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Crank sensor, or DME / Fuel Pump relays having dry joints inside are common possibilities.
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i have tried using the king lead too, again there is no spark, i will check the others shortly, still don't understand why they would just fail though, would the fuel pump relay prevent spark?
chris
Edited by thomp1983 on 19/01/2009 at 10:29
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ok a few readings for you,
crankshaft sensor - 3 wire inductive type
resistance 497 ohms with the meter set to 2000
voltage 4.3v with the meter set to 20
according to the details on autodata the resistance should be roughly between 575-750 ohms and the voltage 2-8v so those figures aren't far off so i presume the sensor is fine
ignition coil
supply voltage 12.3v with the meter set to 20
primary resistance 001 ohms with the meter set to 2000, basically getting no reading for this
secondary resistance 5.42 ohms with the meter set to 20k
looking sat those figures im assuming the coil is dead, anyone else care to confirm this?
cheers
chris
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I had a coil fail(not on a BMW)after a lot of starts with little running.I think coil was aleady on it's way out and starts were putting 12v. into a 8v. coil repeatedly and this finished it off.
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well i sourced another coil today which does meet the autodata figures and ive still got no spark so where do i go next?
chris
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Put a test lamp (preferably a low current device like an LED) across the coil, and see if the ECU is switching the coil on and off while cranking. If not;
Check the continuity between the coil low tension and the ECU.
You have tested 12v at one side of the coil, and the ECU switches the other side to earth to make the spark. This might be a wire which is interrupted if there's an alarm or imobiliser fitted, to prevent the engine starting.
If the ECU isn't switching, and the wiring is all OK (including all ECU earths), then I would probably send the ECU to be tested, with an explanation that it's the ignition side that's causing the problem.
Just to double-check - you are sure that the injectors are pulsing correctly?
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how would i check if the injectors were pulsing correctly? im going to have the crankshaft sensor off later to clean it up as there's alot of oil around that area from a previous leak.
there are no alarms or immobilisers, it was all removed some time ago when i was tidying up some bodged wiring, the car has run subsequently since then too.
when you say put the led across the coil is that between the +15 terminal and the -0 terminal the other side or between the +15 and the pin the king lead attaches to?
literally it coughed and spluttered whilst cranking on monday but wouldn't fire, it was flooded, cleaned up the plugs cranked it over for 15 minutes or so with the fuel pump fuse removed, replaced the fuel pump fuse and now i have no spark, im not sure what could of changed or why something has suddenly die when i must of had a spark of sorts the day before to get the spluttering.
cheers
chris
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put the led across the coil
Yes, across the coil LT connectors. You should find when you rurn the ignition on, the LED should be off, and then, as you crank, it should flash.
You'll need a 12v LED (or an ordinary LED in series with some thing like an R330 resistor). Of course, you need to put the LED in the circuit the right way round!
For checking the injector pulses, I use something like this;
www.drapertools.com/b2c/b2citmdsp.pgm?pp_skmno=577...8
It's worth checking the wiring carefully - fixing wiring tends to cost pennies, whereas replacing fuel injection parts without reason isn't a cheap hobby!
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right ive tested both coils with the led, neither of them cause it to light up, would a faulty coil cause this or just an issue with the ecu/ ecu wiring?
cheers
chris
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the original and the replacement i sourced, ive now got doubts as to whether the original coil was faulty at all or if the fault lies elsewhere, so tried the led test on both units.
chris
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Chris,
Testing across the coil wasn't at all a test of the coil - it was testing the rest of the circuit, from the live supply, to the earth path through the ECU - only a coil with a direct short between its 2 low tension terminals could negate the test.
Your LED does work when connected across the battery?, and you did have it connected the right way round?
If you haven't seen any voltage across the coil terminals while cranking AND the injectors are pulsing, then, it's back to the fault finding list I posted higher up.
The reason I asked about the injectors pulsing, is that IF they are pulsing, then, you KNOW that the ECU is being powered up, and is detecting the rotation of the engine properly.
