Engine just died...
Discussion
Morning all,
I'd appreciate some help here. I've just driven (almost) to work, and the MGB died on me about a hundred yards from the office.
Symptoms were: a complete loss of power but the engine seemed to be still running as long as the car was in gear (dip the clutch and the engine died). However pressing the accelerator did nothing to the engine speed.
I'm letting her cool down right now (she's in a car-park next to my office).
So far I know that there is 12v at the points, fuel pump is working, and it's not the coil (I tried my spare).
Plugs are about 2 months old so should be OK, there is half a tank of petrol and oil/water levels are OK.
I'm guessing points/condenser because for both carbs to die simultaneously is unlikely. Also it didn't miss-fire (which would suggest the issue affected all four cylinders at the same time).
All suggestions welcome.
Sheepy
I'd appreciate some help here. I've just driven (almost) to work, and the MGB died on me about a hundred yards from the office.
Symptoms were: a complete loss of power but the engine seemed to be still running as long as the car was in gear (dip the clutch and the engine died). However pressing the accelerator did nothing to the engine speed.
I'm letting her cool down right now (she's in a car-park next to my office).
So far I know that there is 12v at the points, fuel pump is working, and it's not the coil (I tried my spare).
Plugs are about 2 months old so should be OK, there is half a tank of petrol and oil/water levels are OK.
I'm guessing points/condenser because for both carbs to die simultaneously is unlikely. Also it didn't miss-fire (which would suggest the issue affected all four cylinders at the same time).
All suggestions welcome.
Sheepy
I'd vote for the condenser if it was a sudden as that. Try taking of the cap of the dizzy, turn on the ignition and open the points with a screwdriver (assuming you're running "old-fashioned" points). If the spark as you open and close the points open is large, powerful and diffuse rather than a concentrated blue spark then the condenser is shot.
Failing that, rotor arm failure?
Can't beleive that the fuel system would lead to such sudden symptoms.
Failing that, rotor arm failure?
Can't beleive that the fuel system would lead to such sudden symptoms.
I had kind of similar symptoms on my (fuel injected) V8S. The cause in my case was a duff air flow meter, the ECU was not increasing the fuel flow as I opened the throttle so the engine just leaned out more and more until it started misfiring - torque was almost completely constant and just barely enough to keep the engine running even at full throttle full boost.
Obviously you don't have any of this electronic nonesense to contend with, but I suggest you may be looking for a fault that can severely restrict the fuel flow. It's worth noting that manifold depression can be sufficient to maintain some fuel flow even when the pump has died, and this would match the symptoms.
Obviously you don't have any of this electronic nonesense to contend with, but I suggest you may be looking for a fault that can severely restrict the fuel flow. It's worth noting that manifold depression can be sufficient to maintain some fuel flow even when the pump has died, and this would match the symptoms.
OK, just been back out to her. Doesn't start (thought I'd try incase it was because she was hot). Get a large orange spark when I pull the points apart. Does point to condenser. Fitted a "spare" (ie one kicking about in my boot), the spark is smaller but still orange (and she still doesn't fire). I'm guessing my spare is the old one from the last time I changed the points!
Didn't check the carbs (but fuel pump ticks and stops which suggests it is pressuring the supply line OK).
I'll see if I can find a supplier in MK for points and a condenser, and see if that fixes things. Otherwise It will be the low-loader home tonight!
Sheepy
Didn't check the carbs (but fuel pump ticks and stops which suggests it is pressuring the supply line OK).
I'll see if I can find a supplier in MK for points and a condenser, and see if that fixes things. Otherwise It will be the low-loader home tonight!
Sheepy
stevieturbo said:
Are you viewing a spark at the points, or the plug itself ?
Strictly speaking, Im not sure you should see 12v at the points if thats where you are measuring, as it has to travel through the windings in the coil first ??
Goes through the windings of the coil after the points shirley?
But agree that sticking a spare plug earthed to the block in an HT lead to check for a spark is a logical step.
Dont call me Shirley 
lol
depends what way you look at it....
12v from ignition, into LT windings in coil, exits from coil -ve side, into points, then to ground as points open and close..
Although true current does actually travel from ground to +ve, although its not commonly seen that way.
lol
depends what way you look at it....
12v from ignition, into LT windings in coil, exits from coil -ve side, into points, then to ground as points open and close..
Although true current does actually travel from ground to +ve, although its not commonly seen that way.
nel said:I'm initially just looking at the spark as I break the points. I'm not happy with that part yet, so need to change the condenser first. Of course, if that doesn't fix it, then I'll follow the electrics from the points to the plugs. Because of the power-loss being so sudden, it's got to be in the common part of the supply, so I'm starting with the easiest bits!!
Are you viewing a spark at the points, or the plug itself ?
Strictly speaking, Im not sure you should see 12v at the points if thats where you are measuring, as it has to travel through the windings in the coil first ??
