Hello All,

You may have been following the thread re my XM's head gasket probs, well now it has become or been diagnosed as electronic. Last night the borrowed ELIT diagnosis computer finally determined that there is a "permanent error" in the ignition computer. (see http://club-xm.com/forum/index.php?showtopic=1194&st=0)

Yesterday afternoon after having the battery recharge for 24 hours, I ran as many tests as I could without the engine running. All injection systems etc work fine, but ignition will not. The car would not even start this time on even four of the six cylinders.

I had made arrangements with a dealer to borrow a computer from their used spares stock and picked it up this afternoon (Monday). The only differences we can see/know of are:

The loaner is from a late series 1 car, my car is '96 series two
Both engines are 90deg V6 12valve
The original computer is a SIEMENS FENIX 3 BVA/SO2 9625575280 and S111700211 are the only identifiable numbers on it

The borrowed computer is a BENDIX FENIX 3 S101700201 are the numbers on this one.

Now... Can anyone advise whether the computers are compatible/swappable and reasons for or against?

If you know of a reason why the original may have failed, any info there would be helpful too. I have not taken the lid off it to look for potential problems yet.

I intend to try swapping the computers tommorow night (Tuesday) unless someone tells me there is a reason I shouldn't. I will be careful with electrical reattachment procedures too!

Your thoughts would be useful.

Thanks

Hello UFO.

Just had a quick gander at Autodata (the aftermarket info. bible). As usual with XMs it's patchy, but the pages relating to 89 - 94 12v V6 and 94 on are definitely different. What you need to be careful about in general terms is that by connecting a different box of tricks, you don't damage existing good components and the test box itself.
I haven't got your detailed page up at the minute, but in case it wasn't on your list, there is both a crank position sensor and an RPM sensor on the later version. I strongly suggest you have a gander at www.atpelectronics.co.uk who list a precise matching replacement unit. (No, I'm not on commission with them !)

Good luck, Mike.

Hi UFO

I understand your reluctance to risk swapping ECU modules particularly where they have different version codes/part numbers. A few months ago Jorgy was having ECU/immobiliser problems with his Mk1 V6. Two of us lent him working ECU's that we had tested in different V6 cars. There did not seem to be any ill effects from the various combinations we tried but we did restrict to those from a single engine type. The one I sent Jorgy was from a 92 V6 but I tried it in a 95M V6 car to check that it worked before I sent it. I now have the ECU back so will check for reference numbers when I can.

Regards

XMexc

Yes, Fenix 3s should all be interchangeable, even between manual Vs auto box (BVM Vs BVA code). I have tried 2 different ones on my V6 and all appeared to work fine. At least for starting up and testing purposes, I didn't drive around with them.

regards
George

There is a software difference between computers. If you put a computer for automatic gearbox into car with manual, the rpm will drop very fast, which makes uncomfortable driving. Vice versa the result will be high fuel consumption (24.5 instead 12 ltr/km in the city), on the highway there is no problem.