Misfire

[skertonman]

It was getting very hot to touch, more than just warm.

It was when I was driving, and not with my multi meter to test for internal resistances of the actual coil windings, it was a case of seeing, and feeling what was wrong.

Turns out the oil inside had leaked out, hence the overheating, and only showed up after driving for some time, usually about half an hour.

Maybe someone somewhere still has an old crypton diagnostic machine with the oscilliscope out there to see whats going on with the ignition and spark dissipations.

[sonscar]

I think some form of oscilloscope is required to measure firing voltages etc.Eons ago my local garage obtained one of the first diagnostic testers.I asked him if it was any good,his reply was you cannot sell someone new parts because this machine says you will soon need them,far better to break down then replace them.Roll forward to today;Have you plugged it in? is the first question.Steve

[Monkeyzak]

Fuel pump file of crap. And I mean properly packed tight. Cleaned out throughly now. Still a misfire so new needle valves and new matching floats.

An inline fuel filter fitted but I have a feeling the tank will be out some time and either a refurbished or replacement

Quick road test today. No misfire. Woo hoo. So hopefully that's all it was. Electrician pulled out a bunch of wires and did something too which he said would affect the running

Electrics getting tidied up this week hopefully. I might have the car driving about next weekend and see what falls off next.

This is the most action it's seen in 25 years so I'm sure it's sensible doing all these little runs

As always. Thanks for the advice

[UKPhilTR7]

That is great news that you have got here running better without any misfire. It may of been one of the many things that you seem to have done or just one. The main point is that it is done. The cleaning out of the fuel pump would of helped a great deal. I have had an online fuel filter in mine now for a long time and sure glad I have.

Oh yes more things will go wrong, it is the nature of the beast. However, I bet it is a good feeling knowing you have fixed this issue. Enjoy it while it lasts.

[Hasbeen]

Get & carry a spare in line filter.

When I was having dirty fuel tank problems in one of my 7s, I jacked the car up on one side, removed the sender fitting, & syphoned all the fuel out of the tank. By jacking one side I could concentrate the fuel & rubbish in one corner, & get more out.

I strained about 5 gallons of fuel, & put it back in, & did the syphoning again 4 times, & still had some dirt.

I thought it was getting pretty good, but the inline filter was becoming so choked in about 100 miles, the car would start to suffer fuel starvation, which is of course, what your miss has been. It slowly got better, but I finally pulled the tank out, & gave it the POR15 treatment.

That lasted about 12 years.

If I had been able to find one of the old fashioned filter bowls, I think that would have fixed it, but could never find one.

At least for a few cheap filters you can run & enjoy the car.

Just remember, THIS IS FUN.

Hasbeen

[Monkeyzak]

Finally took the car out tonight as been working all week. Sadly it's still got a misfire. I'll run through all the recommendations this weekend

[Hasbeen]

Yes, thinking about it, a choked fuel filter, or pump, gives fuel starvation. This is similar to a complete cut of the motor, rather than a miss fire.

I suggest you have a look inside the float chamber of your carbs. Dried petrol from lack of use can cause a miss fire, which cleaning can easily fix. You are also likely to have some corrosion in the float bowl from any water that found it's way into there.

If you did not have an inline filter at all, & a choked fuel pump, I would not be surprised to find a pile of junk in the fuel line above the needle & seat, & in the float chamber.

Hasbeen

[Monkeyzak]

Carbs and float chambers cleaned out. New needle valves and floats. Fuel pump cleaned out and fuel filter fitted. It doesn't misfire when it's ticking over. Mostly when im pulling away. If i rev it hard it clears after a second or 2.

Distributor cap looks new.

Tempted to buy new plugs, cap, rotor arm leads and coil. If that doesn't cure it then I don't know. I have electronic ignition and I don't even know where to start diagnosising or repairing

Is it a standard coil with electronic ignition?

[saabfast]

Give in to the temptation. I have found that most slight misfires are caused by a fault in the ignition. A slight crack in the rotor arm can cause havoc, similar a bad HT lead. I have also had a bad new plug which caused, I always use NGK but even they can have the odd duff one. The coil is generally standard (at least it is on mine with Pertronix). Note that it is a 6V coil unless it has been changed along with the resistor wire.

[Monkeyzak]

That's the way I'm thinking now.

How do I find out about the coil?

I just want to use the car. With the misfiring it's not useable

[skertonman]

Threads getting a bit long now, so not sure if you've explained the symptoms.
When you say it's happening under load, is it a constant misfire, or just for a few seconds, and then clears.

Once you get up to speed say 30 MPH with constant revs is the misfire still there?

[Monkeyzak]

Pulling away from a junction you've got to drop the clutch and rev hard as it misfires . then slowly let the clutch back out or it misfires again

There's a slight hesitation in normal driving but not always

[toneinblack]

My tr was running rough, had a misfire as well, one of the green pipes from the carb nearest the bulkhead was blocked up with crud , also one of the jets wasn't as low as the other carb, and needed balancing . A neighbour sorted it for me and it's running fine now and passed it's m o t .

[littlepippin]

what do your plugs look like ? I like to clean them from time to time with some fine Dick Emery cloth.....

[Hasbeen]

My 7 had similar symptoms for a couple of years. They would disappear after 5 to 10 kilometres, & she would run beautifully.

I thought I had cured it a few times, by replacing cable ends in the ignition system, cleaning the same things, new plugs & leads etc. I had also been through the fuel system a few times. It kept coming back in a few months of even a year, but would never produce the symptoms when near anyone with the gear to track it down.

Finally the miss became long enough for the rev counter to drop when it happened pinpointing the problem to spark. As I had already fitted a new coil, we replaced the electronic ignition, & it has not happened again id many years.

Hasbeen