Goes through the windings of the coil after the points shirley?
But agree that sticking a spare plug earthed to the block in an HT lead to check for a spark is a logical step.
Sheepy
You might want to use the opportunity to switch to electronic ignition which on my Triumph also gave much better fuel economy than points ever did. The engine never went 'off' either.
Don't dismiss the fuel filter being clogged up, that can starve fuel no matter how well the pump works.
Don't dismiss the fuel filter being clogged up, that can starve fuel no matter how well the pump works.
You really need to know whether you're looking for a spark or ignition fault, and the best way to tell for sure is to pull a plug out. If it's dry you aren't getting fuel and probably have a fuel fault. If it's wet, you're getting fuel and probably have an ignition fault. Also, mental note, you'll find it very difficult to get it to fire (even after you're cured the fault) while the plugs are wet. You can improve your chances considerably by pulling them all and cleaning them.
Gah! 
Condenser and points OK now. Nice sharp "snap" and a blue spark when the points seperate, but still no joy.
Looks like the cap/leads/rotor-arm are suspect as well. I'm getting a spark directly off the coil (but not a great spark), and there's nothing at the end of the plug leads.
Now if I'd only thought to buy the whole lot at the same time as the points....
BTW, the points were seriously burnt so needed changing.
Plugs aren't totally wet, but do stink of fuel. Pump is delivering fuel to the carbs. Carbs have fuel in bowls, and no obvious sign of contamination (water or rust). I'll clean them when I replace the leads.
Fingers crossed that the parts supplier can get the bits today.
Sheepy
Condenser and points OK now. Nice sharp "snap" and a blue spark when the points seperate, but still no joy.
Looks like the cap/leads/rotor-arm are suspect as well. I'm getting a spark directly off the coil (but not a great spark), and there's nothing at the end of the plug leads.
Now if I'd only thought to buy the whole lot at the same time as the points....
BTW, the points were seriously burnt so needed changing.
Plugs aren't totally wet, but do stink of fuel. Pump is delivering fuel to the carbs. Carbs have fuel in bowls, and no obvious sign of contamination (water or rust). I'll clean them when I replace the leads.
Fingers crossed that the parts supplier can get the bits today.
Sheepy
Have you looked inside the cap to check that it's clean and that the sprung graphite connection from the coil is OK? Logically your problem is due to a single, discrete component failure, so it's unlikely to be all the HT leads at once for instance. I'd suggest dizzy cap and central HT lead, assuming that you're sure the replacement coil is functioning OK.
By the way, there were no unpleasant mechanical noises before the breakdown happened were there? E.g. chain drive to cam, etc. When you look in the through the oil fill hole are the valve rockers headbangin' away like they should be?
By the way, there were no unpleasant mechanical noises before the breakdown happened were there? E.g. chain drive to cam, etc. When you look in the through the oil fill hole are the valve rockers headbangin' away like they should be?
OK, so she's still not happy.
Friday night she made it home with quite a bit of knocking and a slight miss-fire. "OK" I thought, "I didn't check the timing too accurately once I fitted the new points, that will be the cause".
Saturday afternoon, rechecked the points gap, way off! Set it to .38mm. Checked the timing: 15-20 degrees advanced (should be about 7). OK, so adjusted that to about the required amount. Engine fires and runs nicely. Didn't have a chance to go for a run.
Today, drive her to work. Seemed OK while warming up, but then I began to notice a miss-fire on acceleration. This got worse and worse. The car is fine if accelerating cleanly in the right gear, but if you let her get a bit bogged down and try accelerating in a higer gear (3rd or 4th), it missfires very badly. I also noticed that when she was miss-firing, the tacho needle was bouncing arround madly.
The only thing I didn't change on Friday was the dizzy cap (due to a supply issue), and I will do that at lunchtime. I'll also re-check the static timing and points gap (and change the plugs).
Any other ideas?
Sheepy
Friday night she made it home with quite a bit of knocking and a slight miss-fire. "OK" I thought, "I didn't check the timing too accurately once I fitted the new points, that will be the cause".
Saturday afternoon, rechecked the points gap, way off! Set it to .38mm. Checked the timing: 15-20 degrees advanced (should be about 7). OK, so adjusted that to about the required amount. Engine fires and runs nicely. Didn't have a chance to go for a run.
Today, drive her to work. Seemed OK while warming up, but then I began to notice a miss-fire on acceleration. This got worse and worse. The car is fine if accelerating cleanly in the right gear, but if you let her get a bit bogged down and try accelerating in a higer gear (3rd or 4th), it missfires very badly. I also noticed that when she was miss-firing, the tacho needle was bouncing arround madly.
The only thing I didn't change on Friday was the dizzy cap (due to a supply issue), and I will do that at lunchtime. I'll also re-check the static timing and points gap (and change the plugs).
Any other ideas?
Sheepy
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff