free hit
Misfire Diagnosis - Page 2 - Engine/Ancilliaries - The Lotus Forums - Lotus Community Partner #ForTheOwners Jump to content


Misfire Diagnosis


Recommended Posts

Upgrade today to remove Google ads and support TLF.

fuel pump is fine. Engine turns over, so live feed should be ok. Guess vapor lock or similar stuff. The car never liked to start when hot, but in the past (years ago...) it did after turning over the engine for 10-15 sek. Now it doesn´t.

Update: ok, now, after roughly 1/2 hour it did start after lots of cranking, but when I carefully tried to push the pedal it died. So.. seems about the same behavior as before. I will throw the hole distributor and Lumenition out next and replace it with a 123 ignition.

Edited by marode
Link to comment
Share on other sites

I do not have access to any wiring diagrams atm,  but off memory just because the engine cranks over does not mean the ignition side has a live feed,  I see that you say the fuel pumps working ,  i cant remember if that is on the same circuit as the ignition.   Temps can affect an excisting electrical  problem  quite a lot when hot.  


Link to comment
Share on other sites

Take a plug out and see if you have a spark Don't guess. Also, ignition switches fail...sometimes they cut off the ignition whilst the starter is engaged....


  • Like 1

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

Link to comment
Share on other sites

19 hours ago, marode said:

I will throw the hole distributor and Lumenition out next and replace it with a 123 ignition.

Why throw expensive parts at this problem before properly diagnosing. As John suggests, check for spark first to confirm. Then it can be diagnosed from there if no spark. The connections can be checked, there are easy metering checks which can be done on the sensor. If all connections and live feed checks out then you can start to blame the Lumenition module but this is the last suspect. 

A cause of not hot-starting (apart from fuelling issues, vaporization) can be the circuit which bypasses the ballast resistor under cranking not working. This function does affect hot-start capability although most people think its only for very cold starts. I know this from experience.

Also, you mention replacing the distributor. Be aware that unless the dizzy is specifically the Lotus type which has an oil seal internally on the shaft, oil will leak out of it in large amounts.

  • Like 1
Link to comment
Share on other sites

ok, ok.. your ablosulety right. I have had found the page in the manual about metering the lumenition and will do more investigations before changing anything. Was just tempted with that 123 idea, because it could rule out serval suspects at once. Also I would get he 123 ignition for half the price. But for today: the sun is shining here and I won´t let the Esprit ruin the day. I´m off to the lake. Thanks very much for your help.

Link to comment
Share on other sites

Haven´t changed to red rotor arm yet. But here´s the news of today: the test run this evening endet at home in the garage (best point). Car was heated well up to 95°, my 4 spal fan setup was making quite a noise. Approx. 100m in front of my house I had to stop to let a tram pass. With the car standing, it suddenly went off. But started again easily. This could possibly be because of low fuel, although I have had put 20 liters of 98 octane in (the brand new tanks), and have only done three short test drives of approx. 5miles each. I was standing quite downhill, so maybe not enough fuel at the tank exit. In front of my garage I was able to repeat this behavior. With the engine idling while the car was parked downhill, it went off after half a minute or so and did not go off when parked even. Bummer, I have had no extra fuel to check, if that helps to keep it running when parked downhill. Good point also: no more misfire, no more ignition miss on any cylinder while the test-drive when hot, car was accelerating as it should. Either has changing the coil helped or changing the tanks and cleaning the whole fuel systems or both. 

Now the most important finding: left the car standing for 5 minutes and it did not want to start again (as before). I removed the engine cover and air filter. Smoke was coming out of the trumpets and the crankcase breather. Without the air filter and still hot, the car started immediately. There is a fat spark coming from the coil cold or hot. There are obviously sparks at all plugs. Pulled the plugs - all of them looked ok.

So, I would say it is a lack of fresh air that causes the trouble. This also makes sense to me, because I have been more into trouble with the car standing then with it moving. Air in the "ears" definitely helps. Now, what to do? Where is the failure? I could add a purge pump to the air box, but the car has worked before even on hot days. It`s just getting too hot now. Hotter then in the past. I don´t know why. Today I get in trouble at traffic lights and years ago I could drive through the madness of Napoli in the heat with no trouble even with the old original 2-fan-setup. Now I have the 4 modern fans, have cleaned the radiator, but still the car only cools down when driving. What would you do next?

Link to comment
Share on other sites

All sounds very frustrating.  On the cutting-out issue - you could try replacing the fuel pump relay?  I had a dodgy one and I noticed it took about 30 seconds for the carbs to stop supplying fuel.  On mine you can hear the pump constantly, but on yours I think it is an intermittent clicky one so hard to tell if stops?

Carb float level too high so going too rich?

