No gas smell on the dipstick , ( or anywhere else for that matter ) , no black soot on the tailpipe , so sounds more and more like the check valve , eh ? And I get the toilet analogy ( thanks Bob, leave it to you to always come up with creative examples, LOL, but ' ya know, for a technically-challenged layman such as myself those actually help illustrate things ) but still a bit puzzled why one whole week of sitting is not sufficient to cause the symptom, but three weeks is...
I seem to recall injector pulse width is affected by battery voltage - the computer adjusts for it, but I wonder if your car sits for three weeks and the battery voltage drops enough, if it might cause a rough start?
[quote name='tamathumper' timestamp='1346022766' post='131671']
I seem to recall injector pulse width is affected by battery voltage - the computer adjusts for it, but I wonder if your car sits for three weeks and the battery voltage drops enough, if it might cause a rough start?
[/quote]
Hmmm, in the words of Arte Johnson :
http://video.search.yahoo.com/video/play...=yfp-t-701
Usually what I notice is that the battery voltage on starts is at least half of a bar higher ( closer to 14 ) than when driving when it dips a bit.. seems almost counter=logic, as the alternator is charging the battery when driving, shouldn't the voltage reading be higher than after the car sits for a while ?!
[quote name='ds968' timestamp='1346026997' post='131676']
Hmmm, in the words of Arte Johnson :
http://video.search.yahoo.com/video/play...=yfp-t-701
Usually what I notice is that the battery voltage on starts is at least half of a bar higher ( closer to 14 ) than when driving when it dips a bit.. seems almost counter=logic, as the alternator is charging the battery when driving, shouldn't the voltage reading be higher than after the car sits for a while ?!
[/quote]
Mine does this as well. I'm curious as to why. I've seen suggestions that if one cable from the battery is hotter than the other you might have lots of resistance in the cable. While the car is running, heat will cause even more resistance.
Have you changed your battery/alternator cables?
[quote name='mbardeen' timestamp='1346027810' post='131677']
Have you changed your battery/alternator cables?[/quote]
No, still the original cables.
[quote name='ds968' timestamp='1346026997' post='131676']
Usually what I notice is that the battery voltage on starts is at least half of a bar higher ( closer to 14 ) than when driving when it dips a bit..
[/quote]
That is because of the voltage regulator which adjusts the voltage to the battery depending on the state of its charge. A typical car alternator puts out about 14.5 or 14.7 volts (or something like that). When starting the car, the battery gets drained quite a bit to provide power to the starter. So initially after start the regulator allows high voltage to recharge the battery faster. Later after driving a bit the battery has recharged, so there is no need for a higher voltage so the voltage regulator cuts the alternator output to 12.5 or 12.1 or some such number. Providing the 14.5 volts to a charged battery may damage it, or I guess reduce its life.
The gauge is an indicator of the charging voltage, not the stand alone battery voltage. If you let your car sit for some time, take a measurement of the battery voltage before starting the car. You might see it at 11.8 or 11.5 volts. That is not a problem for the starter, since the important thing for the starter is the AMPS (like we see in battery specs "amp-hours"). All of the other electronics are of course designed to operate correctly within some voltage range -- I have no idea what that might be, but think of the starter and electronics all working and happy within a range of 10-16 volts (for example). I have no idea what the spec is on the fuel injector, but the point above was very interesting, that the computer adjust for slight variations in voltage. As a silly example I just checked the spec on my radio, it is happy at any voltage between 10.8 - 15.1 volts.
Roland
My apologies, I should have said - *Some* computers adjust for it. I have no idea whether or not the 968's computer, specifically, adjusts for battery voltage.
Hey Dan, I was curious if there is any additional news on this problem, is it still there, or any further diagnosis?
[quote name='968Syncro' timestamp='1347123369' post='132362']Hey Dan, I was curious if there is any additional news on this problem, is it still there, or any further diagnosis?[/quote]
Not yet, it starts perfectly ok at its one week intervals so I probably won't deal with this until it goes to my mechanic for whatever else is needed next, at which time I'll have him check into this issue as well..
As a means of testing, the next time it sits for a while, hook a charger up to it that has a "starter boost" function and then start it, and see if it stumbles. If it doesn't, that would be an argument for a low-voltage-situation.