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MGB 79 MGB runs, quits and time lag before re-starting

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Naomi

Jedi Hopeful
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Back again with another question for the experts here. My 79 MGB will start, runs for about 15-17 minutes (ya can pretty well set your clock by it) and then shuts down. After that it won't re-start for about two hours. Now I'm going to quote the hubby on what's happening: The car has a Crane XR700 ignition. When it shuts down there is no arc from the coil wire to ground for about two hours. We were able to find a new XR700 and replaced that both parts inside and outside the distributor--same problem. Replaced coil--same problem. Replaced ignition relay--same problem. The coil primary resistance is 1.42 ohms and the secondary is 1.5 on both coils. When the engine shuts down we have immediatley replaced each individual part, one at a time, and it will not restart for that two hour period. New plug wires, new plugs, new distributor cap, new rotor button etc., have also been installed. Again--runs for 15-17 minutes just as if it has a timer on it and then shuts down. About 5 seconds prior to shutdown it will begin to miss, backfire once or twice and that's it. Have also disconnected all circuits other than the starter and ignition by removing the two bottom fuses. No problem with fuel and when it does start it runs fine until that time period kicks in.

HELP AGAIN!!

Your turn:smile:


(1964 MGB, 1979 MGB, & 1980 MGB, all repaired 4000 times but still loved /ubbthreads/images/graemlins/smile.gif
 
Re: 79 MGB runs, quits and time lag before re-star

is the coil over heating? do you have the external balast resister installed correctly?

I can recall my car developing a miss when the coil got too hot (nearly too hot to handle with bare hands). However, it never shut down for 2 hours "like clock work" on me. Then again, different brands of coils may behave differently when they over heat.

I've since replaced my "over heating" coil with a name brand coil and properly installed external ballast resistor. The ignition seems to work excellent now, and the coil only gets warm to the touch now.
 
Re: 79 MGB runs, quits and time lag before re-star

Rob, the hubby says the coil does receive it's supply from the resistive wire that loops around the front of the car and back to the coil. Voltage at the coil between terminals is 6.78 volts and between th + terminal and ground is 12.03 volts. The alternator is putting out 13.89 volts. As for the coil getting "hot"--yes it does get very warm but we have two and have exchanged them while the car was down and the same results --no start. Put the same coil in my 80 MGB and it starts right up. The hubby says he has given up --- I haven't and thanks so much for jumping in and helping. Looking forward to more suggestions from you and the others /ubbthreads/images/graemlins/smile.gif
 
Re: 79 MGB runs, quits and time lag before re-star

Ignition relay?

Do you still have the electronic ignition or have yoh changed over to points?
 
Re: 79 MGB runs, quits and time lag before re-star

Rick it has a Crane XR700 ignition. A guy in our neighborhood just happend to have a new one in the box and we have exchanged the complete set and still have the same problem. Matter of fact we've switched them out several times. The hubby was also on the phone with Crane last week and they are too at a loss as to what is happening. The hubby says he feels something is breaking down due to heat and it must be looking him in the face making a fool of him but he can't find it /ubbthreads/images/graemlins/smile.gif
 
Re: 79 MGB runs, quits and time lag before re-star

My bet is with a faulty electronic ignition. Just because it's new doesn't mean it's good.

My stock electronic ignition on my '78 MGB did the same thing...I've since replaced it with a points distributor.

Also check the ignition relay on the inner fenderwell, same side as the distributor. (There will be two relays...one is the starter relay, the other the ignition relay. I *think* the ignition relay is the one more forward towards the radiator.)
 
Re: 79 MGB runs, quits and time lag before re-star

If it had a condenser, I'd bet on that but as it doesn't, I'm lost...not knowing much about auto electrics.
 
Re: 79 MGB runs, quits and time lag before re-star

Rick we replaced the ignition relay but do have a question for you about the distributor. I looked at two MGBs today a guy wanted to trade me for my Fiat Spider. They are a 71 and a 73 and both are junk and it would take thousands to make either a driver. With that said will one of the distributors off either one of them fit my 79? Maybe worth a shot for the hubby to ask him to borrow one just to check if it will work.

Your turn /ubbthreads/images/graemlins/smile.gif
 
Re: 79 MGB runs, quits and time lag before re-star

Naomi - which distributor does it have (not the Crane setup - which distributor did they put the Crane it)? Is it the OPUS distributor, the C.E.I distributor, or another?
 
Re: 79 MGB runs, quits and time lag before re-star

Yes, I believe that either would work.
 
Re: 79 MGB runs, quits and time lag before re-star

[ QUOTE ]
Naomi - which distributor does it have (not the Crane setup - which distributor did they put the Crane it)? Is it the OPUS distributor, the C.E.I distributor, or another?

[/ QUOTE ]

It's the OPUS distributor /ubbthreads/images/graemlins/smile.gif
 
Re: 79 MGB runs, quits and time lag before re-star

[ QUOTE ]
It's the OPUS distributor

[/ QUOTE ]

There's your answer!
 
Re: 79 MGB runs, quits and time lag before re-star

What's the answer Tony?
 
Re: 79 MGB runs, quits and time lag before re-star

I don't personally like OPUS for any application - others will say that once the Crane went in it, the OPUS weaknesses no longer matter & they may be right....take the distributor out of your other B & see what happens - if its not an OPUS also.
 
Re: 79 MGB runs, quits and time lag before re-star

Do ya'll recon I should just buy a new point type distributor at Advance Auto for $68.00? Hubby says he is considering it since we've had several problems with the ignition on this MGB.

Your turn again:smile:
 
Re: 79 MGB runs, quits and time lag before re-star

You could if they have it.
 
Re: 79 MGB runs, quits and time lag before re-star

They do have em Tony and actually have one on the shelf. I had mentioned this once before and some folks said something about the "advance curve" not being right and the condensor failing right away.

Rick--trid to talk the owner of those two junkers into letting me "borrow" one and he turned me donw /ubbthreads/images/graemlins/smile.gif

I guess for now the hubby has really given up on it. He didn't touch it yesterday and is off fishing this morning /ubbthreads/images/graemlins/smile.gif
 
Re: 79 MGB runs, quits and time lag before re-star

Don't get upset about the advance being off - that's only something that bothers a craftsman...the distributor off the shelf has the same curve as the one that came in your car!
 
Re: 79 MGB runs, quits and time lag before re-star

Then that's good enough for me. I've always liked the MGBs, be they CB or RB, just as they were built and have great fun with both /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/smile.gif
 
Re: 79 MGB runs, quits and time lag before re-star

I think it might be helpful to swap the distributors between your '79 and '80. If the problem persists, you know it is not is the distributor/Crane system. If it moves to the '80, you can pretty much eliminate a lot of other possibilities.
 
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