3000M bad misfire when hot

[plasticpig72]

When i collected my 3000M and started to drive to the Ferry it was perfect, running well. But as the engine warmed up it started to misfire very badly. So bad i needed to left foot brake and keep the engine on high revs with lots of throttle to stop it cutting out.
I know i did a thing which i tell others never to do and that's collect a car and drive it home. I always say take a car trailer to transport it home. To take the Brittany Ferry Portsmouth to Saint Malo with a car trailer behind is mega expensive in High Season. I had about 50 miles to drive to take the Ferry and so took a risk.
Well to return to the misfire when hot i had exactly the same problem with my 3000S.
I fitted a Bosch HT Coil 12 volt and removed also the cold start resistor.
I also moved the position of the HT Coil as far away as possible from the Exhaust Manifold.
Is this a common problem on "M" series with V6 Engines?
Alan

[plasticpig72]

Maybe i have been unlucky a 3000S and a 3000M. Both have had the same problem, no chance. Never mind it keeps me busy.
Imho it's best to position the HT Coil as far away as possible from any heat source.
With a V6 both sides of the Engine compartment are hot
Alan

[plasticpig72]

Thanks for the idea about the choke.
I have already bought a Bosch coil so i will fit that first, only takes 5 mins.
Start the car and watch the choke to see if it goes off as the engine warms up.
In fact when i got the car home and looked at the coolant level in the swirlpot it was very low. That would mean no hot coolant reaching autochoke to turn it off.
I will give it a try tomorrow and report back.
Thanks
Alan

[plasticpig72]

I have run the engine now and bled the system of airlocks. The coolant is circulating through the auto choke and heating system so the choke can operate correctly now.
I have also fitted a high quality Bosch coil and removed the ballast resistor.
I will take the car for a run for a few kilometres and remove the top of the kn filter to check that the auto choke shuts off.
I will come back with results after
Alan

[plasticpig72]

Well just got back from a drive and she is running very well indeed, drove about 12 miles.
When i collected the car i did not check coolant level so it may have been low then.
I will keep a check on coolant very closely now the car is at my home.
Next drive will be 30 or 40 miles to check.
My car has Stainless manifolds and gets warm under the bonnet.
On my 3000S which also has stainless manifolds i repositioned the replacement coil as far away as possible from the heat. Since then no problem.
Auto choke is operating correctly as i have checked.
I will come back after a longer run
Alan

[plasticpig72]

Well i have done a 24 mile run and misfire has returned.
I have just looked at the Facet pump and it is very Facet hot. Removed it while still very hot and tested, it did not function but when it cooled down it functioned.
Now the question is why does it overheat. Is it because of a Vapour Lock in the line between the pump next to the tank and the carb. This could be because there is no return from carb to tank = permanent circulation and cool fuel flowing through pump. Or at least hot bubbles of fuel being return to tank and so cooling fuel supply.
I'm in the dark here and brain storming;)
Alan

Edited by plasticpig72 on Tuesday 19th July 15:19

[plasticpig72]

There is a pressure regulateur in the line just before the carb.
The pump is just above the tank at rear and maybe it should be below. If it's below that means it always has fuel inside and so doesn't need priming. But if vapour lock is happening in the run between the tank and carb with no return line from carb to tank!!!!
The return line from carb to tank was a modification to try to reduce vapour lock as far as i know.
I will try a new fuel pump first positioned below the tank and see what happens. Also a return line with restrictor so flow preference will be to carb
Alan

Edited by plasticpig72 on Tuesday 19th July 16:07

[plasticpig72]

I have added a return to tank "T" just after pump outlet. To act as a restrictor i have used a weber air corrector 175 inside the return petrol hose. I put a hose clip on outside to stop it moving inside hose.
Road test to follow
Alan

[plasticpig72]

Just got back from road test of 30 miles and a big success . Fuel lines cool and NO VAPOUR LOCK. Conclusion fit return line to tank just after exit from electric pump with a restrictor in return to tank. No cavitation in electric pump and cool petrol.Left return to tank and right supply to engine

