No Spark

[m-dtech]

Ok I cant get a spark

Engine was running some time ago but now wont.

I have taken a wire from the battery to the +ve side of the coil, tried another coil changed ht leads. still no spark.

the engine was running fine, dont understand how it can just stop ?

any ideas ?

[m-dtech]

i have replaced the rotor & cap

still no joy. !

help!

[craigieeb]

have you try'd replacing the coil?

if there is no spark there is not much it could be,
plugs,
leads,
cap,
arm,
coil,
power to the coil.

[m-dtech]

i have tried a spare coil i had from the 2.5 still no joy....

[m-dtech]

should there be +12v on the negative terminal ???

[x-works]

What year and engine is it? Do you have a multi-meter to check if the coil negative terminal is being switched by the ecu?

[m-dtech]

1985 m20 525e

yeah i have a multi meter.

ok so the negative gets switched by the ecu...

can i apply current to this to force it to spark ?

[x-works]

I've worked on a '86 325 with simlar problems and am presuming they have the same management system.
Before you try anything else disconnect the multi-plug from the ecu and reconnect it again, then try it to see
will it start. The coil is fed a constant 12v to the positive terminal while ignition is on and when the ecu sences
the engine is turning over it makes and breaks the earth to the negitive terminal to create the spark.
If you put the multi-meter in to "tach" position and conect one lead to the negitive pole of the coil and the other
to 12v, the multi-meter should read the engine rpm as it is turning over if the ecu is doing it's job correctly.
If it doesn't then there could be a problem with the engine speed pick up sensors, which, if it's the same as
mine, there should be 2 of them in the gearbox bellhousing. If these have gone faulty the ecu doesn't know
the engine is turning over and as such won't trigger a spark or work the injectors. Again you can do the same
test to see if the injectors are being triggered. Pull off one of the connectors to one injector,
there is two terminals, one will be a constant 12v with ignition on the other is the earth wire which the ecu
triggers to open the injector. Rig up the multi-meter the same way again to the earth terminal and see if it reads
anything while the engine is turned over. If there's a strong smell of petrol while turning the engine over
for a while it's probably an ignition isolated problem which narrows down the amount of things that could have
gone t i t s up. Hope some of this helps.

[m-dtech]

no petrol smell so im thinking its speed sensor..

on the auto box there is two sensors ?

can i test the sensors in any way ? is there a siginal from them ?

[x-works]

Still have never found a way of testing these sensors, sorry. Our rally car still gives this exact problem every once in a while and we've changed the ecu and sensors, when it happens now we just plug out the ecu loom and then reconnect it and she fire's straight up. Can't find the problem till I get some detailed wireing diagrams. Another problem we had which could be the cause of your troubles (which was highlighed to me by an ingenious member of this forum) is the actuall peices of metal that the sensors pick up on. The two sensors each pick up a signal from different teeth on the flywheel or i'm guessing the torque convertor on your autobox. One sensor reads off all the teeth on the starter ring gear, the other reads off one metal peg inserted into the flywheel. On our car the metal peg had become dislogded from the flywheel so the sensor had nothing to read off and as such the ecu didn't know the engine was turning over, hence no spark or fuel. When we removed the sensor and turned over the engine and looked in through the hole with a tourch you could see the peg was missing. These sensors work by using a magnetic field so if there's any metal crap stuck to the tip of the sensor it can mess it up.
The other thing that might be worth checking is if the ecu is powered up, is there any voltage at the throttle position switch or the idle control valve or airflow meter?