AAF vs. ACU engine

[IdeaNerd]

I'm looking at possibly buying an imported (already titled) 1994 T4 that has a 2.5L inline five-cylinder (gasoline), which I think is an AAF engine. Aside all the normal import-related caveats, I don't know much about the inline five-cylinders. Were both the ACU and AAF engines imported to the United States in the 1993-1997 time period? Any advantages of one over the other? Are they used on any other VAG vehicles? (I'm guessing they are, but am not certain at all.)

On the T4 platform, I'm coming from only owning vans with the VR6 24V engine. Anything else I should know about re: the 5-cylinder vans, other than lower horsepower and torgue? (Note: this van in question also has an automatic transmission.)

Thanks for any and all info!

[wannabecamper]

AAF was on 94 and previous model year. 95 is the only MY with ACU from what I understand in the US. ACU had added emission stuff and is bit more complex in diagnostics and repairs related to the engine control and management. Mechanically both are bullet proof from what I understand. As for the power difference between the two, there is no difference. Compression was higher on ACU, but it didn't add any power.

As for the use in other vehicles, there were no other ACU in any other vehicles in the US. It is my understanding that it was used specifically for the Eurovan application for its low end torque.

If you are comparing to a VR6, then a 5 cylinder eurovan will feel like driving a snail. I have a camper, and the added weight makes it worse.

[Zeitgeist 13]

I seem to recall reading that the ACU had a better exhaust manifold design
_________________
Casey--

'89 Bluestar ALH w/12mm Waldo pump, PP764 and GT2052
'01 Weekender --> full camper
y u rune klassik?

[BatesEV]

Yes the manifold is better on the ACU. It’s a tubular header and the Downpipe is a 2 pipe into one. The AAF is a cast iron and is prone to crack with the most common failure is the bellow between 2-3 cylinder. The engines are like tractor engines and mechanically take some abuse. One thing that is a weak spot is no knock sensors on the AAF, so if you high load the engine in heat with 87 you could cause some damage.

[IdeaNerd]

Thanks for the info (and pictures!) guys -- very helpful!

[fulvia]

did you buy it?

[IdeaNerd]

No, I ended up passing on this one.

[Danilot4]

Hi guys I am now on this forum. I have t4 2.5L aaf and my exhaust is noisy but i cant locate the sorce of noice(where the exhaust is broken). It sounds that is somewhere close to manifold but it is so hard to reach there. Is this part betven 2. And 3. Cilindar on exhaust manifold prone to failure? I took a picture somehow with my phone and it looks like there is something black behind that metal cover.
My question is: is the only way to get to the exhaust manifold by taking off intake manifold? And is it posible to fix that part or i have to find a new one?

[CdnVWJunkie]

Danilot4,

Check out this informative post. IN your photo, your heat shield is still in place on the exhaust manifold. In BateEV's post you can view what the exhaust manifold looks like minus the cover. I would wager you have a crack in the 1-2-3 piece. I've seen countless units with this issue. Some have claimed success with welding but be aware it's cast iron and welding this is a dying artform. I'm sure this piece is NLA from VW. The ACU exhaust manifold is a nice upgrade and far less failure prone.

[Danilot4]

Thank you on info! It was very helpful 🙂

[Joshwa]

[BatesEV]

But to weld any cast correctly you have to heat it with a torch to get the metal hot, weld, then burry in sand to cool it slowly. It requires a feel to know when to stop heating and what rods to use as a filler on what settings.

[Alan Brase]