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MG Midget and Sprite Technical - Misfire & cut's out

1293 midget that when warm and you put lights,wipers, indicators interior light (for navigator) Brantz Rally Clock on the revs become erratic and engine misfires and cuts out. When this happens the volts shoot up to 32 volts. any ideas?
Peter King

Peter. It would be of my diagnostic value to know the year of the car or the conformation of the charging system you are running rather than the engine size.

"any ideas?" Assuming that you have the standard 12 volt electrical system, the fact that, under load, the system is putting out 32 volts would, to me, be an indication that the charging system is at fault. Good way to destroy a battery, electronic ignition systems, other electronic devices, etc. Again, knowing the systems involved would help, but we know you have an overcharging system under load.

Les
Les Bengtson

Peter,
I agree with Les. Are you running a Lucas alternator? Which one? What voltage are you seeing at idle? 3000rpm? How good is the ground strap from the body to the engine?
David "more questions than answers" Lieb
David Lieb

David. We always have more questions than answers. That is what makes us Gurus. But, Peter presents a quite interesting problem, one that I should enjoy hearing about. Wonder what happens when you put excessive voltage through an "electronic ignition" vice a set of points? How does the condenser handle the excessive voltage in a points type ignition system? If Peter responds with more information, it might be worth getting Paul Hunt down here to offer up advice. Dave DuBois might also be of help, but he commonly checks the Sprite/Midget boards. Much more interesting that watching old Robert slag off poor Prop!

Les
Les Bengtson

Yeah, but I still think I missed something there. I have a feeling that Robert is still pining for the fjords of Flame Wars.

I imagine points are a lot more tolerant, but some of the electronic gimmcrackery is amazingly tolerant, too. My Delco alternator had a rectifier problem wherein it would work fine for an hour or so and then pack it in. It was a 2.5 hour drive home from Tire Rack in South Bend a few years back and the battery was weak when I left. By the time I got home, the brake lights were no longer detectable (fun!), but the fully electronic 123/Mini distributor never skipped a beat.

Barring further evidence, I strongly suspect a weak alternator and/or a bad earth to the engine.
David "battery will probably need replaced before he is done..." Lieb
David Lieb

Peter

How are you measuring 32v? What's your instrument and where are your measuring points?

A
Anthony Cutler

You heard it here first.

Les Bengtson is now an official, self-appointed MG guru.
Steve Clark

>>> Les Bengtson is now an official, self-appointed MG guru. <<<

This is news? I realized that a long time ago!

;-)

-:G:-
Gryf Ketcherside

LOL Steve, indeed who are we mere mortals to argue?
Not sure this simple problem requires the efforts of Les and his MG Gurus to resolve.

It is obvious that if the 32 volts is a correct reading then that certainly needs addressing before any other issue.

As non Guru Anthony says how accurate was the voltage measurement and what type of charging system is the car fitted with Dynamo or alternator.

As regards myself and Prop Mr Guru, I personally do not beliebve we should stand idly by as a questioner on these boards may be given information by a so called expert that could be considered dangerous to the extreme. Perhaps I am wrong to believe that.
Robert (Bob) Midget Turbo

Indeed Bob.

I like to get down to the nitty - in this case it's "how do you know you have 32V".

It's a bit like someone asking on a medical BB: "how do you treat scarlet fever"; and then being bombarded with loads of advice.

I'd rather ask: what's your temperature? describe your rash?

And hopefully advise them on treating something less severe than they feared!

A
Anthony Cutler

Anthony,
So you start by assuming the guy is wrong? A trifle disrepectful, no?

By now poor Peter is so intimidated we will never get any closure on this. It is ok, Peter, come on out and play. We simply enjoy sniping at each other in our eagerness to be the one perceived as most helpful. Or else it is a long-standing feud between Robert and Les. ;-)

From the way Peter has phrased things, I would tend to believe that he has a voltmeter on his dash (not at all far-fetched when you consider the engine mods and rally equipment present) and that the needle is swinging way up when he turns all this stuff on at once and the engine starts to stop (so to speak). I would like to know what the tacho needle is doing at the time.

Based on this assumption, I would tend to suspect that the lights in question are rather more than the load of stock headlights. I also suspect that the car is running a Lucas alternator with only one heavy brown wire to the solenoid. My recommendation is to install a pair of relays to drive the headlights (one for low beams and one for high), pulling the load power from a dedicated line from the battery side of the solenoid via a fuse; clean all power connections to the battery,the ignition switch, and the coil; and clean both ends of the ground strap as well as its mounting points.

