Hesitating Engine!

[grandpascot]

Hi All

Help and advice needed please. My Stag is a three speed auto and up to this year I have had no engine problems whatsoever. Then suddenly every time I reach between 1500 and 2000 revs under load the car stutters, hesitates call it what you will the engine almost stops. Blipping the pedal a couple of times and everything is then OK and she carries on as though there is nothing wrong. I have a Lumenition module fitted and I borrowed another to check that mine was not this breaking down. Same result. There appears to be nothing wrong with the plugs and I have just fitted new leads but no difference. I currently have the tops off the carbs with a view to changing the diaphragms. (New ones arrived today) but really can't see anything wrong with them. Help please with any advice. I should add that this only happens under load. Free reving is fine.

Thanks

Mike

[Gresley]

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Hi Mike,

That sounds like a split diaphragm to me. When I had one split on a Triumph 2000 once the symptoms were exactly that, but I could not see a split either. A new one cured it, see what it is like with new ones. Another cause could be fuel starvation maybe? Is the filter blocked?

Brian

[grandpascot]

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Hi Brian

I really can't see a split but I intend to put the new diaphragms in anyway. If it was fuel starvation surely this would happen both under load and when free revving?

Mike

[alistair260661]

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does it do it every time? or just under heavy load (i.e acceleration / going up hill)?

I'm thinking electrical? Coil / capacitor - especially if it doesn't do it every time.

Anyway if you have the diaphramsput them in - if it doesn't cure it then I'd think more latterly.........

PS where r u, I'm in Edinburgh...........

[Moraystag]

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Mike I forgot to say viamy private email address to try the diaphragms, but was a bit busy here. Change the diaphragmsas suggested it's all about a process ofelimination I would think. NOT EXPENSIVE



Mike

[SwissSteve]

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Ihad the same problem a year ago and after a process of ellimination it turned out to be a hairline crack in Distributor cap. Good luck

[staggering]

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Had similar with mine - turned out to be a faulty tacho and / or cables to / from it, might be worth temporarily disconnecting tacho to see if problem clears + coil breakdown gives similar symptoms, good luck these "intermittent problems" are always a pain to find

[jleyton]

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If I had to guess at just one thing then, from experience, I'd go for coil. (So that pretty much means it won't be the coil :shock

[alistair260661]

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yes the coil, thats why i asked if the problem is intermittent - if it is and it coincides with a hot engine (and incidently a very hot coil) it would suggest that the coil is breaking down..............

[grandpascot]

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Hi All

Thanks for all the advice. I'm just heading out to the garage to change the diaphragms and will check the distributor cap. The coil is new about 18 months ago but I will change it if the new diaphragms dont sort the problem. The coil currently installed has no name or marks on it what do you suggest that it should be replaced with?

Alistair it's just under heavy load just as you describe and it does only happen after the car has warmed up. I stay at Muir of Ord.

I'll let you know the outcome

Mike

[alistair260661]

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Firstly when the engine is warm feel the coil if you cant comfortable hold it (very hot) then its very suspect - mind you it depends if it is still mounted in the original place (engine) or has been moved to the bulkhead. Anyway if it very hot its probably that. The question is if its that new (how many miles running?) what has caused it to break down...... it is the right one??? - the car should have a 6-9 volt coil and a ballast resistor if it is on points - if you have switched to electronic ignition (when - recently?) you may find that the new system needs a 12 volt coil (and the ballast resistor should be bypassed.

I had this issue the other way round (the Electronic were taken out of my car just before I bought it - hencewhen I renewed the coil (with the correct 6-9 volt one) because there was no ballast resistor it burnt out within 200 miles.

If I were you, I think I'd go back to basics and check from scratch - you probably need to start with checking the timing, then the low tension wire at the dizzy to coil (good clean and tight connection, check the connection inside the dizzy (the capacitor) - you could change this if you want (£4)..... is the cap clean/cracked? Make sure your sparkleads are in good condition. Points set right? is thevucumn & mechanical advance working?......

A good place to check will bethe coil ballast resistor issue - if you have a mk1 or 1.5 its easy its a white thing usually on the bulkhead wired in series with the coil. If its a MK2 then its a pink wire in the loom (between the tacho and the coil) and more difficult to find - the Haynes manual describes - I think I have a description of ballasted ignition - whay and how it works.

[grandpascot]

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Thanks for all your help.

There was a quarter inch split in one of the diaphragms and Brian was right. Until I actually removed it and was able to stretch it just could not see the split.

I haven't had a chance to give it a good run yet but hope to tomorrow. I shall be checking out the electrics as well because I'm not entirely happy with them and having had the top half of both carbs off and seen how dirty they are inside they will need to be stripped.

Mike

[Giles]

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good to hear it was quite simple - sounds like you have found the problem