Another car, another problem - Page 2

Jim Warren wrote:

<snip tale of hot-starting problem>

Did the coil feel very hot?

If so, it's possible that someone has fitted a modern coil, designed to
work with a ballast resistor.  They soon get a bit warm with 12v across
them...


--
Kevin Poole
****Use current date to reply (e.g. jun2008@mainbeam.co.uk)****

Kevin Poole wrote:

The coil is mounted on top of the dynamo and behind the radiator, so
although it did feel hot, I put that down to the location.  It could be
a 6V coil working without a ballast resistor though.  I hadn't thought
of that.

I have ordered another one.  It will be interesting to find out whether
it runs cooler.

Thanks for the suggestion.

Jim

Kevin Poole wrote:

The coil did feel hot when it wouldn't start - but when I took it off
earlier today and checked the markings, it was definitely not the
ballast resistor type.

I have now fitted a new coil, and checked the rotor arm, which is
perfect, but has no maker's name, and the points gap is a generous 15
thou, but less than 20 thou.  It will probably be the weekend before I
get time to take it on a long run, but I did describe the symptoms to
Charlie Ware and he said it was characteristic of a failing coil.  So
the new coil should have fixed it.

Thanks for all the helpful suggestions.

Jim

Jim Warren wrote:

Back to the drawing board...
I took the car for a run - it started first time and drove perfectly.  I
eventually stopped at a shop, and when I went back to it a few minutes
later, it wouldn't start.  Again.

So I wandered off, and came back nearly 2 hours later and it started
first time.  But when I put it in gear ready to drive off, the engine
died.  And didn't restart in the couple of tries.

So, a chance to do a bit of diagnostics.  I put the starting handle in,
took the HT lead running from the coil to the distributor off at the
distributor end, held it near a cylinder head nut and turned the handle.
  A nice fat spark!  I put it back on the distributor, turned the
starting handle to line it up to remove it - and the engine started.
And I drove home.  No problems, no misfires, it drove normally, and I
parked it.

So I switched off the engine, counted 20, switched it back on - and it
wouldn't start.  I put a multimeter across the coil LT and it showed
battery voltage then 0V alternately as I wound the starting handle.
Again the HT lead from the coil gave a good spark.  I tried No 1
cylinder HT lead which is the shrouded type, and got a nice jolt up my
arm at the appropriate time.

Yet still it wouldn't go.  While I was doing all this, the petrol pump
ticked occasionally, so I know the pump points aren't corroded.

So now the electrics show no faults, the spark is generous, proving that
there can't be much wrong with the condenser or points, and it is a
brand new coil.  And when the engine starts, it runs normally which
indicates the plugs are OK, it is just that sometimes (when the engine
is hot) it won't start.

Have I missed anything on the electrics side?  If not, then the problem
has to be fuel - either a vacuum in the tank, a blocked petrol pipe or a
dodgy needle valve are the next to be eliminated.  Unless anyone has a
better idea?

Jim

Jim Warren wrote:

Vapour Lock in the fuel line?

Stuart H.
** Posted from http://www.teranews.com **

Stuart H. wrote:

That is a possibility I haven't checked for yet, but I would have
thought the electric fuel pump would tick rapidly if it was trying to
move vapour rather than petrol.  Also, the incoming pipe to the pump is
a reasonable distance from the engine and manifolds - though I admit I
haven't checked how close it gets to the exhaust along its run from the
tank.

It is certainly worth checking for.  And when I left the car last night,
it was still refusing to start, so it will be interesting to see how
much fuel is in the float chamber before the pump refills it.

Jim

Jim Warren wrote:

You can pull the hose off the float bowl and check the flow also the
pump pressure is very low for the SU carby.

Secondly if you tap the side of the bowl and it starts the pump ticking
rapidly its a sure sign its empty or if it overflows its a needle and
seat problem.

Rob wrote:

Thanks.  I am fed up with dodging the showers today, but I will try
that.  Also, I notice that the pump has a filter which could be blocked
- I will check and clean that too.

Jim

Jim Warren wrote:

Just as a suggestion, this happens to my MG. I only drive it
infrequently, the batteries are not charged very well, it will start
when cold, I can drive it some distance etc and when I stop, can't
restart the motor, will turn over on the starter but not enough the fire
the spark.(hills and a push start help after that), Have found that
there is not enough power in the batteries to do both, turn the motor
over and fire the ignition, placing the car on charge fixes the problem.

