“Also, I did some reading up, and it seems that as the line voltage increases (due to more secondary circuit resistance) the spark duration decreases, and vice versa.”
There is a resistance that gives you maximum duration. Higher or lower resistances will shorten the duration.
Well, I can believe that, Keith. Some of these automotive textbooks simplify things too much.
Well Karl where do you suggest we get this type of info, the back of cereal boxes? You can perform practical automotive repairs all your life and never be confronted with the need to know the answer to this question, it is a perfect one to refer to the textbook for, much to the dismay of those that downplay “book learning”
oldschool, you misinterpreted one of my posts again. If you jump to conclusions about an offhand comment someone makes on this board, then criticizing your own misinterpretation is counter productive to what we’re trying to do here.
If you drop the attitude and ask me how I feel about learning automotive theory from written sources (trade school textbooks, dealer technician school handouts & booklets, TSB’s, repair manuals, publications like MOTOR & Motor Age)–I’ll be glad to answer your question.
Gonna bite?
Yeah, state your opinion on ASE certifications.
You asking me or telling me? Haha, just kidding. I’m re-certifying in all 8 automotive categories in May. 110 big ones. I’ve been out of work since late '08 when I was laid off at the Volvo Dealer. No one wants to hire a 58 year old mechanic. Maybe if we get national healthcare.
If I get all 8 badges and then the Advanced Engine Performance, I’ll have a fighting chance to get hired somewhere. I have like 6 textbooks we used at the trade school I went to '95-'97, and about $300 worth of similar but more up to date textbooks I got on Amazon. Being out of work, I’ve got beaucoup time to digest this stuff.
On April 20 it’s 100 bucks for the privilege of renewing my PA I/M license. You gotta read the state manual to pass this test, but it’s worth it.
OK, but I haven’t really answered your question regarding the ASE’s. They’re a double edged sword: On the up side, they impress customers, sitting there on the wall of the
waiting room–until Mrs McGillicuddy finds out that the guy who has the A/T certificate has never rebuilt a transmission–and that’s the rub.
Many incompetent mechanics, if they studied the right books, could get a 95% percent on all 9 tests. 10 if you count the “automotive” diesel test. The tests do however, get an otherwise uninterested mechanic involved more in the theory part of the job. Other side of the coin: It’s possible to rebuild engines up the kazoo and not know the 2 factors that control manifold vacuum, for example, or not understand why the spark has to advance or retard depending on operating conditions.
So yeah, you need book learning, as you call it, and this ties in with my statement about some textbooks being too simplified. The books I looked at regarding the subject of this thread all said that as the firing volts increased, the spark duration decreased. Keith, an electronics expert, disagreed, and put the whole thing in perspective, I believe, with his comment about there being a secondary resistance level that gives max spark duration; go higher or lower, and the duration decreases.
I guess my textbooks must have been talking about normal operating conditions, as opposed to an extremely flooded condition, but that’s not made clear in the books in question. So my point is that the info we get as mechanics is kind of lame. There’s a parallel here with Keith’s scenario of him having to rewrite military electronics manuals that were sub-par to begin with.
We need better manuals and publications so we can figure these damn cars out better. What in heck were you talking about with your cereal box comment?
I offer this simplified explanation as a reason why spark can be made to jump the gap of a fouled plug by adding an external spark gap.
With a conventional battery and coil ignition setup, the fouled plug center electrode insulator can shunt off the spark energy, dissipating the voltage before it rises high enough to jump the spark plug gap due to the relatively slow voltage rise time of the coil’s secondary output.
With an additional spark gap introduced into the fouled spark plug circuit, the ignition coil secondary output voltage rise takes place to a much higher level before any current flows. When the voltage rises high enough to jump the extra gap, much of the electrical energy also jumps the spark plug gap of the fouled plug because the current path represented by the fouled insulator is not only a resistor but more importantly due to the reverse current path relative to the center electrode, is also an inductor that initially resists current flow.
I used to do this often by partially removing the plug wire terminals when I owned an old Yamaha motorcycle that required oil-gas mix and would frequently foul spark plugs.
Consumers have little interest in supporting the auto repair industry…They want and will demand cars that require few if any repairs. Cars with “bad reputations” will be left on the industrial scrap-heap…
cereal boxes typically just have information to keep you occupied while you eat, nothing of value, I was implying that you thought nothing of value comes from " book learning".
So do you automaticaly conclude that if a guy does have his ASE’s this means he is incapable of actualy doing the job? we do have members that feel exactly this way when it comes to ASE, that is, having ASE is an indication of being book smart but praticaly incompetent.
About a year ago I posted a question asking if members saw any value in the way ASE has made what they call a “composite vehicle” to teach modern systems, this vehicle doesn’t really exist, it is just a teaching tool, my question brought out an overwhelming negative opinion towards mechanics who have ASE’s
You will find materialin the ASE test booklets that would help you answer the question that started this thread.
“So do you automaticaly conclude that if a guy does have his ASE’s this means he is incapable of actualy doing the job?”
Loaded question, but no.
It is loaded, but not pointed at you Karl, you just seem to be someone who if was to give an opinion on this it would be an opinion with merit.
