Is it a throttle body or an anti-shudder valve ?

[titan1]

So, as title says which is it, Have cleaned mine and all pipes but now has now come back with the flashing glow plug. If it is a throttle body why denote as an anti shudder valve. As in virtually all pics and parts sellers describe it a a throttle body. Which is the actual pce of equipment that makes the engine rev anyway...............................thanks.

[Schtum]

Originally, diesel engines didn't have throttles.  They ran at full throttle all the time and engine revs and output were determined by the amount of diesel injected.  The ASV was introduced to stop the engine dead when you switched off the ignition.  If you'd ever driven an old diesel truck and pulled the engine stop knob, you'd have understood about the shudder.  However, more recently, the ASV has been used to provide some throttling of the intake air; notably during DPF regeneration.  Hence it's become known as a 'throttle body'.     HTH

[Breezy_Pete]

It is similar in appearance and function to the throttle body on a petrol engine, but as above it's not for rev control.

It has two main uses as I understand it, anti-shudder at shutdown, and to create variable pressure levels in the intake manifold in order to allow more control over flow rates of the exhaust gas recirculation system.

 

[titan1]

hi, yes I do know you come to mention it. Well, well, well. So when you see so many Youtubers cleaning the throttle body, all that they are doing is cleaning the judder valve. Of course cleaning is the way to go but nothiing to do with the engine revs. Am I right in thinking that all diesels would go full on if not controlled. 

You learn something everyday.....LOL

     Anyway, so what does control the engine when you drive ?  Is it the electronic throttle pedal/actuator, if so i been barking up the wrong tree all this time.  Will have look a removal for a genuine part number.

p.s see how I feel as 2 hrs ago tested positive for Covid, my first one

[J.R.]

3 hours ago, titan1 said:

Which is the actual pce of equipment that makes the engine rev anyway

 

42 minutes ago, titan1 said:

Anyway, so what does control the engine when you drive ?  Is it the electronic throttle pedal/actuator, if so i been barking up the wrong tree all this time. 

 

Learning is the great thing about this forum!

 

At its most basic, because like a petrol engine all the modern added emissions stuff is superfluous to the basic function, a diesel engine has an open intake & hence no vacuum, engine speed and power is controlled by the amount of fuel injected.

 

Throttling should not be thought to be accelerating, it literally means to choke or restrict like strangling someone, on a modern diesel it is used to create some vacuum to suck through EGR gases and also to stop shudder on shut down, on a petrol engine it is used to modulate the airflow to control engine speed, the mixture is taken care of by the fuel injection.

 

Additionally the throttle body on a diesel engine will prevent an engine from runaway if the turbo blows and it starts running on its lubricating oil.

 

The term wide open throttle actually means no throttling!

[J.R.]

When ECU controlled injection, timing, 3d mapping etc took off on petrol engines I fully expected that the throttle butterfly would soon be a thing of the past as it is bad for airflow and volumetric efficiency but it has never come to pass, there must be a good explanation but I don't know what it is.

[titan1]

hi J.R........... to me this is a revalation I will never look at a diesel engine in the same way again. I have automatically believed they are exact to a petrol. MAF throttle body and an ECU to injectors etc. Thank you.

J.R how do you know all this stuff ?

[krisp1]

Going back to basics a diesel or compression ignition engine is controlled by the amount of fuel injected. In the pre electronics age, the accelerator pedal on a diesel engine was connected to the injection pump and varied the amount of fuel injected. A centrifugal governor increased the amount of fuel injected as speed increased. The amount of fuel was the deciding factor hence no need for a throttle plate restricting airflow. The air fuel mixture is ignited by the heat generated by the relatively high compression ratio. All of the electronic systems are to increase power output and reduce emissions.

A petrol or spark ignition engine is controlled by varying the amount of air admitted to the engine and supplied with petrol across a wide range of mixture strengths. The spark supplied at the appropriate time ignites the mixture. Excess fuel or too little fuel means the engine will not run.

