[V8] Father/Daughter V8s & 4.2L 5-Speed Programming

[Allan Vega]

If you have access to the v8 wiring diagrams (everyone here should have a PDF version by now) it actually not difficult at all for the average do-it-yourselfer to figure out.
When originally did my 4.2 conversion, I went with the 3.6 harness and ecu for several reasons. 1. I already had it installed in the car. 2) it was already chipped with the abt software. 3) while reading through the 4.2 self training manual, I discovered that if I used the proper 4.2 harness and ecu found in the US spec cars (which only came in automatic) I would have an issue with the timing being retarded. You see, with the 4.2 auto ecu, it has additional imputes from the tcu. If the 4.2 ecu doesn't see this signal (which cannot be practically duplicated) it just retards the timing. This is why the 3.6 ecu harness and ecu has been used in most 4.2 swaps. That is also the reason the 4.2 cars are much more responsive the the 3.6 cars. 
Now, let's forget about the sequential vs bank injection argument for a second(though valid) there is also the issue of proper fueling and timing for the hotter cams the 4.2 posses. The 3.6 ecu cannot take advantage of this,because it was not designed for it( though the abt chip 3.6 ecu probably makes up for it a little). 
So, what does one do in this paradoxal situation? Well let's see, where in the world can one find a proper 4.2 v8 quattro with a factory manual transmission ? That's right kids, Europe....more specifically, Germany. If somehow were able to get your hands on an ecu from a  
Factory 4.2 6-gang, you would solve the issue of not haveing proper fueling and timing with the 3.6 ecu, as well as solve the issue of having the timing pulled back because the euro ecu is not looking for the tcu signal ( remember, euro ecu must be from a manual car) 
So, how does one know if one is buying a true euro ecu from a manual 4.2 car? Easy, cross the part number in the European section of etka using the ATP feature( you should all have a copy of etka as well at this point.
Now for the easy part, the wireing. The beuty of the v8 engine harness, is that it's modular. It's a direct swap, plug and play between the two, the the exception of the o2 sensor. If you simply just repin this wire to the correct location, you would still have an issue. You see, on the 4.2 cars there was an o2 sensor relay added for the heated element. While the 3.6 cars had a constant ground, and power supplied the the fuel pump relay ( Read....heating element energized anytime car was running) the 4.2 cars had it's ground supplied and controlled by the ecu via a dedicated output. Power was still supplied by the fuel pump relay, but now the ecu could control when the heating element turns on and off, by killing or supplying a ground signal to the o2 sensor relay. Furthermore, this ground signal is current sensing( read: the ecu knows if you bypass the relay, and turns on the check engine light and retardsthe timing. BTDT. Make sure you wire this relay in using a standard auto relay and your 4.2 wiring diagram.
All of the above has been proven and done to my factory five speed, including the proper euro ecu.
For the record, motronic remapping has been available for a while here in CT( Tony Chick @ EPL) and for those who want to tune there motronic themselves ( I wouldn't recommend this option unless you know someone who knows how to tune) o34motorsport will be offering this option shortly

-Allan  

Sent from my iPad

On Aug 13, 2011, at 10:11 PM, Professor GT gmail <CavalloGT at gmail.com> wrote:

> Well I was finally able to find a good engine (3.6L) for my pearl white 91 automatic V8 (16 yr old daughter's car) (thanks George), and I already have a good 92 donor 4.2L for my pearl white 91 5-speed (my toy) ( thanks Allan), so all I have to do now is start spinnin' wrenches!
> 
> Yep, made the trip today with my buddy and his flatbed (thanks Scotty N) to pick up a good running 90 automatic car, so I can make the white automatic car whole for my daughter - lucky kid, I wish I had someone to build me a nice car when I was 16.
> 
> Anyway, can't wait to hit the road with our Father/Daughter Pearl White Twins! Doubt they will be ready for sFest this year, but should be no problem for next year.
> 
> Gotta vet out the details of the 4.2 swap because it is true that to go backwards in technology from sequential fire to bank fire, while totally possible, on the surface just doesn't make good sense. That said, if the 4.2 Motronic cannot be programmed to forget about the auto trans ......... Well it might be the only viable option without completely scrapping the Motronic control unit altogether and going with something else. 
> 
> Come on, there has to be a techie out there who can crack the Motronic code and make it work. The BMW boys seem to have figured it out. How about you Audi Gurus - what gives?
> 
> Thanks,
> 
> ProfessorGT
> (Sent from my iPhone4)
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