Right now I am studying for a degree in computer networking (called a CCNA) and the impression that if you are a good student (OK an “A” student) has carried over to some of the “part timers” at the school with comments about how “I have seen many “A” students that can’t do the job”. I am searching for why this link between being good at taking tests and writing technical papers is associated with not being able to do the job. It is uncanny that the concept exists even in the IT field.I asked the instructor “don’t you believe that an “A” student can also be competent?” and was met with silence.
It is also uncanny how many people will report “yeah, I know of many people hired at my work with good credentials but could not do the work” it is almost like good grades or some other sign of grasphing the concepts presented works against you, much prejudice against those that come with the credentials, we deserve the same chance to prove ourselves that others get before the “cold shoulder” is given. Really it is not so easy to get “A’s” in this field.
oldschool, I completely agree that nowadays you’ve gotta have some background, like a two year technical college, or something. You don’t have to, but it helps. Some of the best techs where I used to work had an associate’s degree from a community college. They weren’t overwhelmed by, you know, technical phrases in a TSB or something like that. You gotta have the hands on education, too. The guys that built hot rods when they were 15 don’t seem overwhelmed by the mechanical challenges–the R&R on a hard job. Like I say, it’s a two edge sword. I completely agree we have an anti-education bias in this country.
OK, I was going to let this sort of die out. I am comfortable with my explanation, but I have to ask, where is it said that gasoline is conductive, and more to the point, highly conductive? I really don’t know the answer to that one. I’m sure it does have some conductivity, but how much?
Does the environment the electrode end of the spark plug end is in prevent the presence of a conductive path between outside and center electrode in some circumstances? (I certainly could say yes if that environment insulated the electrodes).
Won’t a spark be possible even if the plug is in a vacuum environment?
Air is normally not electrically conductive either. I don’t know the dielectric strength of a spark plug center electrode insulator with combustion deposits and wet with gasoline. It would be interesting to measure that using a megger without and with the gasoline. Air has a dielectric strength of approx. 60,000 volts per inch so with a plug gap of .035 inch, the voltage needed to jump the gap would be approx 2100 volts. I am going with the assumption that a spark plug center electrode insulator as described would not withstand this voltage.
Books have been written about the center insulators used in spark plugs, the quality of the porcelain, it’s dielectric strength, its porosity…But the fact is, these insulators get a coating of combustion deposits on them very quickly…When the porcelain and these deposits are soaked with gasoline that plug will have great difficulty arcing across its electrodes…CDI ignition, a whole different approach, can overcome much of that with its MUCH faster rise time…
I thought after 54 posts, we would be well into Capacitive Reactance, Inductive Reactance all combining into the circuits Impedance, a more correct term that “Resistance” which has been used somewhat incorrectly in this discussion…
With points-fired spark coils, you get into a netherworld where DC & AC physics combine…On the primary, DC, side of the coil, we see nothing but plain resistance…But over on the high-tension secondary side, where an arc will be produced, impedance plays an important role…If that high-tension lead led to a transmitting antenna instead of a spark plug, things would get considerably more interesting…
Yup, 100% right on the carb. My Fleetwood had a 472, and the Quadrajet was good for 750cfm. Some people do assume "bigger is better" but too large a carb makes it hard for it to meter the fuel properly (because vacuum will drop too low), and makes it so the engine is already at maximum flow before the throttle is even opened all the way -- this would harm driveability, fuel mileage and emissions. Unless he's got a supercharger or something that radically increases the fuel and air requirements. Anyway, I've never heard of that plug wire trick -- very interesting 8-) So, I figure the voltage in the coil builds up (to some extent) until it is high enough to jump the gap in the distributor + spark plug. I wonder if the extra gap between coil and wire would make the voltage higher than normal (it'd have to build up extra to jump that second gap) -- jumping the gap would lose some voltage, but it could still be higher than normal even after that jump.
I do agree, though, excess gas would have been blowing out the whole time, and it's possible that is the main factor in it starting -- simply enough gas blew out for it to no longer be flooded.On the primary, DC, side of the coil, we see nothing but plain resistance…But over on the high-tension secondary side, where an arc will be produced, impedance plays an important role
I’m not going to disagree with what you’re saying but offer a caution because I see it could be misintepreted- remember, this is an autotransformer so it varies slightly in operation from what might be considered a conventional transformer with separate primary and secondary windings.
I wish I could devote more time to the discussion because it is interesting. I stand by my first post and have refrained from commenting further because I don’t feel I can devote the time necessary to do it justice. I agree with you 100%.
Forgive me jumping in the middle of this one, but I see the same sort of thing oldschool is talking about in the IT business. I’ve been doing computer engineering work for 30+ years, and I’ve got some certifications, but I’ve also seen that there are people I would call “professional test takers.” They know how to study for and pass a cert test, but they have trouble applying what they know to the real world. I’ve seen it in pretty much every field I’ve become familiar with. What this means to me is the ASE may or may not mean anything. If it’s backed up with practical experience, then it’s a plus. If you see a guy with lots of certs, but his job history seems to have a lot of jobs on it, you should wonder a bit. I’ve seen often enough guys with some cert being hired who then proved to be incompetent. On the other hand, I know a lot of guy with certs that are some of the best IT people in the world. Many of them could write the cert tests.