S3 "miss On Tickover. Baffling..........

[elans3]

Hello everyone, I wonder if anyone has encountered my problem before ? My S3 has a freshly rebuilt (only 1500 miles) engine, which is standard apart from Sprint head, S/E cams, vernier timing gear. It runs 40DCOE 18's with Sprint jets and 32mm chokes. Running a Magnetronic ignition, with copper leads. It is very fast and responsive at anything above 1500 rpm, but under 1500 half misses on one cylinder. Yesterday it was No 2 cylinder, another day it can be a different pot.....
I've checked the timing, which is spot-on. I've checked every jet in the carbs,several times, all clear, New Lucas Sports coil, new cap and leads, tryed two new sets of plugs (NGK's).
I believe that it is definitely electrical.
The only thing I can think of is maybe that the copper leads are making the (new) magnetronic play up ? Although I don't think so, as it ran a Full Lumenition system before and the problem was still there. My only other experience of a similar problem was with my MGA and it turned out to be the voltage regulator.
The car is a positive -converted to negative earth car before I got it, and still runs a dynamo. Any thoughts anyone ? I would appreciate your help and advice.
elans3

[steveww]

If you are running solid copper HT leads then I would suggest using a resistor spark plug. This will supress the RFI/EMI.

[storrar54]

I suggest you make sure you have resistor plugs and leads. Then check your distributor for freeplay on the gears and also the bob weight mechanism inside. I had all sorts of problems until I discovered gummed up bob weights and springs all solved by a reconditioned distributor.
Richard

[elans3]

Thanks chaps, I will try plugs and silicon carbon leads, although my previous car ran copper cored leads and an Aldon Ignitor with no problems whatsoever.
Distributor is ok, I have 3, all reconditioned and have the problem with all of them.
Will keep you posted.
elans3

[steveww]

Stick with the copper leads, just make sure you use a resistor plug. I run copper leads with lumenition magatron (or whatever it is called) with no problems at all. Copper leads are more in keeping and look really good if you use the striped ones from Holden B)

[type26owner]

I believe that it is definitely electrical.

Why so?

Have you been seating in the new Hepolite(?) rings by giving it full throttle often enough? What oil are you using? How long has it been since the DCOE_18s were serviced to reduce the airleaks at idle? Are the original 79 degree 30 minute butterflies still in the carbies? Does the car backfire or pop out the exhaust on overruns? Is the exhaust collector flange leak tight? Do the carbies get hot? Too hot to leave your hands on them for more than few seconds?

Sounds like the usual problem of getting the spent, incorrectly factory-tuned carbies to idle smoothly to me. BTDT. They can be retuned to nearly the expected performance from fuel injection. You can resolve these issues but it's one hell of a lot of work to do it.

[berni29]

Hi There

Although I am in no way anywhere near (not even) as qualified as Mr type26owner to pass comment, I would think that it is the carbs. Can you not swap them over with another owner just to find out?

Best of luck

Berni

[type26owner]

Oh, hey! Forgot one of the fundamentals. Don't overcool the engine. Running it too cool saps the heat away from the combustion process and overcooling's most detrimental impact is at an idle. Engine should never go below 90C. 90 to 105C is perfect and where the engine will put out maximum power and respond to tuning the best. It also is where the engine is greenest to the environment except for the oxides.

[elans3]

OK here we go in answer to your kind advice, (in order) :-

Rings will be well seated by now, I worry sometimes that I'm giving it too much of full throttle sometimes, perhaps too early. Will do compression test at the weekend.
DCOE 18's just serviced, with new gaskets, needle valves, jets cleaned, new mixture screws, absolutely no play whatsoever in the spindles, and the correct 79 deg 30 min butterflies therein !
Carbs don't get hot at all.
Have had 3 sets of carbs on, a pair of freshly serviced DCOE 31's, another pair of 18's in excellent order, and a pair of Dellorto's from a Sprint in similar condition.
Problem same with them all.
That's why I believe it's electrical. underlined by the "miss" appearing to change cylinders ? As I say, as soon as the revs get to 13 - 1500 it's as clean as a whistle and really quick.
The engine doesn't get as hot as that. It has a 78 deg thermostat ? in it which I believe is as original. I would have thought that 105 deg C was far too hot for normal winter running ? The only time it has got anything like that hot was a few weeks ago when we had the warmer spell and I was in some traffic and didn't notice it creeping up. Switched the fan on and it pulled it down ok.