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i checked the led worked, and i had it the right way round. in the morning i will test the wiring from the dme to the coil, along with the dme relay aswell.
chris
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No spark on these is often caused by a failed ignition coil drive transistor in the engine Ecu.This is usually the only item that gives problems on these old Bosch control units.hth
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do you know of anyway of directly testing for this, or is it a case of eliminating everything else first? i assume a new transistor would be available from somewhere such as farnell or rs?
chris
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>>No spark on these is often caused by a failed ignition coil drive transistor in the engine Ecu.
Yes, I've been suggesting checks to make before condemning the ECU. It's always a hope that if it is the ECU, that it's only the power transistors which have failed.
However, Chris, continue with your fault finding, to make yourself SURE - don't revert to poke and hope at this stage!
Checking the wiring between ECU and coil for continuity, and shorts to earth, is after all only 10 minutes work with a multlimeter!
Edited by Number_Cruncher on 21/01/2009 at 20:33
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ok i finally got the chance to do some continuity testing the results are as follows,
ignition off,
+15 on coil has continuity to pin 87 on the 5 pin dme relay
-1 on coil has continuity to pin 87 on the 5 pin dme relay
ignition on
+15 on coil has continuity to pins 86 and 30 on the 5 pin dme relay
-1 on coil has continuity to pins 86 and 30 on the 5 pin dme relay
ignition off
pin 87 on the 5 pin dme relay has continuity to pins 3,4,16,17 and 22 on the connector to the dme ecu
pin 85 on the 5 pin dme relay has continuity to pin 36 on the connector to the dme ecu
pin 87 (centre pin) on the 5 pin dme relay has continuity to pin 37 on the connector to the dme ecu
pin 86 on the 5 pin dme relay has continuity to pins 13 and 18 on the connector to the dme ecu
pin 30 on the 5 pin dme relay has continuity to pins 13 and 18 on the connector to the dme ecu
i haven't checked for continuity with the ignition on for the ecu connector as a) i wasn't sure if it would damage anything and b) i don't know if anything would change as i assume that the signals go through set pins to the ecu which then sends the relevent signals back out through different pins?
i also haven't checked for shorts to earth in the wiring as i don't actually have a wiring diagram so i can't be 100% certain as to which wires should or shouldn't be earthed.
cheers
chris
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I should have explained in more detail.
First, always do continuity checks on dead circuits, never live ones, so, the ignition should stay off.
You aren't too bothered by pin 15 in the coil, because you KNOW that it gets a 12v supply - you had already tested for this.
What you aren't sure about is the path from pin 1 back to the ECU.
Disconnect the wire at pin 1 from the coil, and check its continuity to the appropriate pin on the ECU connector.
Do you get continuity?
No - find the break in the wire, or the bad connection, and fix it
Yes - move the multimeter contact from the approriate pin on the ECU, and connect it to earth - you should read a high resistance
You read a low resistance - unplug the ECU - does the value change?
Yes - there's a short to earth in the ECU, have it sent away to be tested, or, if you're bold, have a look at the ignition drive trnasistors yourself
No - there's a short to earth in the wire between coil and ECU - find it and mend it
You read a high resistance - the wiring checks out. Send the ECU away for testing, or, if you're bold.....
I don't know which pin on the ECU you need to check - either consult a wiring diagram, or follow the wire colour codes and the wire back from coil to ECU.
I hope this helps,
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thanks for that nc it gives me something to do in the morning.
as another thought ive just been reading through a basic workshop manual i have for the car and have found that there is a cylinder recognition sensor on spark plug lead no. 6 (ive noticed it before and never really thought about it) would having this effectively disconnected (im using the plug in the end of the king lead, and the car is rotor arm less at the moment) cause the ecu to to tell the engine not to fire as it can't detect at which stage of the cycle it's at?
cheers
chris
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Don't worry about the cylinder recognition sensor ,this will not cause a non-start.If I recall,this wire goes back to the diagnostic plug.hth
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>>Don't worry about the cylinder recognition sensor
Yes, I fully agree. IIRC, it allows the ECU to switch to sequential injection mode - without it, the ECU reverts to ganged injection, like L jetronic. Nothing to worry about.
