Let's assume you decide to develop and gain mechanical experience and knowledge by buying an absolute wreck of a car...

Let's assume you decide to develop and gain mechanical experience and knowledge by buying an absolute wreck of a car, with the intention of bringing it back to life and get it running. Assume that you also have a blank check for ordering parts needed, and have the tools that you need to repair the car. Assume that you have access to the Internet, the car's owner's manual, a Haynes motor manual for that car and any other information you might need. Assume that you also have some very basic knowledge of how a car works, e.g. how the 4 stage piston system works, how pistons fire and turn the crankshaft, how power is directed from the engine to the rear axle through the differential etc.

Without any mechanical experience, how do you diagnose a problem with a car and know how to fix it? e.g. You get in the car, turn the key and the car just doesn't start - no noises, no obvious signs or anything like that. How do you know where to begin? You could either just google "dead car won't start", but that's too vague. You could also look through both the owner's manual or the Haynes manual for troubleshooting or try and work out the problem by working through the chain of processes that are involved in starting the car, e.g. is the battery flat? Are the wires broken or making poor contact? Is the fuse blown? Is the engine not working (and which part)?

tl;dr - How do you know what needs to be fixed in a car until it runs? How do you gain the skill to diagnose if you have no knowledge or no idea of what's wrong with the car?

You start with the first problem you encounter, and then check the easiest solution for that problem first before progressing to the more difficult solutions

No sound when turning the key? Check battery
Battery good? Check starter
Starter turns with direct battery contact? Check wires from ignition
Wires from ignition good? Check ignition itself

And so on

As for how to gain skill - you use books, the internet or someone who knows already

Either that or you just use a general understanding of how electric power works, how fuel and air needs to be mixed and ignited

well you have to do all of those things first to even find out whats broken. You just keep looking and eventually you find it. there arent really all that many parts in a car.

>it's an "op bought a busted down shitbox with a dead battery and doesn't even know how to recognize it, but expects to completely restore the car on his own" episode.

That's what I figured. But how do you know what to check? i.e. how do you know to move from the battery to the starter to the wires, if that makes sense?

For a starter system luckily I know how that works, but what if it's an an engine or a clutch problem?

I haven't bought a car at all, but I've been thinking of buying a shitbox to fix it up for experience.

For basic things like battery checks I can do, but what if it's a deeper problem with the engine or the tranny or the cooling system or whatever?

If you don't outright know off the top of your head, you look it up. There's no shame in googling random problems and their solutions

Engines need three things: fuel, spark and air.
So you check if the engine can get air (throttle body, intake piping), spark (sparkplugs, leads, distributor, ignition coil if applicable), and fuel (fuel lines, injectors/carb, fuel pump).
Break your problems down into smaller parts that you can easily check.

I "know" because I started fucking around with mopeds when I was 13, and just progressed from there

And its not that I know what exactly to check in the scenario where I bought a non-running piece of shit - its just a process of elimination, and before you start trying to troubleshoot an injection system or similar you will need to have the engine cranking, so its a very natural first place to start

I mean, there are not all that many essentials for a car to run

You need electricity to get it started and to keep the ignition going (some diesels with mechanical pumps can go without)
You need fuel to it combust and produce energy
You need air for that fuel to combust

If there is fuel and it cranks with good spark - ok, maybe its air?
If its sparks like crazy but no fuel is coming through - maybe check the pump to see if its functioning at all or maybe blocked

>look it up
>there's no shame in looking things up
I realise that. But it's more of how do you know what to begin to look for? Like say you didn't know how the starter system of a car worked - you wouldn't know to think about the starter or the fuses, you'd just think wires or battery.

i had the same problem you just described in the OP a month ago, and i didn't really know fuck all about how the starter system worked. but by doing a bit of research and process of elimination and shit i was able to learn about it, find out which things to test, diagnose the exact problem, and fix it.

shit ain't hard. google makes shit so easy now. and if you can't find an answer, ask someone. there's a million different message boards and shit at your disposal. take advantage of it.

Breaking it down seems useful, thank you.
As for knowing parts to break down into, e.g. splitting electricals for an engine into spark plugs, leads, ignition coil, distributor, etc. - how do you know what to split into? Is it just by learning how a car works?

I wouldn't have thought to put the distributor cap on there, for example

What you do is check the wires and battery. Then if those don't fix the problem, and you run out of ideas, you look into it. For example, when my car was jerking, I looked into the fuel system and the ignition system. When both of those turned out to be fine, I googled a bit and found out my problem was the throttle position sensor, something I didn't know existed beforehand

I'm going to say that the learning curve with such a project would be so steep as to be discouraging and anybody who took something like that on would soon abandon it.

Quite frankly, diagnostics of any kind require some familiarity with the system in question and also that of procedures that you would apply in diagnosing a failure. Now a bad battery/bad connection wouldn't stop me for even five minutes but that's after many years of the school of hard knocks and working as a mechanic for a few years. OTOH, I also remember when I was 15 and I couldn't figure out a battery with a bad cell that appeared to work lights and everything but wouldn't crank the engine and kept me basically stalled for 6 months or more.

IMO better to start with something that runs and drives but needs some sorting out and then set about doing what the car needs one thing at a time. This way you can see and enjoy the fruits of your labor without getting quite so frustrated.

