loss of power

[kimbest88]

Took our t25 on her first trip out took her to Whitby 3hour drive drove fab untill 3 miles outside campsite where she died and would not fire back up rac came changed the amplifier didn't work put old one bk said it was the coil so changed it and whoooop she lives gets us half way home and starts to lose power like running out of fuel then cut out but started straight bk up so filled up to be on safe side but she did it 3 more times then she didn't fire bk up ....... No spark being produced so played with wires attached to amplifier got spark fires bk up on way again loss of power while engine running I played with wires but engine carried running any ideas what's wrong or what to try please help me get betty bk on road and home

[kevtherev]

To understand this you need to know the route of your spark
The distributor calls for the spark through the hall sender (magnet and pick up) on the distributor, it asks the ignition amplifier to tell the coil to release hell
The coil releases the spark and it is delivered to the distributor and directed to the plug via the rotor arm

If there is no spark at the plug then it needs to be isolated to either the plug, the rotor arm, the cap, or the lead, replacing these is easy and should be done as a matter of course.

if the king lead is not giving a spark then the amplifier or the hall sender is not talking to the coil, if the coil gets too hot it won't listen to the amplifier
All these things are testable and explained in the haynes or bently manuals

lets stop guessing and wiggling and be more methodical

[Smosh]

just to learn... what/where is the amplyfier!?

[kevtherev]

left hand side engine bay, little black plastic box with wires going to it
looks like this..



Also called ignition control unit

[Smosh]

Oh okay, what does it do?

My knowledge was:
Battery to coil, coil ups voltage, HT to dizzy, dizzy cap receives spark from rotor arm, rotor arm receives spark from points which open and close timed and spaced to the engine, or from and electric signal interpreted by the dizzy unit/magic?!

[kevtherev]

Oh okay, what does it do?

My knowledge was:
Battery to coil, coil ups voltage, HT to dizzy, dizzy cap receives spark from rotor arm, rotor arm receives spark from points which open and close timed and spaced to the engine, or from and electric signal interpreted by the dizzy unit/magic?!

Well there are no points, so the magnet and pick up (hall sensor) that replace them produce very low output signals, the amplifier boosts the signal from the distributor into a pulse that the coil can use
To quote from the wiki..
The hall sensor output is shaped and processed by suitable circuitry, then used to trigger a switching device such as a thyristor, which switches a large current through the coil.

It's the birth of engine management, allbeit rudimentary, it solved the problem of points erosion and the constant resetting of them, however it was something else that moved owners away from home maintenance and into the eager arms of garages..and ultimately dealerships.
Where your trousers will be pulled sharply down and the position assumed.

[Smosh]

thanks for the patient response Kev!