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thanks very much, it was just a thought. ive managed to find a very comprehensive wiring diagram for all of the cars systems, it shows all the wiring paths, pictures of all the different wiring connectors with pin numbers, descriptions of all components locations along with pictures and diagrams of all loom splices and there locations too.
i quickly checked the continuity of the -1 on the coil to the ecu plug and there is continuity between pin 1 on the ecu and -1 on the coil with a very low resistance. i had the ecu out and apart earlier, after a quick inspection i can't see any immediate signs of blown components or damaged tracks, or dry solder joints although i haven't had chance to check it with a magnifying glass. i will likely just reflow all the joints anyway and see if this helps, if not i know a man who will be able to look at it in more depth and diagnose if any of the components are faulty.
and alongside the above i will be using the new found wiring diagrams to follow the whole starter circuit from the ignition switch and hopefully the fault will become apparent.
another small question, the diagrams show a crash detection sensor on the drivers side wing, would this cut just the spark? id suspect it would actually cut the fuel and spark if triggered, or is it a sensor for setting off airbags in the event of an accident?
chris
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I have been to many non start BMW where the batt is in the boot & they give a symptom of no spark but spin over fine. I have even been to two where they spin over at speed but no spark & they have had a tyre depot battery fitted.
BMW's with rear end batterys often require the full monty ( a monster quality & heavy duty) due to the voltage drop from rear to front.
I remember going to one where the owner had fiited a brandnew battery & it still didn't start & i took along the BMW recommended one, dropped it in & fired straight up!
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if it still has the old type air flow meter flap ( yours should be air mass meter ) check the flap hasn't got stuck due to corrosion in the aluminum due to standing
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it does have an air mass meter and it was fine when i last checked it over a couple of weeks ago (was trying to even out the idle a bit so went over the whole induction system, it's now as good as it'll get with the exhaust that's currently on it.)
as for the battery, the battery has had a charge for at least 12 hours a day for the last week or so to keep it topped up as it's been severely cold the last month or so and i didn't want it dying where it's been stood, also all of the battery and charging cables have had new runs of 0 gauge cable ran alongside the oem wiring to reduce voltage drop to a bare minimum for the stereo system im installing so id be surprised if it were a battery issue but i will also try starting it whilst connected with heavy duty jump leads to my step dads diesel focus.
chris
Edited by thomp1983 on 23/01/2009 at 20:51
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quick inspection i can't see any immediate signs of blown components or damaged tracks or dry solder joints
Very few components fail with physical damage - this will only occur if they have overheated owing to miss-treatment or poor design.
Now that you've had a proper nose and confirmed the ECU, if you can find the switching transistor coming off the coil wire then you will do no wrong by replacing this first - the numbers written on the side will tell you what type it is. I suppose you could make sure by testing it in-situ to make sure you have switching at the base. Got an oscilloscope?
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no unfortunately an oscilloscope hasn't made it's way into our family of tools although i do keep meaning to get one for setting gains on amplifiers.
i will try and trace down the transistor tomorrow and see if i can spec a replacement for it, with any luck the local maplins will have a suitable replacement in stock and i can get this resolved tomorrow, if not ill have to get one from rs or farnell to be delivered during the week, they are cheap enough to have a punt at replacing on a whim.
of course that will come after i have been back over the wiring and sensor system again to double check it now i have a decent wiring diagram to refer to.
chris
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I suppose you could test the transistor base switching yourself using a generic transistor/LED circuit wired onto a bit of stripboard. I wouldn't use the LED by itself mind.
any luck the local maplins will have a suitable replacement
I stopped shopping at Maplin about 4 years ago since they got rid of lead solder - now it's mainly RS, Farnell (CPC) or Rapid I go to.
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ok so boredom has struck, friday telly is just a waste of time, so ive done a bit of testing on the ecu.
just to check im right here, digital meter set to diode mode, to test transistor then the following should be right, (shamelessly stolen from google)
The base-emitter (BE) junction should behave like a diode and conduct one way only.
The base-collector (BC) junction should behave like a diode and conduct one way only.
The collector-emitter (CE) should not conduct either way.
so ive located 3 transistors on the ecu (helpfully they've got b,c and e marked on the pcb) and ive got the following results,
transistor 1
BE conducts one way
BC conducts one way
CE conducts one way
transistor 2
BE conducts both ways
BC conducts one way
CE conducts both ways
transistor 3
BE conducts both ways
BC conducts one way
CE conducts both ways
now presuming what i have read is correct that would mean all 3 of the above transistors have failed? would that be correct or am i missing something?
cheers
chris
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you have checked that the distributor is turning when you crank the engine over
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It would be interesting to see the circuit diagram - is it available online?
you have checked that the distributor is turning when you crank the engine over
He has checked and he isn't getting any power to it. Though there's no harm checking to see if there's been an unfortunate coincidence.
