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MG MGB Technical - mgb gt 1980

my mg cuts out!it can run sweet ,as soon as you drive it for 5 mins and cuts out takes five mins and starts sounds and runs and stop again ?
cliff

Start with the simple stuff. If it's got a fuel filter, change it.If that doesn't cure it, substitute the ignition relay by swapping it with the start relay. Barrie E
Barrie Egerton

Remove the fuel filler cap and drive without it on. If the problem goes away, the vent line for your tank is clogged. Cheers - Dave
David DuBois

Change change change? Oh dear me no! A penny in diagnosis saves a pound in parts.

Connect a timing light to the coil and plug leads and watch for flashing as you crank. If you get none then further diagnosis of the ignition is required, if it flashes then when on 1 or 4 point it at the crank pulley and check the timing, if that's OK it must be fuel. David's fuel cap trick is a satisfyingly cheap step, presumably 'staffs' is UK and so a vented filler cap is required, a blocked vent or incorrect unvented cap will cause fuel starvation.
Paul Hunt

My apologies Cliff, I didn't realise how expensive it would be to interchange two adjacent relays. The time & cost spent to eliminate a cause or even cure the fault must be prohibitive. As for the fuel filter,usually the most neglected part on a car,it would be sheer extravagence to change it before it is completely clogged. Being from the Colonies, I had no idea that they were so expensive in the UK .I've gone through life believing that substitution of parts when possible,was the quickest way to solve intermittant defects.Live & learn ,I guess. Barrie E

You opened the door on this one Paul.
Barrie Egerton

Gee, first it was Ponting, now Barrie. The week is not going well (lol).

In fairness, I think Paul has made a good point. Diagnosis allows us to progressively eliminate possible contributing causes in systems/components. That narrows down the area of effort/expense.

We need to remember that any change may have unintended consequences - eg fixing one problem but exposing another. Of course that fix can also be tempory as well, then we are back to where we were but in a more confusing place. I liken it to adjusting carb jet screws in pursuit of better tuning/running without keeping an accurate record of screw turns from the starting point.

Regards
Roger
Roger T

"I've gone through life believing that substitution of parts when possible,was the quickest way to solve intermittant defects"

Now I really must disagree on that one. After 30 years working on electro-mechanical and electronic switching systems one of the first things I learned was that you *don't* go swapping things, either around or new. Mind you I did used to get laughed at for testing removed transistors to make sure they *were* faulty, before I wrote the fault off as cleared, whereas others would just bin it and hope their diagnosis was good. It is all too likely to disturb the fault and make it go away, only for it to come back again another day, much as Roger has said. Which is why I keep recommending one looks at the tach and ignition warning light before the car has even come to a halt in situations like this, and to listen to the fuel pump i.e. without even getting out of the car. Next stage is a timing light on the HT leads and watch the flashes (or not), only then a voltmeter if the diagnosis so far points that way. Even use of a voltmeter can distrurb an erratic connection, which is why a couple of times in the past I've rigged up indicator lights or a meter in the cabin connected to parts of the circuitry I suspect, so can see instantly what the status is when the problem next occurs. But that's just me :o)
Paul Hunt

I'm fully in agreement with a methodical diagnostic approach to trouble shooting. However,for INTERMITTANT defects,I prefer a more practical approach. Even if the faulty part is isolated theoretically, chances are ,it will be working when you come to test it. Under these conditions I prefer to substitute the part.If it fixes the problem, fine,if not,move on.
Unless it is obviously damaged,I never throw replaced parts away without testing them. Quite often they can be fixed at a later date & put on the shelf for a future spare. I haven't quite come to terms with the "throw away society" yet. Barrie E
Barrie Egerton

*You* haven't come to terms with the throw-away society? I don't throw things away even when they have failed - "If you haven't found a use for something yet you haven't kept it long enough". Anything with screws or removable parts is worth hanging on to, may come in for something else. I chopped up our kids pushchair and made ladder brackets out of the frame, probably 10 years after they grew out of it. Still waiting for a use for all those sets of plugs ...
Paul Hunt

Paul,
So you have all the other bits. I wondered who scored the half I'd missed.

If its a screw, washer, bolt, nut, fastener, spring, pump, motor, hose et al from a radio, TV, computer, washing machine, clothes dryer et al, I have it. Wonderful how handy those jars of bits have been over the years.

Don't envy my executor in clearing my garage though, and I'm certainly never going to move - I couldn't face the packing.
Regards
Roger
Roger T

Oh boy, neither am I! Although I had a rush of blood to the head just this week and got a passing scrap-metal merchant to take away an old Metro engine that had been sitting there for years (didn't get a goldfish in a plastic bag though). I foolishly let them take the starter as it was the inertia type (even though the Metro was years younger than when the MGB changed to pre-engaged), but I kept the solenoid and alternator, which I've test-fitted to the roadster and works even though it has a larger pulley.
Paul Hunt

A big thank you ! i started from bottom and worked up using both ideas cleaned fueltank took my new pump filter ! and to my delight hip hip hooray it runs tiptop!!!!!!!!!!!!!!!! once again THANK YOU BOTH take a bow your both right !!!!!!!!!!
c guest

This thread was discussed between 20/07/2009 and 23/07/2009

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