Ignition cut-out

Doesn't this assume that it's mechanical motion of the
crankshaft or camshaft that actuates the tachometer? If so,
I'm not so sure I buy your reasoning.

I thought it was strictly a digital signal from the igniter
(in particular, its computer chip) that actuated the
tachometer. That is, the igniter computer chip certainly is
not actually sensing degrees of crank- or camshaft rotation.
Instead it receives signals from the ECU to excite the base
of the igniter's transistor yada, in proportion to the rate
at which the primary of the coil is supposed to be
energized. This of course determines the plug firing rate,
which will certainly determine, ordinarily, the engine RPM.
The computer chip "measures" engine RPM through on/off
switching of some kind (and so is digital and not analog in
nature?). I would think that the momentary signals from the
ECU at starting may very well cause something like noise in
the tachometer signal, causing it to jump a bit.

Again, Tegger's site puts a lot of emphasis on watching the
tach to diagnose a bad igniter.

 

Makes sense to me. If the ignitor's drive comes from the ECM and
clearly fires when the car is starting (one needs spark, after all),
you should see it on the tach, albeit at a very low frequency.

I had not read tegger's page on the ignitor in quite a while until
today. Seems like you can indeed tell by looking at the tach wheter the
ignitor is bad.
(That site is quite a great resource, isn't it? He's done a hell of a
job on it - can't get over that every time I visit it..)

Remco

 

Remember that the internal circuit of the "igniter" has an IC to measure
coil current("dwell")and provide the proper drive to the Darlinton current
switch. The tach drive could come from the IC. I haven't yet found the
exact IC number to provide a datasheet to examine,to know for certain.

 

But during CRANKING,the ECU reads the crankshaft (CK)sensor to determine
firing pulses to FEED the igniter.So,tach pulses are still dependent on the
ECU and engine RPM.

No,the crankshaft sensor is doing that.
Spark plugs fire -at a certain position of the piston in each cylinder-
,determined by the ECU,thru the CK sensor.Not by RPM.

You have it backwards.On *starting*(cranking),the CK sensor reads engine
crank position,and the ECU reads that and calculates the triggers for the
igniter.The starter determines the cranking RPM,the ECU reads it thru the
CKsensor (piston position)and triggers the igniter,where a supplementary
signal is tapped to run the tach.
BTW,the igniter fires the coil *4 times* for each revolution of the
crank,so the tach circuit divides by 4 to get true RPM,or the igniter IC
does that internally.Probably the latter.

The IC inside the igniter is to optimize coil current for hottest spark,and
provide proper base drive for the Darlinton.The coil generates it's HV on
the *shut-off* of the Darlington (that's the "flyback" pulse),not the turn-
on,which is only to *charge* the coil's magnetic field.The IC is there to
insure the coil gets a full charge no matter what RPM,that used to be
called "dwell time",the time the points were closed and charging the
coil,flyback and HV occuring when the points *opened* after charging the
coil.

 

I just omitted the effect of the CK sensor. The main
point--that the signal to the tach is digital and in
response to the ECU signal, and may be sufficiently
electronically yada noisy to yield some jiggling of the tach
upon starting--stands.

Yeahbut while starting, well within one camshaft revolution
the ECU is signalling the igniter, whose computer chip is
still signalling the tach.

I'm just saying ISTM there's some kind of signal to the tach
being generated, starting well within one camshaft
revolution.

I believe you mean for each /two revolutions/ of the crank.
It's a four-stroke engine; takes two revolutions for each
piston to have gone through firing TDC (in a four-cylinder
car) once; etc.

 

Today I was reading his fairly new "online OEM parts
sources" site. Quite an interesting read. I hope to try the
Colorado online parts store he lists sometime soon. Its
shipping appears a little more straightforward and may be
cheaper than Majestic's or SLHonda's. The parts prices
themselves look about the same.

 

FWIW, there's no real reason to "NOT" have it fire. There's just nothing there
to burn half the time.

 

Sure there is. For one thing, it would shorten the life of
spark plugs, wires, and coil, potentially by quite a lot.

Weird comment...

