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MG MGB Technical - Strange symptoms

OK, diagnosticians, here's one for you. My 71 BGT engine starts stumbling, or cutting out for a few seconds, when driving and rpms reach 2500 and above. It doesn't do it continuously in that range, just for about two seconds, then OK, then again, etc, and the ignition light flickers. It also does it only under load so I haven't been able to duplicated it while sitting at home. Any ideas?
Paul Briggs

My B did same in driveway, no load. Hit 2500 rpm and sputter, rattle sonds, miss like mad, let it settle to idle, got smooth again! I enriched my mixture, idle got rough but car accelerated all the way up. Also check for points dwell and timing, vacuum leaks, plugs, wires, rotors, cap, etc. first.
Dennis P.

One of the many things I've learnt from this board is that an ignition light shining whilst the engine does 2500rpm is a good clue that the problem is electrical. Bad condensors seem a common issue and a cheap one to start on?
Steve Postins

Does the tach needle also suddenly die and drop to or near 0 (zero) when this happens?

Disconnect the batteries, jack up the right side of the car - and check the brown wire connection that
is at the starter solenoid. Give it a wriggle to test it for looseness. While there, check all of the other
connections there for tightness. Inspect all the wires for chaffed insulation.

On U.S. cars, the brown wire uses a spade-tab push-on connector at the starter solenoid. Over time
it loses it's springiness and engine vibration helps to work it loose. It also doesn't help that it is located
down low, where it gets lubed with spilled oil at every filter change.

When this happens, at first, you'll get the exact symptoms that you describe. Then it slowly and
progressively gets worse at lower rpms and at idle - until the wire fully drops away and then the
car conks-out completely.

Clean off the spade connector, crimp it slightly with pliers, and slip it back on.

While you still have the batteries disconnected, check all the leads at the alternator and distributor
as well.

If all this is OK, I'd would then next change out both the condensor and rotor.

Condensors sometimes poop-out without provocation (although this is rare if they are renewed at
regularly scheduled tune-ups).

Rotors - especially some Lucas rotors - have been known to develope a short between the rotor blade
electrode and the distributor spindle. This one is not obvious as the electrical "juice" invisibly leaks
right through the plastic bakelite and onto the distributor spindle. In effect, it shorts-out the ignition
and the spark plugs go lifeless.

Although I have long ago converted to an electronic ignition, I always keep a spare set of points, rotor,
condensor and cap (along with the appropriate tools and feeler guages) in my trunk.
Daniel Wong

RE: Daniel's loose connector. Been there, done that, had exactly those symptoms. I'd check that first -- it's easy and free!
Rob Edwards

Can't remember for sure, but your symptoms sound similar to a distributor problem I once had. Check that little wire, inside the distributor, that feeds the points. Mine was broken under the insulation. Couldn't see the break. Above a certain RPM, the engine sputtered. I can't recall how I finally figured that one out. However, it is a very quick thing to check and eliminate.
Terrence Goodell

Daniel's suggestion and description certainly seems to fit the symptoms, and that is the first thing I will try, but not tonite. Probably I will have to test the diagnosis Sunday, as I just got home from work, and back in first thing tomorrow(Yes, I work Saturdays!) If that doesn't do it, down the list I go.
Paul Briggs

I'd check the above mentioned things first but.. if those fail to solve the problem, tyr this.. At night, look under the hood for faulty plug wires or slight flaws in the dis cap. Bring the RPMs up to where you found the problem before (2500+) and while checking for shorts under the hood at night.
kids1

The envelope please... And the winner is- Daniel Wong! It was exactly as you described, except that the wire had broken loose from the solder spot in the spade connector and was loosely held by the fold over strain relief portion. I have soldered it back up for a temporary fix, but the wire itself is too short, putting a strain on the spade connection. I will scab in an additional length of heavy wire in a week or so. Thanks for everybody's help.
Paul Briggs

I got (or I still have) that exact problem on my '71 B GT! I asked on the BBS last week about that, but got only one suggestion from someone..
It's funny, same car, same year, same problem...
it's only after 2500 RPM, under load, on fourth gear. Around at low speed but with an high RPM' I can't reproduce it, it's only on the highway...

Anyway, I replaced the condensor, rotor and cap on and for now, it seems to be good..But maybe it will come back on a long ride, so I will check my connections as you suggested to Paul...

thanks.
JF
JF

I found my problem finaly, on my car, it was the fuel pump..
it started to it on the idle, then I saw that the fuel filter was almost dry..so I knock on the pump and it started to pump again..I was just lucky enough to go back to my house without any other problem..
I changed it and now my car is running perfectly.
JF
JF

This thread was discussed between 13/06/2003 and 22/06/2003

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