Alan

Edited by plasticpig72 on Thursday 4th August 06:56

[plasticpig72]

Well the saga continues, at least when you have a TVR there is never a due moment. When you have 2 you are looking for trouble.
Let's get to the subject. I went for a drive again today and after 6 or 7 kms my 3000M started to misfire again but with a BONUS the Windscreen Washers started to function and water everywhere. A small detail i hadn't switched them on which is quite a mind bender for me a TVR Virgin
I managed to get home with a very clean Windscreen. Switched off engine but would not start except when the Ignition Key was turned the Windscreen Washers worked by themselves
I went indoors to take a nice coooool beer and think. After the car had cooled down it restarted no problem, i'm confused. Any ideas chaps
Alan

[plasticpig72]

I will try a new cable from the Ignition switched first position (white wire) to the Coil, thereby bypassing the wiring harness . To start from basics.
Results to follow
Alan

[plasticpig72]

GAjon said:

Check all the electrical joints and earths behind the dashboard and switch panels, especially those on knurled nuts that hold the gauges in place.

Just looked behind dashboard and found some knurled nuts loose on backs of gauges that hole them in place and serve as earths. I had a look behind rocker switches and found the reason for washers running with switch off. It was an illumination bulb and metal clip loose, short circuiting washer switch terminals. Spades at back of switch without insulating sleeves
Does anyone know a source for rocker switches like original because i need one for the Wipers.
Alan

[plasticpig72]

Just got back from 20 mile run and suddenly starts to misfire again.
When i touched the carb it's very warm and i wonder if it's heat transfer to carb.
Has anyone fitted a heat shield to reduce heat transfer to carb.
Maybe i need to go for another run until it misfires then vaporise the carb with water to cool it down. Then see if it runs without misfire.
Alan

[plasticpig72]

I buy the same place, same petrol and same grade for my 3000S also Lotus Elan Sprint NO PROBLEM.
I'm thinking 1. condenser
2. vent in filler cap.
3.carb float level wrong too high/too rich when hot.
4. dissy cap.
5. spark plugs wrong grade fitted.
6.rotor arm.
7. power valve carb.
8. H.T. leads breaking down when hot.
The spark plugs have heat insulating tape around the porcelaine, could it make them too hot.
Well that's my brain storming list for the moment.
Alan

[plasticpig72]

If it was head gaskets surely it would misfire from cold or am i missing something. Plus coolant would be pressurised and blow back into expansion bottle.
I will remove all the spark plugs to look at the colours first.
How can it be head gaskets if it only misfires when hot. Sorry but i find it difficult to follow the reasoning here. Could you explain please, i'm always ready to learn.
many thanks
Alan

[plasticpig72]

Yes i see what you mean, i'll have a chat with a local garage to check for gas in coolant.
thanks
Alan

[plasticpig72]

o.k. i'll do a test for gas in coolant to check head gasket but i hope it's not the head gaskets. I've never taken the heads off a V6 before. I'll cross my fingers when i do the test and hope it proves head gaskets to be good
I've just ordered the kit RESTOM DETECT 8840 it's a pink liquid that changes colour if gas present
Alan

Edited by plasticpig72 on Wednesday 10th August 08:23

[plasticpig72]

TVRMs said:

Would have thought most "local" garages would have been able to do the test for you?

I imagine so but the kit is 12.50 Euros = £10.I live in Brittany.
Alan

[plasticpig72]

I will double check the auto-choke. Maybe fix in off position and bypass the coolant hose to stop carb getting hot coolant through it.
I have put it on my list of things to do
Alan

[plasticpig72]

Maybe i'm wrong and it won't be the first from far but i think it's a misfire which suggests Electrical problem. I have ordered new condenser and points which are easy to change. For me the problem is not a splutter which would be carb.
1.I am sure the return line i have added at the fuel pump outlet was needed, now pump stays cool and also fuel line.
2. I have fitted a Bosch 12V pressure filled coil and removed the cold start with resistor.
When i have fitted a new condenser and points i will road test and see
Alan