Re: Problem with 75 TS

[jonathan coates <alfa@domain.elided>]

In message <36DB92F4.E958D462@domain.elided>, Anders Nilsson
<anders.nilsson@domain.elided> writes
>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.
Have you checked that the crank sensor is close enough to the teeth?
Is the toothed pulley clean, I'm guessing that dirt in the teeth will
not help.
It does sound to me that it is either the sensor or the ECU.
If you get the oscilloscope you should get a big peak from the missing
tooth, followed by a series of smaller peaks for the teeth.
BTW what is the imfamous 5 lead switch? Never heard of this.
Wild guesses follow:-
Making lots of sparks loads the ECU so that the ground connection is OK
for a few sparks but no good for lots, especially with the injectors as
well. Same goes for power feed.
Inductive sensor makes more volts with more pulses, or faster pulses and
when it makes enough volts it sparks across and stops feeding the
signals.

- -- 
jonathan coates

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