My truck idles very erratically. I spent some time datalogging, and it seems that when it idles fine, my downstream 02's read normal and similar. when it is idling rough, both downstream 02's are either at 0.0v, or bank one is at 0.0 and bank 2 is at 63.something volts.

I know something is wrong here. I'm wondering if anyone can help me sort it out. It seems logical that one of the sensors could be bad, but why would the other read correctly sometimes, and no voltage at other times?

Please help!

 

your downstream sensors only monitor and report on the effectiveness of your catalytic converters, they have no affect on idle, air/fuel, or any other engine control function.

both upstream and downstream sensors read between 0 (zero) and 1 (one) volt. the upstream sensors should switch from high to low, the downstream should remain steady and not switch.

you need to be watching the upstream sensors HO2S11 for bank 1 which is the right or passenger side, and HO2S21 for bank 2 which is the left or driver side.

you may have a vacuum leak or a missfire causing erratic air/fuel ratios.

good luck.

later,
chris

 

wouldn't a misfire trigger a code or show up while datalogging? Also, the truck runs totally fine while driving. I would think that a misfire would be noticeable, and or traceable. But maybe I'm wrong. please let me know.

 

no, some types of missfires do not set codes or illuminate the check engine light.

what type of data logging tool are you using, most aren't going to directly show a missfire.

what do you mean by "erratic idle" I took that to mean missfiring or running rough.

good luck.

later,
chris

 

thanks for responding again Chris. I'm using a Predator.

what I mean by erratic idle, is that at times it seems to idle fine, and then all of a sudden the engine drops rpm's quickly. sometimes it catches itself before stalling... other times it stalls out. this happens only when the truck is at operating temperature, and seems to switch back and forth from idling fine for a few minutes to idling rough, and or stalling.

so far, the only clue I have is what seems to be a very strange voltage reading from my downstream bank 2 sensor.

otherwise, while driving the truck, it seems strong with no hesitations or fluctuations

 

i feel your pain. keep an eye on it and don't go cowboying it around. I went through hell last year, i'm sure chris remembers cause he tried to help me. I'm pretty sure it's all good now.

I'm not 100 positive, but my hypothesis is that my fuel mixture richened drastically when adding the longtubes and was dumping so much fuel that my o2's weren't functioning. JDM retuned my truck and all seems good. More testing to follow once the snow melts. Unfortunatley when i returned from JDM day i put the truck away a few days later.

Have you added any mods or done any kind of service lately?

 

tallimeca,

I haven't driven the truck more than twice since December. It was doing it then, and I figured it had to do with the winter tune I put in about a month or two prior. After it started snowing, I let the L sit, and just recently started messing around with trying to figure out what's wrong. I started by reinstalling my regular tune which did not change anything. Other than changing the tune, I hadn't added any mods for a while.

Since you brought up the exhaust idea, I should say that I have quite a bit of condensation leaking out of the exhause tips every time I start the truck up and let it run. It seems like a lot and it's every time I let it run (3-4 times a week).

Thanks, and p.s. great sig