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MG MGB Technical - Strange engine problem - any ideas, please

At the moment, I am at a loss to know whats' wrong with my MG following the car griding to a halt on a (thankfully empty) French motorway. I would greatly appreciate any ideas. The symptons are:

Last Monday I drove the car approximately 250 miles from England to near Paris. On setting off, I heard the occasional misfiring sound, which I put down to the engine still being cold. At 60mph, the engine started to reverberate, making excessive groaning noises. However, at 70mph, all seemed fine with no excessive noise. At low speeds (< say 15mph) you could hear a sort of constant low clicking noise from the (left) passenger side of the engine.

After 50 miles, going uphill, the car suddenly lost lots of power. If I kept my foot on the accelerator, I could just about maintain this speed, but the engine was growling more than ever. Once, there was a loud bang from somewhere on the left side of the engine. I drove on, however, and after a couple of minutes, I had full power again.

There then followed 200 or so miles of motoring, interrupted only by crossing via the Eurotunnel. Then, some 30 miles from Paris, the car suddenly started losing speed. I kept my foot on the accelerator, but nothing, suggesting the car had stalled totally. I let the car come to a complete stop on the hard shoulder and called RAC. The car is now at an mg specialist near Paris being looked at.

Here is the problem: the dealer has apparently looked at the car and, since it starts fine and drive around ok, he's not sure what the problem is. I've asked him to do a compression test and a full road test. I can only imagine there is a serious engine problem and the fact it was operating on low power suggests 1 or more of the cylinders was out of action. But if that was the case, then why did full power kick-in again? Could it be an electrical problem?

Would appreciate any theories that I can ask the dealer to look at. Many thanks!
Anthony Charlton

The obvious electrical classics are the distributor, cap, rotor, points and capacitor.

Another less likely possibility is an intermittant blocking of the fuel supply.

The big bang suggests a backfire caused by a spark plug firing when the valve is open - this points to a bad distributor cap.
Chris at Octarine Services

Bloody hell, talk about flogging it till it dies!

Have *you* tried it since? The dealer may not know how good or bad it is supposed to run. If it really is running normally now then it is something simple like electrics or fuel as Chris suggests, in which case there isn't much that can be done excpet to confirm fuel delivery at the carbs, should be at least one pint per minute. If it is still running poorly then it may be something more serious but check spark delivery to each plug.

Unless the dealer is familiar with classics in general and the MGB in particular then they are unlikely to be able to do much with it as there is nowhere to plug their computer (and even that is nowhere near infallible, just enough to remove all real knowledge from the mechanics).
Paul Hunt

<Bloody hell, talk about flogging it till it dies>

You have a point there! That said, for reasons I won't bore you with, it was essential at least to make it across the channel.

Thanks for the theories so far, will let you know the outcome.
Anthony Charlton

What year car?

Offhand, blind, guesses:

...#1 melted points.
...#2 shorted distributor rotor.

Daniel Wong

I have had the same problem with my midget. I did not have any of the engine noise although the rest of the syptoms were exact. It turned out to be the fuel fump, intermitantly working. I changed it to an new electric and never had the problems. Maybe you have a loose wire feeding power to it? Maybe I am way off. But I got stranded several times along the highway for a few minutes at a time because of it and I figured I should mention.

Neil
Neil

If it is not the usual suspects could be an intermittentley stuck open exhaust valve . This could give you the "clicking" noise and the explosion in the exhaust . If it was this it would show up on a compression test , or you could wait until it happens again and watch with the rocker cover off ( bit messy though .)
Another possible is an intermittent letting through needle valve on one of the float chambers . When this happened to me the car just went onto 2 cylinders . Easily spotted as fuel will pour out of the overflow pipe on that carb.
S Best

Pretty sure this is a fuel problem and the bang was due to weak mixture and spit back through the air cleaners.

I too think that there could be something floating about in the fuel system. Blow out the fuel line to ensure that it is free from residue. Alternatively this could be a classic SU pump problem becoming intermittent. At least remove it, clean the contacts and refit.

Do you still have the opportunity to remove the float chamber covers to examine whether or not there is fuel in them ?
Iain MacKintosh

Ok, quick update - the garage did a compression test then drove another 50kM. Result: no fault. Having had the vehicle recovered and lots of money spent on it by my insurer, this is a little embarrassing. I've asked them to check over the fuel system & electrics; the fact that the "problems" only happened intermittently are suggestive of something loose?
Anthony Charlton

Did you notice the tach flicking about when it was happening? Or the ignition warning light flickering? Tack flicker but no warning light flicker (assuming it works as it should in the first place) indicates an ignition LT problem in the white from the ignition switch plug, through the coil, points and distributor ground wire or possibly the condenser. Although a condenser usually fails and stays failed the others can cause intermittent problems.

A flickering warning light indicates an intermittent connection in the brown from the solenoid, through the ignition switch to the white at the column plug.
You might get banging in the exhaust with an intermittent ignition LT problem, but not in the intake, and no banging in either with a fuel supply problem.
Paul Hunt

No, Paul, I saw no flickering and I'm pretty sure all dials/ warning lights work. Should know more today - if the problem is not i/d I'll collect it from the French garage anyway, and try to get to the bottom of it myself. Thanks.
Anthony Charlton

I had a similar problem which turned out to be due to an intermittent fault in the ignition switch. The switch eventually failed to the point where the ignition was only live when the key was at the starter position; the car would fire up but cut out when the key was released.
C Linn

The original report sounded similar to my 1989 Metro, which the seller assured me had been converted to unleaded fuel. Ove a month or two it ran worse and worse, sometimes running OK, then losing power, occasionally stalling. I tried stripping the carb, timing, lots of things, what cured it is using castrol lead replacement additive. I assume lack of lead caused a valve to stick intermittently, though this is not what the textbooks say!

Could this be related?

regards, Rod
Rod Dalitz

Bizarre. As the garage seemed no closer to identifying the problem, I went to collect the car myself this weekend. Result: no strange noises, no breakdown on my 25 mile journey home, nothing. I'm going to do a thorough check myself over the next few days.
Anthony Charlton

Anthony, it sounds like the fuel is still flowing, but the ignition is cutting out. A backfire would be expected when the ignition cuts back in, since fuel has been passed through to your exhaust sytem where it could ignite. Try wiggling the ignition key around at idle and see if you can get it to cut out, without turning the key off. By chance do you have multiple keys or a fob on your keychain that can swing around when you drive? It is common to see damaged keys (and potentially ignition switches) from too much weight being applied to the switch.

Jeff Schlemmer

This thread was discussed between 20/04/2004 and 26/04/2004

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