W124 ecu

[Williamwoo]

Hi all,

I am having a spot of bother with a misfire on my E320. Having replaced all the coil packs, spark plugs and associated cabling etc, when the engine is warm the supply to cylinders 1 & 6 cuts out (it's fine until it gets warm). My long-suffering mechanic has tested everything and come to the conclusion it must be the ECU. He sent it away for testing but they said they could find no fault with it. (I suppose it's possible that their test conditions do not stretch to getting it to the same temperature as when it's in the car?)

I'm reluctant to fork out £300+ for a replacement until or unless I've proven that it is the ECU, so I was wondering if anyone has one I could borrow short term (ideally in Somerset/Bristol area)?

The serial numbers are Bosch 0261203492 and Mercedes 0165456032.

Thanks in advance.

 

[BlackC55]

Are you sure its not the wiring loom?

 

[P12NLL]

As above, sounds suspiciously like the loom of doom.

 

[GP801]

When the ECU died on our 280 it would misfire randomly. Hot, cold, intermittently. Apparently it was killed by dodgy coil packs. That aside £300 sounds a bargain. Presumably a used part. Ours was £1400 + Vat for a new one.

 

[Williamwoo]

Sorry, forgot to mention that I rebuilt the wiring loom a couple of years ago.

The £300 I referred to was for the typical price of a second hand one.

 

[carat 3.6]

Does sound like the loom, when the ht leads were replaced did you change the coil extenders?

 

[Williamwoo]

Does sound like the loom, when the ht leads were replaced did you change the coil extenders?

Yes I did replace the extenders.

 

[kth286]

What fault codes come off pin 8 of the diagnostic connector ?

 

[Williamwoo]

What fault codes come off pin 8 of the diagnostic connector ?

Not sure at the moment, but my man did ask where the engine control relay is, as he suspects that, if the power supply to the ECU is not consistent it could be the cause of the issue. Can anyone point me in the direction of where the relay is?

He also said that if he turns the engine off and then immediately turns the ignition back on (i.e. before the engine has stopped spinning), it runs perfectly for 10 seconds or so before reverting to misfiring again.

 

[BlackC55]

Has he done a compression test or a cylinder leak off test?

Open the loom up for the coils and have a look inside.

 

[Williamwoo]

Has he done a compression test or a cylinder leak off test?

Open the loom up for the coils and have a look inside.

No he hasn't done a compression test - there's nothing wrong mechanically as the engine runs fine until it gets up to temperature.

Also, the coils and associated wiring are all newish and the loom was rebuilt a couple of years ago.

 

[BlackC55]

How do you know there is nothing mechanically wrong with it without doing a compression test or leakage test?

There still could be a wiring fault. Has the continuity been checked to and from the coils?

 

[Niks]

Try moving the coils around and see if the misfire moves with it, if it doesn't and ends up being cylinder specific, then that could be your ECU blown an output transistor or like Olly says... do a compression/leakage test.

 

[1001ab]

William,
I've got a '92 320TE that I'm breaking just now, let me know if there are any bits you need?
I had no idea that part was worth so much.

Moving the coils around sounds like a great way of proving/disproving the theory by the way.
AB

 

[Williamwoo]

Thanks all for your replies. I have tried moving the coils about, but it makes no difference - i.e. it's something to do with a fault in the supply to 1 & 6.
AB, I'll pm you re the 320 you're breaking...

 

[grober]

Why not replace the ECU transistor that sinks the coil supplying Cylinders 1 AND 6 to earth [ i.e. the switching transistor]. Lot cheaper than a second hand ECU?
http://www.mbclub.co.uk/forums/electronics/144774-how-repair-your-ecu-ignition-part-1-a.html

http://www.mbclub.co.uk/forums/electronics/144776-how-repair-your-ecu-ignition-part-2-a.html

PS The engine control relay is also known as the OVP [ OVER VOLTAGE PROTECTION] RELAY

 

[hfmscan]

What error gives the ECU?
try to position 7 for HFM corrector (from factory position 1)

0165456032- Bosch ecu, usually has no problems with ignition.
for the test, you can take the same ECU 0165455932

 

[Williamwoo]

Hi all,

Problem solved - it turns out that one of the ht leads breaks down when it gets hot (even though the leads are only about a year old). Seems very strange and my mechanic says he's never seen it before.

Anyway, many thanks to all of you who contributed with your advice.

 

[bolide]

It's easy to pinch cables under the cover of an M104 engine

Nick Froome