Mystery misfire frustration

[mike3md]

I am totally frustrated by a misfire that has appeared all of a sudden on the 3a. We were out for a run, and having covered about 100 miles were bowling along when its started to misfire, very quickly getting worse and leading to total loss of power, engine will not run. As you can imagine its awkward sometimes to find a place to pull in when all you have is momentum!

We progressively changed the condensor (twice!), coil, points, rotor arm, distributor cap and leads but cannot get rid of the fault. I have checked the LT leads, including the short wire in the distributor.

 

If cold, the car starts and runs fine - for 30 mins at 2000 rpm in the garage last weekend to try and sort it out, however once warmed through and on the road it goes about 3 miles if I am lucky before misfiring and stopping. If left for a few minutes it will restart and run a bit more.

 

There is fuel in the tank, and it pumps through OK. I have run with the filler open to check there isn't a breather blockage

 

The collective view is that it is electrical, and probably on the HT side. The coil gets very hot, (but then it is fixed to the block). The TR has an alternator and -ive earth, the engine being rebuilt about 2000 miles ago, including conversion to unleaded. Its on standard twin SUs.

 

I have spent all afternoon at this and got nowhere - I struggled to get the car home, it will only run for short bursts.

 

Now that the sun has come out I would like to use it! Any helpful suggestions?

 

Mike3md

[67_gt6]

Hi Mike

 

Seems that the only thing you haven't changed is the LT lead in the distributor. A break can be very difficult to detect in these...

 

Could there be something in your petrol tank that is stopping fuel flow once you are on the move? golf ball?

 

As you have already gone to alternator / neg earth, maybe you would consider an electronic ignition conversion? If you order an Ignitor from these guys http://www.vintageperformance.com/retrorockets/ignitor.htm you'll pay for it in dollars but it will be sent out from a European warehouse and you'll get it in a couple of days at half the usual cost. 15 mins to fit, I've never looked back since.

 

Andy

[Menno van Rij]

A few things and easy to check:

* Mount the coil to the inner front wing (cooler place) and

* Check the spade connector on the low tension wire.

* When installing a new coil, did you use the new male connector that came with the new coil, or did you reused the old male connectors that came off the old coil. (This is written by an experienced man I reused an old one once. It wasn't clean, hence not conducting properly, which gave about the same problems)

 

Regards,

 

Menno

[marvmul]

If possible, fit a distributor from another car. It's sometimes very difficult to find a fault in the distributor. The LT lead can be broken but with intact insulation. More often it's a short between the insulated part of the plate/points and the housing. The small plastic moulding holding the spring of the points can be mounted wrongly : the small nut can be very close to the spring of the the points : when warm, the 2 parts can come that close that a spark can jump between the points and the nut.

[RogerH]

Hi Mike,

Andy may have hit on the area (seeing that you have changed everything else). I was on tour a few years ago when a TR5 had the same problem. It turned out to be a fungal mass in the fuel tank.

Be very careful how you look in the tank but if there is something in there it may be blocking the fuel outlet due to suction.

When you stop it eventually floats away and allows you to drive a short distance before blocking the outlet again.

No harm in looking - be careful.

 

Roger

[sforster]

Mike,

It could be the fuel pump I had a copy of an manual pump which developed an intermittent fault for some time before finally packing up. Is there dirt in the glass bowl? Have you checked the ignition timing, has the distributor worked loose?

Good luck, Simon

[mike3md]

Thanks to all the response - I am away from the car at the moment, and will try out some of the suggestions soon.

[ppenguin]

Mike,

It could be the fuel pump I had a copy of an manual pump which developed an intermittent fault for some time before finally packing up. Is there dirt in the glass bowl? Have you checked the ignition timing, has the distributor worked loose?

Good luck, Simon

 

Hi Mike,

 

Simon could be right with his suggestion of the fuel pump as I had this very problem when I first got my 3A on the road last year. Like you, I changed all the electrical components as well as adding an in-line fuel filter with absolutely no effect. Then I replaced the pump and have had no problems since. Apart from petrol peeing out of the carburettor float chamber overflow tubes, I cured that by replacing the needle valves with Grose jets.

 

Regards

Pete

[julian c]

The easiest way is to wait for it to conk out.

 

Then you quickly see if its fuel or ignition related.

 

With ignition on, take the cap and rotor off, then open and close the points manually or short with a screwdriver. It should spark. If not, then your problem lies in the condensor to coil/ignition switch area.

Unplug the negative (dizzy side) of the coil, connect a new wire to dizzy side of coil, then try to (briefley) short it to earth. It should spark. If not, check the power supply to coil. If you have multimeter or test light, thats great, but if not, use another length of wire to connect to the plus side (the other side) of coil from positive battery terminal. If still no sparks when you short the coil side of wire, the suspect faulty coil.

 

If it sparks, then refit original LT wire to coil and try to short coil again. If no sparks, fault lies in coil to dizzy LT lead.If it sparks, then reconnect to dizzy.

 

Then remove condensor wire and try getting the points to spark. If the points spark, then its a dodgy condensor. If it still doesnt spark, then the fault must lie in the LT lead inside the dizzy.

