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MG MGB Technical - Prince is lurking

Gentlemen,
I have had my 1977 MGB out a few times this spring after garaging it for the winter. In preparation for the driving season I have sanded the contacts on the starter and a few of the connections at the fuse box and coil, cleaned the battery connections, and done a few other maintenance things.
Now, here is the problem: The car dies for about one second, then goes on as if nothing happened! This has happened three times, once while the engine was cold, and twice while hot. The last time, a few minutes ago, I was going about 60 mph and it happened. My heart almost stopped as well.
I believe it is an electrical problem. Does anyone have any suggestions on what might be causing it and where to start searching?
Thanks in advance.
Randy
randy olson

Randy

Intermittent faults are the hardest but I'd check connections and wire condition along the low tension side of the ignition circuit,

BROWN feed from the starter > regulator > ign switch then
WHITE > fusebox > ignition coil then
WHITE/BLACK > distributor then the fine
CLOTH COVERED wire from distributor connection to the points.

The last can fracture and all could be damaged or have poor tag connectors.

Would also be worth cleaning or replacing the points.

Rich

Rich

I'll check the wires you mention now, Rich.
I can add the following:
There are no points; it has an electronic ignition.
I lubricated the contacts that I cleaned with a light coating of dielectric grease. This was done before the intermittent electrical glitch.
Randy
1977 MGB with twin HIF4's
randy olson

Randy,
It may be the rotor,theres some bad ones out in the field.It happened to me,car just quit.Good thing I had a spare.HTH Steve
Steve G

No rotor, Steve. It has an Allison ignition.
I just checked some of the wires, and wiggled them around a little. Nothing was obviously wrong.
Randy
1977 MGB
randy olson

Is this an old Allison ignition ? If so it may well have a problem . I had similar experience and replaced it with a Petronix as it is simpler and cheaper That was 3 years ago.Also on the Allison make sure the air gap is correct as this is critical on those . HTH

Gil Price

The ignition, Allison, was installed by the PO, and since I have owned the car about 6 years it could be getting on in age.
I have no idea what the gap is or should be. Is it something I can adjust? Would it cause a momentary stall?
I'm still thinking I might simply have a loose wire as noted in Rich's memo. I have to get the car on the road tonight after work and see if it happens again.
Tell me about checking the air gap.
Thanks,
Randy
randy olson

Randy, I had a similar thing happen on my midget. Started out just dieing for a second then coming back, got worse. Sometimes just jiggling the wiring while checking things would bring it back. Traced it down finally to a poor connection on the fuse block. Corrosion had gotten in between the rivet and the spade connectors. A little flux and solder and it's good as new.
Bill Young

Randy. Your 77 has an ignition relay, a round, can shaped object with an L bracket, on top, to mount it to the firewall ahead of the fuse box and four tabs with wires running to them, at the bottom. If this is going bad, and they do, the symptons are as you describe.

You will also want to take a look at how the system is normally wired and how it is wired with your aftermarket ignition system. It will be different from factory wiring and you need to see if the work was done properly. The 77B used a two wire input to the coil. One wire, coming off the starter, provided 12V input to the coil during engine cranking. The second wire came off the ignition circuit and incorporated a resistance wire to lower the voltage to 6-8V when running. Thus, the car has a "6 Volt Coil" designed to run with a 12V system. You need to find out what all you have and how it is hooked up to see what may be the problem.

If you have a copy of the wiring diagram out of the factory workshop manual, have it blown up about 300%, then laminated. This keeps it clean and allows you to draw on it, with a water erasable marker, to trace out circuits. The Bentley manual has a 1976 wiring diagram, then a "1977 Supplement". I have found the 76 diagram and 77 supplement do not accurately reflect the wiring of my daughter's 77. The 78 and later diagram does. Thus, I had two of them made up, one for her car and one for mine. A great help over the years.

As to the additional wiring for the "electronic ignition system", make up your own drawing of it and compare how it is wired up. A bad coil could also cause the problem you describe and, if as part of the rewiring full time 12V input was run to your coil, it will overheat and cause problems.

Knowing exactly what you have right now will make it easier to find out what the problem is. Les
Les Bengtson

Follow up:
I took the MGB on a long trip today and it ran perfectly!
Before the run I checked all the connnections around the coil and fuse box, relays, and starter.
Only problem on the high speed run was my first flat tire in the B. It was due to a pothole in the road, and the valve stem hit the wheel causing the old, rotten stem to leak air.
Life is good.
Randy
1977 MGB
randy olson

Randy--sorry for not replying sooner --glad car is running fine.All the info you need on these systems can be found at---www.cranecams.com ---look under the Fireball Ignition section and all tech info is there.Crane now owns the Allison product.I was in error on air gap --its trigger alignment --SORRY.At any rate if yours is marked Allison it is fairly old.
All the best ---Gil
Gil Price

This thread was discussed between 06/05/2005 and 08/05/2005

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