Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Intermittent engine stopping 1975 +8

Good morning all (from Aust)

I am new to the Morgan family, and we have a 1975 +8 which we have given a new home only a few weeks ago.

She has developed a recent problem, with the engine stopping/restarting intermittently when hot and when >1500 rpm

When she stops, the tacho drops to 0 (which suggests the coil power is unpowered), but then in a fraction of a second the tacho comes back, and the engine restarts (similar to a clutch start).

The odd thing is that this only happens after 5-10km of driving (when she is hot), but then occurs regularly whenever the revs reach 1500rpm. She does however idle normally.

We have an original Lucas coil and a FAST XR700 ignition system.

We have had our local mechanic scratching his head for a couple of weeks, but thought you guys may provide a little wisdom ...

Thanks, Barney

Do you have access to another coil ? ... might be breaking down when hot. Similarly the optical trigger may be intermittent when it gets hot so you're losing the pulse that drives both the coil and tacho. Harder to check the trigger (does the ignition box have any diagnostics?)

K

Thanks K for the reply

At this stage they have consdered removing the coil, to allow it to be checked.

Unfortunately I don't think the ignition box has any diagnostics, and therefore whether this is the fault is uncertain.

The puzzling factor is that this is a recent problem, as she was running well only a few weeks ago when she first arrived from Western Australia.

The heat aspect is also interesting, although as mentioned was not a problem until now.

I was hoping that the vast experience of UK drivers may shed some light on this type of intermittent failure ... maybe not hot enough in the UK though ???

Should be a pretty bog-standard coil ... a trawl round local old car enthusiasts should pull up one from someone's workshop for a substitution ... it's wakey-up time here so smarter folks than me will be along in a bit I'm sure 🙂 .....good luck

K

As it is intermittent I would swap the coil. Years ago I had one fail on me in a similar way.

Some thoughts:

Does a +8 of that era have an amplifier module on the side of the distributor? If so, they have been known to fail in this mode.

Swapping the coil is a good idea but a lot of the modern replacements are poor quality - if a new coil doesn't fix it, do swap back to the original coil.

Petrol starvation can produce very similar symptoms. A friend had this with an MG Midget and we were all convinced it was an ignition problem. It transpired that one of the fuel lines had started to break up internally and was causing an intermittent stop.

Just in case, here is a link to the instructions for your XR700 system - includes some useful information on fault finding:

XR700 Instructions

Think also of the main HT lead from coil to distributer cap. the distributer cap itself and rotor arm

Oh! vacuum advance and retard system too. check vacuum line by sucking, distributer base plate should move/rotate. if not assess tube, if ok suck line line and if no resistance it'll be the diaphragm in the vacuum unit. It has to be something that is cutting the engine at a consistent 1500 revs. air filter? dirty or MAF if fitted.

Thanks very much K and GrumpyPa and Paul F and sewin for your generous time, and your amazing input.

Sadly I am only a structiral engineer, and must have missed the lessons regarding mechanical issues with motors and therefore it has been a steep learning curve (still at ground level )

However my logical mind thought that the fact the tacho drops to 0 rpm as soon as the engine cuts out would suggest it is not a fuel or air problem. I assume fuel or air would cause the engine to splutter but would not immediately cause the coil to unpower the tacho ?

I will pass on your comments and suggestions to our local mechanic (son of owener who is away until May), which will add to his knowledge base, and hopefully find the fault.

Thanks again everyone, Barney

On mine (1978 1600 Kent) a similar issue was a loose connection on the ignition lock barrel - took me ages to find. When worn, they sometimes move around. Good Luck (also from Aus)