Who said physics has no real-world applications for the average person? It does if you're an auto mechanic. Your automobile is a rolling physics laboratory!
I am no professional mechanic. There are times when I'm stumped. When I am, I go to brickboard and volvoforums. The experience of many enlightens the tasks of the few. Thanks, fellow do-it-yourselfers. Thanks also to some professional mechanics, who have given me valuable tidbits of information.
With most new cars (and their plastic bumpers) costing upward of $20,000 these days, perhaps it's not so bad to keep old Volvos and work on them. After all, once you're familiar with a particular engine, it's difficult to learn about a different engine in a newer car from a different car manufacturer. The Volvo 4-cylinder engines are roomy. A mechanic can get his or her hand amongst all the engine components. And most components take a minimal effort to access. In some vehicles (a Japanese model), a professional mechanic once told me that it took him 3 hours just to access the starter motor!
The B20, B21, B23, and B230 engines in 240/740/940 Volvos are non-interference engines, meaning that the camshaft can be rotated independently of the crankshaft and no damage will be done. That is, if the timing belt breaks, the valves will not hit the pistons; the engine will simply stop (I've experienced this personally). This is not true in newer Volvo models. And, I've since read that many automakers have incorporated interference engines because they are supposedly more efficient. But, owners run the risk of damaged valves, pistons, and cylinder head if the timing belt breaks. But, hey, it's just more money for mechanics and auto dealers! So, it may well be that these engines of the 240/740/940 Volvos may be the last of breed. So, hang on to these old Volvos!
And though I lament the disappearance of the carburetor, I've since found that there is some logic to the fuel injection system, especially the LH-Jetronic one. On the 240, there are a lot of mechanical parts to the fuel injection system, but in the 740, many of the fuel injection components are electromechanical. This means the mechanical function of the component is driven electrically, so if there is no electrical current or voltage delivered to that particular component, then it can't do its job. On the other hand, if there is a current or voltage present, and the component doesn't function, then that component is faulty. The best websites for fuel injection wiring diagrams are the autoelectric 740 and autoelectric 940 ones.
Some words of wisdom: I have been a do-it-yourselfer for many years now. I learned from my father when he had my brother and me (teenagers) work on our Ford Falcon. Over the years, doing things myself has probably saved me thousands of dollars in labor costs. I've learned a lot and gained a certain satisfaction from being a DIYer. My advice, though, is not to get carried away. A case in point: I was really set on replacing the clutch assembly on my 740 Volvo, but the more I thought about it, the wiser I got. I did not have a transmission jack. I was about 55 years old, if I remember right. I thought to myself, "What if the car shifts and falls on me. If it doesn't kill me, it sure would maim me. Is it worth it?" I finally decided, "No." I paid the professionals a few hundred dollars to do the job. At least I had my life and limbs intact.
I avoid jobs where I have to
be underneath the car for long periods of time and where I have
to rely solely on jackstands. Ever look at the footprint of a
jackstand? It's small. Therefore, if there is a small force at
the top of the jackstand, it will topple. I've experienced this
myself when I rotated the tires on my wife's 940. I'm trying to
recall the incident. The car was set on a slight incline. I believe
the right front wheel and left rear wheel were supported by jackstands,
with their respective tires removed. I thought I could jack up
all four corners of the car at once, and leisurely rotate the
tires. But, as I was jacking up the left front wheel, the car
started to shift to the right front, even with the unjacked wheels
chocked. The jackstands were leaning like the Tower of Pisa. I
quickly lowered the left front wheel and decided to immediately
put the left rear tire onto the right front, to support that end
of the car. In finishing the job, with only two wheels off the
ground at once, I used a concrete cinder block with 2x6"
pieces of wood on top to back up one of the jackstands and used
the floor jack to back up the other jackstand. The on-the-ground
wheels were chocked.
Whew! I barely prevented the car from toppling onto its brake rotors, perhaps bending an axle. (My wife would never have forgiven me.) Do not trust jackstands with your life! Recently, a man was working on his transmission when the jackstands failed and the vehicle came crashing down, killing him. Professional mechanics have hydraulic lifts, which makes life safer and easier. Look at the cost/benefits, not only in terms of money, but also in terms of your health. Sometimes, it is just plain wiser to spend a little money to have the professionals do it and live to see another day.
Gremlins, to me, are those strange
occurrences that happen when testing a circuit. You expect one
result and you get quite another. I don't mean surprises that
lead you to a good conclusion where you finally identify the problem
and correct it.
Gremlins are short-lived surprise results when testing a circuit, and when that test is repeated a few times, quietly disappear. Gremlins are inconsistent test results. For example, recently I was using a Cen-Tech CE P37772 model multimeter, a fairly high end model. I strongly suspected that there was NO ground connection between the negative pin of the #1 fuel injector and ground. With no key in the ignition, I put the multimeter on beep (diode tester) mode. I then probed the negative pin of the #1 fuel injector with one lead and touched the other probe to battery ground. I got a beep! I couldn't believe my ears! How could this be? I did this test again. Same result! Then, I did it a third time. This time there was no beep, which confirmed my initial suspicion. To be sure, I probed two to three more times and got no beeps. Therefore, I now had conclusive proof that there was no ground connection to the negative lead of the #1 fuel injector. My only guess as to why I initially got a beep was that I had to lift the head of the fuel injector up to run the test and somehow that motion connected broken wires somewhere.
So, when you get inconclusive results, keep running the tests until they are all consistent. If need be, use a different model multimeter to run the test. Of course, if you get consistent results, then that tells you something, as well.