sending unit, when he moves it, it turns on the fuel pump--even with the key "off". So GM must have wired that circuit direct to battery voltage, not switched with the key. I don't understand why they'd do that. Connecting the O2 heater to the fuel pump circuit might make the heater run all the time--discharging the battery.I'm more concerned about accidentally flattening the battery. Kind of gotten used to it being safe to leave it 'key on' without the engine running since electronics became common place.
I have an AFR gauge on the dash and with the heaters connected I can see the mixture cycling. The cycling starts sooner from cold and and during warm up cycles at a higher frequency. Having the heaters makes a difference.What does matter, is that the hesitation/bog the truck had during warm-up in colder weather has been entirely gone in the three times I've driven it after the latest round of modifications. That is, heated O2 instead of the one-wire sensor that "seemed" to be OK; and dicking around with the TBI fuel pressure regulator to jack-up the fuel pressure. At this point, I'm really happy with my fuel trims and it stays in closed-loop at idle reliably.