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Good News ...and niggles (ignition?)

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ThomasH84 Avatar
ThomasH84 Thomas Horsley
Woolton, England, UK   GBR
The good new this morning...

The car past its MOT with no advisories. It's now back on the road after a couple of years 'resting'.

The less good news...

It broke down on the way to the testing station smiling smileysmiling smileysmiling smiley Lucky I know the mechanic, who's a great guy and we got the car to the garage safely.

It's working fine until warmed up when it will just cut out and refuse to fire up again (until it's cooled a little) - the repeat. It had been doing this before when i was bringing the car back to life in the garage in preparation for the return to the road. I had suspected it might be ignition related (the fuel pump is working + new filter etc; the carbs have been refurbed in recent years; new battery; good earth; working alternator) so replaced the HT leads and the coil. I thought the coil might be the source of the problem - it've never replaced it in 5 years ownership, plus it was getting hot. New lucas sports coil fitted last month.

Anyway, new coil installed and problem is still here. Any thought on how best to diagnose the problem methodologically? I don't want to annoy any more commuters by having the engine cut out at the lights!!

For info: I have luminition magnatronic electronic ignition in place (installed by previous owner and untouched by me). Trying to work out how to diagnose the problem correctly? Mechanic does think it's ignition related - and points to coil (which also has never had a ballast resistor fitted).

Cheers guys!

ps some pics - we all love 'em smiling smiley

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Ex-Calif Avatar
Ex-Calif Gold Member Dan D
Cincinnati, Ohio, USA   USA
1968 MG MGB GT "Bart - Yellow And Naughty"
1977 MG MGB "Red Betty"
2012 Jeep Liberty "Tank"
2014 Hyundai Accent "Skate"
Nice pictures of the car but it might be more useful to post pictures of your coil, inside of the dizzy etc...

If the cut out is immediate I would agree electrical but if it "stutters" a bit make sure that the fuel delivery system is working right and the tank is vented properly. i.e. you aren't getting a rapid set of fuel pump clicking, right?

For the electrical, I do not know your ignition system but if you are sure there is no condenser which there shouldn't be it could be the tach.

Your ignition system runs through the tach. What does the tach do when it cuts out?

I would run a jumper from the white side of the fuse box to the coil +ive and run it for a while.



The goal - Reliable summer driver interspersed with mechanical tinkering...
Motto - "Driving fifty in the twisties..."
On Mods - It's your damn car - Do what you want. Haters gonna hate...
On SUVs - Drive your B like a soccer mom is texting her friends about how she wants to kill you...
Red Betty - http://www.mgexp.com/registry/GHN5UH418165
Bart - http://www.mgexp.com/registry/GHD4U146898G

ThomasH84 Avatar
ThomasH84 Thomas Horsley
Woolton, England, UK   GBR
Cheers for that Dan!

I'll post some more pic when I get back from work tonight.

Yes, it cuts out cleanly with no sputtering etc, which does make me think it's electrical / ignition related not fuel. I've had the fuel cut out problem before. The pump is certainly clicking away normally. I'll doubly check the connections though to make sure there's no issue here.

When it cuts out, the tach just returns to 0rpm and the red ignition light glows. Again, these probs only appear after the car is warm (5/10mins driving).

tbh, I'm pretty unfamiliar with the luminition electronic ignition set up. It was in place when I got the car in 2009 (replacing the points/condenser) and has worked until now.

I do hate niggles!!

Cheers!

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ThomasH84 Avatar
ThomasH84 Thomas Horsley
Woolton, England, UK   GBR
Back home from work at last.

I've had closer look at the ignition parts - see pics.

The dizzy cap / rotor arm do look pretty warn. Is that a poss? The cap was also a bit lose - the clips don't seem to hold in place very well. Eek.

It's also occurred to me that the fuel in the tank is old (prob a couple of years). I topped it up with 5litres of fresh but at 1/4 full, there's still some old stuff in there. Could that trigger vaporisation problems when the car is hot triggering the cut out? It certainly isn't helping for sure. Will drain off what i can and refill with full tank of fresh petrol / gas asap

the coil is non-ballasted. The pic is the old one; the new one is a lucas sports coil also unballasted. the cut off has occurred with both coils in place so not sure that's the key fault - unless, of course, i should have been running a ballasted coil for the last 8 years ha ha

Cheers for any diagnostic tips !


