ahu to 1z swap(A3 to B4)

I did a B4VR6 to tdi swap this spring. Its been a disaster. So far I have had to replace the transmission in the donor car, replaced the head, and a whole slew of other odds and ends. Ultimatley, I cannot rely on this motor, its making a racket from somwhere in the vicinity of the oil pan.

I know this swap isn't generally recommended. I have a B4 with a lower end noise, the engine is a 1z. I also own an A3 with an engine that runs fairly well, but the car has rust issues and wouldn't sell for much.

I'd like to swap the good engine from the A3 into the B4. The A3 has limp mode, I believe its the wastegate, everything else has been replaced including the actuator. So I would like to swap the whole intake/turbo assembly over. I think I need to do that anyway as the downpipes are different, so I assume the exhaust flange coming off the turbo is different too.

1. Is the engine wiring harness different? I am wondering if I can plug the B4 ECU harness into the A3 engine harness, or if I need to swap engine harnesses as well. I am talking about the harness that is on the engine starting at that big round plug that you undo to pull the engine out.

2. I think the transmissions are the same, do I have to swap flanges or anything?

3. Is the gasket between the head and the exhaust manifold reuseable? Its only been on there for about 700 miles.

4. Anything else that I would need to swap from the B4 engine over to the A3 engine?

Thanks!

The AHU and 1Z differ only in emissions controls (watercooled EGR on the AHU, maybe 5th injector and cat sensors on the 96 1Z), and in internal components (valve guides valve stem diameter, valve springs). The engines are otherwise completely interchangeable.
The cannon plug on the engine is wired the same on both.
Pull the A3 engine and transmission as a set, drop it in the B4.

Oh, the A3 engine top cover is a bit shorter than the B4's so plan in putting on the B4 cover if you want it to look 'right'.

You want to put the AHU into the B4 in place of the 1Z?
Go for it, its a better engine, not drasticly, but its has some improvements. Most 97 B4's had an AHU, mine does.

As long as you use all the electronics from the 1Z setup, you wont have to change anything, this includes the injection pump most importantly. Little stuff like the coolant sensors are the same though. The mechanicals of the motor are basicly the same.

The ecu / harnesses are NOT compatable assuming the B4 is either a BK / GQ, and the A3 is a JB / FA.

Turbo flange and downpipe are pretty much the same, Ive swapped them myself before.

Transmissions the same, so are the axles beleive it or not, granted its not 5 lug to 4 lug / vise versa.

I wouldnt re-use the exhaust manifold gasket, but you should not need to remove the manifold for any reason.

Thanks guys. I'll be tackling this after the wife's birthday next week. I need to bankroll some points between now and then.

The only reason I think I may have to swap exhaust manifolds is because the wastegate on the A3 sticks causing limp mode. I suppose I could try to clean it but the B4 wastegate seems to operate ok, and I would rather not have to revisit the issue a few months from now.

If you are using the GLX's cluster with MFA, the oil temp wire is missing on an A3 between the cannon plug and engine. The B4 haness will work on the AHU. It would be best to diagnose the limp mode before removing the AHU. Most likely it will be an N75 or "vacuum" (pressure) hose.

The limp mode has been diagnosed. The car has been looked at by the local guru. The hoses have been replaced, the n75, the wastegate actuator was even replaced. And yes, the hose inside the ECU. It overboosts because the wastegate doesn't open.