Re: Problem with 75 TS

[David Masters <david@domain.elided>]

jonathan coates   and  I are concerned for Anders' Twin Spark ....

Anders says ...
Symptoms:
I have seen (with a timing lamp) that it is missing sparks. Occasional 
sparks at
lower revs, just enough to see the lamp flicker, and the engine hesitating. 
When
revs rise to >2000rpm (or sometimes 4000rpm) the sparks are out completely 
until
revs are down below the limit again. I've checked on various plug wires, 
with
one or two coils in action and on the coil-to-dist wire. It seems as it 
misses
the sparks of a complete revolution(sp?) and not just for one plug at a 
time.
When the engine dies, there is no spark whatsoever to any of the plugs, 
which
make me think that the problem is not something around the coils/dists.

Checked things:
Resistances in the coils are ok.
No voltage drop from battery to coils.
Infamous 5 lead switch and relays checked and cleaned.
idle switch checked.
AFM checked.
Crank sensor has ok resistance and does give a voltage signal when the 
crank
turns. Only measured with a volt meter, I'll try to borrow an oscilloscope
tomorrow to measure the actual signal.
Then I'll also try to measure the ignition pulse signal from ECU to coils.

My potential culprits are now down to two; crank sensor missing the missing
tooth, or (God forbid) the ECU itself.

More hints anyone?

Clutching at straws, I say ...
Was that you who changed the rotor buttons?  I was most amused when on of 
mine failed a few months ago. Especially since it showed a healthy 
resistance, but was breaking down under the power of the spark.  Nothing 
showed on the timing lamp on either the plug leads or coil lead.  I felt 
just as frustrated.  The car would idle but make no power.  You could blip 
the throttle, but not load up the drivetrain.

Your symptoms seem similar.  (identical!?) I feel that because your car 
will idle, that there is nothing wrong with the crank angle sensor, or the 
ECU.  The coils are still questionable, but simple rotation should check 
that.  The temp sensor in the head has been known to cause strange effects, 
but even this seems far fetched.  You could pull it and clean it.

Have you put the coil wire to earth, without the distributor involved.  It 
should spark?

Cheers,
david masters - Newcastle, Australia
ALFA75 TS

------------------------------