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ozieagle Avatar
ozieagle Gold Member Herb Adler
Geelong Victoria, Australia   AUS
1958 Wolseley 1500 "Wooly"
1966 MG MGB "Bl**dy B"
Your comment about it stalling at the lights nudged my memory. When I first got my Wolseley it died everytime I stopped. Had to wait a while for it to cool a bit before I could start it again. Turned out that the wire, not the starter cable, from the battery (starter post on the B) was loose. By stopping the engine revs dropped below the kick in voltage of the dynamo and no power to the ign. When running the dynamo provided the power to keep things going. I know! your car car has an alternator, but...

Herb



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BigIg Avatar
BigIg Ian B
E. Yorks, UK   GBR
1980 MG MGB GT
1999 MG MGF
It certainly does sound electrical.
The distributor cap looks clean at the business end. One segment looks damaged or displaced but that isn't going to cause a temerature-related fault. In any case it would only affect one cylinder.

I'd hang a voltmeter on it & make sure you still have 12V on the top side of the coil when it stops.
From your description it sounds like it is very repeatable which is good for trouble shooting.

I don't know much about the lumenition but it basically acts as a switch from the -ve side of the coil to ground. After it has stopped I'd try touching a wire from the -ve side of the coil to ground while holding the king lead close to the block & see if you still have a spark when you pull the test wire off._



Edited 1 time(s). Last edit at 2017-10-05 03:04 PM by BigIg.

Ex-Calif Avatar
Ex-Calif Gold Member Dan D
Cincinnati, Ohio, USA   USA
1968 MG MGB GT "Bart - Yellow And Naughty"
1977 MG MGB "Red Betty"
2012 Jeep Liberty "Tank"
2014 Hyundai Accent "Skate"
Cap and rotor are definitely past their sell date and need replacing but doubt they are prime at this point.

Good idea about battery terminals and grounds especially connections at the starter - that's all free to do and good medicine.

I would still run a jumper from fuse box white to coil and see what happens and if you can get one stick a voltmeter in the cigarette lighter and monitor the voltage - especially if it cuts out. This will be on the purple circuit and runs through a few connections but should give you an idea of the "system" voltage - i.e. what the rest of the car is seeing.

Ultimately all voltage in the car is "shared" and each item puts a drag on the battery/alternator - with everything running you will should get an idea of what the average component is seeing including the tach and coil.



The goal - Reliable summer driver interspersed with mechanical tinkering...
Motto - "Driving fifty in the twisties..."
On Mods - It's your damn car - Do what you want. Haters gonna hate...
On SUVs - Drive your B like a soccer mom is texting her friends about how she wants to kill you...
Red Betty - http://www.mgexp.com/registry/GHN5UH418165
Bart - http://www.mgexp.com/registry/GHD4U146898G

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course2kid Jeffrey Johnson
Fountain Valley, CA, USA   USA
1979 MG MGB "Lucy (Lucifer)"
This is a vexing problem to figure out! I've started two previous posts to explain it and they both rambled on and seemed to come to conclusions not supported by the facts as I understand them (the tach immediately drops to zero, the ignition warning lamp illuminates, and the fuel pump continues to run). I'm also assuming that, if any of the brown wires (from the alternator to the starter, fuse box, hazard switch, headlight switch, and starter relay) had started smoldering, you would have noticed.

If you can, try to replicate the problem in your driveway and observe and report back on the following:

1) When the engine cuts out, does the tach drop to zero faster than the engine rpms spool down?
2) Hook a voltmeter to the white wire circuit (left side of third fuse down,) and note if this voltage drops to zero right when the engine cuts out.
3) Hook a voltmeter to coil + and see if this voltage drops to zero right when the engine cuts out.

