Oxygen sensor graph - trying to solve rough idle
07-18-2016, 12:18 PM
#61
RL Community Team
Rennlist Member
Rennlist Member
Lots of technical discussion here driven by a rough idle, a qualitative description. Does the poster have a better definition of a rough idle, as in RPM range, constant stalling as in unable to maintain idle, surging idle? 993 do not have perfectly smooth idle and it is unclear as to how far the issue deviates from a normal condition.
07-18-2016, 12:52 PM
#62
Racer
Thread Starter
Wow. Great information there. Thank you bruce7!
It may take me a week to digest it.
What I am finding is that my rough idle -almost- completely disappears when the engine has some load on it. For example, when the engine is warm enough to run the oil cooling fan, or if I switch on my high beam headlights. My theory is that the additional electrical load results in additional mechanical load from the alternator. And, like others, the idle gets better when the AC is switched on (but this also boosts the idle, whereas the oil cooler fan and high beam headlights don't seem to).
BTB
It may take me a week to digest it.
What I am finding is that my rough idle -almost- completely disappears when the engine has some load on it. For example, when the engine is warm enough to run the oil cooling fan, or if I switch on my high beam headlights. My theory is that the additional electrical load results in additional mechanical load from the alternator. And, like others, the idle gets better when the AC is switched on (but this also boosts the idle, whereas the oil cooler fan and high beam headlights don't seem to).
BTB
07-18-2016, 12:53 PM
#63
Racer
Thread Starter
07-18-2016, 01:57 PM
#64
Racer
Thread Starter
Lots of technical discussion here driven by a rough idle, a qualitative description. Does the poster have a better definition of a rough idle, as in RPM range, constant stalling as in unable to maintain idle, surging idle? 993 do not have perfectly smooth idle and it is unclear as to how far the issue deviates from a normal condition.
If you go post #27 there are two video links that will give you a good idea of what i am seeing now. Although i have made some progress there is an occasional small jolt/shake that you can feel. There is also a random "phut" sound which i think is a combustion misfire and it coincides with a stumble and shake.
There is no stalling, surging ,etc.
07-18-2016, 03:58 PM
#65
To find the cause of the intermittent problem (the misfire) I think that you
will need to use the data-logging capability of the scope to record some
system parameters while listening for the misfire (phut sound). At the
moment the misfire is heard, stop the logging and then go back through the
data log to the point that corresponds to the misfire. Try to find a glitch
that might explain the misfire. For example, maybe a coil failed to saturate,
or an injector failed to spray or the spray time was too short, or maybe a
valve didn't seat. It's going to be a lot of work and require some specialized
equipment.
I would pick one bank that is having the intermittent misfire to narrow the
possibilities to look at.
I've attached a couple of docs related to misfires. One of them appears
to be missing the beginning, but so is the website page from where it came.
Maybe something in there will help to focus where and what to look at.
-bruce7
The docs are not Porsche-specific so you could add to them such false
misfire causes as fan belts and failing DMF.
will need to use the data-logging capability of the scope to record some
system parameters while listening for the misfire (phut sound). At the
moment the misfire is heard, stop the logging and then go back through the
data log to the point that corresponds to the misfire. Try to find a glitch
that might explain the misfire. For example, maybe a coil failed to saturate,
or an injector failed to spray or the spray time was too short, or maybe a
valve didn't seat. It's going to be a lot of work and require some specialized
equipment.
I would pick one bank that is having the intermittent misfire to narrow the
possibilities to look at.
I've attached a couple of docs related to misfires. One of them appears
to be missing the beginning, but so is the website page from where it came.
Maybe something in there will help to focus where and what to look at.
-bruce7
The docs are not Porsche-specific so you could add to them such false
misfire causes as fan belts and failing DMF.