Mis-firing TR6

[Mike Sevenoaks]

Hi

I've been a TR Register member for many years (no. 37095) and have had my 1973 PI TR6 since about 2000. I barely touch it mechanically and always take it to Fourways Engineering (near where I live in Sevenoaks) for any work, and am pleased with their work.

When the car came out of 'hibernation' last spring, I charged the battery and turned it over, expecting it to fire up as usual. It started, but was misfiring, backfiring, lumpy, and generally undriveable. Fourways picked it up on the trailer, sorted the problem (they thought) by cleaning the points, and also fitted a new clutch and got it through an MOT. All good, but obviously expensive! Trouble is, I'm still having misfiring problems. Not as bad, and it runs OK for say 10 minutes, but then starts mis-firing, lurching, and the occasional backfire. I'm tempted to ask Fourways to take it away again (I don't fancy driving there and breaking down) and do more diagnostics to get to the root problem, but as it's intermittent, this may take time and be costly.

So - are there some easy checks I can make myself to try to narrow it down? I could change points/condenser but does that mean getting a strobe etc? Would a problem like this be easy for the garage to diagnose or is it a process of elimination, starting with plugs and ending with the metering unit or something?

Sorry to be an ignoramus, but grateful for any advice.

Thanks

Mike

[mleadbeater]

sounds like coil on the way out.

 

Mike

[Waldi]

A Mike suggests,

It would be cheap to change the coil, the rotor and condenser, no re-adjusting of the timing needed if you do that. Best to order from the Distributor Doctor, to avoid cheap poor quality items.

Have you filled the tank with new (fresh) fuel since spring, 98 Octane?

Waldi

[PodOne]

+1 Dizzy Doc coil etc and consider fitting electronic ignition keeping the points as back up.

Sounds like a coil issue.

Andy

[mleadbeater]

as Waldi suggests, it could also be possibly the rotor arm or condenser.

you can check the rotor arm by removing the cap, remove the central lead , and hold the end near to the rotor arm, then crank the engine with ignition on, if the spark jumps to the arm it must be shorting to earth under the high tension.

ive had this happen to a midget some years ago, instantly fixed with a new better quality arm

good luck

Mike

[Mike Sevenoaks]

Thanks chaps - coil, condenser and arm sound like the place to start!

[TonyC]

Mike, Grab a coffee and watch this video. It’s a bit inconclusive but will give you a good idea of what to check and how, and in what order. What is important is, as is illustrated here, change each part in turn and if there is no improvement replace the original and move on to the next.

TonyC

TonyC

 

 

[Mike Sevenoaks]

Hi Tony - thanks for this. Just watched it - fascinating! You can sense his frustration that he can't explain how he's fixed it.

[mleadbeater]

intriguing, a complete mystery.

been watching some of his other vids, very informative.

Mike

[Jules TR6]

I started a couple of threads here recently, misfire getting worse and worse, and that was after a temporary reprieve - after changing many bits (new points, condenser, rotor arm, HT leads, cap, coil, spark plugs, etc, and then even a drop-in electronic ignition, and bled the injectors twice).

In the end it seemed to be the new resin-filled coil. In the first few minutes all would be ok, then the misfire got almost to 'no-fire'! Testing the coil with a meter, inc the primary and secondary windings seemed ok, but somehow it isn't (and I can't keep testing). While others trust solid-resin filled coils, it soured my opinion of them, so I'm sticking to the oil-filled type from now on (which dissipate heat better).

So I'd try a new coil - just get one and put it in yourself (but make sure you get the correct ohm! 3ohm, or 1.5ohm for a ballast system, either you know this or you need a meter to test it). Then maybe new plugs, then maybe the HT leads (if they are old or have been over-flexed or the connectors have gone bad).

I'd also get a strobe (gives you knowledge of where your engine is 'at'). I recommend the Draper 52616 (£21). I've tried higher-tech digital lights (bigger, heavier, easy to change settings accidentality), but I found this more basic Draper one better for my needs (there's other similar looking ones, all are basically the same and have replacement bulbs, but I'd get this one), NB the spark induction pick-up must never be knocked (or dropped) - true for all timing-light pickups, in a garage a drop or hard knock can often happen when getting gear out of the way, so just take care of the timing light as a whole, and it'll last, but it's only £21 so no worries really. Order one today along with a coil (and maybe try oil-filled before resin). For all your points bits, yes, as others have said here - Distributor Doctor.

[tr6tuga]

Chek the reuturn lever on the MU it must be spot on, or it could be a loose screw on the condenser, or progressive coil failure until,  road side! carry a replecement it's a easy road side replacement.

13 years PI, and still learnig