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[aaronjb]

lol only the v6 is made of choccy!11

That bit was only tongue in cheek, really

Never did get 'round to fitting the WI to my 1ZZ-FE powered MR2 Then again I did have an enormous air/water chargecooler as well

[Webby the Bear]

Afternoon chaps, hope you're well. This isn't a school update sadly but to save starting a new thread I thought I'd post this arvo's thoughts on my own car and its diagnostics and perhaps we could discuss

Ok so as you may know I have had some fuel consumption troubles. I went to TB and did a TechII session where we found I have some lazy O2 sensors. So as soon as I get to swapping those out the better. I also swapped out the fuel filter for good measure. So anyway I'm happy with where we are on that front and obviously thanks to the TB-meister for his help there.

HOWEVER. he did mention that it felt low on power. I felt at the time that it was ok and didnt really pursue it. but i do feel after thinking about it that he must be right as its not spritely anymore. its quite dim-witted at the moment and sloth like. anyways i have my cambelt due next year but as vx did it i'm planning on doing that before then just in case.
there is also a ticking that doesnt go away.

just thinking out loud i'm wondering if the timing is slightly out (ticking's certainly not loud but defo there) and perhaps thats whats affecting the performance.

so i presume if its slightly out that would nacker the whole 4 stroke cycle and could contribute to the power loss and perhaps the fuel economy?

what are your thoughts?

[Andy B]

.......
just thinking out loud i'm wondering if the timing is slightly out (ticking's certainly not loud but defo there) and perhaps thats whats affecting the performance.

Is the ticking not just the normal sound of an injector injecting?

so i presume if its slightly out that would nacker the whole 4 stroke cycle and could contribute to the power loss and perhaps the fuel economy?

what are your thoughts?

Yes! The valve over lap will be wrong .......... it could be firing with a valve still slightly open etc

[Webby the Bear]

Evening chaps, well just had a full week back at school after a nice half term break.

Practical was easy but theory has got very involved and I feel quite out of my depth.

Just picking up laptop from me mam's and shooting off home... so will give full update tonight 

[Webby the Bear]

Tried to post this yesterday but my freaking internet went down 

Right then chaps.... here goes....

Let's cover the first look at diesel knowledge.... what i dont understand in red 

Induction:
ONLY AIR is drawn in to the cylinder. The downward motion of the piston lowers cylinder pressure and creates a vacuum for the air to enter.

Compression:
The piston then moves up and compresses the air raising cylinder pressure due to the air heating up during compression. Towards the end of this stroke the diesel is injected.

Power:
After the ''Delay period'' (the time span from injection to ignition) the piston is forced down as in the normal 4 stroke cycle. It's important to note that there is flame spread when the diesel ignites. this creates shockwaves and due to the high compression ratio the shockwaves hit the piston crown and the combustion chamber. this is called ''Diesel knock'' and is the tell tale sound of a diesel 

There are 3 things that can be done to reduce the delay period, give quiter operation, better fuel economy and a smoother running engine:

1. increase temperature (higher compression ratio, the addition of glow plugs)
2. increased atomisation (breaking down the fuel.... increase injection pressure)
3. increased swirl (valve with a mask on the head, special piston crown shape)

next:

Direct Injection:
where the injector nozzle is directly in the combustion chamber and fuel injected straight in at the right time. simples

Indirect Injection:
where the injection of fuel is pre-swirled in to a ''pre-combustion chamber''. What i dont get is this... if the fuel and air are already mixed is it this thats pulled in on the induction stroke? or is just air pulled in and compressed and then this pre-mixed fuel/air mixture injected?

A very, very, very awful picture i've drawn (sorry its a ''paint'' jobbie) of the main components in the diesel engine...


fuel is stored in the fuel tank and moved through the fuel lines by the lift pump. it then goes through a fuel filter (this has a water bleed and air bleed... why would water or airget in your fuel lines??? 
the fuel then travels to the injector pump and from the injector pump to the injectors.
NOTE the red and green lines..... red are high pressure lines from the injection pump to the injectors which is about 2000psi. the green lines are low pressure lines just to move the fuel between tank and injector pump and also the excess not used from the injectors in to the ''run off''.

