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Misfire Diagnosis

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Help!

The situation is that after a lay up fitting an interior my S1 is running like a dog.

  • It appears to run ok when cold and starts well
  • when it gets to temperature it develops a misfire at low revs, eg setting off normally.
  • If I continue to try to drive it does get worse 
  • Starting when hot is very difficult.
  • I have replaced the dizzy cap and rotor arm and the spark plugs leads and coil are only a year old
  • it has an accuspark electronic ignition 
  • i have new petrol in the tank 
  • A mate brought round a vacuum gauge which moved so much it broke! He did Rev when using it. Attached to the breather pipe at the back of the manifold near bulkhead. 
  • checked the carb jets they appear to not be blocked.
  • When looking in the trumpets though they do appear to drip rather than spray fuel, is this normal?

Anyone got any ideas. Will swap the coil and get new plugs tomorrow, but not convinced it's either of these. Just cheap to check.

Mark


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After the misfire phase are the spark plugs wet or dry, do they give any clues?

Is the fuel pump delivering volume & pressure of fuel?  Are the petrol strainers/filters clear

You refer to a 'breather' from the manifold.  There will be no breather upstream of the butterflies 

Does it run OK on the choke circuit when misfiring?

If possible, maybe worth substituting the Accuspark unit with points to rule it outt

possibly worth just temporarily enriching the mixture by 1/2 turn anticlockwise to see if it is a weak running issue

Also double check the idle jets are clear from any residue/varnish   

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Mine's about the same Mark. I've always had a low RPM stumble and mine also never starts very well when it's hot. It also pops and farts a lot when I take my foot off the gas and although a lot of people seem to like this it irritates the hell out of me!

As far as the hot starting goes the only way to get mine to start is to slowly depress the throttle and hold it there, then crank it over to clear the thing and only then will it start.

I have the AccuSpark points replacement like you but I doubt that's causing the problem. At some point I'm going to check the timing and balance the carbs - when was the last time you checked yours? I have an MOT looming so I'll probably do it after that.


Lotus Esprit [meaning] a 1:1 scale Airfix kit with a propensity to catch fire

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Paul, Ive put new plugs in and half a bottle of Redex then tested just in the garage and it does run better. No backfire or popping. I couldn't take for a run because I stripped the thread on one of the plugs and it wouldn't tighten up properly.(another job to do now!) I suspect it was on the way out so that may also have contributed.

Tested compression and that was even across all cylinders. (Before stripping the thread). I suspect my carbs are out as I've never had them professionally set up. So that is certainly on my radar. After I've done the thread. LOL. Classic cars!


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Have a word with Jon - he recently had to have one of his plugs helicoiled and he got somebody to do it who was recommended by Mark at Stocks Coachworks. It didn't cost him a lot.

What's the timing set to and have you checked it?


Lotus Esprit [meaning] a 1:1 scale Airfix kit with a propensity to catch fire

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Checked recently and set up as per the manual. Sorry I have a rubbish memory. If it's written down somewhere I just forget it!


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Hi, just to hijack the thread, I've had an ongoing misfire issue that I think might be the lumenition module. How hard is it to do:

19 hours ago, 910Esprit said:

If possible, maybe worth substituting the Accuspark unit with points to rule it outt

 

The car had points when I bought it, I replaced them with the lumenition quite early on. I know these units normally work or don't... intermittent issues are not likely to be the actual module failing. However if it's relatively easy to revert to points and rule the lumenition out I might try it. 

The reason I suspect the lumenition is when the engine is misfiring, if you use a timing light you can see that it is sparking at fairly random times. Since the spark timing is determined by a mechanical/optical process in the distributor the random factor may be in the module. I've cleaned and tightened the three pole connector. 

For the trial, I'll need points, obviously, a condenser? and what else?

Thanks,

Simon

 

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On the Lumenition I would personally do some testing rather than going to the hassle of reverting to points, especially given the location of the distributor!

There is a voltage check procedure in the workshop manual which will confirm the sensor is outputting the correct voltage when the light path is blocked/unblocked.

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On 18.6.2016 at 23:58, winners said:

Help!

The situation is that after a lay up fitting an interior my S1 is running like a dog.

