VWDiesel.net The IDI, TDI, and mTDI source.
General Information => FAQ/Tech Tips/Please Read First => Topic started by: Vincent Waldon on June 20, 2009, 07:22:32 pm
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This question comes up often, and I recently found a couple of cool pictures that help explain it.
IDI Engines:
The acronym "IDI" generally refers to "InDirect Injection. In this configuration diesel fuel is injected indirectly into the combustion chamber via a "pre-combustion chamber" inserted into the head:
(https://i.imgur.com/cqy4eWg.jpg)
The IDI diesel engine was standard VW passenger car fare until mid 1997 and may or may not be coupled with a turbo. Engines of this vintage without a turbo are often referred to as NA or normally aspirated engines. IDI engines uses a pintle-style nozzle that sprays fuel in a mist and are threaded into the head like spark plugs. Due to the heat-sinking capacity of the surrounding head IDI engines generally require the use of glow plugs on all but warm days.
The fuel system for an IDI engine is almost always 100% mechanically controlled via a Bosch VE distributor-type pump, although Europe got a late version of the AAZ engine that had some vestiges of electronic timing control. Throttle control is via mechanical cable to the throttle pedal.
TDI Engines:
The acronym "TDI" generally refers to "Turbo Direct Injection. In this configuration diesel fuel is injected directly into the combustion chamber formed by a depression machined into the crown of the piston:
(https://i.imgur.com/qNnyvyS.jpg)
The Direct Injection engine started appearing in European VW passenger cars in 1991, in some North American Passats in 1996, and were in general circulation world-wide by mid-1997. In all but rare cases the direct injection configuration is equipped with a turbo, hence the confusion some folks have thinking their turbo-equipped IDI motors is a TDI. The nozzle sprays fuel in 5 discrete jets and is held into the head with a top-mounted clamp. Glow plugs are not generally needed until the engine temperature drops near freezing.
The fuel system on a TDI generally uses a electronically-controlled Bosch pump with an Engine Control Unit, and the throttle is drive-by-wire using a potentiometer-equipped pedal.
A primarily home-built variant of the TDI pump known as "m-TDI" uses the TDI pump body and nozzles but substitutes parts required for manual (ie cable) throttle control.
A more recent version of the TDI design, commonly referred to as "PD" or "pump duse", uses individual injector/pumps that are driven off the valve camshaft to pressurize the fuel to extremely high pressures and spray it out a nozzle with 7 holes. North America got PD engines from 2003-2006.
In 2009 VW introduced the so-called "Clean" TDI design... a common rail system with a completely different injection system yet again.
For a variety of reasons, including more precise fuel control and fewer thermal losses, TDI engines generally obtain better fuel economy than their turbo-equipped IDI cousins.
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Great cutaways! The Passats started getting the TDI engines in '96.
Thanks Andrew...
And, in general guys and gals... correct at will... I'll update the top post accordingly
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1Z was introduced in ´91 Audi 80 B4 and ´93 in Vw Passat, Golf and Vento. (´92 and ´94 model years)
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1Z was introduced in ´91 Audi 80 B4 and ´93 in Vw Passat, Golf and Vento. (´92 and ´94 model years)
Not in North America
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Awesome write up. Now i can show people what i"m talking about when then ask what the difference is between the two.
Quote from: MJF on June 21, 2009, 06:52:10 AM
1Z was introduced in ´91 Audi 80 B4 and ´93 in Vw Passat, Golf and Vento. (´92 and ´94 model years)
Not in North America
I wish we would have gotten half of the sweet diesels from over the pond.
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Awesome write up. Now i can show people what i"m talking about when then ask what the difference is between the two.
Quote from: MJF on June 21, 2009, 06:52:10 AM
1Z was introduced in ´91 Audi 80 B4 and ´93 in Vw Passat, Golf and Vento. (´92 and ´94 model years)
Not in North America
I wish we would have gotten half of the sweet diesels from over the pond.
Amen to this, Brother. Amazing how many American* cars are over there with diesel engines. I'd love to get their cetane numbers as well in our diesel
*Yes, I know some of these cars are made in Canada..... :)
Nice work, Vince..
Stay safe, stay well. Jimmy.
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Later TDIs had/have seven hole nozzles, but that didn't start until the PD engines so you're probably not covering that here. :D
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Nice writeup Vince! 8)
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Thanks all... I've incorporated your various (great) suggestions.
If I ever find cut-aways for the PD or common-rail design I'll add their own sections... anyone willing to take a bandsaw to their 2009 Jetta??!! ;D
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I'm sure there are enough people with PD engines that have lunched their camshafts, should't be that hard. ;)
Brendan
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Very informative, thanks very much
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Wow i just got schooled. Thanks for the info.
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PD
(http://i60.photobucket.com/albums/h23/ardy-photo/PDpics/PDcutaway.gif)
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the PD injectors basically operate just like a Jimmy does, correct? just has electronic correction features too?
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those are beautiful pictures!
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Polished cut lines and everything.
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Nice post! Very helpful!
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Cool write up
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