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mg_tf
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The electrical side has been suggested already and I agree with those that suggested it - it's a prime contender for this sort of problem. An erratic misfire on my TF got traced to leads in the end - even though they looked fine.

I'm not familiar with the F ignition setup. I believe it uses a distributor and rotor arm though, which were eliminated in the TF. Does it use points or some kind of electronic sensor in the distributor?

You've already replaced the coil, I'd want to eliminate the plugs, leads, distributor, rotor arm and condenser (if there is one).
I appreciate you think the problem is one that is common to all cylinders after your test pulling leads, so start on more of the the common items. There will be an HT lead coming from the coil to the dizzy that is common, yes?

High voltage is a funny thing and it can track across surfaces that are contaminated or defective in a way that isn't obvious. You might initially try giving the inside of your distributor a squirt of WD40 just to try and disperse any moisture that might be in there. Running an engine in the dark (I mean, really dark, not moonlight or under a streetlight) can sometimes show up corona around the HT components.
 

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Discussion Starter · #22 ·
Have you checked condition of plug leads? on my 1996 F they became brittle and were falling apart when I went to remove plugs...
Yes I have, all good there.
 

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Discussion Starter · #23 ·
The electrical side has been suggested already and I agree with those that suggested it - it's a prime contender for this sort of problem. An erratic misfire on my TF got traced to leads in the end - even though they looked fine.

I'm not familiar with the F ignition setup. I believe it uses a distributor and rotor arm though, which were eliminated in the TF. Does it use points or some kind of electronic sensor in the distributor?

You've already replaced the coil, I'd want to eliminate the plugs, leads, distributor, rotor arm and condenser (if there is one).
I appreciate you think the problem is one that is common to all cylinders after your test pulling leads, so start on more of the the common items. There will be an HT lead coming from the coil to the dizzy that is common, yes?

High voltage is a funny thing and it can track across surfaces that are contaminated or defective in a way that isn't obvious. You might initially try giving the inside of your distributor a squirt of WD40 just to try and disperse any moisture that might be in there. Running an engine in the dark (I mean, really dark, not moonlight or under a streetlight) can sometimes show up corona around the HT components.
Thank you. I have already inspected and (visually) passed the dizzy cap and rotor arm, but that doesn’t necessarily mean they are ok of course.

I think that I might have to replace those with new, just to strike them off the list of suspects.

The thing that gets me is that it literally starts so well, even with this misfire. I would have thought that if it was ignition relatedI would have had some kind of signal on startup?
 

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Discussion Starter · #24 ·
Later I will pull the dipstick and remove the coolant reservoir cap to see if there is any telltale signs of you know what...
 

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MG ZT, Rover 25
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Coolant loss would indicate IMG leak. If no coolant loss I would run a fuel cleaner through (change the fuel filter if it hasn’t been done for years) and then concentrate on the HT circuit. Change plugs, leads, dizzy cap, rotor arm, coil. Probably one or two at a time in that order and test if money is tight, otherwise just renew the lot in one. Oh, and repair the oil leaks.
 

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Discussion Starter · #26 ·
Coolant loss would indicate IMG leak. If no coolant loss I would run a fuel cleaner through (change the fuel filter if it hasn’t been done for years) and then concentrate on the HT circuit. Change plugs, leads, dizzy cap, rotor arm, coil. Probably one or two at a time in that order and test if money is tight, otherwise just renew the lot in one. Oh, and repair the oil leaks.
Hi gnu, hope you are keeping well?

The camshaft oil seal (at the dizzy) has been replaced and all seems well there now.

Just checked the oils and coolant - coolant level at the seam of the reservoir (where I have it) and the oil is clean/no signs of chocolate milkshake. So far, so good in the HGF stakes anyway...

The fuel filter was changed only a few weeks ago as a precaution when I ran VERY low on fuel.

So I guess I am back to electrical again?

Does anyone know if any of the sensors might cause this if dirty? I am wondering if the outside storage, albeit with a cover over the top might have let something start wandering around the engine bay, or perhaps just dust or dirt from the ground?
 

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Cam shaft position sensor, under the cam cover (although I can’t remember whether it’s there on the dizzy version of the k). The sensor maybe on the flywheel on the earlier engine?
 

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Discussion Starter · #28 ·
Cam shaft position sensor, under the cam cover (although I can’t remember whether it’s there on the dizzy version of the k). The sensor maybe on the flywheel on the earlier engine?
I did wonder about the camshaft position sensor, but wasn’t sure if it would cause my kind of fault - will have to Google it.
In the meantime, I have ordered new plugs, dizzy cap and rotor arm.

My luck at the moment though says that this will turn out to have the same result as putting £30 straight in the bin 😂🙄
 

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Discussion Starter · #30 ·
New rotor arm and dizzy cap fitted, no better.

Waiting for the spark plugs to arrive...
 

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Discussion Starter · #31 ·
Spark plugs finally arrived yesterday afternoon and this morning I fitted them. The result.....




misfire gone!

I am pleased to advise that my car is now running better than ever!

A great start to the weekend - I am a very happy bunny 👍👍👍
 

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Spark plugs finally arrived yesterday afternoon and this morning I fitted them. The result.....




misfire gone!

I am pleased to advise that my car is now running better than ever!

A great start to the weekend - I am a very happy bunny 👍👍👍
This is good to hear, I am glad the culprit was someting this simple.
 

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Discussion Starter · #33 ·
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Starlight Silver MG TF 135
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Yes, Great to hear that it was a "simple" problem, but as ever, FINDING the culprit is the hard (and in many cases including this one) the worrying bit.
Also, this was a very useful set of posts, because someone with a similar problem in future who will read this story will get lots of useful advice and reassurance.
Best Wishes
John E
 

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Discussion Starter · #36 · (Edited)
The strange thing was that I wasn't able to narrow it down to (what I assume) must have been one defective spark plug. Regardless of which plug lead I removed, the engine note stayed the same. This was the reason I went back to assuming it must have been a fault common to all four cylinders i.e. coil, dizzy cap, rotor of fuel.

Its difficult to imagine that more than one plug would have failed at the same/similar time - let alone all four?! So clearly, I either missed something, or something I had not experienced before was going on.

So it turns out that my running (very) low on fuel was a complete red herring and seemingly nothing at all to do with the fault...

Thats old car though isn't it - they continue to test your knowledge and your patience!

Another example: my 1979 restored Cavalier Coupe (see the thread over in the Other Manufacturers section) randomly decided that it would idle and not change up and down the gears (its an auto). It was running absolutely fine the day before, then the wheels came off, so to speak.

After a few hours of head scratching a found a length of rubber pipe, less than 50 mm long was perished and had popped off. It turns out this was a vacuum pipe that joined a stub on the inlet manifold to the auto box. A salvaged piece of Mini washer hose later and it was running good as gold again lol
 
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