WHLST ENJOYING A ENTHUSIASTIC DRIVE IN THE BEEMER, THE ENGINE CUTOUT AND WOULD NOT RESTART. ENGINE SPEED AND POSITION SENSORS CONFIRMED OK BY BMW. COIL AND ECU REPLACED BUT STILL NO SPARK

WHEN IGNITION IS ON THERE IS 12V ON EACH TERMINAL OF THE COIL, BUT WHEN ENGINE TURNED OVER THERE IS NO SPARK FROM COIL.

WHEN THE TWO WIRES ARE DISCONNECTED FROM COIL, 12V PRESENT ON GREEN AND 0V ON BLACK.

THE CAR IS AN 87 325I SPORT WITH MOTRONIC INJ.

ANY HELP APPRECIATED AS WE ARE AT A LOSS.

Hi,

Your test of supplys at the coil is ok. The coil should be earthed through the ECU to induce a spark. If you put a volt meter on the neg side and crank, what do you see? The problem you have here is that a meter can not read fast enough to capture the switching action. Since you have tried a new coil and you have a supply then the fault must lie with the earth side of the circuit. Either you have a wiring problem or the ECU is not switching the coil to earth. With the latter, this could be for any number of reasons. You should check the wiring from the coil to the ECU and ECU supplys and earths.

What way were the sensors checked?

If you flick the starter ie. just barely enough for the engine to jerk and listen, can you hear the fuel pump run?

If you switch the key to the run position can you hear the pump run?

Do you have supply at both sides of any or all injectors with the key on?

Do you have a 5v supply to the coolant sensor (blue one with 2 pins)?

Alan

alan,

cheers for the advice, will check this afternoon and get back to let u know how i got on.

cheers.

alan,

had a quick look at car thisafternoon but due to rain didnt get much done.

we confirmed 5v on coolant sensor, checked two injectors for voltage but none present(is this due to engine position?) couldnt gain access to others. traced green wire on coil back to ignition barrell switch, wire continuity ok-insulation ok. could the ignition switch be at fault?

can u advise on how to check ecu earth is ok and how to check if ecu neg supply ok(plus 12v present on pin 35)

any info welcome, many thanks.

Hi,

First off I should say I dont see many of these old ones any more so bear with me as I exercise the old grey mater.

The injectors are supplied from the fuel pump relay, as far as I can recall they should have supply key on engine off but for sure they should have supply engine cranking. Engine position has no effect on this.

Lack of supply to the injectors is a good clue in this case. Check the fuel pump works as suggested above. If not, then the crank sensor would be my next thing to check. As I asked above, in what manner were the sensors checked. The reason I would suspect the crank sensor is that if the ECU does not see a valid signal from it then it will not trigger the relay so no supply to the injectors, it will not trigger the coil so no spark and it will not trigger the fuel pump part of the relay. Another reason is that these fail often. The relay itself also gives trouble.

At this stage the crank sensor is only a possible cause.

There are at least 3 earths and at least 2 pos supplys to the ECU. I would have to dig out the pin numbers to tell you which ones. The best way to test an earth is something that you should not do unless you are sure it is an earth, unless you are happy to roast something. It involves induceing current flow through the earth wire in question to check its ability to carry that load.

If you can check the above you may fix it or at least be closer. Let us know how you get on.

Alan. 

alan,

have been having a look at the car today and can now confirm we have voltage to the injectors with key 'on' and when engine cranked. removed position and speed switches measured resistance on pin 1 and 2 found to be 860ohms which is within spec given in haynes manual. actuated swithes while measuring on pins 1 and 2 and confirmed resistance changed when a metallic object is passed over the sensing head of the switch.

a few questions; the green wire from coil traced back to ignition barrell, could this switch cause a problem, and will this wire then go back to ecu?

traced injector supplies from battery through relay and to injector and then back to pins 14 and 15 on ecu, how can i confirm ecu is switching to earth (or neg)?

and can u tell me what the unit above the glovebox is which has an ecu type connection?

at this time we have;

5v on coolant sensor, voltage on injectors, speed and position sensor resistance in spec and continuity to ecu pins ok, coil primary and secondary resistance in spec, but still no spark from plugs!!!!

any info appreciated!

Hi,

I am pretty sure the coil is not fed directly from the ign switch. However, you have already said that you have 12v on coil so no real need to worry about that. The 12v that you have there should go to the pos side (sometimes marked 15). This supply travels through the coil and is earthed by the ECU to switch the coil on and off. As this happens very quickly it can be hard to see on a multi meter. if you have a dwell / duty cycle meter, use that to check for some kind of action on the neg side. If there is no earth being applied then the reading on your meter will not change. The only way to measure this is with a scope.

I assume that you have checked the spark at the coil tower first, and not just at the plug leads so as the bypass the king lead, cap, rotor and leads?

Your method of testing the coil and sensors is not too good. These can really only be tested with a scope or changed for known good parts.

As with any electrical circuit, you have to start at one end and prove it all the way through. Chech that the 12v from the coil neg is present at the ECU. if it is then check as best you can if this is being switched to earth. If at this point you are sure it is and you have tried a new coil then it would be safe to assume the ECU is not switching the coil. You must be sure of the above tests of going further could be a waste of time.

The ECU will not switch for one of the following reasons -

Lack of one or more pos supplies.

Lack of one or more neg's

Lack of a valid signal from the crank or cam sensors

The reason i suggested that you check that the fuel pump runs is because the ECU will not trigger it's relay unless it sees a valid signal from the 2 sensors. 

Alan

alan,

i have checked the car for the things you have suggested, all seem ok but still no luck. have heard on the grape vine that the tag on the fly wheel  which the position sensor looks at within the bell housing can come off. this then causes no signal from the position sensor.

there is supply to the injectors but they cant be heard to 'tick' when engine cranked.

fuel pump in tank and secondary fuel pump in engine bay run when engine cracked

have hand cranked the engine and found what looks like a pin laying horizontal within a circular recess on the flywheel. is this what the position sensor looks at or is there supposed to be a raised tag which may of fallen off?

please advise, if this doesnt work its going in the river.

cheers.

well guys i'm pleased to say she is running again, after a visit to bmw and a supposed bmw specialist who were'nt much help -we have sorted it ourselves. it seems the tag has somehow came off the flywheel, therefore sensor not sending signal to ecu and no spark etc!!!! we have a secondhand flywheel on the way and will put in a new clutch while it's all in bits. we have decided to turn the car into a bit of a track machine (as a new e30 325 has been purchased)which brings me onto my next subject; TUNING, anyone tried any tuning on a e30 325i and what gives best bang for ur buck?

cheers for the replies and tech help.