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MG MGA - Spark Plugs Not Firing?

I've been having trouble getting the car started. It sat during the winter. Last week after quite a few tries I got it to run and idle well enough.

Since then I can't get the car to start at all. I've even tried removing the spark plugs, spraying starter fluid in the cylinder, quickly putting the plugs back in and giving it a go. No success.

However, when I pulled the plugs back out again they where still wet. If the plugs were firing wouldn't that have at least dried them out a bit? Particularly with starter fluid?

I'm here on my own so I can't visually test to see of the plugs are firing.

Any suggestions?
Tysen McCarthy

Hi Tysen
I am sure people more able than me will be along with help soon, but first I am not sure why you cant test for a spark on your own as you can easily activate the starter switch under the bonnet. Make sure you're in neutral, and be very careful as it is an extremely high voltage. If you are not 100% sure, come back here first and someone will explain in much more detail.
Is the fuel coming through - when you first switch the ignition on, you should hear the petrol pump click a few times until the bowls are full, then stop.

Clearly there could be many reasons, but if you can track it down to fuel or electrics first, that will be a good start, so as you say yourself, finding if the plugs are sparking is a great place to start
Graham V

Yep, no spark to the plugs.

I'm a bit surprised. Its a new distributor cap and as I recall it a relatively new ignition coil.

Tysen McCarthy

Tysen. There are two circuits in the distributor--the low tension circuit and the high tension circuit.

The low tension circuit consists of most of the internals within the distributor--points, condenser, points cam, distributor shaft, and the mechanical and vacuum advance mechanisms. All, basically, to induce a spark out of the coil.

The high tension circuit consists of the distributor cap, rotor, and spark plug/coil leads.

The first test to make is to remove the coil lead from the center of the distributor cap, hold it near the block and, with the ignition switch turned on, activate the starter motor while observing if there is a strong spark from the end of the coil lead to the block. If there is a strong spark, the low tension circuit is verified. If not, the problem with the low tension circuit needs to be detected and corrected before moving forwards with the testing.

If you have a good, strong spark from the coil lead, reattach it to the distributor cap, pull a spark plug lead, stick a round screwdriver into the hole in the spark plug boot and, while holding onto the insulated handle of the screwdriver, again crank over the engine to see if you can cause a spark to fly between the screwdriver shaft and the cylinder head.

Years ago, I wrote several articles concerning ignition system trouble shooting and testing spark plug wires. We dropped my website several years ago, but it may be possible to do a Google search using my name and "ignition system troubleshooting" to find a copy of the article which was reproduced several places.

If the simple testing does not tell you what the problem is, we need much more information than you have provided, including make and model of the distributor, type of distributor cap and leads (e.g. does it have push on connectors or the screw in connectors?) and what coil you are using. All of these may have been changed out over the last sixty plus years and all with have an impact on what needs to be done to solve your problem.

Les
Les Bengtson

Most common cause if the car has been sitting is that the contacts on the ign. points get corroded up --a simple cleanup and reset the gap and away it'll go
William Revit

Tysen,
when I was younger, had better eyesight and was much more flexible, I used to check and re-adjust the points with the distributor in situ.
But now I find it much less of a challenge if I remove it from the engine and work on it on the workbench.

Leaving the distributor clamp nut alone so as not to lose the timing, you just remove the two fixing screws and lift the dizzy straight out. Just make a note of which direction the rotor arm is pointing before you remove it so that you can more easily re-install i.

Now that I use electronic distributors, I carry a spare dizzy with me in the car so that I can swap it in the event of a failure.
It takes me about 15 minutes.

Let us know how you get on.

Cheers
Colyn
Colyn Firth

Hi Tysen

You are clearly getting plenty of good advice but one extra point from me is don’t assume new components don’t have faults. There are plenty of bad ones. I had a new distributor from a leading supplier fail at 150 miles due to bad condenser so beware.

Paul
Paul Dean

Hi Tysen

Good to see you are still having fun with the MGA.

You can check if the spark plugs are sparking by turning the ignition at the key switch, and the move to the passenger side front wheel and try pulling at the starter switch under the hood. If the spark plug is grounded on the head, it will spark if the HT is doing its job.

Make sure you haven't moved the distributor so that the timing os too far out - then it won't start
Dominic Clancy

Back again and thank you to all for your suggestions.

I have verified there is a strong spark from the coil.

It is a pertronix electric ignition system. The cap is a brand new MGM cap. The wires are also newer.

Dominic, thanks for the "hello". Thailand eh? That's a bit of a jump from Switzerland.

Yep, still knocking around in the MG. I made the silly choice to also get a sailboat. Talk about two hobbies that drain time and money! Its working out nicely. We keep both over on the Lake Michigan side of the State and we spend the weekends galivanting up and down the coast either by boat or by car.
Tysen McCarthy

Tysen
Good to see you have a good spark. As Dominic says if you've moved the distributor the timing could be out, but from your original post, I assume you havent disturbed the distributor.
As you have electrnic ignition, I would be inclined to look at the fuel side. How long has the current fuel been in the tank? (it can get stale). Why not take a look in the carb to see if the fuel is getting through?
Graham V

Graham, I may not have worded it clearly.

