TorontoTim Posted July 7, 2012 Author Report Share Posted July 7, 2012 Again, thanks for everyone's input and help on this - I'm sure not only I but many others appreciate the experience shared on the Forum. With that in mind, I thought I should provide an update to help anyone else who finds they have this problem. First, a recap on the symptoms: - Under certain, very specific conditions my engine "missed" - seemingly on all or at least several (more than two) cylinders. - This would start to kick in above 2500 revs in ANY gear - below that, everything seemed close to normal - This appeared with anything more than a VERY small throttle opening (with just a "tickle" revs would gently climb to c. 3500 before the missing started - The missing started the INSTANT any greater throttle opening was applied (I could cut the engine in and out with the throttle seemingly at will...) - This ONLY happened under load (the engine would happily rev out of gear) SO - what did I try? (the following is in chronological order, with test drives after each one that only proved I hadn't fixed the problem) - I replaced all the rubber hoses in the fuel delivery to the carbs (H6, btw) and I removed the metal-cased in-line fuel filter - I checked piston damping oil levels and topped up - i checked (roughly by eye) the float levels and that the needle valves were closing ok - I replaced the coil - first with a spare, then with a brand new one - I checked the coil > points LT lead via the "wiggle" test and closely inspected the soldered connections (thanks Roger - this was a good one and I thought it would be the answer...) - I replaced the rotor arm, points and capacitor and checked the (fairly new) distributor cap and carbon bush by eye - I checked the carb springs and THOUGHT I'd found the problem when when of the pistons appeard sticky in the dashpot due to a bit of carbon build-up - I watched the carb pistons rise and fall together while revving the engine; but not under load - too tricky while also driving ;-) - Oh, and I looked at the spark plugs several times during the whole process - they looked FINE!! - I started to seriously worry that I couldn't fix it... - This morning, I replaced the (as I say, fairly new) dizzy cap and silicone leads with my old dizzy cap and silicone leads GUESS WHAT? Yep, it's now running PERFECTLY!! So.......I know (?) that it's somewhere in the coil > distributor HT lead, or the distributor cap. I've checked them with a multi-meter and the usual close visual inspection etc. and can't see anything. But I suppose that as this problem only appeared under load, maybe these components are fine sitting on a bench... So, moral of the story: 1. Always ask people on the Forum - you can always learn something new (even if it doesn't turn out to be the actual answer) 2. If the specific symptoms and your gut tells you it's electrical/ignition, it probably is 3. Just because something LOOKS ok, doesn't mean it is; similarly, just because it's fairly new doesn't mean it's ok either ;-) 4. If you keep going, eventually you'll find it 5. TR's are absolutely f***ing BRILLIANT to drive when they're working well. I LOVE IT. I've only had a couple of weeks of frustration (interrupted by a long weekend with a 1966 Mustang and moving house) but I couldn't keep the smile off my face once 4500+ revs under hard acceleration was back. As you will have guessed, #5 is by FAR the most important. Cheers! Quote Link to post Share on other sites
RogerH Posted July 7, 2012 Report Share Posted July 7, 2012 Hi Tim, I think it was forumite John R Davis once said always check the last thing you did prior to the fault. Had you renewed the dizzy cap and leads for any particular reason. Well done in persisting and finding the fault. Roger Quote Link to post Share on other sites
TorontoTim Posted July 7, 2012 Author Report Share Posted July 7, 2012 Hi Tim, I think it was forumite John R Davis once said always check the last thing you did prior to the fault. Had you renewed the dizzy cap and leads for any particular reason. There's no doubt that that is a good rule of thumb. However, in this case I changed the dizzy cap and leads maybe a year ago (so they're only new-ish ). Cap was changed as part of a general service and the leads as a "fail-safe" for rallying. Ah well... Quote Link to post Share on other sites