 

The only definite coil failures I've had have been a Nissan that gave one
"pop" when starting, then nothing, and my son's Acura coil that objected to
not having a place for the spark to go. Old time coils practically never
failed; like the old Mopar slant 6s, they didn't have the power to blow
themselves up. Modern coils run at much higher power and are no longer oil
filled, so failures are not unusual. My experience with electrical parts of
all sorts shows the pattern that power handling devices gradually cook
themselves one way or another. 200K+ miles on a coil certainly puts it in
the range of "untrustworthy," and when a contributor I respect says she has
seen intermittent failures in them before they die I think that's reason to
change it out on suspicion... while still investigating other possibilities.

I don't think I described it well. The surging was intermittent loss of
power, and of course she instinctively pressed on the gas to compensate. We
all know it rarely helps, but we all do it

A follow-up... the symptoms haven't returned yet. This model has a solid
ground to the chassis near the battery, and the battery negative cable also
takes the ground to the engine, so my concern that we left the ground loose
was unfounded. The ignition switch seems solid, but I'd like to check it
when it is cold, too.

Mike

 

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TOPIC: Ignition cut-out
http://groups.google.com/group/alt.autos.honda/browse_thread/thread/e8a5fd8cba927459
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Most interesting.



..

 

other possibilities.

Toss in that Tegger put this item's troubleshooting and
replacement, with quite a lot of detail, into his FAQ.
Meaning the coil's failure is reported quite a bit here.

My 91 Civic's first coil lasted ten years, 120k miles. My
one non-OEM coil lasted less than two years, about 35k
miles. Firestone charged me an arm and a leg for that
non-OEM coil, too.

'Course, let me be the first to point out that non-OEM
ignition wires may have played a role. Tegger's 1991
Integra, at over 240k miles IIRC, is still on its original
coil. He appears to take fastidious care of his ignition
electrical parts (rotor, cap, wires, plugs all replaced at
five years by him, all OEM IIRC). A lesson for us all, IMO.

I read the other day an article by Auto tech writer Larry
Carley. He also reported that not taking good care of
ignition wires will shorten coil lives.

This might not solve your daughter's car's problem. Again,
it's just where I would start. Though I would have taken
resistance measurements, per the manual's specs, on the old
coil before replacing it, too. Not that you have time over a
possible holiday to deal with this.

 

Meaning there's ON and OFF and no inbetween.

The jitter would be due to normal timing variation of firing pulses from
the ECU/CKsensor system,not from "noise" which would not affect a digital
signal.(after all,it's a closed-LOOP system.)
And the inertia of the digital to analog conversion to drive the tach
needle smooths out jitter.
The tach jitter is essentially meaningless,as the motor is not turning fast
enough to give a true indication of RPM,RPMs being below the minimum
calibrations of the tach dial.
Note I previously said "significant reading".

Actually,I think the RPM calibration begins at a few hundred RPM,then
linearly increases from there.

(well,the igniter chip is not a "computer" chip,it's analog;a current-
sensing comparator to insure a full coil charge,that "dwell" stuff.)

Yes,the tach pulses get generated,but not enough pulses or fast enough to
be significant.I haven't gotten a look at the specific circuitry of the
igniter IC to be sure that tach pulses would not be generated even if the
Darlington was blown and no current being switched thru the coil.The ECU
could be triggering the IC and tach pulses passed on,but no Darlington
drive or a dead Darlington.

You got me there.

 

Sure. I was being loose with "noise" and probably crossed
the line to inaccuracy.

AFAIC, noise can be a problem, regardless of whether the
system is closed loop or open loop.

For example, the ignition system has a radio noise condenser
in it (meaning, I hope as you know, this condenser reduces
interference with the ECU, the car radio, and probably the
igniter's transistors. Reports from two of our regulars here
are that this condenser's removal or aging can definitely
adversely affect ignition and so engine performance.

Meaningless as far as indicating actual RPM. Meaningful as
far as possibly using it to diagnose an igniter failure. Or
so it seems to me for now.

I don't agree or disagree with the rest. My only interest
was proposing that the Tach response could give an
indication of igniter mis-operation. No disrespect intended;
I prefer to get the bulk of my electronics lessons from
other than Usenet. It's too hard to communicate important
detail on internet boards.