MGB not running right, misfiring [ New issue]

[adam73bgt]

Hello all

Have had some issues with my MGB lately, starting from when the rotor arm in the distributor decided to fall apart. I also found the carbon contact in the centre of the distributor cap was quite worn.

So today I've fitted a new rotor arm, cap, leads and plugs. When I went to fire up the car, it started and was happily running on choke until it suddenly started spluttering and running rough. I took out the plugs to have a look and the plug from cylinder 1 looked wet so I'm assuming it wasn't firing.

Put the old plugs in to see if the new plugs were duds (also checked all the HT leads were tight) but when I turn the key to ignition all the electrics on the car die. Clock stops, interior light goes off, voltmeter doesn't even register the battery voltage. It had done this before I changed the parts but I assumed that was due to the old cap or temporary rotor arm I had on there (didn't fit very well)

So now I'm stumped, could this be an issue with the ignition coil? I can't think why the electrics would all die when turning the key to ignition..

Any help is greatly appreciated

Its a standard B series engine, Lucas 45d4 distributor, Lucas Gold ignition coil, other ignition parts from accuspark

Also it has an accuspark electric ignition kit fitted in the distributor

[andyborris]

Simple things first.

Check the battery leads aren't lose, check the earth to engine braided lead is good condition and tight.

Then check if a circuit that isn't controlled by the ignition switch still works when you turn the key, probably the sidelights, that;ll tell you if it's a general fault or something in the ignition circuit with a problem.

Please report back!

[bavarianretro]

Sounds like a bad engine or battery earth or bad positive connection at the battery, alternator or starter.

[Seth]

I'm wondering if the insulation on the thin wire that earths the points plate in the dizzy has broken down/fallen apart and it is causing a short somehow?

[adam73bgt]

Little update to this, managed to have a quick look at the car after I got back from work. tried to turn on the sidelights with the key out and nothing happened except the interior light extinguished..

So I'm thinking its an earth issue? the engine earth strap definitely isn't looking too clever, think I did actually buy a replacement but I couldn't get the nuts holding the old one on undone, thats a job for the morning

[dodgerover]

Have you checked the connections to the battery (or batteries if its still got 2x6v's) it used to be common to throw in any 12v battery that could be made to fit when the 6v ones failed, one some were a pig to get in/ out or fit the connectors to without shorting on something....

EDIT - Just had another thought you haven't had anything heavy in the back seat have you - it is possible to bend the battery covers down but have only seen this once in a BGT that was used as a builders van!

[adam73bgt]

I was going to but I chickened out this evening because of the cold and I couldn't be bothered with shoving the back seat out of the way (not entirely sure why I put it back in....) I shall have a look at it first thing tomorrow as I have had issues with the earth before but the symptoms are a bit different this time. Its got a 12V battery which fits quite nicely except the positive terminal is a little close to the bodywork but it had been pretty thoroughly insulated with tape

can't think of anything particularly heavy I've had in the back recently

[adam73bgt]

Battery connections are tight, going to change engine earth strap and will update

[djefk]

Sounds odd but put the battery (batteries if its an MGB) on trickle charge over night. It defo sounds like a battery / connection issue

[adam73bgt]

Just changed the engine earth strap and it starts and runs, notably it took a lot less churning over on the starter than it has done recently, started up almost instantly

I replaced this:



With this:



The old is still half on there as one end is attached to a stud which is just spinning with the nut..

[adam73bgt]

Also thanks for the advice everyone I think I need to get a big sign saying 'CHECK EARTHS' stuck to the underside of the bonnet as thats what most of my electrical problems seem to revolve around..

[andyborris]

Just be thankful it's not a fiberglass car!

[adam73bgt]

Nov 15, 2013 16:19:30 GMT andyborris said:

Just be thankful it's not a fiberglass car!

And there was me thinking the other day 'why didn't I get a Scimitar?...'