So my questions are:

Is the battery in good condition??

And have you tried a push start??


You may want to check the fan belt and charge rate as well.

r

Rob wrote:


The battery is fine.  It always turns the engine over quickly with no
sign that it hasn't got enough charge.

Not a push start, but it has got a starting handle, which will start the
engine if it is going to start, and won't start it when it refuses.

The fan belt looks quite new.  It is adjusted properly.  The car has a
dynamo and regulator arrangement, and the ignition warning light behaves
the way it should and the battery has always got plenty of charge.

Jim

That doesn't necessarily mean a lot - check the battery voltage while
cranking. If that falls below 10V on a 12V system you may have a
problem.

What's the battery voltage with the ignition off?


Did you measure that or do you infer that from observations?

Timo Geusch wrote:

I will check later today and report back.

Again, I haven't checked exactly this.  But with the ignition on last
night, I was getting 12.6V across the coil terminals.

The first time it failed to start (last week), I used the starter motor
and 1st and reverse gears to park the car tidily.  There was enough in
the battery to move the whole car like that, which is a pretty clear
indication that I haven't got a weak battery.  Also, a weak battery will
either spin the motor slowly or reduce the speed it turns it over after
several tries.  There is no sign of either.

Jim

Hmm. Check the voltage at the battery terminals - a fully charged 12V
battery should have around 13V-13.2V if it's good. If you get around 13V
at the battery but 12.6V at the coil, you may have a couple of corroded
connections that increase the resistance in the circuits.

Trouble with added resistance is that is heats up the affected
connectors, which may increase resistance over time. The symptoms you
describe suggest that heat may well play a part in the non-starter
scenario.


Yes and no. I was wondering if you had a dead cell - I've had that
before, one cell was dead and the others were OK, so your basic checks
suggest that you've got a working battery, but it won't play ball that
well with the starter cranking, even though you don't get any of the
obvious duff battery symptoms. But your 12.6V mentioned above pretty
much rules this out.

Timo

Voltage drop, check by bridging the fuses and starting off the solenoid,
bypasses the ignition switch circuit. Which is the most likely source of
voltage drop.

This is the most common way and I would suggest this is the problem.

Gee its a Morris Minor there ain't much to go wrong. :)

You're not wrong about that :)

Rob wrote:

Or run a wire direct from the battery to the coil? Then it also avoids
any bad connections in the circuit.

Willy Eckerslyke wrote:

Yes, that is one of my To Do list.

The trouble is that the car has now cooled down and the problem will
have gone away, so further diagnostics will have to wait until I have
time to take the car on another decent run.

Jim

Timo Geusch wrote:

Bearing in mind that the battery is definitely not fully charged now - I
spent nearly an hour last night turning the engine over checking sparks
and voltages and I haven't put any charge back in it yet.  A meter
across the battery terminals showed 12.5V late this morning, ignition
off.  This dropped to 10.4V when the starter motor was turning (again
with ignition off)

I have seen this with a dropper resistance on a Triumph.  The Minor
hasn't got a dropper though.
I will follow up Rob's suggestion of cleaning the connections to the
fuse box. A couple of the spades looked as if they could do with a clean.
Unfortunately then the showers started, so I have given up for today. It
is pointless trying to sort out starting problems with wet electrics.


I will have to go for another run to get everything hot before I can
experiment any further - it always starts first time when cold.  So I
will measure it again when it is charged up.  But I have had a dead cell
before (in another car, a long time ago), and it definitely affected the
cranking speed.

Jim

Jim

Small spark insufficient to fire the motor.

Then, whats the compression like?   No compression when hot, also makes
starting difficult.

Thats just to throw another spanner in the works :)

r

Rob wrote:

According to the documentation that came with the car, it had a full
recon engine 2 years ago.  Plenty of compression felt when turning the
engine on the starting handle.  I will, in desperation, check with a
compression tester, but I really don't think it will show a problem.

A nice fat spark is seen at the end of the coil HT lead, though I admit
that I haven't observed the spark at the end of a spark plug lead.
Something else to check.  Thanks for the hint.

Jim