markysparky

Hi there, new to this site and have a couple of questions for you guys. This may be a bit drawn out but I want to give you some background before posing my questions. I'm including some pictures to go with my text to make it simpler I hope.

I'm currently running a 2.6E ABC engined Coupe with a leaking head gasket (oil into the v). I took the IM off thnking it would probably be what you guys call the valley pan gasket (the engines covered +200k miles). I degreased the entire top of the engine with the IM off, and did the same to the IM. I replaced the valley pan gasket (which looked suspect) and re-fitted everything, thinking I'd cured the leak. A quick 5 mile blast around the lanes and all looked promising. The next day I decided to use it for my 40 mile trip to work, instead of my bike, just to make sure all was well. When I arrived at work I checked in the v and there was evidence of oil around the valley pan gasket and slight oiling on the block below the left hand side head gasket. Knowing that the pan gasket is highly unlikely to be leaking again I concluded that it's most likely to be the head gasket leaking the oil into the v as apparently it's a common problem. When I priced up a complete gasket set, head bolts, lifters etc I decided to save myself some cash and fit a 2.8 AAH engine that I'd promised myself for some time now. Having now bought a '93 AAH engine and gearbox (with half the miles of my ABC for less than a set of gaskets and bolts, including delivery!) I'm setting about cleaning it up and fitting a new cambelt kit, water pump, thermostat etc. I'm going to match the IM to the heads for the recognised power/economy improvements but need some info/opinions as to a problem I have. There are differences in the IM designs (possibly due to the difference in ages of the engines, rather than the capacity difference?) which are listed below.

The ABC engine has a 3 piece IM using a 2 bolt fixing, 4 pin idle stabilisation valve. The AAH has 2 piece IM with a 3 bolt, 2 pin one, ie, they're not interchangeable and the AAH one wont connect to my wiring loom.

The AAH IM has no air temperature sensor or provision for one unlike the ABC IM.

The AAH IM has a vacuum operated lever system attatched to the manifold which appears to operate something inside it for the short/long inlet tract system, the ABC IM has nothing like this.

My main question is this, which IM is going to give me the best power/torque? I suspect the later, simpler design of the ABC engine will be better myself. As it poses no electrical fitting problems (the air temp sender and idle valve will connect straight to my original wiring harness)I'm tempted just to go ahead and fit it. I'm not sure on the reliability of the vacuum operated inlet tract system either. The one fitted to my AAH engine hasn't done worked for a while, I suspect, as the vaccum take off from the throttle body is blocked solid. If there are significant gains to be had by adapting the AAH one I'll find a way round these problems.

Can anybody on here give me any asistance on these matters? If the earlier AAH IM is a better system, does anyone have any info to assisntme in using it?

My other questions are simpler;

1, Are the 2.8 and 2.6 injectors the same?

2, Are the 2.8 and 2.6 ECU's the same? (it appears they are from the info I have already discovered online)

3, Can anybody tell me what the 1/4" dia pipes are fitted next to the manifold Lambda sensors? On my AAH they travel towards the front of the car but both are capped off.

That's about it for now, thanks in advance, Mark.

mdecsi

What is your goal? Do you want to keep your existing IM and swap "just" the engine and the heads?

mdecsi

Oh, I read it again and now I understand. Sorry.

The AAH IM is much more advanced an you should use that one. The changeover butterfly valves rarely go bad, they are reliable pieces.

Unlike the ABC, the AAH has a MAF sensor (your ABC had a MAP sensor), and so the ECU measures the air temperature with the MAF, no need for stand alone air temp sensor. Do you got the MAF with your engine?

For operating the changeover valve you will need either a vacuum pump (used on early AAH engines) or a reservoir "ball".

Of course it is not enough, your ECU will no nothing about it, so you will need to change your ECU too, but chances that the pinout for the new ECU will not be compatible with the old one. I think you have the MMS200 ECU. More about ECUs here:

http://12v.org/engine/index.php?section=hw


Those pipe next to the oxygen sensor is the "intake" for the EGR system.

Anyway, you are in a problematic situation. It is not just that easy to swap the engines. I have never heard someone who used a 2.6 ABC system with a 2.8 AAH engine, but the other way around it is possible, I seen it at least one time, but I don't know how hard it is.

As you already bought the engine I suppose you want to use it anyway. The easiest solution would be to use your existing 2.6 ABC parts with the 2.8 AAH engine, as you planned, but I don't think anyone will be able to tell you how will it perform.

markysparky

Thanks for your quick reply!


