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[Webby the Bear]

Keep one in the boot along with dwell meter along with carb=that way drive to drags change carb do timing undo headers and viola instant v8 roar  no use whatsoever on any car from late 90's though.

 
i think he was trying to teach us that so we get a better understanding of everything. although its a bit point;ess as nowt is adjustable. if it dont work replace it 

[Webby the Bear]

Right chaps..... HEEEEEEEEEEEEEELP 

Bear unblievably forgot to do his christmas homework 

Below is a picture of a scope trace of a contact breaker ignition system (primary charging and then magnetic field collapsing, high voltage through secondary winding to the spark plug)



point 1 shows the points cloed and the primary winding being charged.

i need to highlight on the scope where the points have opened and the spark occurs.... is that the spike at ms point 0.0?

if the spark duration ends ar 1.0 ms i'm going to say the spark occurs for 1.0 milisecond? am i right?

the rest i can answer myself. i think 

cheers guys

[Kevin Wood]

Keep one in the boot along with dwell meter along with carb =that way drive to drags change carb do timing undo headers and viola instant v8 roar  no use whatsoever on any car from late 90's though.

 
i think he was trying to teach us that so we get a better understanding of everything. although its a bit point;ess as nowt is adjustable. if it dont work replace it 

I disagree. A scope is a great diagnostic tool on any car old or new, you've just got to know what to look for. It can show you cam and crank sensor outputs, ignition primary waveforms, fuel injector, ICV and EGR valve drive signals. You might not have any adjustments, but knowing what you expect to see and comparing this with what you actually see is a great diagnostic tool. You can still look at the ignition signal and determine what the fault is likely to be.

Anyway, to your homework. Once the points have opened you are looking at the primary voltage from the coil, and this will follow the secondary voltage reasonably closely, although will be lower due to the turns ratio of the coil. So, you get a huge peak as the points open. Here the current in the coil has stopped suddenly due to the points opening and back to Marks V=L(di/dt), di/dt is large, so voltage is large. We have 200 volts at the primary of the coil. We will have much more at the secondary (probably 40,000 volts or more).

This high voltage quickly ionises the air in the gaps in the distributor cap and spark plug and a spark forms. The spark draws current from the coil, reducing the rate of decay of the magnetic field, and this reduces the voltage seen at the primary, in this case to around 40 volts. Eventually, the current in the spark reduces to a point where the spark can no longer be sustained. The rest of the energy in the coil just dissipates in the internal losses in the coil. This is what the wavy line after 1ms shows. Notice that the voltage doesn't return to 0V after this. That's because the points are now open and we're looking at the voltage across the points, not the coil, so we see the 12 volts from the battery until the points close again.

So, yes, I'd say the spark duration is about 1ms in this case.

The big spike to 200V is where the points open.

The point where this collapses down to 40V is where the spark starts.

[Webby the Bear]

thanks for the info kev. that confirms exactly what i thought 

the comment (well from me anyway) wasnt about the use of a scope. it was about spending so much time learning the old distributor system and contact breakers, seperate coils etc.

on reflection however i think its good to know how these work as the modern coilpacks/ CPP's are easier to unerstand 

this bit of homework (that ive just completed in 20 mins  ) was our first look at the scope.

i've seen videos of their use and love the idea. i do hope we do a lot more as they're awesome. for diagnostics

sadly however we start fuel systems tomorrow.... i say sadly cos i bet me balls its gonna be fuel filter R&Rs all day 

[Kevin Wood]

the comment (well from me anyway) wasnt about the use of a scope. it was about spending so much time learning the old distributor system and contact breakers, seperate coils etc.

Well, the principles are exactly the same on more modern cars, there just aren't any adjustments to make, so it's well worth learning the theory on a mechanical ignition setup so you can apply it when you get problems with a more modern system.

[Webby the Bear]

the comment (well from me anyway) wasnt about the use of a scope. it was about spending so much time learning the old distributor system and contact breakers, seperate coils etc.

