morris minor woes

[Lyn_Lancaster]

Hi all
I am looking for some help with morris minor 1971 Traveller,
its a 1098 engine
electronic ignition
it was running fine last week but today as I took it out on a run the car started to misfire I believe certainly not firing correctly and progressing above forty as un-driveable
I have taken out all the plugs there is no fouling and look like a nice biscuit colour
the plug leads are fairly new along side the new electronic distributor all are connected I re checked the coil is an high powered one recommended for the electronic system. I cant see any thing obvious ,
there is a bit of tappet noise but only on one valve rear not sure if that would cause the rough running

I cant see any thing obvious and suggestions what I can look for or next steps

thanks
Linda

[svenedin]

Basically it is likely to be either fuel related or ignition related so we need to narrow down where the problem lies.

Does it sound rough and misfire just idling?

With the plugs looking a good colour it points away from a fuel issue but does not rule it out. Even with quite short periods of fuel starvation the plugs look pale. I had sudden onset of very rough running some time ago and it was related to a leak on the induction side (air being drawn in making the fuel mixture weak). This showed as pale looking spark plugs even though the engine was only run for a short time.

It sounds more like an ignition issue. I would go through checking things. Take the distributor cap off and check the rotor looks ok. Check the electronic module looks ok and the wires to the module have not been chafed and damaged. Check electrical connections to coil are clean and tight. Check the king lead from distributor to coil is tight.

To diagnose further if no fault found so far, get some of the neon spark plug testers and observe the spark with the engine running. It is costly to replace parts on a guess and much better to identify the problem accurately.

Ignition coils are notoriously unreliable these days so that is a suspect as is the electronic ignition module.

Check the carburettor dashpot has oil.

Another little test, when running rough does giving come choke make it better?

Stephen

[Lyn_Lancaster]

Basically it is likely to be either fuel related or ignition related so we need to narrow down where the problem lies.

Does it sound rough and misfire just idling?

With the plugs looking a good colour it points away from a fuel issue but does not rule it out. Even with quite short periods of fuel starvation the plugs look pale. I had sudden onset of very rough running some time ago and it was related to a leak on the induction side (air being drawn in making the fuel mixture weak). This showed as pale looking spark plugs even though the engine was only run for a short time.

It sounds more like an ignition issue. I would go through checking things. Take the distributor cap off and check the rotor looks ok. Check the electronic module looks ok and the wires to the module have not been chafed and damaged. Check electrical connections to coil are clean and tight. Check the king lead from distributor to coil is tight.

To diagnose further if no fault found so far, get some of the neon spark plug testers and observe the spark with the engine running. It is costly to replace parts on a guess and much better to identify the problem accurately.

Ignition coils are notoriously unreliable these days so that is a suspect as is the electronic ignition module.

Check the carburettor dashpot has oil.

Another little test, when running rough does giving come choke make it better?

Stephen

Thanks I will need to get some neon plug testers and I have a spare distributor with an electronic ignition if needed. the one thing we did between last week and today as to move the tail pipe on the exhaust, as the down pipe was touching the bodywork, not sure if that could have done any thing
cab has oil but we will strip it down to see if there issue and try the choke

[59Elva]

It’s a long shot but do you have a good engine ground? I found one of my previous MGs was only grounded thru the choke cable. Perhaps your exhaust pipe was your ground.

[myoldjalopy]

What Stephen said. Plus: swap in your spare dizzy and see - unexpected failures of electronic ignition units are posted on here not infrequently.
Highly unlikely to be anything to do with the exhaust pipe.

[svenedin]

It’s a long shot but do you have a good engine ground? I found one of my previous MGs was only grounded thru the choke cable. Perhaps your exhaust pipe was your ground.

That's a good suggestion. The engine earth is from the gearbox to the crossmember.

If I had to guess to win a sweepstake I'd say it was the ignition coil. I had one fail almost immediately it was installed on the car. It lasted such a short time I never even got the car off the drive!

Stephen

[Grumpy21]

Another simple check would be the rotor arm. Some new ones (often black but not always) are riveted and the ‘spark’ leaks to earth via the rivet. Simple check to swap the arm.

[Lyn_Lancaster]

It’s a long shot but do you have a good engine ground? I found one of my previous MGs was only grounded thru the choke cable. Perhaps your exhaust pipe was your ground.

hi the exhaust doesn’t touch the body only rattles against it when it runs,.
We need to sort this out but the down pipe is a bit long so we might have to fettle the body work a bit .
while we am at this we will go ahead and remove the carb and change the manifold gasket. its not a big job and will resolve the noise issue

[Lyn_Lancaster]

Another simple check would be the rotor arm. Some new ones (often black but not always) are riveted and the ‘spark’ leaks to earth via the rivet. Simple check to swap the arm.

will do! the whole dizzy was new last year hope that this is not the issue but I have the old one still and will swap out for sure

[Lyn_Lancaster]

What Stephen said. Plus: swap in your spare dizzy and see - unexpected failures of electronic ignition units are posted on here not infrequently.
Highly unlikely to be anything to do with the exhaust pipe.

yes I can see that although it was not a retro fit but a new dizzy complete, fingers crossed with by old one back on

[mobylette]

What make is the replacement distributor? There are known to be some very poor copies available.

[59Elva]

It’s a long shot but do you have a good engine ground? I found one of my previous MGs was only grounded thru the choke cable. Perhaps your exhaust pipe was your ground.

I only discovered the missing ground strap when extending cranking caused the choke cable to overheat and start smoking. I assume someone had removed the drive train at some point and didn’t replace the strap.