>IMO better to start with something that runs and drives but needs some sorting out and then set about doing what the car needs one thing at a time. This way you can see and enjoy the fruits of your labor without getting quite so frustrated.
This. Starting out with a total pos will turn you away real fast. Starting out with something that at least runs and drives is much better when you're new to this

An engine needs 4 things to run
Air
Fuel
Spark (at the right time)
Compression

Look up youtube videos of how the starter motor/circuit works. Once you have that working you can use the starter motor to "turn the engine over" and start checking for the four things i listed above.

Air: all cars take in air generaly the same way. It gets sucked in by the movement of the pistons (rotary fags go home) moving up and down creating a vacuum. It gets sucked through a tube called the intake through a filter to filter out any particulate in the air that could damage the engine. There's things like turbochargers and superchargers that force compressed air into the engine, but don't worry about those now. What is importand is that the air filter isn't clogged as shit and there isn't a mountain of acorns in the intake. Now in cars with modern electric fuel injection the air going into the engine is metered by a kind of sensor, which varries depending on make, model, and year. The sensor is there to "tell" the engine computer exactly how much air is going into the engine so it can decide how much fuel to add to achieve the right ratio of air to fuel. If there are any "leaks" into the intake (which is under vacuum due to the movement of the pistons) after the air metering sensor it means there is air the engine computer doesn't know about, so it doesn't send enough fuel. If the leaks are small they'll just make your car run like shit. Big ones will make your car not run at all.

More coming.

Even experienced mechanics get bogged down and unmotivated if too many things are wrong with the car (even though they absolutely know how to fix it all). See Eric O's Civic that has languished in his garage for months on end. See Nestor M's Mustang that languishes at his shop for months on end too.

Get something that just needs a few things done to it, you get a project car later on.

I am also assuming this is for older, less tech heavy cars. New shit is more complex

Older cars may have carbs, which usually sit directly on top of the intake manifold, (the part of the intake that connects to the motor) works by using the vacuum of the air being drawn into the engine to suck fuel through tiny nozzles in the carb called "jets." The size of the hole in the jet determines how much fuel is pulled into the engine. If these holes are clogged or any number of otgter shit goes wrong with a carb, look up how to rebuild yours on youtube. I'm going to make dinner and get more drunk so i'll post more later maybe.

That's not something I'd give a beginner to do. You had better be good at following directions and attention to detail if you try this, OP. Odds of success go up if you just buy a new carb and bolt it on.

The way I do it is to check the simplest parts first/the ones that coincide the most with the current issue. If not I'll just start at the outmost point of the "chain" and work my way from there - like starting with the spark plug, going to the wires, then to to the coils, then further into the igniton system

Fuel, Air, Spark, Timing, Logic. (fuel/air/spark boomers GTFO. With no timing chain or no cam signal, that stuff ain't doing shit)

That's what any computer controlled car needs to run, basically anything 1985+. A lot of this is trial and error, and watching others before learning the technique to diag no-start.

For a basic fuel injected car here's the (very basic) case study: 99 civic (because Veeky Forums) arrives on the hook, no start, dead battery.


Step one, can it crank? If no, check battery. Dead battery replaced. Does it crank? No- starter circuit. Jump the solenoid, see if it spins. If it does not, have someone crank the key, make sure you have ignition signal at the solinoid. Knock on the starter itself, when they die they usually jam, sometime you can free them up. If you have input, and it doesn't crank, the starter is bad, or the engine is locked up.

So the starter is swapped, it cranks like a champ, but doesn't start. Cont.

Cont.

#1, does it have compression? Google engine no compression sound. It's hollow and fast. We don't care what the compression numbers are at this point, just that it sounds like it has some. Okay, it sounds good.

Does the fuel pump prime with the key in the ON position. A slight hum should come from the tank when the car is switched on. If it is silent, the pump and its circuit are suspect. Have and assistant crank, while you open the throttle plate slightly and spray starting fluid, intake cleaner, etc into the engine. If it starts, diag that fuel pump.

Okay, so the fuel pump DID prime on the civic. We're cranking it, it smells Fuel-y from us flooding the shit out of it. Onto spark.

Spark is annoying to check on a lot of coil on plug cars, but our civic has wires. So, remove the plug boot at the distributor. Yes, at the distributor, trust me. Stick a test light to battery negative (or a block ground you have confirmed) with the business end where are spark plug boot was removed from on the dizzy cap. Crank the engine, and look for a strong blue spark. Hold the test light just a bit away from the cap, if you don't see the jump, move it closer. If it has spark, you have cam/crank signals. If it doesn't have spark, you need to confirm cam/crank and RPM input (usually derived from one of these, typically crank).

Cont.

Having live data makes all of this shade tree stuff much easier, but most people just have access to a basic code reader.

The shade tree method works more often than not, but is way harder than having the proper tools. For instance, do I have injector pulse command on the civic? Yes? Cam crank signals are good. Do I have commanded coil dwell times? Cool, timing is stable. Can I confirm engine health with a relative compression test?

It's all about learning the basic systems, and applying general concepts. Had a new guy at the shop comment on doing his first Volvo brake job. Every disc brake system has calipers, pins of some sort, piston(s), rotor, pads. It gets fed brake fluid under pressure. Anything else is just fluff, the brakes on a car work just like the brakes on a bike. The same goes for every other system.

Do you have input signal? Is the NUMBER ONE thing I ask when people want my help. Most don't bother to check. But if you want to know why a power window doesn't work, confirm the thing is getting 12 volts before you replace the motor. The switch could be bad. Know what you have, what that should produce, that will tell you where most faults are.