I am getting a strong spark from the coil. There is still no spark at the spark plug.
Tysen McCarthy

If there is spark at the coil, then it can only be leads, rotor or cap that may be faulty
Dominic Clancy

Dominic,

No chance its the Pertronix module?
Tysen McCarthy

Tysen. The Petronix is a points replacement system and part of the low tension circuit. If you have a good, strong spark from the coil lead it indicates that the low tension circuit is functioning correctly. Thus, the fault for the lack of spark at the plug(s) must lie in the high tension circuit--coil lead to center post of the distributor, center post of the distributor to the rotor through the carbon bushing in the center of the cap, rotor to the four brass terminals in the distributor cap, then from the brass terminals to the spark plug leads, ending at the spark plugs.

The rotor is a common point of failure with the spark burning through the rotor and grounding to the distributor shaft. The distributor cap can have the carbon bushing disintegrate and fail to transmit the surge of electricity to the rotor. The spark plug wires can (depending on what they are made of) break down internally and, regardless of what they are made of, the outer insulation can break down causing the spark to ground to various items in the engine compartment. Spark plugs can be fouled and not firing properly, especially when under compression.

Remove the rotor and examine it carefully for signs of arcing and/or burning. Inspect the interior of the distributor cap for the condition of the carbon bushing, the four metal terminals, and look for signs of carbon tracking, which look like pencil lines running across the cap near the terminals. If the cap has the older type of terminal (the ones with a screw to hold the wire into the cap rather than a push type connection), ensure the leads are firmly attached. Examine the leads for signs of the insulation cracking and to see what the leads are made out of. (Old ones were made of copper wire, which worked well with the old style dizzy caps. Modern leads are made out of carbon fiber or silicone and may not do well with the old style caps.)

Again, knowing what distributor you have installed and how it is set up is an important part of diagnosing the lack of spark problem. I have seen three different British distributors installed on MGAs and one brand of US made distributor. Without knowing what is present, all you can do is make guesses based on what was originally installed.

Les
Les Bengtson

Les,

It’s a DM2 50410 H distributor. It has a newer MGB distributor cap (see photos for wear) with modern Cobalt (blue color) wires and a photo of the rotor is included. I polished it up a bit and it still didn’t make a difference.






Tysen McCarthy

Tyson
IF you have spark from the coil and none from the leads it has to be the rotor button
To test the button-
With the cap off--hold the coil lead(with something insulated, preferably plastic pliers) about 1/4" or so above the centre of the rotor button----get someone to crank the engine over--as in trying to start it----
If the spark jumps to the rotor it is faulty-
William Revit

Thank you all.

Right as always. A new cap, rotor and wires and she's outside idling.

Next is a trip to the body shop. The garage door where the car was kept was left open during a wind storm and a variety tools and heavy/sharp objects fell off the walls and hit the rear fender and the front fender.

Thank goodness for Hagerty
Tysen McCarthy

Sorry, just couldn't help myself.

About three weeks ago we had a new garage door installed. Fortunately, at the same time we were having some new carpeting installed so the cars were out of the garage and much household goods were being stored in the garage.

About a week after the new garage door had been installed we were in the room next to the garage having a late lunch/early supper when it sounded like someone had driven through the garage door. Quite a racket.

This happened on a Saturday and I have to give the garage door company credit, they had the door reinstalled by the next Sunday afternoon. It hasn't fallen again so I hope this time the fix sticks.

Jud (TD, MGA, MGB)






J K Chapin

Tysen. Glad you got it sorted and back in running condition.

Willy. That is a great "trick" for testing the integrety of the rotor. Fast, easy, does not require tools. Splendid suggestion. Thank you. I will add that to my "bag of tricks".

Les
Les Bengtson

My pleasure Les--honoured to get a spot in your bag.

A word of WARNING though, not to you directly exactly but to others who read these posts
Treat electricity like the enemy, always use insulated tools preferably full plasic pliers or wooden ones when holding high tension leads etc to test for spark. Some coils now are very high powered and can cause considerable damage to you--The old act of pulling a plug lead off with bare hands is a very dangerous thing to do nowadays---I got caught with a car that i didn't realise had MSD ignition and it very nearly finished me off--18 months off work with daily rehab so just be carefull---PLEASE
William Revit

My "A" simply cut out on a run. Fiddled about for while as you do. Eventually got the rotor off, a black one, and discovered it had a burnt smell. That must have been shorting out through there very nicely.
Replaced it with the carried spare and we were off again.
I thought this might be of use to you sometime, that old rotor stunk for days too!
PeteT

This thread was discussed between 15/03/2023 and 10/04/2023

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