3000M bad misfire when hot

3000M bad misfire when hot

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plasticpig72

Original Poster:

1,647 posts

148 months

Wednesday 13th July 2016
quotequote all
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

anonymous-user

53 months

Wednesday 13th July 2016
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Alan, what you describe is not a common problem.

plasticpig72

Original Poster:

1,647 posts

148 months

Wednesday 13th July 2016
quotequote all
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

Dollyman1850

6,316 posts

249 months

Wednesday 13th July 2016
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It sounds like a carb / choke problem to me rather than an ignition / cil problem.

N.

bluezeeland

1,965 posts

158 months

Wednesday 13th July 2016
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Dollyman1850 said:
It sounds like a carb / choke problem to me rather than an ignition / cil problem.

N.
+1

plasticpig72

Original Poster:

1,647 posts

148 months

Thursday 14th July 2016
quotequote all
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

oliverb205

705 posts

225 months

Thursday 14th July 2016
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A leak in one of the carb floats?

Oliver.

anonymous-user

53 months

Friday 15th July 2016
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Its most likely carb. Same happened here - misfire after a rebore and it had to be the rebuild didnt it, but it wasnt it was the jolly old carbs all along.

plasticpig72

Original Poster:

1,647 posts

148 months

Saturday 16th July 2016
quotequote all
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

Dollyman1850

6,316 posts

249 months

Saturday 16th July 2016
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Mount the coil on the bulkhead away from the block and exhausts but it isn't your coil…How have you lost water??
N.

GAjon

3,721 posts

212 months

Saturday 16th July 2016
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If it persists, check for debris and water/moisture at the bottom of the float chamber, remove the two jets and blow them through.

tvrmallorca

265 posts

137 months

Saturday 16th July 2016
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or its plugs.... I found my plugs oil up if idling and being used in traffic. Blast it for 10mins cured my misfires... although I am running a modified performance engine

plasticpig72

Original Poster:

1,647 posts

148 months

Saturday 16th July 2016
quotequote all
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

Original Poster:

1,647 posts

148 months

Tuesday 19th July 2016
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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

anonymous-user

53 months

Tuesday 19th July 2016
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If it ran ok before I would have thought the next option is to replace the pump and maybe get a slightly weaker one?

Dollyman1850

6,316 posts

249 months

Tuesday 19th July 2016
quotequote all
If there is no return then you are pumping fuel to a needle valve at some 6-7 psi for a carb requiring approx 3. The pump has an in built return but you are essentially pumping against a closed head and the pump will be heating fuel and re-circulating it in the pump body then sending the warmed fuel up the line.

You could re-fit your mechanical pump as a temp fix to see if they cures your problem.

I always run a return on my cars.

N.

plasticpig72

Original Poster:

1,647 posts

148 months

Tuesday 19th July 2016
quotequote all
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

Dollyman1850

6,316 posts

249 months

Tuesday 19th July 2016
quotequote all
plasticpig72 said:
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
A pressure regulator just regulates the flow beyond the regulator so it doesn't over power the needle valve in the float chamber. if your pump is producing more flow and pressure than the carb needs then it will re-circulate what it cannot get rid of within the pump body and this cavitation causes the heat. A new pump doubtless will be a temp fix but the heat problem is all down in this case to supply versus demand!!
The pump should always be at lowest point, that said once it has siphoned the fuel up to the impellor low that won't make much difference

Dollyman1850

6,316 posts

249 months

anonymous-user

53 months

Tuesday 19th July 2016
quotequote all
That is an excellent read.