1800ES Electrics & Ignition
 

OK, so this will be a bit of a long post as looking for help with electrics. My P1800ES, over the course of a mile or so went from driving perfectly to what sounded like misfiring and then completely conked out.
After checking all the HT leads I moved to the LT system. All normal tests ran fine until testing the voltage from the -ve of the coil to earth with the points closed and ignition on. Result - battery voltage. Immediately think perhaps the points aren't closing properly but under same conditions all parts of contact breaker and LT contact to distributor are reading zero voltage to earth. So there's some issue (resistance) between the coil and the distributor in the LT circuit thinks I.... I know that the tacho is in between those two from the wiring diagram, and when I run the resistance meter across the unplugged LT lead from the coil to the distributor indeed it seems to have infinite resistance. Bingo.
So to see if I can fix it I attach the coil (-ve) direct to the distributor (primary terminal) - thus bypassing the tacho, re-attach all the HT system and does she start? Does she f**k! Exactly the same sound on turning - loads of starter motor - no ignition.
So now I'm left that I think I've got a problem with my tacho circuit, but that bypassing it doesn't get rid of the problem with the ignition.... agghhh. Any ideas? It's my first time with any of this so running low on ideas myself.

New coil needed but also with a new coil fitted if it still acts like somethings not right but runs until you use the throttle a lot check the throttle body unit 😎👍

Bells;

"testing the voltage from the -ve of the coil to earth with the points closed and ignition on. Result - battery voltage." ...that sounds like the crux of the issue: Reminder...when points are closed, they are (or should be!) closed to chassis, enabling Ign Coil primary current to flow...if you are measuring Batt V on Ign Coil Neg (Points node) with points "closed"...they are not electrically closed, and that is not right! I'd concentrate further troubleshooting in this area...it may be as simple as something has come loose where the wire connects to the Points...

See also: http://www.sw-em.com/Volvo%20Ignitio...ition%20System ...yes, it is written based on the armored Ign Sys of models other than your ES, but that involves the Ign Coil +, not the Ign Coil - (Points node) where you should be concentrating efforts.

Good Hunting!

Thanks Ron, I agree with you as to where the issue looks like it lies and I'll take a look at that doc after work.
Note also if I test -ve coil to earth with the points open - then it shows battery voltage AND all points on the Points (coil side) also show battery voltage - so there is some connection between coil and points. Also if I turn over the starter with the dist cap off I can see a spark when the points open and close - so something is getting to the points, even though I'm measuring infinite resistance between the two with the resitance meter..... makes no sense.... agghhh. More investigation needed.

Bell;

With Ign ON, when Points are open, you should measure 12V on that node! Remember, you measure V across the open switch of a circuit which has V supplied and where the switch is on the low side, supplying the return current path. ...and that is precisely the situation we have in the Ign Coil circuit.
http://www.sw-em.com/IGN%20SYS%20lores.JPG

Cheers

Edit: ...and to part two of your description...if you are seeing sparks at the Points when cranking, that is rather expected and not unusual (the Ign Condensor minimizes but does not eliminate them entirely)...in that case you should also get HiV sparks from the Ign Coil secondary (which then must "distributed" and sent to the correct Sp Plug)...

It would seem like you have an ignition problem; but, have you confirmed that? It would be easy to remove a spark plug, insert it back in it boot and hold the spark plug ground electrode against the block while having someone crank the starter to check for spark. No point in thrashing around with the ignition system if the problem is elsewhere. If you can do the test with an inductive timing light that will allow you to check for spark and it will also allow you to check the ignition timing. You might have an ignition problem; but, it might not be a lack of spark if the distributor moved or something broke in the advance mechanism.

"I can see a spark when the points open and close" That would suggest that the circuit from the +12 v supply through the ignition switch and coil down to the connection on the distributor is intact. I presume that this spark is occurring across the points as they open up? The last time I had occasion to work on a vehicle with points ignition was in the previous century. If Ron says some sparking is normal, I will go with that. I don't ever recall seeing sparking if things were working - motorcycles typically being distributorless allow you to observe the points in operation. That said, if you have confirmed that you are getting no spark at all and if you are getting nice healthy sparks across the points as they open up I would be inclined to think that the capacitor might be suspect or that the capacitor connection at that little through bushing connection has failed.