  • It appears to run ok when cold and starts well
  • when it gets to temperature it develops a misfire at low revs, eg setting off normally.
  • If I continue to try to drive it does get worse 
  • Starting when hot is very difficult.
  • I have replaced the dizzy cap and rotor arm and the spark plugs leads and coil are only a year old

Hi Mark! Did you ever cured this problem? Your description sound exactly like the faults I have on my S2 (with a Luminition fitted). I am still in the process of investigation and haven´t found the solution yet. 

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Mine ended up being a fuel or more accurately the carb. I put additive in the fuel and some directly in the carb itself and that sorted it. Also replaced the duels filter. But pretty sure it was the carb after being left. 


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ok, time for a carb overhaul (although the additive sounds tempting). It been 8-9 years since I´ve done that. I remember it cured the lack of power within 2000-3000rpm I´ve had these days. I would also love to throw the rusty tanks out an replace them for SJs Aluminium ones.

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Modern petrols leave varnish residue which blocks jets. The jet sizes on an Esprit are marginal, at the low end of possible sizes for the size of engine, so having the varnish reduce the jet diameter even a small amount can cause trouble. I had dreadful misfiring at one point and it was only when I physically cleared the jets with a carefully measured and selected piece of guitar string that I got all the varnish out, I coudldn't find any sort of solvent that would touch it. Once I had them clear, it has been fine ever since.


Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

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 I have found this sludge in my fuel pump (it a Mitsuba with filter element). And this is actually only half of the amount that has been in there. Let´s see how it goes without this...

IMG_2815.JPG

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I can now confirm, that rebuilding the carbs (including an ultrasonic clean), fitting two new aluminium tanks, fitting an all new tank to tank hose, cleaning the fuel pump and changing the cam belt does not make any difference. Car still runs only until it gets warm. After a 15min drive i cannot get off from a standing car. The engine chokes itself somehow, in 90% it will die down with a loud misfire when you try to get off,  if you very carefully push the throttle and get into higher revs you may get to the next traffic light or crossing where you will get into the same trouble. I will change the (pretty new) coil next.

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Have you changed the coil ?  Sounds like it may be an electrical issue ?  Just looked back through posts, yes coil has been changed, but never rule out new parts been duff,  also has the fuel pump been changed or checked when the problem happens ?


A

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It would be worth checking if the coil is getting very hot. If it is, someone may have accidentally bypassed the ballast resistance.

But equally could be a Lumenition problem, either sensor or module. 

Assuming all the normal stuff checked such as rotor arm, cap,  HT leads etc.

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I had replaced the rotor arm, so it´s new. But I may order anotherone here without the rivet. http://www.distributordoctor.com/red-rotor-arms.html. Leads are newish Magnecor ones. Connections of the Lumenition have been checked, seemed to be ok.

I checked the coils temperature when the car failed, coil was pretty hot, though I was able to touch it. Don´t know.. everything is hot in the engine bay then. I missed to say it is not possible to start the engine again for about 1-2 hours once it´s off. Starter is brand new (Powerlite Unit).

Edited by marode

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The red rotor arm sorted it for me. I to had replaced  my rotor arm with one from a local motor factor but the red one from that website sorted it.  My symptoms were exactly as yours. If that doesn't work try your fuel pump. But the rotor arm is the cheaper option. I did it the other way round ?


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I´ll try with the rotor red arm. Assuming no 54422803 is the right one? I also have a used coil for  tomorrows test drive.

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Good luck with tomorrows test run,    To be honest i would be much happier to have a problem like yours that would not start for a long time after the fault has happened,  nothing worse than an intermintent fault, this one at least gives you plenty of time to swap and change things out.   Blessing in disquise really imo :)

Just a thought as you say its dead,  i.e turns over etc but will not start,  may also be worth checking the ignition switch is feeding a live, check the fuel pump also  ?


A

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On 19/06/2016 at 05:58, winners said:

 

  • When looking in the trumpets though they do appear to drip rather than spray fuel, is this normal?

They are supposed to spray, not drip.


Ad initium

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I changed the coil to a used one and the car seems to run. I don´t trust it yet (guess I will never be able to trust in its former long journey proven reliability), but so far...  I only do test-drives uphill from my house, to be able to roll back again in case.

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Great news,  Glad it worked  :thumbup:   Just keep your fingers crossed :)


A

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