[adam73bgt]

Damn, not out of the woods yet, just went for a little drive to get petrol and when the engine is under load and accelerating it seems to be spluttering/misfiring again. Accelerating under light throttle seems to stop it though

Any ideas anyone?

[ChasR]

Have you run it out of fuel lately? It could be as simple as a sticking chamber or an iffy fuel, although I would not expect that to cause misfiring, more like the car holding back. If you have an empty bottle you could perform a flow test.

Sounds silly but did you gap your spark plugs correctly (it is unlikely though).

When this happened on my Stag it was down to the coil, which oddly enough was made worse with a new coil. When I acquired a Bosch coil the problem went away. I have a dwell meter and ignition tester (it tests the HT voltage at various points of the system) if you wish to narrow down the issue.

Dashpots is a good shout, but IME service seems to go back to normal after the initial splutter once a few seconds have passed (after all,the purpose of the filled dashpots is to enrich the mixture after initially putting your foot down, thus resisting the dashpot shooting upwards).

[andyborris]

Try a coil you know to be good?

I'd also check that the distributor is advancing and retarding correctly.

Wouldn't even look at the carbs or fuel pump, they tend to "go off" so slowly, it's not till you service or cold weather hits that you realise they not working correctly! Something that worked fine yesterday and doesn't work today, is usually electrical or electronic.

And just because they're new parts, doesn't mean they're any good, unfortunately. Try watching the engine in the dark, can often see the spark leaking out!

[adam73bgt]

Nov 16, 2013 8:51:15 GMT ChasR said:

Have you run it out of fuel lately? It could be as simple as a sticking chamber or an iffy fuel, although I would not expect that to cause misfiring, more like the car holding back. If you have an empty bottle you could perform a flow test.

Sounds silly but did you gap your spark plugs correctly (it is unlikely though).

When this happened on my Stag it was down to the coil, which oddly enough was made worse with a new coil. When I acquired a Bosch coil the problem went away. I have a dwell meter and ignition tester (it tests the HT voltage at various points of the system) if you wish to narrow down the issue.

Dashpots is a good shout, but IME service seems to go back to normal after the initial splutter once a few seconds have passed (after all,the purpose of the filled dashpots is to enrich the mixture after initially putting your foot down, thus resisting the dashpot shooting upwards).

Was a little low but not run out, plenty in there now, its currently got the old spark plugs in there which were gapped correctly but that was a while back to be fair, may try another set I have. I had issues with the dashpots before when I was running thinner oil in them but this doesn't feel like the same issue to me, got pretty thick oil in there now though

[adam73bgt]

Nov 16, 2013 15:46:32 GMT andyborris said:

Try a coil you know to be good?

I'd also check that the distributor is advancing and retarding correctly.

Wouldn't even look at the carbs or fuel pump, they tend to "go off" so slowly, it's not till you service or cold weather hits that you realise they not working correctly! Something that worked fine yesterday and doesn't work today, is usually electrical or electronic.

And just because they're new parts, doesn't mean they're any good, unfortunately. Try watching the engine in the dark, can often see the spark leaking out!

The coil thats in it was good for the past year or so I think the old one is either not at uni with me or thrown away.. Mmm you have a point about the new stuff possibly being a bit dodgy, think I might have another nose round the distributor

[andyborris]

It's a long time time since I too struggled with a rough running BGT, but I think you can check the vacuum advance/retard by sucking on the the manifold vacuum pipe.

Possibly!

Any filters in the fuel system, does the fuel pump have good pressure? Has DPO fitted a fuel pressure regulator?

[adam73bgt]

Think I've heard that mentioned before too so may give it a go, I think the centrifugal advance is working ok

I've got one filter in the system near the carbs (had run for quite a while without one.. oops! ) I think the fuel pump is ok, would have to do a flow test to double check though. But the filter always seems to be full of fuel when running, theres no pressure regulator that I can see, pretty sure its a standard setup