e34 535i ecu swap

[octanejunkie]

Hi all
Is it safe to swap motronic ecu's?
I have a 535i with a manual box and i think i traced a hunting idle problem to the ecu after swapping out the air flow meter, idle stabalizer valve and temperature switch etc. I looked for a used ecu bearing the same part number but could not find one for sensible money. Then i found a 530i manual in a scrap yard and took the ecu from it and put it in my car. It seems much better with a smoother idle and no noticable loss in power etc. I'm not sure if this is safe to do in the long run. Can anyone advise?
The original ecu part no. is 0 261 200 150. The one i pinched from the scrappie is 0 261 200 178.

[Dash01]

I don't know the answer to your swap question, but suggest that while you have the old ecu unit off the car, you may want to re-flow its solder joints.

Bosch ecu boxes are quite reliable and sturdy, but after nearly 18 years of heat cycles and vibration, the solder joints can develope hairline cracks. Re-flow with a ~$10 Radio Shack solder pen can renew and solidify these old joints, and may fix your original ecu problem.

[bill g]

The 530i ECU will have ignition timing and fuel mixture maps specifically for that engine. Your engine may seem to be running OK with the swapped ECU but could be running lean or over-advanced which will cause damage to the engine. Maps are usually programmed onto a chip in the ECU. I do not know whether either of those particular ECUs have removeable chips and if they do, whether the chips can simply be swapped over. For all I know they may have the exact same chip in them. You really need to investigate this further - anyone else got more specific info?

Bill G

[MarkD]

The 530i ECU will have ignition timing and fuel mixture maps specifically for that engine. Your engine may seem to be running OK with the swapped ECU but could be running lean or over-advanced which will cause damage to the engine. Maps are usually programmed onto a chip in the ECU. I do not know whether either of those particular ECUs have removeable chips and if they do, whether the chips can simply be swapped over. For all I know they may have the exact same chip in them. You really need to investigate this further - anyone else got more specific info?

Bill G

I don't think you could swap a chip between a 150 and a 178 ECU as the hardware is quite different. He could try taking a chip from a 179 (3.5l) and installing in the 178 as that would me a closer match.

MarkD

[cosworth]

try to find ECU 0 261 200 179 meant for E32 735 Auto.

It works - i hv used it before. Power loss very marginal (did a dyno on that to compare against ECU 150).

BTW, the chip is not interchangeable ... I did put the ECU 179 chip in my ECU 150 .. the engine gives a BIG 'POP' sound.. Thought it's a gonner ... phew ...