 

It sounds long-winded, but in reality, this would only take about 3 minutes to do, bearing in mind you are in a race against time before it cools down and fixes itself.

 

To see if its fuel related, all you have to do is spray easi-start into the carbs and see if it fires up.

 

The only mechanical fault that could do something similar is the valve clearances getting tight once warmed up, but I`ve never seen any that would cause it to conk out altogether, and in any case your symptoms dont seem to match that of tight tappets.

 

ps.....if your TR is positive earth, then you swap the polarity of the wires. (as if you didnt know)

 

Personally, I would replace the wire inside the dizzy and the coil. Ther really isnt much to go wrong on these old cars.

 

Hope this helps..Julian

[mike3md]

Julian,

 

A very comprehensive elimination process! I'll give it a try (next weekend - away at the moment) and report back. I feel it really is electrical, fuel side seems OK, with a good gush when the engine is cranked.

 

Mike

[ianc]

If your fuel tank is shedding rust from its inside, it will make its way to the glass bowl alongside the pump. When ticking over, there is no problem, but when motoring swiftly, the small particles of rust will be forced upwards by the petrol flow against the gauze filter and can cut-off the supply of fuel to the extent that all power is lost and the engine may stop. Once the engine stops, the rust will descend to the bottom of the bowl and the car can be started and will run at tickover.

If this is your problem, see my article in TRaction 144/Technicalities CD about treating your tank with "Slosh Tank Sealant" (available from Moss), or get your tank to Northern Radiators in Leeds (see website radiatorsonline.co.uk).

Ian Cornish

[mike3md]

Ian,

 

Thanks, I will have a good look at that as well - although it seemed pretty clear when I scanned the pump, I will drop the bowl to check.

 

mike

[Don Elliott]

I had a similar problem recently while driving in USA. My TR3A would feel like it was running on 2 cylinders. Other times, it was like I had run out of petrol. I finally guessed (no proof) that it was caused by the 10% ethanol that they add to their petrol in USA. I usually use Shell here in Canada where there is no ethanol in Shell. I once filled up with Sunoco here in Canada and experienced similar problems. The float bowls were empty. I waited for it to cool, then used the lever on the bottom of the fuel pump to fill them and the problem was "fixed" - until it happened again. Now I avoid driving in USA and no longer use Sunoco or Petro-Can petrol here in Canada.

[Richardtr3a]

Best to avoid any dodgy petrol.

[Don Elliott]

All petrol in USA has at least 10% ethanol added. There is no way to avoid it. It has been mandated by law. To me they are all "dodgy". I had trouble in my TR3A with Exxon and with Mobil, two of the largest suppliers of petrol in USA.

[tony-qld]

All petrol in USA has at least 10% ethanol added. There is no way to avoid it. It has been mandated by law. To me they are all "dodgy". I had trouble in my TR3A with Exxon and with Mobil, two of the largest suppliers of petrol in USA.

I had a similar problem with my tr4. I was posative that it was the condensor and the problem vanished after I fitted a new condensor only to raise its ugly head again a couple of months later. In the end I found that it was the screw that fixes the condensor to the distributor plate was working slightly loose due to a dodgy lock washer. I replaced the lock washer and have not had a problem since.

[ianc]

Some 40 years ago, I had a persistent misfire on my TR2. After a very long search, I noticed that the bracket which loops over the body of the condenser had cracked its solder joint, so was relying solely on downward pressure to maintain the circuit. Once re-soldered (don't heat it too much!), the misfire disappeared.

I have also suffered a crack of the solder joint in the low tension connection from coil to the distributor. It occurred at the ring connector at the distributor end, and was not obvious because the wire remained "coonected", but when I pulled it, it came away!

The lesson: solder joints can work harden and crack over time.

Ian Cornish

[Richardtr3a]

Should we be soldering new connectors or rely on crimping. If I try to solder I find that I damage the insulation before the job is done.

 

Richard

[jonlar]

Hi Richard, personally, I crimp (using a good quality ratchet crimping tool) then run a little bit of solder onto the terminal side - the crimp gives the mechanical strength then the solder ensures electrical continuity, without solder capilliaring (I think I just made up a new word!) along the strands of wire which then becomes stiff and will break with vibration.

[Dick]

Had something similar on a series 111 Landrover. Took 3 years to solve. I made the mistake of believing that all of the electrical equipment that was fitted was correct and so replaced like for like. To cut a long story short......there are two different distributor caps that will fit your distributor and each has it's own rotor arm. The difference is that the segments in the two caps are on a different diameter and the ones on the larger diameter need a longer rotor arm. If the shorter one is used there is a bigger air gap for the spark to jump. It usually will when everything is cold but when hot, the coil probably is less efficient and cannot provide sufficient potential. I also noticed that my 3a has the long type arm in it's current distributor......which was a new replacement......whilst the original is the short one. The message is to make sure that the cap and the arm match. Hope this helps Dick.

[ianc]

If in doubt about Rotor Arms, contact Martin Jay (a.k.a. Distributor Doctor - see TRaction) and he will put you right. He is selling proper Rotor Arms (not the crappy Lucas repros, which just drop dead - I know, it has happened to me twice!).

Ian Cornish