|
|
Post by jeff on Dec 21, 2020 17:02:57 GMT
Took the car out for a drive today. First time I've used the blower.
When I got back I turned off the ignition before the blower and engine kept running for a couple of seconds before cutting.
Turn blower off and the engine stops As soon as key is turned.
I do wonder if it's anything to do with electrics being swapped from positive to negative earth.
How weird.. I'm sure I read something on this site but cant remember what the answer was.
Any ideas folks???
|
|
|
|
Post by Penguin45 on Dec 21, 2020 18:50:05 GMT
TommyDP had this problem. Thread's HERE. Not sure that he ever got to the bottom of it. Chris. |
|
|
|
Post by Penguin45 on Dec 22, 2020 0:01:46 GMT
I've just re-read that thread again properly (all these years later!) and realised that Tommy's motor was a two speed one. Green, and green and yellow are the power wires for low and high speed; there should have been a black earth wire somewhere. The motor appears to have been cross wired using two lives.
Chris.
|
|
|
|
Post by jeff on Dec 22, 2020 10:58:53 GMT
Thanks Chris
I will have a ponder and a look at the diagram. As it's only single speed it should be (theoretically)possible to sort out without creating a heating element in the loom.
|
|
|
|
Post by jeff on Dec 27, 2020 15:11:51 GMT
Hope everyone had a quiet Christmas. Now it's time to get my head back into the morass.
I've had a good read of TommyDP's old thread on this problem which like mine, only occurs following a polarity swap for the whole system.
The only progress I've made is that a reconditioned heater motor was fitted in 1989 and as these motors are not of a permanent magnet type, they "shouldn't " be polarity sensitive. I haven't swapped any wires over yet as I'm quite cautious so far and, it looks a pig of a job to get at. I'm more concerned with why the engine continues to run when keyed off with the heater blower running.
I'm puzzled as to why the coil should still be getting +ve after the the key is off for just a few seconds with the blower on.
I've studied the wiring diagram to find common connections from the ignition switch. Ignition coil, fuel pump, wiper, brake lights, oil pressure and filter lights and ignition warning/charging light, indicators.
The blower switch when on just puts and earth to the armature and the field coils.it runs but not as powerful as I'd like.
Ruling things out:
The day/night relay for the rear lights has its earth disconnected so cant operate.(dreadful design idea). All rear lights operate properly individually and together.
I fitted a 2 speed wiper which works and parks correctly.
The only common items I can see which takes both ignition switched and unswitched power is the RB340 control box and day/night relay. I'm happy all connections I can get at are sound including earths.
I'm now baffled as to why or how the white ignition wire is getting power for a few seconds after killing the ignition with the blower on, which simply earths the motor to complete its circuit. I'm even more baffled as to why it only seems to happen when a car has had its polarity reversed (and ignition wires on the coil swapped). I'm even more and more baffled as the why the engine cuts after a couple of seconds....what's holding power to the coil for a couple of seconds and then dropping off as it should?? Maybe the RB340 control box holds onto a connection until the dynamo dies?
I still cant see how the blower could affect the ignition unless the ignition switch itself is faulty.
Years ago, I swapped polarity on my MK2 and the blower efficiency or engine kill time didnt suffer.
I've read on MG forums about extending engine kill time being due to a faulty relay,or incorrect relay wiring, but no mention of the fault occurring involving blower, or polarity swaps. But, no such relay exists on my car.
All ideas are welcome, in particular if anyone else has come across the problem.
Jeff
|
|
|
|
Post by tonymark3 on Dec 27, 2020 16:09:31 GMT
The only other thing I can think of (apologies if you’ve already covered this) is it definitely electrical or is it running on? Used to have an awful time with my old mark 1. Seems odd it’s short lived.Does it keep running if you leave the blower switched on?
Tony S
|
|
|
|
Post by jeff on Dec 27, 2020 17:42:50 GMT
Hi Tony thanks for the reply.
The car doesn't run on (dieseling) it's in good mechanical order.
