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IdeaNerd Samba Member
Joined: May 24, 2016 Posts: 597 Location: Central California
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Posted: Mon Nov 16, 2020 2:07 pm Post subject: AAF vs. ACU engine |
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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! |
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wannabecamper Samba Member
Joined: May 09, 2019 Posts: 211 Location: Sunnyside, US
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Posted: Mon Nov 16, 2020 3:21 pm Post subject: Re: AAF vs. ACU engine |
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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. |
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Zeitgeist 13 Samba Member
Joined: March 05, 2009 Posts: 12115 Location: Port Manteau
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Posted: Mon Nov 16, 2020 5:04 pm Post subject: Re: AAF vs. ACU engine |
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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? |
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BatesEV Samba Member
Joined: October 01, 2019 Posts: 182 Location: Los Angeles
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Posted: Tue Nov 17, 2020 5:20 am Post subject: Re: AAF vs. ACU engine |
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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.
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IdeaNerd Samba Member
Joined: May 24, 2016 Posts: 597 Location: Central California
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Posted: Tue Nov 17, 2020 6:23 pm Post subject: Re: AAF vs. ACU engine |
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Thanks for the info (and pictures!) guys -- very helpful! |
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fulvia Samba Member
Joined: December 01, 2010 Posts: 2 Location: Los Angeles, CA
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Posted: Wed Nov 18, 2020 7:59 pm Post subject: Re: AAF vs. ACU engine |
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did you buy it? |
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IdeaNerd Samba Member
Joined: May 24, 2016 Posts: 597 Location: Central California
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Posted: Mon Nov 23, 2020 10:27 am Post subject: Re: AAF vs. ACU engine |
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No, I ended up passing on this one. |
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Danilot4 Samba Member
Joined: December 04, 2021 Posts: 3 Location: Montenegro
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Posted: Sat Dec 04, 2021 9:13 am Post subject: Re: AAF vs. ACU engine |
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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?
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CdnVWJunkie Samba Member
Joined: February 01, 2004 Posts: 1110 Location: Sarnia, Ontario, Canada
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Posted: Sun Dec 05, 2021 3:05 pm Post subject: Re: AAF vs. ACU engine |
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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.
BatesEV wrote: |
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.
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Danilot4 Samba Member
Joined: December 04, 2021 Posts: 3 Location: Montenegro
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Posted: Tue Dec 07, 2021 1:25 am Post subject: Re: AAF vs. ACU engine |
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Thank you on info! It was very helpful 🙂 |
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Joshwa Samba Member
Joined: November 18, 2015 Posts: 810 Location: North Seattle WA
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BatesEV Samba Member
Joined: October 01, 2019 Posts: 182 Location: Los Angeles
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Posted: Wed Dec 08, 2021 7:45 pm Post subject: Re: AAF vs. ACU engine |
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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. |
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Alan Brase Samba Member
Joined: March 28, 2004 Posts: 4532 Location: Cedar Falls, Iowa
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Posted: Sat Dec 18, 2021 5:57 am Post subject: Re: AAF vs. ACU engine |
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Joshwa wrote: |
CdnVWJunkie wrote: |
Danilot4,
Some have claimed success with welding but be aware it's cast iron and welding this is a dying artform. |
The AAF Exhaust manifold is cast stainless. The fixes I’ve seen are to grind out the crack and weld in the dug out seam. |
What is cast stainless? Probably some kinda cast iron with a lot of nickel in it? Might be, they do get reddish but seem to not have very much rust present.
I have a welding shop in central Iowa that is the very best at welding cast, mostly cylinder heads. He says probably $100-200 range. I've been to his previous shop, they put them in a natural gas fired furnace, covered with moveable plates when red hot they stop the furnace, open an access and used oxy-acetylene torch to weld in using strips of similar cast filler rod. Head it agan then let it cool for a day. Cylinder heads then need to have surfaces ground/ trued. I can't imagine this 3 cylinder long part could be warped much that one couldn't fix it with sandpaper on a piece of glass in minutes. _________________ Al Brase
Projects: 67 sunroof bug, 67 Porsche 912 Targa, 70 Westy
Dec 1955 Single Cab pickup WANT 15" BUS RIMS dated 8/55, thru 12/55
To New owners: 1969 doublecab, 1971 Dormobile
Vanagons:
80 P27 Westy JUL 1979, 3rd oldest known US
83 1.6TD Vanagon, 87 Wolfie Westy daily driver, swap meet home |
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