I'm suspecting that either a) the alternator rectifier, alternator sense diode half bridge, or alternator regulator is failing when it gets warm (i.e. thermal expansion causes a solder joint to open up), b) either the ignition switch, one of the white wires, or one of the components connected to the white wires (fuel pump, fuse box, tach, O/D switch, or coil) is shorting the white wire to ground, or c) the tach connection between the white wire input and white wire output is opening up.

The problem is that none of these problems can support all the facts as I understand them combined with my assumption that a smoking brown wire would certainly be noticed.

Here is my reasoning:
1) If your fuel pump is still ticking right after the engine cuts out, this means you still have power on the white wire circuits. But, if the alternator is good and you still have power on the white wire circuits, then the ignitiin warning light should not come on.
2) If the Tach connection between the input white wire and output white wire opens up, this will cut power to the coil and kill the engine and (I think) cause the tach reading to immediately drop to zero. The fuel pump could also still be running, but, the ignition warning light shouldn't come on.
3) If the alternator voltage sense circuitry voltage drops, this will illuminate the warning light, but the tach, coil, and fuel pump will still have power and the engine will continue to run.
4) If the alternator somehow shorts to ground, this would kill the engine, fuel pump, and ignition, but would also short the battery to ground, so, the warning light would not illuminate and the brown wiring from starter to relay would burn up in very short order.
5) If the ignition switch fails in a way that opens the connection from 12v in on the brown wire to 12v out on the white wire, this would kill the engine by cutting power to the tach and coil, but would not illuminate the warning light or allow the fuel pump to keep running.
6) If any of the white wiring or associated components shorts the white wiring to ground, this would kill the engine and the warning light would illuminate, but, whichever white wire is shorted will smoke in short order and the fuel pump won't keep running. Here again, I assume you'd notice the smell of burn't insulation from the shoted white wire or the offending shorted component.

Now, having thought all this through, I have a new and, I think plausible/possible diagnosis. If you have a points type fuel pump and if it's a bit "sticky" perhaps it can stop at a point where the contacts are closed and this creates a short circuit, but, with enough resistance in the circuit so as not to draw enough current to fry its white wire but enough current such that the voltage drop across the ignition switch contacts makes the warning light illuminate and lowers the voltage to the electronic ignition module enough that it cuts out and kills the ignition. Of course, if the engine is still spinning and the ignition switch is still on when the fuel pump frees itself and starts running again, then the engine would restart.



Edited 1 time(s). Last edit at 2017-10-05 03:41 PM by course2kid.

Jwpotts Avatar
Jwpotts James Potts
Lexington, Kentucky, USA   USA
1970 MG MGB
Just picked up 5 chrome wire wheels and like new tires for my '70 B. Will not be able to mount them till Sunday.
Does anyone want to buy my 1970 painted wire wheels? Five with old tires but plenty of tread

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ThomasH84 Avatar
ThomasH84 Thomas Horsley
Woolton, England, UK   GBR
As ever, thanks so much for taking time to reply and assist!

I've spent a few hours today trying to narrow down the problem.

Summary:

-didn't manage to get the car to shut off in the garage even when warm. But once hot, it didn't restart after I had turned it off. It started up again after if had cooled a little

- as it didn't quit by itself, I couldn't diagnose using the tach.

-when it was hot and wouldn't start, I switch the coil for a working (and cold) one. That made no difference! The car still wouldn't fire.

- I check for a spark using the coil to dizzy HT lead on the engine block. Got a spark - looked more yellow than blue though

- removed the tach to eliminate that part of the ignition circuit (e.g. shorts). No change. Car didn't fire up until it had cooled

-finally I drained the gas tank as the fuel was 2years old. Replaced with fresh unleaded. Checked fuel pump - steady flow looks ok

Am now a bit stuck.... !!

It's either a heat-related electrical / ignition issue before the coil or perhaps even a carb issue?!?

Shame as I want to get back on the road and have some fun again.

Cheers

Ex-Calif Avatar
Ex-Calif Gold Member Dan D
Cincinnati, Ohio, USA   USA
1968 MG MGB GT "Bart - Yellow And Naughty"
1977 MG MGB "Red Betty"
2012 Jeep Liberty "Tank"
2014 Hyundai Accent "Skate"
When you say the new coil is a Lucas Sports coil is it a new coil or a used coil that you put in?

