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MG MGA - Was running / Is Dead / and I need help

Ok
I am at a total loss. My Coupe won't start after just stopping dead on the street. Towed it home and for the life of me, I can not get it to start. Here is the list of checks I have done:

coil main HT wire / + & - coil terminal wires / points gap / dist HT lead / condenser / small wire to dist / spark plug wires / dist cap HT connections / dist cap.

There is a spark when I manually open the points', and I have verified the correct points & condenser wire mounting.

The problem is that I am not getting "any" spark at the spark plug. I have not verified the rotor, (Please tell me how).

Finally, the car ran like a clock before this and is there some other "thing" that I should be looking at before I pull the distributor , for a compltet overhaul?
Gordon Harrison

1. Is it getting any fuel at the carb?
2. Did it make any other strange noise before stopping.?
3. Does the battery have a good charge?
4. How strongly does it turn over?

The issue is most likely electrical. bit unlikely to be a defect in the distributor (not counting condensor & rotor)
Condensor is a very likely culprit. It is simplest to just exchange the rotor and condensor.

dominic clancy

Gordon. As Dom suggests, fuel is the first thing to check out. If you have good flow from the fuel pump, it will be adequate to get the engine started.

The rotor fails by having the plastic under the rivet burn through and the coil lead, then, grounds directly to the distributor shaft. A visual inspection may show an area of burning or carbon tracking. Or, it may not. Best check is to either use a new rotor or a used rotor that was working well when removed.

But, there are two parts to the system which can fail and allow you to have spark at the coil lead, but not at the spark plug leads. The first is the rotor and the second is the distributor cap itself. There is a carbon bush in the center of the cap which transmits the voltage spike from the coil lead to the spark plug terminal. If this bushing is not working correctly, you will not be able to transmit spark to any of the spark plug terminals in the cap, nor to the rotor itself in many cases. This assumes that you have tested for spark at all of your spark plug leads. Spark at some leads, but not all leads, indicates either bad leads or a bad distributor cap.

I would check for fuel, then replace the rotor and distributor cap and check for spark at each of the spark plug leads.

Les
Les Bengtson

You've already narrowed it down to not getting spark at the plugs and you get spark if you manually open the points. You have already replaced the dist cap. The remaining common failure point is the rotor as has already been stated. Just replace it. When you get the car started, don't forget to toss the bad part(s) and not end up in your used parts bin.
Chuck Schaefer

Dominic
Fuel, yes...no strange noises....battery perfect...turns over rapidly,no lagging

Les,
Is it possible for that tiny carbon post in the center of the cap to have split, and I can't see that?
Is there a test for that/
Gordon Harrison

I checked Barney's site an see a whole thing about my regulator. is this something I should check?
Gordon Harrison

Gordon. Yes, it is possible for the carbon center bush to be non-conductive without having a visible point of failure. Easiest method of checking is by using a VOM, or Volt-Ohm Meter. Set to the Ohms (resistance) scale and touch the probes together. You should read zero ohms resistance. The, touch one probe to the center terminal of the distributor cap and one to the carbon bushing. You should read zero ohms resistance. (Just verified on one of my spare caps.)

I am not sure what regulator you are writing of. If it is a fuel pressure regulator, used to drop the pressure of a high pressure fuel pump down to about 3.5 psi, it may have an effect on how the car runs if the pressure is too high or too low. Should not have any effect on whether you get a spark at the end of a spark plug lead. If you are writing of the control box (mechanical voltage regulator) this will have an effect on the charging circuit, but will not keep your engine from starting and running.

If you have fuel, the problem causing no spark at the ends of the spark plug leads, but having a good spark at the coil lead, can only be three things--distributor cap carbon bushing, rotor, or bad spark plug leads. Tech article on checking spark plug leads and another on ignition system trouble shooting on the MG section of my website, www.custompistols.com/ .

Les
Les Bengtson

If you have a spark at the points then it most likely the rotor arm as that is the only thing that you haven't changed yet - we have had a lot of dud ones over here in UK. There is also a tiny wire inside the dizzy that you could also check as I have seen that snap unnoticed before now.
Cam Cunningham

It's been mentioned by Cam above and others....if it stopped suddenly and you have no spark at the plugs, then the rotor arm is a very likely candidate. I have had exactly the same happen, just like an invisible hand turned the ignition key off! Many modern black rotor arms are rubbish. Get a red one from Jeff Schlemmer http://www.advanceddistributors.com/index.htm
Lindsay Sampford

Thanks everyone, I will get a new rotor and report back.
Gordon Harrison

I too think it is the rotor but I can't understand why people simply do not check to assess the fault rather than simple speculation.

I note you suggest that you have checked various items but how?

I like the way you have checked the points and that is the classic check. After that check you did not need to justify the connections of the condenser because they would be right otherwise the points would not spark.

