Poor running MK2

[weddingjags]

All summer I have been having a catalogue of problems with my 3.4 which seem to get fixed only to return. I had an engine rebuild over the winter and when I got it back it ran fine. After 500 miles or so the car spluttered to a halt and was recovered to the same garage. They diagnosed a failed electronic ignition (Pertronix fitted 10 years ago). They fitted a Lumenition system and the car ran ok for a short while then started faltering "lurching". A second unit was fitted, same thing happened. With help from Lumenition it was confirmed the unit was ok so they made some changes to the carbs.
The car broke down soon after and was recovered back. They were able to start the car but said the coil was overheating/braking down and replaced it.
When I got it back it still hesitating under load which another garage diagnosed as lean running, adjusted it and for 300 miles or so all was well.
Then the hesitation and "lurching" has now reoccurred across the speed range and it is not a well car as we speak. I am at a loss as to what to do next, any ideas out there?

[Tilleyjon]

I would look at a carb overhaul if you have eliminated the distributor and coil, I assume the leads and plugs are OK, you can get misfires from poor plugs and or leads.

If the carbs are worn, you will find it difficult to maintain the tuning, but I would eliminate leads and plugs first.

If it is misfiring at idle, you can pull 1 lead off at a time to see which cylinder /s is at fault, the engine may stall if you pull off a good firing lead and there is more than one other cylinder misfiring.

You will get a distinct change when you take the lead off obviously, but if the cylinder is misfiring there will be little or no change that will determine which cylinder. If there is a change on all cylinders, then the fault is most likely the carbs.

Check for debris in the filter, there maybe crud in the tank which keeps getting pulled through.

Hope this helps some way.

[piman]

Hello Weddingjags,

you do not seem to have had much luck with your garages.

My first thought on reading the report is dirt in the fuel tank. I would check fuel filters and have a look inside the float chambers. I wonder how many garages these days are familiar with HD type S.U. carburettors? If set up to book settings it should run pretty well, if not you need to look for something wrong, e/g. needle incorrectly fitted to the piston, worn jet and or needle, incorrect needle, fuel level in the float chamber etc. Is the pump O.K.?
Coils should not run 'hot', and the likely reason is the wrong coil designed for a ballast type ignition. They have an impedance on the primary side of about 1.5 ohm as opposed to 3 ohms on a 12v coil. Confusingly ballast type coils are sometimes marked 12v.

Alec

[PPV]

Hi, there is plenty of advice on the website (search ignition under mk2 section). I myself had problems and tried many things but it came down to poor earth connection in the distributor (mine had electronic ignition) at the end of it. Now runs smoothly (touch wood) and starts first time. Just have to be thorough checking things like ignition items then fuel and timing.
Best of look getting it sorted.
Regards,
Paul

[weddingjags]

Thanks for the replies.
The current issue isn't a misfire or though I did have this which turned out to be a plug lead arcing on the head.
I will check the earth on the distributor.
The coils have been the correct type and the floats and jets and needles have been checked and replaced.
I think I am going to have to get a new set of eyes on it starting with new leads. I know the plugs are ok and the fuel tank was replaced earlier this year. Very frustrating.

[PPV]

You can check the fuel by just disconecting at the carbs and puting the end over a suitable receptacle and switching on the engine. The pump should operate then helping to eliminate items before the carbs.
Regards,

[weddingjags]

I get the car back today from a different garage. They found the fuel was contaminated. Fingers crossed this resolves it.

[Ronniebiggs]

Indeed, fingers crossed - but also check the tank can breathe. I've known of this on other vehicles and can be a pig - no apparent problems with anything but the thing exhibits the symptoms of fuel starvation after a while. Often worst with a full tank

Jay

[weddingjags]

I can finally close this issue. After various false trails including a carb rebuild (which was needed anyway) the fault has proven to be the Lumenition electronic ignition system. A 1-2-3 unit has been fitted and the problem solved.
I don't know if there is an issue with the Lunenition on +ve earth cars but 3 units were tried on my car and clearly it didn't like them.