This stuff needn't be this hard but if you have clean 12V+ going into a known good coil, points, rotor, cap and wires, well... It's gotta run, right?

If the spark is "yellow,"based on what I've picked up form this thread - I am back to coil but...

You sitll have really questionable ignition parts in the rotor and cap. I have seen caps short to ground when cracked or damaged. And you know the rotor and cap are shot so get that crap outta there - throw in new wires while you are at it as they are probably past their sell date as well.

Look at it another way - Put $50 worth of parts on there and enjoy their reliability for the next 20k miles.



The goal - Reliable summer driver interspersed with mechanical tinkering...
Motto - "Driving fifty in the twisties..."
On Mods - It's your damn car - Do what you want. Haters gonna hate...
On SUVs - Drive your B like a soccer mom is texting her friends about how she wants to kill you...
Red Betty - http://www.mgexp.com/registry/GHN5UH418165
Bart - http://www.mgexp.com/registry/GHD4U146898G

ozieagle Avatar
ozieagle Gold Member Herb Adler
Geelong Victoria, Australia   AUS
1958 Wolseley 1500 "Wooly"
1966 MG MGB "Bl**dy B"
In reply to # 3605630 by Ex-Calif

Look at it another way - Put $50 worth of parts on there and enjoy their reliability for the next 20k miles.

That is, of course, if one of those parts are the problem, otherwise $50 gone for no improvement.

Herb



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ThomasH84 Avatar
ThomasH84 Thomas Horsley
Woolton, England, UK   GBR
Thanks guys

Yes, new cap rotor and plugs on order. I don’t think they are the primary culprit tho - unless there’s heat expansion that’s causing a short when the car is warm.

Coil is new. Previous one was replaced thinking that was the problem. I swapped out new for old today to diagnose that the coil didn’t seem to be the key issue. Both didn’t get the car firing

It runs well when cold. Just won’t start from warm when I switch it off ...

Will rest some of the wires tomorrow - esp low tension coil to fuse.

Guess this is what happens when you bring back a car that’s been sitting for 2 years... I’ll never let it sit again once I get her sorted!!

Cheers

Ex-Calif Avatar
Ex-Calif Gold Member Dan D
Cincinnati, Ohio, USA   USA
1968 MG MGB GT "Bart - Yellow And Naughty"
1977 MG MGB "Red Betty"
2012 Jeep Liberty "Tank"
2014 Hyundai Accent "Skate"
The $50 is for the future 20,000 miles.

Did you look at that rotor and cap? They are done IMO.

In reply to # 3605637 by ozieagle
In reply to # 3605630 by Ex-Calif

Look at it another way - Put $50 worth of parts on there and enjoy their reliability for the next 20k miles.

That is, of course, if one of those parts are the problem, otherwise $50 gone for no improvement.

Herb



The goal - Reliable summer driver interspersed with mechanical tinkering...
Motto - "Driving fifty in the twisties..."
On Mods - It's your damn car - Do what you want. Haters gonna hate...
On SUVs - Drive your B like a soccer mom is texting her friends about how she wants to kill you...
Red Betty - http://www.mgexp.com/registry/GHN5UH418165
Bart - http://www.mgexp.com/registry/GHD4U146898G

spikerj Avatar
spikerj Josh Spiker
Provo, UT, USA   USA
1973 MG MGB MkIII "Little Red"
I had the same problem for a while and for me it turned out that when the car warmed up, heat from the exhaust manifold would vaporize the fuel in the carbs and fuel line leading to the carbs. When running, the car would behave fine because it always had fresh, cool fuel running through the system, but as soon as I turned it off, I wouldn't be able to start the car again until the carbs and fuel lines had cooled enough for the fuel to condense back into liquid.

I don't know if your having the same problem, but it sounds like your having the same symptoms I did so I figured I'd post my experience.

Installing some insulation on the heat shield ended up fixing the problem for me.

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