Equally the next test is to simply check the coil
remove the king lead from the dissy cap and place the end of it very close to the engine block. Now flash the points again. When flashing the points the king lead should also spark to earth (20 to 30thou gap) this tests the coil. If this is successful then the next 2 items can only be the rotor or dissy cap (carbon brush)
Bob Turbo Midget England

As I have to keep reminding my brother in-law, most problems are simple ones.

Since the car stopped dead it is something in the HT circuit because there is no spark at the plugs either came unplugged, or failed.

The ground wire as Cam suggests may have broken, It is a tiny multi-strand wire sheathed in a reddish brown fabric and is grounded with a screw in the depression of the distributor body where the cap locator goes. The other end goes to the point plate. There is also another sheathed wire inside the distibutor that goes from the low tension connector on the side (white wire with black tracer)to the point spring post.

I have heard of rotors that have sheared their drive peg off and no longer sit in the correct position as far as timing the spark is concerned.

I have also seen aftermarket rotors that had the brass contact strip riveted to another on the top and they developed a break in continuity between where the carbon contact is and the tip.

I don't know if this explanation is of any help but I hope it assists you in finding your problem.

One of the things we do for long journeys is take a spare distributor with fresh points, condenser, cap and wires with us and if there is a problem simply swap it out and continue the journey.

SteveB
S L Bryant

Gordon,
My coupe project car last year started and ran fine. Then it wouldn't start. Was the NEW rotor arm. Have now fitted a red one, and it has done more than 3000 miles without a stutter.
Peter.
P. Tilbury

My bet it the rotor. See my similar story back in 2006
http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=&mode=archiveth&subject=6&subjectar=6&thread=2006012310344815373
Mike
Mike Ellsmore

Link may not work. Type in "Stopped and wont go" into the Archives.
Mike
Mike Ellsmore

Buying a new rotor and will give it a try. I hope that is all it takes.

Gordon Harrison

In 26 years of driving mine it has stopped twice,all within a mile of the house.Fuel pump real obvious,a quick hit and I was on my way.The other time was that darn rotor which also required a tow!
gary starr

Bump

Gordon - what happened?

Was it the rotor?


JIM in NH
AJ Mail

Finally will be able to get the parts this weekend. I guess that what happens when you own your own company and are not retired. NO SPARE TIME. I am hoping to hear the ZOOM ZOOM by Sunday. i will report back.
Gordon Harrison

"I guess that what happens when you own your own company and are not retired. NO SPARE TIME"

Ah yes, work is the curse of a man with a hobby ;-) Cheers - Dave
David DuBois

Gordon

I don't know whether this helps or not, but I had the same symptoms on my 1500 Coupe. It would die after about 10 miles. I replaced most things in the HT circuit, and just thought, whatever it was, I've removed the problem. How wrong I was. The LT wire from fuse box to coil burned out and took the rest of the LT circit with it, all the way into the distributor and back to the fuse box.

What clearly was happening was that the LT circuit in the coil was giving out, and it only took the extra voltage because I'd fitted a high power coil. So instead of the coil overheating and breaking down, it took out the wiring loom.

So if you haven't already tracked down the problem, a little piece of advice: if the LT circuit is taking more energy than it's designed for, don't wait for the wiring loom to melt, run a separate wire from fuse box to coil, and let that be sacrificial rather than the loom.

So why did my LT circuit overheat? I still have no idea! But I have replaced the old Voltage regulator with a new unit, and hope that was the source. It has to be - everything else either burned out or I replaced it. The car's in hibernation, but before I put it back on the road in the spring, I will get an auto-electrician to run over it.

There's one other trick you can use in very cold weather: Borrow a thermographic camera and see if you can spot overheating in any of the wiring or components. You can use such cameras for diagnostics on building LV distribution boards to check for overlaods, so there's no reason why you can do the same on auto electrical circuits. I didn't by the way, and I wish I had...


R Bunn

Like Gary, I've broken down only a few times and one of them was due to a bad "new" coil. It seems I've had more problems with new parts than anything else. I sent 2 days trying to figure out what I could have possibly screwed up on my suspension until I realized that my "new" moss link bolt castle nut was wrong and didn't line up.

I too often overlook "new" parts thinking that with modern quality control they can't be bad.

BTW, there are probably more threads in the archives about bad rotors than any other subject.
Fred H

FWIW.
I had same problem. I checked for spark and it was there. Only not enough spark. Changed coils and bingo. Apparently size matters when it comes to sparks. Good luck.
By the way, my coil was 3 months old when it died.
Lmazoway

Ironically enough for all the heat Lucas took for being unrealible,they were light years ahead of this new junk. I still running my original Lucas coil.
gary starr

Changed the coil, dist cap, wires and rotor and now it is Ok. Thanks for the help. PS: not sure which part was wrong but who cares,it's alive.
Gordon Harrison

This thread was discussed between 02/02/2012 and 18/02/2012

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