TorontoTim Posted September 25, 2012 Author Report Share Posted September 25, 2012 (edited) It's baaaaaaaaa-aaaack...... Odd symptoms: - doesn't happen when cold AT ALL - idling for a bit seems to make it better for a very short time (i.e. initial pulling away) - still 100% hard-wired to throttle opening/accelerator depression - I can literally switch the missfire on and off and "play a tune" simply by moving the accelerator just a small amount with my foot - MUCH worse up-hill than down-hill - I'm assuming this is due to load, but any other ideas...? - definitely affects more than one cylinder - doesn't happen AT ALL when no load - revving the engine in any way (gentle, hard, fast, slow) is PERFECT when sitting still - or with clutch depressed immediately after the missfire has been present. And so far, I've also done this... - changed coil (again) swapping between three to no avail - replaced (again) dizzy cap and leads - this time with brand new copper-core - changed fuel pump - cleaned float chambers - checked carb pistons, butterflies, spindles, etc. So - fuel or ignition? Where to look? Was the "cure" before just a red herring? Oh, and someone reversed into the driver's door yesterday. Not having a good week... Edited September 25, 2012 by TorontoTim Quote Link to post Share on other sites
Guest ntc Posted September 25, 2012 Report Share Posted September 25, 2012 Engine movement under load? electrical connection Quote Link to post Share on other sites
TorontoTim Posted September 25, 2012 Author Report Share Posted September 25, 2012 HA! Good idea, Neil. Certainly something I haven't looked at yet. Quote Link to post Share on other sites
4AIRS Posted September 25, 2012 Report Share Posted September 25, 2012 I'm facing a very similar situation with a TR4 A/Stromberg CD175. From cold the engine runs perfectly. When the engine is really hot, (e.g. driving downtown) the problems appears. I have no problem when the engine is not loaded, so even if it looks like an ignition system, I doubt it is. I dismantled my carbs (and fuel pump,filter, fuel line...) and noticed than one of the pistons is falling back a bit slower. After checking closely, it seems one of the needles is slightly bent: I suspect the needle expands/moves when the engine is very hot and may block/touch the jet, hence block the piston. I ordered new needles. Will try that option... Quote Link to post Share on other sites
GiuliaReis Posted September 26, 2012 Report Share Posted September 26, 2012 (edited) Engine movement under load? electrical connection I don't how is it is with the TR4 engine but normaly the engine has to be grounded to earth (when its negative). Also when you've points the bobine should be 3 ohm and _not_ 1 ohm. The 1 ohm bobine (coil) is for electronic ignition systems like 123. Edited September 26, 2012 by GiuliaReis Quote Link to post Share on other sites
ianc Posted September 26, 2012 Report Share Posted September 26, 2012 I recollect a TR4 in which the lead from the dynamo had become chafed and was too close to the steering column (or was it the exhaust manifold/ - it was a long time ago). When the engine was working hard, and therefore was twisting to the right, the lead shorted to the column, killing the engine! Of course, as soon as the engine ceased to fire, it moved to its normal position and the engine re-started. So the car was 'bunny-hopping'! Ian Cornish Quote Link to post Share on other sites
LGFromage Posted September 26, 2012 Report Share Posted September 26, 2012 Hi Tim, After you solved the problems with your dizzy did you tighten the clamp bolt tight enough? If not the timing may now be out. It is worth checking as it could be a cheap fix. Tim Quote Link to post Share on other sites
graeme Posted September 26, 2012 Report Share Posted September 26, 2012 - Oh, and I looked at the spark plugs several times during the whole process - they looked FINE!! Tim, You can't 'look at' spark plugs and assume they are OK. Change them. Plug insulation can break down under pressure. I had a similar problem a few years ago with 'perfect' brand new Champion plugs. Eventually changed for NGK, problem gone. Champions will never again grace my engine bay. Cheers Graeme Quote Link to post Share on other sites
TorontoTim Posted September 26, 2012 Author Report Share Posted September 26, 2012 Fair comments - thanks. I'm working through them... Quote Link to post Share on other sites
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