Going mental

[New Bloke]

So this is the situation, Gary (our 1969 2 door minor) has been breaking down a lot, and I mean a lot... We took it to our local garage and they changed the condenser and the coil. Still kept breaking down.
I got a mechanic to fit a new distributor, still kept breaking down.
I changed the HT leads still kept breaking down.

I'm 99% sure it's electrical as when you are driving it (on the odd occasion it is not broken down) it will lose power and the engine will die. An hour or two later it will be okay for a few miles but then sometimes even the next day when I am rescuing it from its last breaking down spot, it will start and rev but has no power, as soon as you let the clutch out it dies. then inexplicably it will just be fine and it will start but as you are driving it home, it just cuts dead, the car momentum keeps it turning over and suddenly, vroom, it's okay again. Until 150 yards down the road when it will cut out again. Today was typical, my Daughter drove it to school but phoned me up and had broken down halfway up a very steep hill. When I got there a few hours later it started straight away and drove home fine. Sometimes the rough running is accompanied by a horrible engine note but other times we get the horrible note but it still has power. Apart from a box of swan vestas, does anyone have any idea? I'm at my wit's end on this one....

Thanks
Tim

[les]

I don't think you should dismiss the fuel system, the pump can be erratic, stopping and starting. Check the pump points are clean. On the electrical side rotor arms can play up.

[Budgie]

Petrol issue? Is she getting enough fuel from the tank to the carb via the usual route ?

[New Bloke]

As I've changed just about every electrical bit there is, you may be right, I will try a new petrol pump but I feel I'm throwing good money after bad right now, the old one is a bit ropy but it really seemed electrical.

Thanks for the suggestions.

[Budgie]

Check that it's drawing up petrol first before you shell out for a replacement. Take the pipe off the carb end and turn the ignition on to see if the pump ticks and pulls petrol from the tank and spurts it out from the open end that's in your hand. Someone will be along shortly to say how much it should flow per minute.

[New Bloke]

The problem is Budgie, that because it's an intermittent fault, it will tick and flow as I already did this. Probably need to do it when it's broken down.

Thanks all

[oliver90owner]

Seems to me that there has been no diagnosis and just a lot of guessing. Simply continually changing perfectly good parts at high cost is not the best way to go.

Do check for spark, when it breaks down. If it is an intermittent fault and starts normally later there will be no spark at the time of the breakdown. Simple enough? If there is a good spark at this time it is clearly not the ignition system!

Fuel pipe too close to the exhaust? Or any other vapour lock opportunity? Intermittent fuel pump? Sticking float valve in the carb? Check fuel level in the carb when it breaks down? All simple enough diagnoses.

Electrical connection problem? Anything else stop working at the time? Fuses all clean and not overheating at a junction? Voltages at components at the time of breakdown?

Plenty to go at, without changing anything until you find something which is not as specification at the time? Time spent diagnosing the fault is far cheaper than blindly changing perfectly serviceable parts.

RAB

[beero]

Next time it breaks down take the top off the float chamber and see if the fuel is up to the right level.
Also get a set of these
http://www.halfords.com/workshop-tools/ ... ark-tester
and pop them on when you break down to see if you are getting a good spark.
Good luck

[DAVIDMCCULLOUGH]

Next time it happens try taking off the petrol cap, they have been known to vapour lock from the tank as well. Some of them have a hole drilled in the cap.

[Nickol]

..also start it up after it is dark and lift up the bonnet. See if there is any apparant periodic arcing in the engince room which should not be there.
You will not be able to draw any conclusions if there are no untoward flashes but it will answer a lot of questions if there are.

[New Bloke]

Thanks everyone.

The mechanic told me I need a new fuel pump anyway as the old one was dodgy, so I fitted a brand new SU pump today. This thing is so LOUD. Are you supposed to hear the sound of the pump above the sound of the engine all the time? Anyway, didn't cure the issue I got less than 1/2 mile before it cut out again. I didn't depress the clutch and kept my foot on the accelerator and it cut in and then out again about 5 or 6 times before dying. I'm thinking now it could be the low tension side and I think a really good clean of all of the contacts is now in order.

Thanks for your help.

Tim

[biomed32uk]

Start at the beginning and work through the whole system methodically, it could be a bad connection somewhere, broken wire, LT wire inside the dizzy damaged and earthing out.

Is the condenser a decent one, there are some real poor ones out there, just because its new it means nothing. I personally would put one of the electronic conversions in as it removes the points and condenser.

