MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - No Spark

I am helping a friend get his 1600 MKII back on the road. It has not run for several years. It last ran for about one block after the owner replaced the battery and then would not start. Fast forward about 3 years and the owner and the car have moved from Hawaii to South Carolina. We have been going through the car (rebuilt the master cylinder, new rear wheel cyclinders, installed a spin on oil filter adapter). The starter is strong and the engine turns over. We pulled the distributor cap and noted arching at the points with the ignition on and starter turning the engine.

With the cap on and ignition on, there is no spark at any of the plugs. We changed the points (gapped at .015) and condensor this morning and still no spark. We turned on the ignition and connected a 12 volt test light from the LT connection on the distributor to gound and it lit. We have double checked the internal connection of the LT wires on the points and they are correct (touching the breaker spring and isolated from the breaker plate). We even tried a new coil with the same results.

I suspect we are chasing the problem that stopped his car in Hawaii three years ago and that it had nothing to do with the fuel pump.

Any help from this board would be greatly appreciated.

Thanks,
Don Carlberg
D. R. Carlberg

Sounds like the rotor arm is not distributing the spark to each plug,
Bob (robert) I am turning? yes I once owned an MGWasp!!

Don. See the tech article on trouble shooting the ignition system on my website, www.custompistols.com/ for how to perform the checks in a logical manner.

If you were getting spark at the points, you have some electricity flowing, but it would be good to know if it is at full voltage. If so, are you getting a spark from the distributor cap end of the coil lead when the car is cranked over while the lead is held about a half inch from the block? If so, you are getting spark from the coil to the distributor cap but the cap/rotor/spark plug wires are not transmitting the spark to the plugs. Replace those parts and see what happens.

Les
Les Bengtson

My money's on the rotor. It can have a crack undetectable to the eye but build up a carbon trail that will send your spark right to ground through the distributor shaft.
Mark

The rotor was replaced at the same time the points and condensor were replaced. I was betting on the condensor. We also tried a new coil. The owner and I will check Les' web site too and continue to troubleshoot.

Keep those suggestions coming! Will update on progress.

Thanks,
Don Carlberg
D. R. Carlberg

To check if the rotor arm is faulty simply do the following test.
Take the "king lead" from the dizzy cap and put it almost to earth. Turn the engine over and check for a spark. If you have one then insert it into the cap now check for a spark at the plug if you dont see one then the fault lies with the rotor arm or cap/connection.
Bob (robert) I am turning? yes I once owned an MGWasp!!

One trick I have used to check the coil is to disconnect the point wire from the disty. Using Bob's method of "almost to earth", momentarily touch the point wire to ground. As you lift it from ground, the coil should produce a great big spark. This method can be done from under the hood (oops, I meant bonnet).

No small spark from the point wire? no power to the coil or open primary winding in the coil. No great big spark on the secondary "king lead" bad coil or too far from ground. The spark should jump easily over 1/4 inch.

If all this checks out, reconnect the point wire to the disty and set the disty to a point where the points are closed. Then , with the disty cap off, manually open the points. should still get a big spark from the secondary wire. If not, check the wiring around the ponts including the ground braid from the moving point plate to ground.

Then try the same test using the wire to one of the plug wires held to "almost ground" if no spark then either the rotor is bad or the position of the rotor (highly probable if the disty has been removed and the car has never run since.) Retime the disty using the Factory Service Manual method.

The MGA ignition system is just about as basic as they come.

Chuck


Chuck Schaefer

Yes I also check the coil in a simple manner. All that Chuck is doing is leaving a "hot" wire to the coil and then the other wire from the coil touching it on and of earth. This should cause the "King lead" to spark when placed almost on earth. As Chuck stated these are extremely basic systems that require extremely basic tests. The full system can be checked at the side of the road with possibly a short length of extra wire!
Bob (robert) I am turning? yes I once owned an MGWasp!!

I had similar problem in 2005, see thread "Stopped and won't go", it was the rotor arm! I confirmed the fault with a good ohm meter after testing as per Bob MGWasp's comment.
Mike
Mike Ellsmore

My bet is the rotor arm too. I have had three faulty ones including one brand new (modern design) which failed after only one outing.

Andy
Andy Dear

Don,

I know you have a fully running 1600 of your own. If you're willing to take the risk, why not swap out your dizzy, complete with wires and try that set in your friend's MkII? Or, on the other hand, with no risk to your parts, take his set to your car and see if it works.

- Ken
Ken Doris

One other, rather long shot, suggestion. How good is the ground strap from the engine in your friend's car?
- Ken
Ken Doris

Rotor arm, but replace the condensor as well as a matter of course.
dominic clancy

Thanks to all for the suggestions. I am not sure when my friend and I will get back on this, but I will post the outcome after the problem has been solved.

I have a collection of "used but good" sundry distributor parts which we will probably stick in one at a time to see if the problem is rectified.

To summarize so far - new rotor, condensor, and points have been installed (and set set at .015"). The engine ground strap is in place. I am a little suspicious of the small ground wire inside the distributor (it is covered with electrical tape).

Don Carlberg
D. R. Carlberg

If this little wire was touching earth you would not get a spark at the points. This you have already checked.
Bob (robert) I am turning? yes I once owned an MGWasp!!

This thread was discussed between 01/07/2006 and 03/07/2006

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.