Random timing jumps at idle?
08-08-2013, 10:10 PM
#1
Random timing jumps at idle? I have the 02 Silverado listed in my sig and I have a weird timing issue with it. The truck is stock minus the longtubes, ory and catback. The tune is stock save for turning off the SES light from the deleted rear o2s. At idle the timing will randomly jump about 15 degrees and it causes a stumble. On an HPT log it just shows a quick spike and then back down to the stock idle timing. Sometimes it will spike several times (like sitting at a stop light) and other times it idles smoothly.
I will say right now that I only have the driver side o2 sensor installed because of a clearance issue with the passenger side. On the log that sensor readout just stays pretty much steady at its midpoint. The truck also drives just fine except for it having 2-5 degrees of knock retard at random times during part throttle. I just switched to 89 octane from 87 to see if maybe that problem will go away but I don't see why I can't run 87 in it.
I doubt these issues are related to the missing o2 sensor so I am lost on what to look for. Plugs are pretty close to brand new NGK TR55's gapped to stock spec. Wires are a couple years old but that wouldn't cause a timing jump. I am stumped...
I will say right now that I only have the driver side o2 sensor installed because of a clearance issue with the passenger side. On the log that sensor readout just stays pretty much steady at its midpoint. The truck also drives just fine except for it having 2-5 degrees of knock retard at random times during part throttle. I just switched to 89 octane from 87 to see if maybe that problem will go away but I don't see why I can't run 87 in it.
I doubt these issues are related to the missing o2 sensor so I am lost on what to look for. Plugs are pretty close to brand new NGK TR55's gapped to stock spec. Wires are a couple years old but that wouldn't cause a timing jump. I am stumped...
08-13-2013, 12:55 AM
#3
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No, the timing is not causing your stumble. It's doing
what it can to fight it. Adaptive spark. But it can't
clean a crappy idle fueling situation all by itself. Which
I'd bet is mostly false trimming from the long tubes
cooling down too much at idle.
what it can to fight it. Adaptive spark. But it can't
clean a crappy idle fueling situation all by itself. Which
I'd bet is mostly false trimming from the long tubes
cooling down too much at idle.
08-13-2013, 11:13 PM
#6
Your mods will change what the car must do for proper fueling. Not by much but they will affect it.
If your motor was totally stock it would probably run okay because it could default to open loop and the stock tunes are pretty good and safe. Now that you have changed the Airflow of the motor the only way the PCM can compensate are the O2's in Closed loop. Missing an O2 renders closed loop broken.
If your motor was totally stock it would probably run okay because it could default to open loop and the stock tunes are pretty good and safe. Now that you have changed the Airflow of the motor the only way the PCM can compensate are the O2's in Closed loop. Missing an O2 renders closed loop broken.