Start from the ignition switch and work through, do you have a continuity tester or voltmeter to check wiring, a very useful investment for chasing electrical faults.

If you want to test out the feed to the ignition system down to the coil from the switch make a test lamp up on some long wires. Connect it to the ignition switch side of the coil and earth. Put it in the car and go for a drive, if the lamp goes off when it cuts out you know where the fault is roughly.

The rest of the LT wiring on the CB side between coil and dizzy can be checked best with a continuity tester, take the wires off, connect the tester, wiggle and pull the wires seeing if they go open. One that has an audible buzzer is best as you can hear it stop if you have a break.

The Minor is a simple thing and there really isn't much to any of the electrics, so it should be easy to chase the fault out with some logical fault finding.

Good luck.

[myoldjalopy]

If you hadn't said you had a new distributor fitted, I would suspect the rotor arm. I had exactly the same symptoms once and it turned out to be a dodgy rotor with a loose rivet so that sometimes it transmitted the spark and sometimes it didn't. I have always used Distributor Doc ones since and no problems. (He does reliable condensors too).

[New Bloke]

Thanks guys, I bought the laser spark detectors and tried it, they all sparked fine but the fuel pump was working all the time and I noticed there was fuel seeping from the float chamber top. Is there supposed to be some kind of cut off that stops the fuel pump pumping?

I don't think this is the original issue, still convinced it is electrical and the idea of a test lamp wired through is genius and I will do it just as soon as I get back from my weekend away.

Thanks again chaps
Tim

[biomed32uk]

If there is fuel seeping from the float chamber top then the needle valve in the lid is either dirty or worn, that's what stops the fuel and holds pressure against the pump, stopping it.

Longshot but it may be just simply flooding the engine severely, does it stink of petrol when it dies?.

Using the test lamp will prove the feed to the coil, then you know whether the fault is back from that, or onwards in the system. It's a standard method of fault finding any system - half split method. Look for the signal or condition you want in the middle of the system, if it's not there then the problem is before that point, so then find another point in the middle of that and repeat. You can then isolate the problem to lying within a particular segment.

That's the basis of fault diagnosis in electronics, the 'fiddle poke and hope' method while we all do it usually achieves nothing.

Intermittent problems are horrible, the times I have sat and looked at some piece of electronic apparatus asking it to break and stay broken so I have something definite to find and fix. Always nice to cure something and know for definite 'it was that, and I have fixed it'

The rotor arm is also another good call.

[oliver90owner]

, they all sparked fine 

Was this when it had stopped running and would not restart? If so it won't be either the HT or LT side of the ignition. If you have sorted out that it is not electrical, what colour are the plug electrodes - sooty or ash coloured? It helps to sort out whether the mixture is too rich or too lean. But do stop buying and changing items on a wing and a prayer. Simple diagnosis works nearly every time.

Clearly there should not be fuel seeping from the carburettor? Apart from anything else it may be a fire risk.

[kennatt]

Your getting a lot of advice here and changing components rapidly,but,further back it was suggested that when it cuts out stop and take the top off the carb,three screws and lift it off,nothing more simple than that. and do it by coasting to a stop with the clutch down engine stopped.Have you done this ?,because its the first thing I would have done.it sounds like fuel starvation to me,and easily checked at the road side/ The new SU pump is probably one of the electronic type which are twice a noisy as original mechanical ones.I think someone on here fitted rubber between the pump and body to quieten it down.Check the carb bowl before spending any more cash.Unless you have done so .

[oliver90owner]

Kennatt - you have a PM.

RAB

[jagnut66]

Hi,
I had a similar set of symptoms with an old MG of mine. It turned out to be an extremely silted up petrol tank, the sediment was packed solid in the old fuel pump (which I renewed) and after a while would clog up the latest replacement fuel filter (fortunately the cheap variety) and cause the engine to die again.
In the end I bought a new fuel tank and this cured it, sometimes the only option is to replace / renew. Being a tight git it was an 'Ouch' moment money-wise though!
Best wishes,
Mike.

[David W.]

If it is the silted up fuel tank, it should be easy to check by taking the level sender off and looking with a flashlight (torch.) The usual cautions when working with/near petrol.
There are kits to clean and coat the inside of tanks. Because Moggies are so small, you can get away with a motorcycle size kit.
Pull the filter from your "new" pump. If it is clogged already, then definitely look to the tank.