It only continues to run on for a couple of seconds if the blower is on. I'm out of ideas.
|
|
|
|
Post by jeff on Dec 27, 2020 18:08:32 GMT
Just braved the cold garage to try somethings and made an interesting discovery. Brake lights on, switch off engine. Instant kill. Wipers on, switch off, instant kill. Indicators on, switch off, instant kill. Blower on, switch off, engine 2 second delayed kill, blower goes off instantly. BUT...ignition warning light comes on bright until engine killed. Hmmmm?  Any ideas? |
|
|
|
Post by Penguin45 on Dec 27, 2020 18:20:10 GMT
How about a slightly off the wall theory? Motors can work as (inefficient) generators. So, whizzing away at 14vDC, cut the power, motor winds down over several seconds BUT if there is some sort of circuit, it will generate electricity.....
Chris.
|
|
|
|
Post by jeff on Dec 27, 2020 19:04:15 GMT
Good theory Chris. However as soon as ign is switched off, the blower stops a second or two before engine dies. Something is allowing coil to keep volts going
|
|
|
|
Post by dave1800 on Dec 28, 2020 4:57:02 GMT
This is almost certainly the clue. Just can't get my head around it yet! I assume you have a dynamo as you mention the RB340? David ........Blower on, switch off, engine 2 second delayed kill, blower goes off instantly. BUT...ignition warning light comes on bright until engine killed.Hmmmm? Any ideas? |
|
|
|
Post by jeff on Dec 28, 2020 11:12:39 GMT
Yes, it's a dynamo with RB340 control box..I know the ignition light will normally come on at engine kill until the dynamo runs down, which is almost instant. I think that's normal. So with engine kill delayed the ignition light will remain on until the death. That's as far as my now very scrambled brain has got.
|
|
|
|
Post by dave1800 on Dec 29, 2020 4:43:36 GMT
Still scratching my head! The back emf of the fan has got to be providing sufficient current to drive the ignition coil for a couple of seconds when the ignition is turned off (the ignition coil and fan motor supply leads are effectively joined). Chris made a video a few years back that I am trying to find showing the effect of reversing the leads on a fan motor and that particular version ran faster in one direction. Possibly by reversing the polarity it alters the back emf characteristic and accounts for why this phenomenon has only been reported after such a change? The reason I believe switching on anything else such as the brake lights kills the engine immediately is that they almost instantly absorb the energy of the fan. Clutching at straws I know, I'm not convinced the fan output would provide sufficient current to drive the ignition coil although a hot engine may not need much of a spark. The downside to my hypothesis is you noted the fan stops instantly! However as it is an inductor it does store energy that could feed the coil briefly - more straw clutching! The only way to resolve this is with a scope to take measurements I guess. David Yes, it's a dynamo with RB340 control box..I know the ignition light will normally come on at engine kill until the dynamo runs down, which is almost instant. I think that's normal. So with engine kill delayed the ignition light will remain on until the death. That's as far as my now very scrambled brain has got. |
|
|
|
Post by 1800heap on Dec 29, 2020 9:31:45 GMT
Hi Everybody
Its been a while!
I would like to float a theory which could be incorrect so correct me if I am wrong. It is in line with David's thoughts.
Motors will act as a generator while they slow down given. Motors also have commutator timing set. This is I think generally an advance set to make the motor more efficient in the direction that it spins. This is important for motors that run in one direction in service I think. If you reverse polarity to these motors this timing has the opposite effect so the motor runs quite a bit slower with reverse polarity.
Now for the theory! The timing of a generator is opposite to a motor. Retard makes them more efficient. Thus if the motor is being run in the wrong direction it works better as a generator than a motor and bang we notice the car running on!
Nick
|
|
|
|
Post by 1800heap on Dec 29, 2020 10:26:10 GMT
The theory would not apply to Jeff as I note after a second read he does not have a permenant magnet motor wired backwards!
Oh well back to the drawing board!
Nick
|
|
Any ideas?