Well, the principles are exactly the same on more modern cars, there just aren't any adjustments to make, so it's well worth learning the theory on a mechanical ignition setup so you can apply it when you get problems with a more modern system.

that was my way of thinking when i made the comment.... whats the point in learning about the workings of a part that in modern vehicles (which ill likely only ever work on) can't be fixed, adjusted, serviced or worked on.

but as you say having reflected its good to know how these things work 

[Kevin Wood]

the comment (well from me anyway) wasnt about the use of a scope. it was about spending so much time learning the old distributor system and contact breakers, seperate coils etc.

Well, the principles are exactly the same on more modern cars, there just aren't any adjustments to make, so it's well worth learning the theory on a mechanical ignition setup so you can apply it when you get problems with a more modern system.

that was my way of thinking when i made the comment.... whats the point in learning about the workings of a part that in modern vehicles (which ill likely only ever work on) can't be fixed, adjusted, serviced or worked on.

but as you say having reflected its good to know how these things work 

Because if you know how it works, you can diagnose problems with it, and the basic principles are the same with modern cars.

[Webby the Bear]

Right then girls... TERM 2.... THANK GOD!!!  Can't tell you how much I've missed it 

A bit of housekeeping with the blog first. I really think I should have headed up each section when we moved on to a different area e.g. cooling, ignition, engine etc. SO that's what I'm going to do from now on.

New term, new topic:

FUEL SYSTEMS:

Ok so first thing is to explain the workings of a carburettor, specifically we learned to start withe the ''fixed jet'' carburettor. Even though they're obviously not in modern cars it's important to understand as there's a lot of theory around the vacuum side of things.
A handy cut-out-and-keep guide courtesy of google

some notes anout this...
the progression hole is only a small hole and is used at idle as not much fuel is needed.i believe it relies solely on the vacuum created between the cylinders and the (at this point) closed throttle plate.
when the throttle plate is opened (by pressing the accelerator) the vacuum is placed on the fuel from the ''main jet'' and pulled in with the in-rushing air.
The choke plate is closed on start up so the pressure's higher hence drawing more fuel in for the initial fast idle, then opens as less fiel is needed when at temperature.
(note, these comments are based on what i can remember from this mornings lesson so if anythings incorrect do say  )

our Carburettor in bits...
 


Sorry for the quality of that first photo.

in the first pic you can make out 3 ''areas''. the one on the right is the float chamber. this is simply where the fuelstays while it awaits its journey to the cylinders. its stopped from overflowing by the float which, when full, goes to the top of the chamber and the inlet is stopped by a plunger.
the two areas with a bit of gold in them are the chambers down to the throttle plates (two on this carb).
machined between the float chamber and the throttle plate chambers are the main jets (you cant see them though sadly).
in the second photo the black plastic at the top is the float and the main part of this component is the choke plate.

As I predicted the next thing on our list was fuel filters  i hate these things and the stupid ''quick release'' clips that aren't quick release at all. theyre ridiculous. i'm glad my omegas modified with fuel line and jubilee clips and thats how its staying!!! 

Anyway, the fuel filter on the pug 206 we had to do...

this is our second one on an N reg Fiesta. a total shite box of a car but christ the filter was easy. in the engine bay and the clips you pressed lightly and it sweetly came apart 

one thing to do when removing a filter is to depressurise the system. now on the two cars that we did there were schrieder (spell chack) valves. however if there wasnt a schreider valve you can hook up the fuel regulator to a tool with a gauge (cant remember the name... midi or mini something  ) and this gauge with fuel line will draw the pressure out.
I personally dont think any depressurising is necessary. i've never done it on my car and the fact is you still lose a load of fuel when they come apart. also access (as we know from the V6) can be bloody limited. time vs lost fuel. cover it in a rag. job done. what do you think?

finally, we were informed by the lads that worked on the fiesta before us that when it was running it was surging. no ICV on this car but had a word with the tutor and basically we ripped the air filter out to be presented with a pipe the lads hadnt put back properly  but anyway this was what was underneath.... what looks like a carb and i guess does exactly the same function but the tutor called this a ''single electrode fuel mixer''..... a carb then 


Anyway we tidied up the other lads' mess, hose clamped lose pipes and the car is running super sweet now 

more updates tomorrow 

[Marks DTM Calib]

Its a single point injection throttle body, an electronic carb so a throttle valve with a single fuel injector to replace the carb jet. Often referred to as TBI (throttle body injection) spi (single point injection) etc.