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the wiring diagrams for the car circuits are at, tinyurl.com/ah2xrw they don't show a circuit diagram for inside the ecu i can't seem to find one for that.
unless im missing something the car doesn't have a dizzy, the rotor arm is driven directly off the end of the camshaft, the coil wiring goes back to and is fired by the ecu i believe no dizzy in sight, the rotor arm did turn before removal though yes.
chris
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>>you have checked that the distributor
There isn't one as such - just a rotor arm and cap. Even if this were not turning, there should be a spark from the coil king lead - there isn't one.
Chris - when you tested the transistors, did you remove them from the pcb? If you didn't, then it's highly likely that you have been measuring a parallel path as well as the transistor itself. In other words, your results might not be as meaningful as you might think.
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no they were left in situ on the board, i haven't got as far as actually disassembling the ecu's pcb yet, not going too till later this afternoon once ive gone back over the rest of the systems in the car to make sure i have missed anything or that no wiring is damaged.
chris
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afternoon, i have now removed the only transistor i could find that has continuity to pin 1 of the ecu which we had identified as being connected to the -1 on the coil. after testing it off the pcb as per the same method as earlier in this thread the transistor is indeed dead. now ive taken a photo which can be found at the link below (it had 3 legs when i tested it, i subsequently dropped it, sorry about the picture only have my mobile available.)
tinyurl.com/bupneh
if someone could take the time to spec me another transistor to replace this one that would be great, preferably from maplins so i could get one either today or tomorrow if not then from wherever. the numbers on the transistor are, top left 221, top right 1489, bottom centre 30004 they are the only markings apart from what i assume is the manufacturers logo in the centre.
cheers
chris
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You won't get one of these - it's a Bosch special with an in-house type number. 1489 will be the date code (week 14, 1989).
At a guess it will be a high voltage npn Darlington. If it's short circuit, that's a fairly definite diagnosis but there is always then the risk that a shorted output device will have caused damage further into the ECU.
Because Darlington transistors have multiple junctions, simple continuity tests with multimeters, especially those without diode test facilities, don't always work. I think that without detailed information, adequate test gear and access to the correct spares you are getting into deep water here.
659.
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>>You won't get one of these
Yes - it's now time to pass the ECU to a specialist ECU repairer - or ask them if they have the transistors available as a first pass.
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this is the multimeter ive been using, tinyurl.com/c2kblm i tested the transistor with the diode mode, it does have a transistor testing bit on it but i didn't use it as i have no idea what the result would of meant.
who do recommend using for ecu repairs? do you know a rough cost?
chris
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another quick question, i have managed to find on ebay another ecu from a working car with the same bosch part numbers on it, do we think it'd be worth a punt at £20, as id have it this week and could then see if this is the definate cause, then send my other unit away for repair at a later date?
cheers
chris
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Definitely worth a go for £20.The beauty of these old dinosaurs is the control units are not coded ,so just hook on a s/h unit .As for a repair,I would suggest Avilec electronics on the Isle of Wight.hth
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I would also agree subject to there being no vehicle fault which could have caused the original damage. Although ignition output stages are current limited and therefore theoretically short circuit proof, I would isolate terminal 1 at the coil and also at the ECU connector and check the wiring for shorts, particularly to B+.
A careful examination of the coil itself might be worth making. Most ignition Darlingtons seem to be killed by over-voltage, so check that the HT secondary circuits are in good order and don't operate the system with an open secondary circuit. Check all HT leads for continuity.
The TO-220 device shown in your picture should have the centre leg connected electrically to the tab, so if it were to be functional, you could still use it. A short is pretty final though...
Go carefully and you may well succeed - best of luck.
659.
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well after all the usual trials of ebay an identical ecu arrived in the post this morning, and the verdict is there is now spark at the king lead! so now i just need to pick up a rotor arm this afternoon and all should be running again.
thanks for all the help guys,
chris
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