Link to comment
Share on other sites


1. Am I right to  read, that when standing still downhill ( not level) worsens the problem. The car is stalling @ idle.

2.Your garage is uphill and the car is often parked that way?

3.without the air filter the car started better?

If I evaluate these things, it looks like the car is flooding . It doesnt start because of a to rich situation. Getting fresh air in helps starting. Now the flooding can occur when the float level of the carbs is not right and to high. Standing uphill may worsen things and make fuel drip into the carburator holes flooding the trumpets. Now you have to think what the reason can be , why the float level is to high? It can be , just because the float levels are not adjusted the right way. But the reason can also be that the needles that are shut down by the float levels just do not close well, making the fuel pump filling up the bowls to high causing them to flood. Did you change those needle in the 2 carbs? are they the better Viton ( rubber) tipped needles instead of metal? Also, are you sure that the pivot pins of the floats are not dammaged and let the floats move free. Also , are you using the original SU pump or is it another type of fuel pump that could be delivering more ( to much) fuel pressure and filling up the bowls to high because the tips can not manage the pressure.

Now all my questions are related to an overfill of the carb bowls, causing the engine to flood. So first start by checking your carb float fuel levels when the problem occurs. You can do that as described here: float fuel level

If this is indeed the case, you can examine the reason why this is happening by answering the other questions I mentioned.






Edited by gvy
  • Like 2
Link to comment
Share on other sites

Geert and other kind helpers,

I had just overhauled the carbs and dismantled them (nearly) completely. Float high was set to 16mm, new needle valves have been used (although not the ones with rubber needles). My fuel pump is in good working order. It is a Mitsuba one with additional filter emelent (because of a break down in France years ago, someone at a Bosch Service there has dumped my working SU Pump after a misdiagnosis for a Facet, which was faulty after one year). Anyway, now it´s this Mitsuba ( ), freshly cleaned. This setup has worked before for years and should function in theory. I will check the fuel level in the carbs after the next test drive. My guess is still just low fuel in the tanks, therefore the downhill problem. My car is generaly parked even in the garage, although I have to drive 3 meters a bit downhill to get there, therefore I was able to repeat the fault. With the air-filter off on a still hot engine, the car started immediately. The fuel is cooking in the carbs, so that´s the reason why smoke comes out of the trumpets and the mixture is getting too rich to start the engine with the air filter on. Might possibly be, that the car does not get (enough) fuel while idling, because the fuel evaporates. When driving, I usually don´t get into trouble, because fresh air is delivered from the outside through the air ducts. When standing at traffic lights with a hot car, I get into trouble. My question at the moment is: why is the car getting hotter than in the days before. As I mentioned, it did not like traffic jams ever (who does?), but didn`t fail like now. I will double check the ignition timing next and set the idling mixture with the help of some colortune plugs to be sure, it is not running too lean at idle. I may inspect the water pump or at least flush the cooling system. If the car is still getting too hot when sitting in traffic, I will discuss the next steps here: 

Everyone is invited to join! Thank you very much for your help!



Link to comment
Share on other sites

  • 4 months later...

Resurrecting this topic after what appears to be a four month lull. Any progress with this condition?

Did Andyww’s advice/thought prove the “final fix”? 

Or has it continued to vex you? 

On another forum, it was mentioned by MrDangerUS that a bad catalytic converter = “runs rich, irregular idle, engine cuts off at higher rpm, idles fine but dies at attempt to drive.” 

I have another car with a 2.5” high flow cat, and when my aftermarket high flow catalytic converter’s substrate came loose and clogged my exhaust, my car exhibited strange conditions under load. I could idle the car in the garage, back slowly onto the street, even rev the engine in neutral handily, but as soon as I put it in gear and accelerated with anything approaching fast, my car absolutely would not provide forward motion and the engine whined, whinnied and lugged, and even with all the modern electronics went into “limp mode” and shut down, just turning off— poof! 

The exhaust was trying to cram 2.5” of exhaust pipe worth of exhaust through a scattered jagged tangle of honeycomb wreckage and had nowhere to go, but I don’t quite understand how that caused my engine to shut down (with *zero* OBDII error codes being thrown!)

Anyway, I don’t even know if this particular car in the thread has a catalytic converter, so if it does not, the point is moot.

In the end, how did this turn out? I hope well!!!



1986 Esprit HCI (Bosch-injected)

Link to comment
Share on other sites

Sorry for not reporting any of my results lately. In the end I had found the optical switch of the Lumenition to be faulty. Fitted a new one from autocar and have not had any misfire or similar faults since. But I don´t trust fully in it yet, because I haven´t had much time for longer test runs since. Fingers crossed... I have also flushed my cooling system with the help of some Liqui Moly additive and since then the car seems to keep 90° as years ago. But again, more test drives in summer have to be done to confirm that... Now waiting for better weather and salt-free roads. Cheers, Matthias

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...