OK systems but pretty obsolete these days and not great on larger Cc engines as its difficult to deliver small quantities of fuel for idle with such a large injector ( which has to be sized to meet Max required fueling)

[Webby the Bear]

Its a single point injection throttle body, an electronic carb so a throttle valve with a single fuel injector to replace the carb jet. Often referred to as TBI (throttle body injection) spi (single point injection) etc.

OK systems but pretty obsolete these days and not great on larger Cc engines as its difficult to deliver small quantities of fuel for idle with such a large injector ( which has to be sized to meet Max required fueling)

that was it Mark. sorry, been a long day. i got him to explain it but this was dead in the centre of the manifold so what i couldnt work out was how an injector with a single point could distribute fuel evenly.... or would there be like a pre-injection chamber where thats sorted out? 

[Marks DTM Calib]

Works the same way a carb does, produces a fine atomised mist of fuel which gets drawn into the cylinders 

[Andy B]

Works the same way a carb does, produces a fine atomised mist of fuel which gets drawn into the cylinders 

Mark ..... you have a pm   

(Nothing to do with this thread though 

[Webby the Bear]

Works the same way a carb does, produces a fine atomised mist of fuel which gets drawn into the cylinders 

nice one mate 

I've just remembered something I would like to talk about and although not totally about my schooling it is relevant. And that's getting a career.

This level qualification will be completed in May. i then have the option of doing the next level next year (for just one more year).

i'm kinda missing having money so what i'd like to know is what's the industry like for getting a job these days if anyone knows? i know of 3 of the lads who have scored part time jobs in local garages. i always fancied going in to a dealership thouhg... although obviously i have no work experience. are dealerships better? or local garages?

anyone with any info wud be great 

[tidla]

Keep one in the boot along with dwell meter along with carb =that way drive to drags change carb do timing undo headers and viola instant v8 roar  no use whatsoever on any car from late 90's though.

 
i think he was trying to teach us that so we get a better understanding of everything. although its a bit point;ess as nowt is adjustable. if it dont work replace it 

I disagree. A scope is a great diagnostic tool on any car old or new, you've just got to know what to look for. It can show you cam and crank sensor outputs, ignition primary waveforms, fuel injector, ICV and EGR valve drive signals. You might not have any adjustments, but knowing what you expect to see and comparing this with what you actually see is a great diagnostic tool. You can still look at the ignition signal and determine what the fault is likely to be.

Anyway, to your homework. Once the points have opened you are looking at the primary voltage from the coil, and this will follow the secondary voltage reasonably closely, although will be lower due to the turns ratio of the coil. So, you get a huge peak as the points open. Here the current in the coil has stopped suddenly due to the points opening and back to Marks V=L(di/dt), di/dt is large, so voltage is large. We have 200 volts at the primary of the coil. We will have much more at the secondary (probably 40,000 volts or more).

This high voltage quickly ionises the air in the gaps in the distributor cap and spark plug and a spark forms. The spark draws current from the coil, reducing the rate of decay of the magnetic field, and this reduces the voltage seen at the primary, in this case to around 40 volts. Eventually, the current in the spark reduces to a point where the spark can no longer be sustained. The rest of the energy in the coil just dissipates in the internal losses in the coil. This is what the wavy line after 1ms shows. Notice that the voltage doesn't return to 0V after this. That's because the points are now open and we're looking at the voltage across the points, not the coil, so we see the 12 volts from the battery until the points close again.

So, yes, I'd say the spark duration is about 1ms in this case.

The big spike to 200V is where the points open.

The point where this collapses down to 40V is where the spark starts.

This is a great site for practice videos and sample waveforms.

http://www.picoauto.com/automotive-library.html

The Frank Massey stuff is great too.

Using a scope i have solved a few jobs that code reading even in the hands of specialists have not been able to solve.

[Lazydocker]

Webby, I'd be looking at independent garages myself... Get some all round experience and, if you're lucky, they might put you through as a MOT tester