Lotus Elan

Hot running problem

PostPost by: Phil W » Sun Apr 15, 2007 7:08 pm

Finally got the 2 + 2 on the road after struggling fitting replacement speedo drive as old one sheared as cable had apparantly siezed.

However seem to be having a problem when engine hot and need some advice. Car starts and runs beautifully until engine gets hot than it misfires, backfires and won't idle. It sounds like its running on only two cylinders its that rough.

I supsect an electrical breakdown some where. Possibly the coil?

Once its cooled down it behaves perfectly again.
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PostPost by: worzel » Sun Apr 15, 2007 7:13 pm

Hi Phil

Is this time related ie does it occur after a certain time from cold?

If it is time related rather than the distance covered try electrics- I had a similar problem with the electronic ignition on another car- turned out that the amplifier was breaking down after about 20-25 minutes running.

Might be worth a try.

John
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PostPost by: Phil W » Sun Apr 15, 2007 8:35 pm

Cheers John.
The time scale fits and I do have electronic ignition fitted (10 years ago).
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PostPost by: john.p.clegg » Sun Apr 15, 2007 8:41 pm

Phil
I'd put my money on it being fuel related rather than electrics,if it's missing on two you can rule out the commom components?(coil,condensor,points,black box?)...and start from the rotor cap/arm,leads plugs?

John :wink:
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PostPost by: alaric » Sun Apr 15, 2007 10:29 pm

Hi.

Have you checked the balance of your carbs? Sounds like they're out. My twink had very similar characteristics until I balanced them accurately with a Carbtune 4 column manometer. I have previously posted piccies of this device. From your post I couldn't really work out how the engine performs when not on idle. If it's ok apart from idle and poor pickup then I'd check out the balance of the carbs. Have you developed an air leak on one of the seals etc. If you follow the setup procedure that should become evident.

Hope that helps.

Sean.
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PostPost by: Stuart+2 » Sun Apr 15, 2007 11:42 pm

Hi Phil
I tend to agree that this is electrical in nature.
Heat could be affecting carbs but vapour lock seems unlikely. Your electronic ignition module certainly needs to stay cool - is it in a good location? It might just be old - just replaced the Bosch unit on my +2 after 14 years with a Crane unit (excellent result, too).
Perhaps you could start by shorting plug leads to, say, see if numbers 1 & 2 are misbehaving at the same time (poss. carb) or otherwise (prob. electrical). Hard to check the ignition unit otherwise.

Keep us posted and good luck.
Stuart - Sydney
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PostPost by: berni29 » Mon Apr 16, 2007 12:52 am

Hi

The coil is a possible suspect and is easy to test or swap out. In my experience it is possible to have 2 cylinders fine and the other two misfiring badly with a faulty common component (eg the coil). All you need is for the two misfiring cylinders to have sub par leads or plugs etc compared to the two which seem fine and it is enough to tip the balance on those two. If you see what I mean!

All the best

Berni
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PostPost by: richardcox_lotus » Mon Apr 16, 2007 9:23 am

I agree with Berni et al re the Coil. Had identical symptoms a few years ago - When car cool, all Ok. When gets hot...........it was not. Swap coil, all OK again.
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PostPost by: Phil W » Mon Apr 16, 2007 1:59 pm

Thanks all. Carbs balanced using the special tool recommended on here that I borrowed off a mate and car idles beautifully. When hot it sounds like its only running on two cylinders but I don't know if this is just an illusion. I can't keep the engine running and open the bonnet to tell for sure - it fails that quickly.

Spoken to Lumenition who suggest it more likely the optical switch is this is more likely to fail than the power unit and the symptoms I have are consistent with this. Quote:

The ignition system works perfectly when the engine is cold but misfires or stalls as the optical switch is heated by the rising engine temperature. If the engine is stopped and left to cool for a few minutes (alos cooling the optical switch) the engine will start and run perfectly but fail again a few minutes later when the optical switch heats up - and so on.


I also suspect it could be the coil so go a new one today. I'll try that first and then try the optical switch route.
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PostPost by: Phil W » Thu Apr 19, 2007 12:56 pm

richardcox_lotus wrote:I agree with Berni et al re the Coil. Had identical symptoms a few years ago - When car cool, all Ok. When gets hot...........it was not. Swap coil, all OK again.


Cheers guys.
Swapped the coil out and guess what? All seems to be OK although haven't had chance for a good blast yet. Did run the car a few miles and left it idling on the drive with the electric fan running so it was good and hot.
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PostPost by: Phil W » Fri May 04, 2007 12:50 pm

Problem hadn't gone away it just takes longer to manifest itself. Now taken the distributor out and stripped it right down. Can't see anything wrong but noticed signs of tracking across the top of the rotor arm.

Decided to change all leads, plugs and rotor arm just in case.

Just got to remember how to put the disi back and set the static timing now.......................
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