Lotus Elan

Elan +2 Misfire when hot

PostPost by: Nercw1 » Mon Jul 10, 2006 10:07 pm

I am new to the forum and a recent 1968 Elan +2 owner. The car is suffering from a serious misfire after 10 - 15minutes running. When cold the car runs beautifully. Then progressively develops an electronic misfire. I have so far checked & gapped points. Replaced coil & ballast resistor, stripped checked and replaced HT leads. Replaced plugs. Misfire IS NOT consistent to one cylinder in particular. Does not appear to be fuel related, however I have replaced Vac hose to H/Lamps and Vac hose to servo as both were showing advanced signs of perishing. All cylinders are receiving fuel. It has to said that the 10 - 15 minutes of spot on running still justifies this aggro trying to trace the fault
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PostPost by: schroeder » Mon Jul 10, 2006 11:53 pm

A little more info will help.

Is the misfire present at all times? More prevalent at idle? On Throttle transition? Under load? on Over-run?

Why do you describe it as an electronic misfire?

Have you performed or have had performed any servicing or tune up other than hose replacement? Have you checked hose connections for leaks? This can be done using a gas burner (not lit of course around the joints. If rpm increases you have a leak)

Has it been like this since you have owned it or has it recently developed?

Are you running strombergs or Webers?

Stu
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PostPost by: john.p.clegg » Tue Jul 11, 2006 5:55 am

Have you changed the condenser?

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PostPost by: cliveyboy » Tue Jul 11, 2006 6:55 am

What carbs are you using,
What make/grade of spark plugs and are they sooting or oiling up.

Clive
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PostPost by: Nercw1 » Tue Jul 11, 2006 7:19 am

Thanks to you all for the range and speed of response.
The car is on webers and the misfire only comes in progressively when the car has been run for some 10 - 15 minutes. The car currently has a set of Bosch BPR6ES and when missing there is little or no spark evident when the lead is removed. The car is running rich but not overly so. The points and condenser were both replaced. I can replicate the fault from cold by hooking up the old basllast resistor. The coil has been changed since, but the problem persists. It looks like Lotus ownership is going to be no different from running a 30 yr old BMW R45 or Desmo Ducati!!!!
Thanks again
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PostPost by: rgh0 » Tue Jul 11, 2006 10:20 am

If the voltage is good at the coil when the misfire begins and the missfire is not cylinder specific then its got to be in the components downstream of the coil that are common to all cylinders.

i.e. coil, low tension wire to points, points, condenser, high tension lead from coil to cap, cap or rotor.

Systematic replacement with know good items should eventually find the problem. Access to an engine ignition analyser makes it quicker to diagnose the problem but is not really necessary.

regards
Rohan
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PostPost by: gjz30075 » Tue Jul 11, 2006 12:14 pm

Nercw1 wrote:I have so far checked & gapped points.


If you're going through the trouble to get to the points, I say replace them, along with the cap. Today's caps with aluminum electrodes are not as good as the early brass ones and seems that they just don't last as long. Replace the condenser, too, as pointed out earlier.

Greg Z
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PostPost by: Emma-Knight » Tue Jul 11, 2006 12:59 pm

another one: when exaust system is gettting hotter it might let some air into pipe joints under the car (jointing paste missing or cracked). With the engine running a little rich, sooty deposites might be ignited by hot exaust gasses. My car suddenly started missfiring right after the exaust came off and was refitted without jointing paste. All other systems remained untouched. Looking at the spark plugs the front carb was clean brown,
the rear one both plugs sooted. The exaust was very sooty when taking the car from britain, but as the exaust was still tight and sealed, the gasses were could enough at the end of the system - so did not ignite when mixing with fresh oxigene.


Anna :idea:
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PostPost by: andrewdmoore » Tue Jul 11, 2006 2:28 pm

I had exactly the same with my Sprint - ran fine when cold then misfired when I accelarated hard after 15 mins or so. I changed 2 things simultaneously (stupid I know) so I'm not sure whether it was 1) 2) or both.