It's so pokey that I can't see it being the carbs. I've run Twin sidedraughts on many cars over the past 30 years and never had this problem before. My previous S3 S/E was the fastest accelerating standard Elan I'd ever come across before, even with the "Bullet " ratio box and 3.55 diff, it ws quicker than any Sprint I'd driven, but this is even more wick. It shows no sign of the S/E flat spot on 32mm chokes, and is very tractable on the S/E cams.
Plug change to suppressed type at the weekend as a starter.............

[berni29]

Hi

I remember in a previous post for someone else Keith suggesting having a look with a timing light and seeing if there was any to be deduced from the flashing. I thought that was a very fine idea. It sounds like you have probably tried it though. You seem to have been very thorough!

Best of luck

Berni

[type26owner]

The car is a positive -converted to negative earth car before I got it, and still runs a dynamo.

Oops, missed this fact before. Yup, check the voltage delivered to the coil at an idle. Also across the battery terminals while it's idling. Disconnect the old radio suppressor from the coil in case it's leaking voltage.

Copper plug wires will not affect the hall effect switch one bit. However, you should be using resistor type spark plugs. I use Autolite 63s. Check the resistance is correct right out of the box though. 5 to 10k ohms is okay.

[mikefromengland]

hello.maybe it could be the electronic ignition.i have heard of lots of people having problems with these.i use the aldon ignitor with no probs .it is a favorite with many.also try a hotter plug.i use ngk bp6es with no problems .i use to use bp7es.these were ok on a run but no good in traffic.regards mike

[elans3]

Hello again, superb response from you chaps, you do yourselves great credit.
Here we go again, in order:-

Berni, haven't tried the timing light trick, haven't got one, never had one, don't believe in them, always trusted my ears for pinking under load, and never once damaged an over-advanced engine in 30 + years, 20 of those in competition. (The timing marks on front covers are never right anyway, you would only really get it right if you used a dial gauge down the bore to get true TDC and make your own mark on the cover). Plus I'm an electrical idiot.

Keith, Your point about the pos. to neg. conversion, are you suspecting the dynamo or the voltage regulator ?
Dynamo is ok, checked out, but not voltage reg. Am going to change this weekend for an NOS Lucas one. What should the voltage be across the coil at idle ?
There's no radio suppressor.

Mike, been down the plugs route, or at least the same NGK's that you mention, both 6's and 7's, no difference.

Thanks to you all , keep the idea's coming !
Steve

[type26owner]

Well that depends on if you've got a ballast resistor installed or not and the condition of the battery, wiring and the charging system. Installing a 40k volt coil onto an electrical system that is marginal is just asking for these type of troubles. I don't know for certain what the lower threshhold of voltage would have to be to cause a partial or full misfire. An ignition scope to look at the waveform would spill the beans.... Go have this done cause it only takes 10 minutes for a professional mechanic to diagnose this problem for sure.

A scope can spot if the carbies are the cause also. Better to devote your time fixing the real problem then wasting time chasing your tail.

[rgh0]

Steve

Can you decribe a little more the miss fire characteristics.

eg
Does it occur immediately the revs drop below a certain point and dissapear immediately you get above that point or is their a time delay if so how long.
Is it affected by how fast you move the revs up and down.
Does it characteristic change if the engine is hot or cold
Does anything else affect it ( phase of the moon, day of the week ?)

In diagnosing these sorts of problems it is hard to do it over the internet as you cant get all the data from all you 5 plus senses you normally get when just standing looking at a problem on a car in real life. Thats why I normally dont contribute to these diagnoses type threads, at best you guessing.

Looking for what affects or changes the miss characterisitics helps determine its basic cause

Rohan