Until Peter gets up the courage to speak to us again, there isn't much more we can do but snipe...
David "Whose side am I on today? I seem to have lost track..." Lieb
David Lieb

Certainly I would expect it to be an alternator. I have not seen that kind of voltage from a dynamo. Indeed if it was a dynamo I would expect the commutator to have flown to pieces by now due to the excessive heat from that kind of power being generated and its effect on the solder holding the commutator together.

Not being a Guru, David, what on "earth" has the load (headlights etc) got to do with 32 volts indicated in the system???

By the way the only eagerness I have is to ensure posters are given the best information possible, I can not comment on the motivation of others.
Robert (Bob) Midget Turbo

No, David

As an engineer, I've learned to ask questions to understand a wider picture. And some things that seem very simple, like the measurement of 32V on a nominal 12V rail (with a 12v accumulator connected - which would normally have massive electrical capacity) beg the questions:

- how did you measure this figure: what instrument did you use and where did you connect it?

I'm not saying that 32v was not seen, but before anyone can comment on a cause/solution, we need to know more.

I see this as respecting the originator of the question, and the problem he reports. I would hope that any question I pose on this board would be treated similarly.

A
Anthony Cutler

I'm quite sure that before Geoff's car was converted to alternator the dynamo was showing ^28 dcv on revving, so for a short while the 32v, is a possibility.

Not to ask how the measurements were taken would be wrong David

I would never believe a number I couldn't check for my self or at least get verified by discussion

But then again, I'm no guru either simply a trained breakdown and roadside assistance engineer

I have similar reservations to Bob regarding Prop

He has asked countless questions, whilst ignoring most of the responses he's had and then whenever another poster asks a question they are instantly met with a barrage of suggestions from Prop, some of which make me splutter with amazement.

I like Prop and his enthusiasm but the way he dives in scares me.

If Peter does come back (and how many questions asked are NOT followed up by the OP?) I hope he can spend a little time helping the diagnosing team

I'm sure they will all try to help him as always

personally I'm off out of it all again, this is by far a more contentious place than it used to be and there are plenty of advisors around...
bill sdgpm

Well, I had composed an eloquent reply to all this, then my computer rebooted itself to apply updates while I was brushing my teeth. Sic transit gloria mundi ;-) Now you are stuck with the quick reconstruction.

Bill,
Don't be gone too long; we will miss you. We all have reservations about Prop, but I can accept him for who he is. Fortunately, we are on a forum that allows us to see and rebut the responses of others.

Keep smiling! The vocal minority can get to be a bit much at times, but you are appreciated by a goodly number here. Caustic remarks are more fun and motivated more strongly than the nice things we mean to say and never get around to. Yes, I have gotten annoyed here, too and disappeared for extended periods, but I eventually miss you lot and wander back for more abuse.

Bill, Robert, and Anthony,
I am not a guru, nor an engineer, not a "trained breakdown and roadside assistance engineer". I happen to be a "computer psychologist". When one of our computers has issues, I get to take him aside and help him deal with them. As such, I appreciate a list of actual symptoms like engines missing when I turn these things on and the voltmeter shoots up to 32, rather than leapt-upon conclusions like "my computer has a virus". I sure wish Microsoft would put a print button on some of their error messages... If I had a nickel for every time I have been told, "There was an error message, but I don't remember what it said", I could buy another toy for my Spridgets. I have learned the hard way to believe most observations like this (not all), especially when they have figured out the conditions under which it happens.

In this case, it is probable that Peter has spent the time to figure out how to repeat the situation. There are two probable explanations for the "32". Either he has a voltmeter in the dash and the highest number on the scale is 32 and the needle flicks over to there, or else he has attached a VOM and forced the condition. Of course, most VOMs these days are digital, so it is hard to understand a reading of 32 (as opposed to "about 30 volts" for what sounds like an instantaneous event, so I lean towards the first explanation myself. Always willing to be wrong, you all know I have plenty of experience at it.

As to why a voltage spike, it could be a problem with the voltage regulator, too small of a wire between the load and the battery, any number of things. The actual size of it coould be a matter of conjecture as few instruments available to most of us are capable of an accurate measurement of a single spike like this, repeatable or no. The important thing here is that a voltage spike is observed under these conditions.

I really hope that Peter survives all of this and lets us know a little more. Are the "erratic revs" an aural observation of the engine noise, or a visual observation of the tacho?