[Webby the Bear]

NEXT....

Glow plugs....

these are only found in indirect injection diesel engines and i'm informed that actually they're not that common anymore. they're specifically for cold starts where you turn the ignition on and wait for the glow plugs to warm the air sufficiently (about 10 seconds). diesels WITHOUT glow plugs (direct injection) will simply have a higher compression ratio to aid with cold starts.... air compressed more equals more heat 
a quick word on how glow plugs work.... there should be a wire going to them which is a live and the screw thread creates an earth. the glow plug is just a heater element basically (i liken it to the element in a bulb obviously though producing lots of heat). you can test them using a multimeter...anyone know how? not really sure what a multimeter is used for???

fuel filter:
as mentioned this has an air and water bleed screw (air at the top as its lighter and water screw at the bottom as it will sit at the bottom). the filter also has a ''primer''. is this used when all the diesel has been drained following say someone putting petrol in by mistake???

Fuel injectors:
the fuel is forced in to the injector at 2000psi through the injectors inlet port. the injector has a spring which is forced up by the pessure and allows the fuel to spray from the nozzle. when injection stops the spring closes the injector so there is no drippage. note the correct size and strength spring must be correct as too strong and it wont be allowed to open and too weak it wont close properly. the injector also has a leak off port which then, under much lower pressure, is allowed to go back to the fuel tank saving fuel

Rotary (or distributor) injection pump:
ok, got to be honest i dont understand this too well. can someone explain how this works? it seems that theres a cam which opens and closes two little pressy in things  this allows fuel to go to all the lines and then the line for each individual injector is opened at the correct time as it is also rotating at the same speed as he cam as its driven by the same belt.... ok i'm going to stopthere as i think i'm babbling on something i really dont understand 

PRACTICAL..... Stay with me as this is the easy bit 

Well we started our lubrication section this week. oil and filter changes to start.........piece if p*ss. 
nothing learned doing this that i could really tell you that would be any use apart from i got to use an oil filter wrench for the first time as the filter in my car is the paper element with thousing/24mm nut. 

However, a lot of the group seemed to take ages with this  lazy b....... 
anyway it meant me and my work partner, josh (who also is an apprentice at vauxhall and does 1 million oil/filter changes every thursday and friday lol), stormed off on our work schedule.
we moved quickly on to oil pressure switches.

Oil Pressure Switch:

Its purpose is to register whether the car has oil pressure. Good pressure and the switch will turn the light off on the dash (to signify no problems), bad pressure or lack of pressure and the switch will make a electrical connection which is linked to the bulb and the light comes on. its a very clever system......

let me type some more and providing my net holds on it will be up tonight 

[TheBoy]

Only air is drawn in, diesel is injected directly (or indirectly) into the piston at the end of the compression stroke. Unlike petrol, where the fuel/air is mixed in the inlet.

Diesel - the diesel and and condensation can seperate. The filter catches this, and you can drain it off at the filter.

Not all diesels have priming pumps. The Omega TD is one that doesn't.  The nature of the system, if you run out of fuel (or open the high pressure side of the fuel system) you can get airlocks. Because air will compress, you can't get rid of them through the injectors etc, so diesels need to be bled, and in some cases primed depending on where the airlock is.

Glowplug, usually about 1 ohm resistance. Measured with meter on Ohms scale.

Diesel pump (for non common rail systems). Know how a distributor works? Its a bit like the same for diesel, rather than electric. It builds up the extrem fuel pressures, and distributes it in sequence to the cylinders. Its the pump that controls the timing (as the firing is determined when the diesel is injected in the cylinder).

[TheBoy]

Ok so as you may know I have had some fuel consumption troubles. I went to TB and did a TechII session where we found I have some lazy O2 sensors. So as soon as I get to swapping those out the better. I also swapped out the fuel filter for good measure. So anyway I'm happy with where we are on that front and obviously thanks to the TB-meister for his help there.