1) Try changing the rotor arm. Apparently within a similar batch, some can be of dubious quality. If you look inside the arm, you may see some discolouration of the metal contact, mine was right at the top, so was near invisible to the naked eye. It means a short circuit therefore a malfunction.

2) The other thing I changed was the plugs - BP6ES is a hottish plug and if it gets too hot it breaks down it. I now run BP8ES, but mines a Sprint with high lift cams so try BP7ES, but you never know someone might have changes cams before you owned the car so you could end up with 8s.

Regards, Andrew
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PostPost by: Jason1 » Tue Jul 11, 2006 5:52 pm

Hi

I also have a 1968 +2 (do you know there is a +2 section?) My car also developed a mis-fire recently but has now gone :?

I would replace the ignition system as there is very little of it anyway as the other posts suggest. But I would not rule out the Webers, they can play about.

I am running mine on BP7ES plugs and they seem fine, I have a new rotor arm, brass contact cap (QED), new leads and have fitted Lumenition.

My misfire only started after I operated the headlights, I know trying to drive a +2 in the dark is maness :D But I had to do it. I suspect it was the dash valve as after leaving the car for a white the misfire stopped.

I find the Webers can over fuel if you stomp on the pedal and you really must!!! You should remember that this is not a modern car and it will have a few quirks :) Obiously the exhaust will pop back in the pipe on over-run which can alarm a newbie but you get to enjoy it and try to do it when passing old ladies at bus stops :D

Are you sure it's a mis-fire? Mine pinks as I have not got around to unceasing the advance weights and adjusting the timing.

If the mis-fire is not specific to one cylinder I would suspect the Webers or the coil. But you say the spark is very weak; how are you checking the points gap? If you are using a feeler gauge the cams could be worn? Mine is the same year as yours and my cams are very worn, try using a dwell meter and see how it runs.

I look forward to seeing your many posts, Lotus ownership is never dull :D

Jason
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PostPost by: nebogipfel » Tue Jul 11, 2006 7:45 pm

I replaced the points with an Aldon Ignitor because it seems impossible to find a decent condenser these days. Points were badly burnt after only a few hundred miles

Just a thought but it cured my misfires .......... so far! :shock:

The general quality of parts available is very variable, if you can find "new old stock" go for it every time.
John

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PostPost by: Nercw1 » Tue Jul 11, 2006 8:20 pm

Again thanks for the volume and quality nof replies.
Have now replaced plugs, checked HT leadscut 1/2 " off each and resecured in cap etc. Replaced Luminiton HT coil with intermotor unit. Replaced vac pipes to H/L and Servo, regapped points. Still the problem persists. Next on list is cap, points, & condensor. Anybody got any idea where I might be able to pick these up off the shelf in North Wales where I live, Merseyside where I work and Cheshire where I commute through???
Again congrats on a terrific effort to assist a newbie. Wife thought I was certifiable but after taking her out for a 10 minute drive round Nth Wales lanes last evening (problem kicks in after approx 15 mins!!) she has now agreed to join me and picnic basket in Elan on an outing to Bennetts Superbikes at Oulton next weekend :D
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PostPost by: john.p.clegg » Wed Jul 12, 2006 5:52 am

Chris Neils is on your doorstep-Northwich
John :wink:
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PostPost by: Jason1 » Wed Jul 12, 2006 11:41 am

Try Halfords if you are desperate, if yours is the same mine it is a 23D4 dizzy which was used on the early minis. I bought my Lumenition from www.minispares.com as it was a lot cheaper than the listed Lotus one. I checked the parts numbers and they are the same :D
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PostPost by: RotoFlexible » Wed Jul 12, 2006 4:41 pm

I happened across a reply to a topic in the Things in Common thread that identied the ignition switch as a possible culprit. His symptoms sound a lot like yours.

http://www.lotuselan.net/forums/viewtop ... 8&start=15
Andrew Bodge
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