Misfiring - ECU/loom problem

[TH3R4POR]

Hoi all,

I am looking for some advise. My Z4 has started misfiring, after doing several tests we've discovered it isn't firing on #3 and is intermittently firing on #5.

We've done compression tests, changed out the coils, changed out the plugs etc etc and the only thing my mechanic could think is that (despite being rare) it's an ECU problem.

We spoke with several ECU specialists and apparently similar faults have been seen in the past, we sent the ECU off to them but they were unable to complete a full test (whatever that means) and returned the ECU to us without charge. My mechanic is still of the opinion it's the ECU, or possibly a fault in the loom itself.

The next (and only?) logical step seems to be take the car to the local stealer but I suspect their solution is going to be buy a brand new ECU and then pay the labour on fitting and pairing the keys etc. I don't know if they can do any testing on the loom but will speak with them later today.

Are there any other steps I can take to test possible causes, I was thinking of maybe trying to locate a local donor ECU to test the possible loom fault, would a donor ECU (and paired keys) start the car, I am assuming there isn't any other logic within the loom that would prevent the car turning over?

Cheers in advance,

Dave

 

[bcworkz]

Has the main ECU relay been checked? That is more likely a problem than the ECU itself. You can't practically change ECUs, the matched keys are only a minor part of the problem. The ECU does a security handshake with two other modules, and if the stored security codes of all these modules do not match, nothing will work.

If the ECU does turn out to be the problem, reflashing it would be the next step before actually replacing it.

 

[TH3R4POR]

Cheers for the reply mate,

No idea on the main ECU relay, the only communication I got from the ECU specialists was that they couldn't complete a full test, the test label attached to the ECU states the same "unable to test". That might mean the ECU is completely knackered.

I'm trying local firms to see if they can offer me some support, I am awaiting a call back from a motorsports firm based in Milton Keynes as they have a guy working for them who has been highly recommended by other firms (ex BMW Master Technician).

How would I go about testing the ECU relay, is it located on the ECU itself?

 

[bcworkz]

Your ECU specialists are independent? Unable to test may just mean they've yet to crack this particular ECU yet? Seems to me that if it runs the engine at all, they could test something if they had it cracked? I'm just guessing, so this really means little, but I wouldn't assume it's knackered just because they couldn't test it, but OTOH, it really could be knackered.

The relay is in the electrics box with the ECU, but they have their own wiring connections. On the inner forward corner of the electrics box, there are two small, sort of cubical boxes. (3 with SMG or EGS [WTF is EGS?]) The forward one is the fuel injector relay, the one rear of that is the ECU relay. This information may vary with model year, so take with a grain of salt, may not be totally accurate to your car.

It's a typical normally open relay. The coil, terminals 85 & 86 go to battery and switched ground. There should be some resistance across the coil, but I don't have a spec on what it should be. The switch is terminals 30 & 87, one should have battery voltage, and the switch should be open unless pulled by the coil when voltage is applied to it.

 

[TH3R4POR]

Thanks again for your feedback bcworkz, I stupidly didn't bring the unit into work today so can't see what you are talking about at the moment but will have a look tonight.


Riiiight, I've phoned 8 different people this morning including a BMW main $tealer, BMW HQ (we have contacts there), my mechanic, ECU specialist, an Independent, and an ex BMW Master Technician.

My mechanic switched out the coils, injectors, etc. Codes he got were no spark on #3 no matter what he did. His opinion is either the ECU or the wires from ECU to coil.

BMW Main $tealer said they could plug it in and do a test, but afaik they can't test the ECU specifically. The guy in parts was actually very good, and said he'd try an Indi first, and then an ECU specialist. New ecu is £900 for the unit then god knows how many hours of labour.

The ECU Specialists (BBA Remans) I sent it to said they couldn't perform a full test as they don't have a rig for that ECU (as they never go wrong...) so they tried to cobble together something on the bench, they couldn't communicate with it but the coil drivers worked and physically it looked in good nick (nothing visibly burned out).

BMW Master Tech says he can perform tests on the loom to remove that from the equation, but his advise would be to send the ECU to someone else who can test ECUs, he suggested BBA Remans....

His other suggestions involved borrowing a known working ECU (and matched EWS unit which controls the immobiliser) from another 3.0 Z4 and see if it runs, that's a logical step but involves a few hours as the EWS unit is buried behind the dashboard (he couldn't remember if it was a dashboard out job on a Z4 or not?), similar suggestion was buy a set of units from a breakers via eBay as apparently they sell them as an 'Immobiliser set'.

 

[bcworkz]

I'm afraid I'm rather useless. On further consideration, if you're consistently missing on #3, I can't imagine how the relay can be at fault. My apologies. I can't read either, I mentioned ECU handshake with 2 other modules, but as you discovered, it's only the EWS. I thought it was communicating with CAS as well, but actually the CAS is part of the EWS module.

Pulling the EWS shouldn't be a dash off procedure. On LHD, only the lower trim panel needs to be removed, but access is difficult still. On RHD, I'm not sure how the passenger airbag may further limit access. I think a wiring issue is a real possibility that must be eliminated by thorough testing before continuing to more drastic measures. You may want to investigate what's involved in having BMW re-code or re-program your current ECU before swapping out critical modules as well.

 

[TH3R4POR]

No worries mate

I spoke with another couple of guys and the general thoughts were the ECU needs testing, so I have sent it to another ECU specialist to see if they can get something from it, next step after that will be loom chasing.

I was told by the BMW $tealer that there were a further 2 modules involved in the handshake, the EWS and the DME units, on speaking with the Master Technician he clarified the DMS is the ECU, there are only two modules involved. He was surprised they'd told me anything different.

 

[TH3R4POR]

Just had a call from ECU Testing.com, they weren't able to test it either, they haven't cracked the software on this particular ECU so weren't able to communicate with it.

He could only suggest hitting Google and ringing around for companies that might have cracked it.

EDIT: Just spoke with a thoroughly good guy called Andy from ECU Direct, he said he didn't want to talk himself out of a sale but if it were his car he'd put his money on the wiring. They also do a test exchange program where they can download my map onto a spare ECU and loan it out to me to see if the car runs, that's next on the list after the wiring.

Does anyone have any data on that part of the wiring loom?

 

[TH3R4POR]

OK, after 3 weeks of pain it’s sorted!

I bought a fault code reader from eBay which was delivered yesterday, and also got the wiring diagram from a BMW dealer principle friend of the company yesterday afternoon. I spent 2 hours with a multimeter checking all of the wiring from the ECU, earths etc and couldn’t find anything wrong which would indicate it was the ECU. As a last resort I thought I’d go over the original testing my mechanic did 3 weeks ago and confirm everything we were saying with my own eyes. I moved the plug and coil from the misfiring #3 to #2, reset the codes and the misfire moved to #2.... I then reset the codes and moved just the coil to #1, the misfire moved to #1, same when I moved it to #4.

£37 at Euro Car Parts this morning on a new coil and I just drove into Silverstone with a lovely smooth engine and no problem.

So the error was with the mechanic not the ECU

He's now denying ever telling me to buy a new ECU