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Engine shuts off while driving

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awjensen467 Avatar
awjensen467 Adam Jensen
Tremonton, UT, USA   USA
1977 MG MGB
1977 MGB. It's original outside of removed emissions and HIF4 conversion.

It's happened 3 times now. No rhyme or reason and I'm able to start back up almost immediately after. I finished the conversion 2 weeks ago and had no problems (driving to work probably 6 times, 20 minutes each way) until last Friday on the way into work when it happened the first time. It happened twice on Sunday just running to the store (5 minutes away).

Any ideas?

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Wachtmans Avatar
Wachtmans Wouter Strodijk
OVERVEEN, Noord Holland, Netherlands   NLD
1974 MG MGB "The Bee"
1974 MG MGB "The Bee"
1974 MG MGB MkIII "The Bee"
Fuel pump. My 2 cents. Get a Hardi electronic one.

barry s Avatar
barry s Silver Member Barry Stoll
Alexandria, VA, USA   USA
1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
Blocked fuel tank vent line. Next time you are going to drive, loosen the gas cap enough to allow air to enter the tank. If this solves problem, report back for solution alternatives.

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awjensen467 Avatar
awjensen467 Adam Jensen
Tremonton, UT, USA   USA
1977 MG MGB
I'll give this a shot tomorrow. Thanks.

In reply to # 3717748 by barry s Blocked fuel tank vent line. Next time you are going to drive, loosen the gas cap enough to allow air to enter the tank. If this solves problem, report back for solution alternatives.

JimM Avatar
JimM Jim Martens
Gainesville, GA, USA   USA
1974 MG MGB
Years ago my 77 (my first car) would do this and often at speed while motoring along I-95 in south Florida during rush hour. It would sometimes restart on its own before I could make it to the shoulder. I never solved it, but years later concluded it was a bad battery cable. Might want to check that.


Jim



Never forgot my first vehicle at 17, a 77 B.
30 years later graduated to a 74 chrome bumpered B.

High-torque starter, sports coil, pertronix elect. ignition, SU solid state fuel pump, HIF-4 carbs (rebuilt May 2011).

BRGMGB Avatar
BRGMGB Terry Goodman
Alicante, Spain   ESP
I had exactly this problem a few years ago. It turned out to be simply a loose connection at the starter motor.worth a Quick look under the car.

mgbmac Avatar
mgbmac Silver Member James Patrick
Darien, CT, USA   USA
1980 MG MGB
Adam, I just went through this with my 1980 MGB. If you still have the OPUS ignition system that can be an issue. Does your tach gauge flutter before the engine dies? Mine did. I replaced my ignition relay which is forward of the fusebox and that seemed to take care of the engine suddenly cutting out. Best, Jim

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benhutcherson Avatar
benhutcherson Gold Member Ben Hutcherson
Louisville/Frankfort, KY, USA   USA
1970 MG MGB
With a 77, Opus comes to mind for me also.

Gagadeals Avatar
Gagadeals William Joslyn
New Hartford, CT, USA   USA
My 1980 was running great. After driving about an hour I was heading up hill and it cut out. I changed out my in-line fuel filter (metal canister type) for a clear one. Seems to have done the trick. Just came out of hibernation so I added some Seafoam as well.

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awjensen467 Avatar
awjensen467 Adam Jensen
Tremonton, UT, USA   USA
1977 MG MGB
For a little more clarity. It is an instant shutdown when it happens. No sputtering of any kind.

Ormolu Avatar
Ormolu Barrie Jones
Okehampton, Devon, UK   GBR
1955 MG TF 1500 "Emily"
1973 MG MGB GT V8
If your MGB has overdrive, check the wires underneath the car that go to the inhibitor switch and then to the overdrive solenoid.
This wire is on the same circuit as the power line to the coil.
It has a metal bullet connector that can swing around.
If the connector touches the metal cross-member then it will immediately cut the ignition.
The fix is to zip-tie it so it cannot touch anything.

Defender405 Avatar
Defender405 Silver Member Chris B.
Des Moines, IA, USA   USA
1975 MG MGB
X2 on the battery connection, especially the Pos terminal at the starter. Most things will give a hint of a "not so good" situation but loss of Pos battery terminal connection equals dead right now.



Chris AKA "Defender405"
1975 MGB
1979 Porsche 924
1999 Porsche 996
1987 Nissan 300ZX

barry s Avatar
barry s Silver Member Barry Stoll
Alexandria, VA, USA   USA
1972 MG MGB GT
1974 MG MGB
1976 Triumph TR6
1980 MG MGB
Adam - Your clarification pretty much rules out fuel being the issue. IMHO it also likely rules out both the battery and alternator and their connections. That leaves ignition. You've not told us about your ignition system, however, you did say original save HIFs. I'm not the one to address your system. You might at least check your coil and distributor connections. As you've added the HIFs you might consider replacing what you've got with a 25D points distributor.

Cruisedon66 Avatar
Cruisedon66 Pete W
St. Louis, MO, USA   USA
1976 MG MGB
Check the white wire to the coil from the ballast resistor. Mine had become hot and developed a short.

briandubuc Avatar
briandubuc Gold Member Brian M. Dubuc
Roswell, GA, USA   USA
1976 Datsun 280Z
1977 MG MGB
1977 MG MGB
I have two 77s. My first one would exhibit the same exact symptom at interstate speeds. It would stop running and before I got to the shoulder, it would start again. Intermittent problems can be hard to diagnose - but if it happens again - look at the tachometer. Mine would drop to zero - no signal from the coil. I finally figured out that it was the ignition relay. They are damned testy - if you still have the Lucas SRB 402 (round cylinder), you might try replacing it with a 30 amp relay - I think the SRB 402 is only 25 amp rated. It is not enough to handle both the twin stock cooling fans and the ignition draw at speed. The fans originally had that stock Lucas 17/35 amp slow blow in-line fuse (replaced by a circuit breaker starting in 1978) - so the relay melts and fails with the fans going - while the in-line fuse looks great. Kills the ignition, fuel pump and tach. Can be intermittent.

I found some very inexpensive 30/40 amp relays on amazon that have a 30 replaceable blade amp fuse built in - so if the fuse goes, it doesn't melt the relay. When I go to the local British car meets - I just swap the relay out with the Lucas SRB 402 so that it looks right. I have replaced that relay so many times I have the wiring connections memorized. You can put a 40 amp fuse in that relay, but I don't trust the original wiring to carry that much amperage (I have also replaced the brown wire - main source from the starter solenoid - female connector several times because the plastic sleeve melted).

So far, the new relay seems to work without getting too hot. The real test will be in July when in traffic when the cooling fans run almost constantly.

Good luck.

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