The best efficiency and power is achieved at a mixture strength of about 14 parts air to 1 of fuel. So close control of the amount of air going into the engine is required to vary the output of the engine. No one has developed a mass market solution to replace the throttle body. All of the electronic systems we see are again to increase power output and reduce emission.

This is a short overview. There are many books written on the topic.

[Schtum]

3 minutes ago, krisp1 said:

The best efficiency and power is achieved at a mixture strength of about 14 parts air to 1 of fuel. So close control of the amount of air going into the engine is required to vary the output of the engine. No one has developed a mass market solution to replace the throttle body. All of the electronic systems we see are again to increase power output and reduce emission.

This is a short overview. There are many books written on the topic.

 

As I'm sure you know the exact stoichiometric ratio is 14.7:1 for petrol engines and 14.5:1 for diesels.  However, that's not necessarily best for maximum power.   Viz.  https://aviation.stackexchange.com/...re-ratio-beyond-stoichiometry-give-more-power

[krisp1]

Yes, however I was trying to give a simple overview without too much detail to blow people's mind. Clearly you a have a deep understanding but many contributors of this forum do not.

[titan1]

big thank you to you all , its been very enlightening.

 

So new throttle pedal on the cards then, but which one - a HELLA or an INTERMOTOR ????

[Schtum]

38 minutes ago, krisp1 said:

Yes, however I was trying to give a simple overview without too much detail to blow people's mind. Clearly you a have a deep understanding but many contributors of this forum do not.

 

Nothing like a good bit of mind blowing to start off the week.... 

[Breezy_Pete]

3 hours ago, titan1 said:

big thank you to you all , its been very enlightening.

 

So new throttle pedal on the cards then, but which one - a HELLA or an INTERMOTOR ????

What problem are you trying to solve?

Can you read what fault code or codes are causing the glow plug light?

Edited 25 December, 2023 by Breezy_Pete
Sp

[Breezy_Pete]

There are some petrol engines without throttle bodies actually.

I remember being very doubtful when a young pal of mine told me he'd failed to find one in a petrol BMW he'd been looking at, several years back.

Google confirms:

[krisp1]

I stand corrected. I was not aware these two arrangements dispensed with the throttle body.

However both are very expensive solutions to the control issue, and the Multitronic is not very durable.

[J.R.]

8 hours ago, titan1 said:

J.R how do you know all this stuff ?

 

My knowledge such as it is is mainly on petrol engines from having pulled them apart & tikered with them from the age of 12, later on from building race engines and developing an engine management system.

 

Diesels I had zero practical experience of but I knew they had the same 4 stroke cycle, the only difference being the fuelling, ignition or lack thereof and higher compression.

 

Even through driving nothing but diesels from 2000 onwards I gained zero experience because the early VAG diesels were so reliable and simple, nothing broke down so I learned nothing, I did not even know how to bleed the injectors after running out of fuel.

 

All my learning has been playing catch up since buying a MK2 Octavia 4 years ago and the Yeti 3 years ago and most of that from this forum.

[titan1]

hi , my code is P0123 - throttle / pedal position sensor - A ciruit high.

 

Managed to remove the pedal to retrieve part number = 1K2 721 503 AE ( early 2011 yr of man )

 

Sorry for another question.

 

The part number I can get is an AJ, I take it that the difference is only in the J as this is a later version , so both are able to fit, am i right ?

[Breezy_Pete]

Suffix AJ does seem to be compatible judging by both appearing on this page:

https://www.skoda-parts.com/spare-part/1k2721503aj-accelerator-pedal-skoda-45060.html

 

But the real problem might be a damaged wire or bad contact, not necessarily the pedal electrical part itself. 

 

[titan1]

hi pete, checked as much as I can, still no damage to wire or connection. Would take it apart and have a look at the wiper track assy but dont want to tempt fate