As you have pointed out, my preferred solution is to use the ABC IM so that everything else on the car is compatible with it. As far as I'm aware, the only mechanical difference between the engines is a longer stroke crank in the AAH so there will be a greater volume of air being consumed by the engines larger capacity. I understand that a MAF sensor could also register air temperature as well as flow but on a normally aspirated engine I cant understand how a mass air pressure sensor could work, unless it detects vacuum. If this is the case, wouldn't the increased volume of air entering the larger capacity 2.8 create a greated vacuum that would be detected by the MAP sensor? Together with the signals from the crank/camshaft/air/water temp sensors, wouldn't my current ECU correct the mixture? Where on my ABC engine is the MAP sensor located?
As I said in my post, the AAH is a 1993 engine but the ABC is a 1995. I'm assuming Audi made the intake system cheaper as well as somewhat more efficient over 2 years gap in production but in all the pictures I have found online of 2.8 Coupe's I havent spotted a MAF in any of them. The intake trunking appears identical to mine, ie; air filter box on the inner wing with a continuous piece of trunking to the throttle body. Where would the MAF be situated on a 2.8 AAH engined Coupe and would it be obvious in any pictures?

The two pipes on the exhaust manifold don't appear to have ever been used with an EGR valve as the intake manifold is extremely clean inside for the mileage.

The changeover valves are operated by the diaphram in the picture I posted, which is fed by a conection on the throttle body. Is this what you are describing as a vacuum pump? From what I remeber, this throttle body fitting is connected to the intake trunking on my ABC engine that is fed engine gasses for recirculation from both cam covers. This fitting was blocked solid with a congealed oil/carbon on the ABC when I bought the car so I cleaned it thoroughly with a small drill bit.

My local Audi spares department are quite helpful (unusual in my experience) so I'll be taking a trip there to scan their exploded view diagrams when I get a chance, they even offer to print them off for me if I want them!

Thanks for your input, any further advice/opinions from you or anyone else would be greatly appreciated.

I'm hoping to get a greater understanding of the AAH engine when I finally get delivery of my Haynes manual from USA, maybe I won't need to be posting such long threads in the future when I do?

mdecsi

That is not entirely correct. Even the AAH engine has two generation with several difference. I recommend you to browse 12v.org and the archives here at AW, seems like you're missing some basic things.

The MAF sensor has two very fine titanium wires. One of the wires measures the temperature of the air, the other the mass of the air. It has to be like this way, since colder air is denser, therefore it has a greater weight. So it is not just an "extra capability". Without it the sensor cannot tell precise values.

Also, MAP does NOT mean "mass air pressure", but Manifold Absolute Pressure and yes, it is able to detect vacuum.

It is located inside the ECU, a rubber hose is connected for this reason to your ECU.

Bigger engine doesn't mean more vacuum. It is not that simple. The ECU has to know how much air your engine is consuming and a MAF sensor is one way to measure it, the MAP is an other one, although not that precise.

Your ECU has stored values for your engine. Think about them like a spreadsheet. For a given MAF, temperature,etc. values it injects a given amount of fuel. You are changing the size of the combustion chamber since you put in a bigger engine. These tables are going to be useless, because they are calculated for the previous smaller engine.

And it is not that simple either. Your ECU will detect something is wrong because the oxygen sensors indicates a lean mixture and either it will put in more fuel or will give you a CEL.

Your results are going to be unpredictable mixing components this way. If you are lucky, maybe someone has done it already and will tell you his/her experiences, but theoretically your ECU will have problems preparing the right fuel-air mixture.

The MAF is located just after the airbox on a AAH engine.

No. The diaphragm has a spring in it, so normally it closes the short intakes and only the long ones are open.

When your engine rev. reaches 4100rpm your ECU opens an electrically controlled pneumatic valve and the pre-stored vacuum in the reservoir pulls this diaphragm. Think about it at 4100 WOT you don't have ANY vacuum, because the butterfly valves are open and your engine tries to consume any are it is able to. So a vacuum ball stores some vacuum for the diaphragm to operate.

There is a free online system where you can view and print all parts of your car. You have to register to view the part numbers and the names, but it is free and instant. You can reach it here:

http://www.vagcat.com/

markysparky

Thanks again for the input and education, I've never been good with abbreviations though. CEL? I think it has something to do with error codes but I'd like to know for sure.

I've been putting some thought into how to get round the mismatch between the AAH and ABC management systems and will go into more detail at a later date, it's late, I'm tired and I have an early start tomorrow for work.

One thing I would like to know is your opinion on whether the ABC ECU can be re-mapped to suit the requiremnts of the 2.8 engine? I've had a quick look online at tuners specialising in re-mapping but have yet to find one with my car listed as a straight chip upgrade. I'm hoping that's due to the age/rarity of my car, NOT because it's not possible. I've sent out a few enquiry mails to some of them, just waiting for a response.

Cheers.

mdecsi

CEL = Check Engine Light

Do you have some sort of software and cable to communicate with your ECU? Itt will be essential soon. If you are on a tight budget and have experience in making circuit boards you can build a cable for yourself and there are various "light" and "free" versions of programs.

If you can get a later MMS300 style ECU and all the necessary sensors for your AAH engine, the swap would be much-much easier.