a serious electronikery question

[randomdave325]

hello all. as some of you know i am having major problems with an e34 535. not strictly e30 but it uses the same system so would be the same fault effectively. the problem is a really weak spark from the coil. i asked on a few forums about this problem with no help at all. the zone is the only bmw site worth using in my opinion. i took the ecu apart last night as it is the only componant left. it's a bosch motronic unit no. 0261200179. now i'm no electronics engineer but on close inspection i found 2 resistors??? capacitors??? which appear to have got hot at some time. the numbers of their locations on the pcb are R400 and R401 they have 30R10% written on them. what i was wondering is can anyone tell me what they are? and could they be causing this fault (due to a high resistance?) i've taken some pictures which are below. i know some of you get involved with ecu's i.e chipping etc whereas i'm more of a spanner man. any help would be appreciated as it is doing my head in. i'm gonna plug a spare e30 325 ecu into the loom to see if it does anything. it might do something as they use the same system. just 1 decent spark would cheer me up no end.
heres the pics

the 2 in question!


from another angle (if you look close you can see the insulation is splitting)

location on the ecu pcb

where they solder to the pcb. they look like they have got hot by the solder joints compared to the rest of the board

i've had to type this out twice now as deleted the first one by accident. this really is sent to test me

[Ant]

ECU is basically the same unit, remove the chip from the M30 unit and install in the M20 unit, fit and enjoy dude.

The chip is the only removable onr on the PCB so its an easy swop

[randomdave325]

ant you are a star . i'm on the mo fo. whats the best way to pull the chip out? i've got the plastic thing off but the chip itself kinda likes it in there and i dont want to force it

[randomdave325]

sussed it now m8 (but then i think you knew i would anyway init) just got to go an plug it in now. fingers crossed! i'll keep you posted. thanks

[Toby_Unna]

sorry to suggest daft things which you've probably already checked.

but i'd be looking at the wiring from coil into the engine loom with a multimeter. i guess one of the coil connections goes to ground and one to the ecu.

the car supplies the engine loom with a coil-on 12v feed when you turn the ignition 2 clicks, maybe this is the problem? or the coil's ground connection is poor?

does the car run?

[cros]

No knowledge about these ECUs, but 30R is a 30 ohm resistor, and from the photo it's a high wattage one that'll be be involved in some output stage (injector/coil driver etc.). ...especially as it's near the heatsinked power amp/transistor.

A resistor with that kind of value and slack % tolerence is most likely some kind of current limiting or short protection job.

[Andy335Touring]

I'm not 100% sure but i think the positive for the coil is non-switched with the engine running and it's the negetive thats switched by the ECU to control the coil ?

If you get stuck i've got an manual E34 M30 ECU you can borrow.

Mines also got those resistor things.

[randomdave325]

thats for the advice lads but shes a goer . plug in the remixed 325 535 ecu and she fired up within 2 turns. been fully abusing the 3.5 lsd action today. i neeeeed a diff in the black one. spoke to the bloke i got it off and have got the tax back. 6 months fo £40. result! and it's moted till may. it's cost a total of £60 so far with a load of labour. i pick up a grey leather interior for it tommorrow for a ton. just need a atlantic blue bootlid and shes a minter. i'm gonna use it for a bit then flog it. the black thing looks upset already! seriously tho. big up to ant for sorting my ecu probs. without him it would still not be running and i would be trying to find an ecu. i knew the massive stock of e30 bits would come in handy sometime or another. nice one ant. i owe you a pint!

the sixty quidder. well up for diff abuse