It sounds to me as if there are a number of non-factory gizmos wired in here. My best guess is that a bunch of this stuff (rally clock, interior light, voltmeter, maybe more) is wired to the white circuit and is overloading it. If so, using the white circuit to trigger a relay fed from the battery (via a fuse, of course) and using the relay output to drive all this stuff could take care of it.
David "we need more data" Lieb
David Lieb

David what took this thread in a direction that we don't like was Les claiming that you and himself plus other MGB owners were somehow Gurus, (quote That is what makes us Gurus.) Steve simply wrote what all the Brits on here were thinking, except in a polite manner. I suspect most of us uttered the words WTFDHTHI?
Then from my point of view you accused me of simply wanting to turn the thread into flamewars?? Just not so

Anyway back to the problem

Either I don't understand volts/amps and resistance or you don't but how can you overload the white circuit and cause a voltage increase? thus what purpose would a relay serve?
The only way a voltage increase can occur is if the VOLTAGE regulator fails, whether that be the one used with a dynamo or one fitted inside an alternator. That is simple IMO, what is in question is the statement that voltage was measured at 30+ volts when the engine misfires. (I'll bet it does) If that reading is correct then the answer is simple and that is the information required and asked for by those of us not claiming GURU status.

Not sure this is a "spike" I considered it generated for sometime otherwise how would it be measured?
Robert (Bob) Midget Turbo

Strictly, no-one can actually claim THEMSELVES to be a Guru. The definition is a person thought by OTHERS to be knowledgable and a teacher. You are only a Guru if your peers think you are.

Whilst the 32v output sounds high I have no idea if it is really relevant to the problem. What is troubling Peter is that it misses and cuts out when there is a heavy electrical load drawn. I think mine has at times done the same. I know certainly that when the electric fan cuts in (drawing something more than 10 and less than 15 amps) the revs drop and the idle becomes much rougher.

Guy
Guy Weller

With all due respect Guy that is understandable as you are not experiencing a high voltage but are suffering from high current demand. Naturally when a higher load is applied to a circuit 2 things can happen. The mechanical effort on the generator will remain the same which will cause the voltage to drop which inturn reduces the current! or secondly as in your case a higher mechanical load is put onto the generator. Thus the engine is required to work harder to turn the generator (or alternator) and the result is that the engine slows down. That is not the same as the experience of Peter who is experiencing a rise in VOLTAGE.
With a correctly operating electrical system on a car, if the engine is idling and you switch on the headlights or the blower then the engine will slow down due to the higher electrical load having an effect on the engine.
Robert (Bob) Midget Turbo

Bob,
Consider yourself annointed as a guru. Feel better now? Please note that I do not consider myself a guru. Neither was I attempting to "accuse" anyone of anything. BTW, I appreciate your apology to Prop and respect you even more for it. OTOH, this could be the flip side of Will Rogers' contention that, "We are all equally ignorant, just on different subjects." Relax already and don't take yourself too seriously ;-) Spridgets should be about having fun and helping others do likewise.

IMVHO, it would not be the overloading of the circuit directly causing the fault, but rather the overloading causing something to momentarily fail, suddenly dropping its load, resulting in a voltage spike. Even a spike must exist for a measurable amount of time. The nature of a voltmeter can serve to distort the amount of time the spike is detectable on the voltmeter as the needle movement is not instantaneous.
David "silly me, it must be the condenser" Lieb
David Lieb

Thanks Bob, that explains why my engine slows, which I never really understood. I wasn't proffering my experience as a solution to Peter's problem - just commenting that to me it sounded something vaguely similar! Not much help, I appreciate!

Guy
Guy Weller

Darn it. I took so long crafting that message that both Guy and Robert got words in edgewise.
David "I need more bandwidth" Lieb
David Lieb

David I would never be so arrogant to consider myself a Guru on any subject, let alone understanding the faults on classic cars described by non engineering type people. But here we have the scenario that identifies what is difficult with any BBS such as this.

I believe that my theory is correct and I can not see how your explanation can be valid. Of course that does not mean it is invalid? I could be wrong! who knows?

However what we do need to do on these occassions is to argue the point and see whose explanations stand up to close scruitiny. That is what I have tried to do and you have done your best to support your point of view.

Now only time will tell for Peter to tell all how he measured the 32 volts and then at least I along with others I am sure will be able to deduce what is wrong and thus the way to rectify it.

:-)

Robert (Bob) Midget Turbo

"Rectify it"? Now you think it is in the rectifier?
Just kidding, Bob! Just remember, we have earned every penny we will get from this! In this instance, I will cheerfully arrange for you to be paid five times as much as I will be.
David "heck, make it ten times!" Lieb
David Lieb

This thread was discussed between 07/12/2009 and 09/12/2009

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