As per PM, if both O2's were looking lazy (I can't remember), its possible they are both lazy, or its possible that the fault is something elsewhere that can affect the mixture on both banks...  ...eg, airleaks, maf, duff fuel etc

[Marks DTM Calib]

Sounds like your tutor does not understand diesels either.....where do I start!

As a starter, if you truely do have diesel knock (and you WOULD know) then your injecting to early.

As for glow plugs, old and new have them, there a must even on common rail, direct injection makes the engines start easier but there still needed. Older diesels had heaters either in the pre-combustion chambers or the inlet manifolds, some even had devices such as a thermostart which lit a fire in the inlet using fuel from the bleed off lines.

[TheBoy]

Sounds like your tutor does not understand diesels either.....where do I start!

With some "guides" like before

[Marks DTM Calib]

Right air, its bad news, you inject the fuel at very high pressure (100's of psi), liquids cant be compressed so no worries but gases can so if you get air in the system it will get to the high pressure lines and the result will be no fuel out of the injectors (as the air will compress and act like a spring). The result is that you have to be able to bleed the air out of the system after maintenance work such as changing injectors, pumps or even the fuel filter.

Diesel also sometimes has some water content, this is bad for precision items such as injector nozzles and injetion pumps (can cause corrosion and pitting) and hence it gets trapped in the fuel filter housing and needs to be drained off. This is not as big an issue as it used to be as the fuels are better (on argicultural stuff and years ago it was a bigger problem).

[Marks DTM Calib]

Your fuel pump description sounds more like an inline pump than a rotary one as an inline one has effectively a cam shaft that operates little pistons which pressurises the fuel, one for each fuel line/injector. The throttle control is via spill ports, these are little bleed off points which vent the fuel at a variable point up the injector pump piston bores. The more power required (harder you press) the higher up the bore the spill port is moved which means more fuel is delivered.

There are variations of this like PD on the VW's where the spill ports are electronic controled.

Rotary pumps are very different!

[Webby the Bear]

Right, once again sorry for the delay... been doing nothing but playing with electricity all day 

However...

OIL PRESSURE SWITCHES:

I've drawn this little curcuit showing roughly how these things work:

in short the oil is pressured in to the switch from the threaded end and as long as there IS pressure it will keep the circuit to the light on the dash disconnected using a spring inside. if the pressure drops (indicating a problem) then the spring will go to its relaxed state, complete the circuit and the light will come on the dash. you see it on for a couple of seconds when the car starts as pressure has yet to build up 

i'm still learning about electrics (as per my gen. discussion post  ) but even i can understand this one. very basic circuit set up.

we took a couple out (one off a tigra and one off a 206). however they are hard to find as they can be anywhere from the filter up to the top of the emgine. the 206 was right by the filter easily seen... the one on the tigra was hidden at the back of the block BEHIND some sort of manufactured lip.... vaux obviously doing it to annoy folk 

anyway, thats a piece of piddle so i wont go on too long but i read the haynes and couldnt find out where it lives on the omega. anyone know and perhaps have a piccie?

oil pressure testing tomorrow..... stay tuned 

ps, with regards to the previous comments about the inline and rotary pumps..... yeah youre totally right that the inline one has a camshaft.

however what i was trying to explain was that the ''plungers'' in the rotary pump are depressed via a cam.... admittedly it doesnt look like a cam but performs the same function 

[Marks DTM Calib]

A rotary pump has no real plungers (you could argue there is a single one but its nothing like that of the inline pump) and no real cam, thats the clever bit on them, what they effectively use is a variable quish plate to control the injection duration and a distributor to distribute the fuel.

One point to make, there is no such thing as an earth on a car, its a ground or 0V connection (sometimes referred to as chassis or chassis return), for it to be an 'earth' it would need to be connected to a 2m metal spike inserted into the 'earth' !

[henryd]

A rotary pump has no real plungers and no real cam, thats the clever bit on them!

One point to make, there is no such thing as an earth on a car, its a ground or 0V connection (sometimes referred to as chassis or chassis return), for it to be an 'earth' it would need to be connected to a 2m metal spike inserted into the 'earth' !

Which may be inconvenient on longer runs