Rough idling and cutting out

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Baldbazza
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Rough idling and cutting out

Post by Baldbazza » Sat Sep 23, 2006 9:09 pm

This is one of those daft questions that, at one time, I would have known the answer to straight away. But after years of running new(ish) cars I'm a bit rusty in the engine fault-finding department.

The GT has decided to play a little game with rough idling and cutting out.

For a few weeks it's 'missed a beat' every so often. Nothing much - just a slight shudder no more than once or twice on a journey, so I've ignored it. Today however, I drove about 20 miles. The engine seemed normal on the way there and again when I left 20 mins later, but, when I stopped at the first roundabout on the way back, it spluttered and cut out.

It started on the button, drove normally, then, when I stopped at the next roundabout, spluttered and cut out again. I needed to keep my foot on the loud pedal to keep it running.

Couldn't see anything obvious under the bonnet. I yanked the throttle cable several times and at one point it did seem to run smoothly. I wiggled HT leads one by one, and the engine instantly went lumpy again when I touched one of them. However, I have a suspicion this is a red herring as it didn't run smoothly again as I continued wiggling, and the engine didn't subsequently feel as though it was only firing on 3 cylinders. And the HT leads are only 3 months old.

The car seems to run fine in all gears except at slow speeds, apart from occasionally feeling lumpy. Decided to come home on the motorway as there are too many roundabouts and junctions on other roads. It pulled OK and ran fine at motorway speeds, only feeling slightly lumpy when I braked when being cut up.

There's no hesitiation when accelerating and it seems happier driving at higher speeds than lower; just lumpy at slow speeds and cutting out when I stop.

I've recently changed the plugs, dizzy cap, rotor arm, HT leads, battery and air filter.

The weather was dry and warm, no moisture under the bonnet.

To me, it doesn't seem like fuel starvation, as it accelerates and runs quite happily at 70 mph.

However, it just doesn't feel as though it's electrical either, as I'd expect it to be affected at all engine speeds.

Any ideas about where would be a good place to look?
1985 BX 19 GT
2007 Alfa Romeo GT

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Post by jeremy » Sat Sep 23, 2006 9:23 pm

I'm sure someone else can tell me I'm wrong - but has this car got the coils that fail on other models?

Incidentally its well worth having a good look under the bonnet with the engine running in the dark just to see if you can see anything sparking.

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Post by ellevie » Sat Sep 23, 2006 9:35 pm

I have two petrol BXs and by coincidence I experienced the same fault on both of them whereby a normally fairly healthy idle pattern became erratic leading to idle cut-out. The problem in both cases was traced to poor contact in the low tension wires on the coil. One of these 4 wires just sends pulses to the rev-counter, another is the 12v supply, one is the 12 supply to the ignition amplifier, and one is used by the amplifier to switch the coil. I cleaned up the terminals and applied some battery terminal protective jelly and the problem has not returned in over 6 months. It's probably worth checking this out just with some WD40 and by reseating the connectors.
David

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Post by Baldbazza » Sat Sep 23, 2006 10:22 pm

Seems to be pointing to the coil at the moment then! I've just had a good look in the dark and can't see any sparking. This is the coil it's got - the terminals do look a little manky, so I'll have a go at cleaning them up tomorrow.

Is there any way of testing the coil (apart from putting my finger in the central hole and see how far I can fly)?

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Post by jeremy » Sat Sep 23, 2006 10:38 pm

Haven't seen one of those for years! Do you think its original? - Looks like a British substitute for the original as continental ones seem to be square and look more like transformers (electrical ones rather than toys or C4 ones)

Just a thought - especially if its a substitute - how hot does it run? A favorite was to fit a coil intended for a ballasted circuit to a non-ballasted car. The ballasted coil was actually a 6 or 9 volt one and was intended to be used with a resistor in series except when starting - and so ran hot and may have had a cutout operating when too hot - anyway they would cut out intermittently when hot.

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Post by AndersDK » Sat Sep 23, 2006 10:53 pm

Oh yes -

Thats the early type. A standard round coil. But windings specified for the electronic ignition module. The primary has got some 0.8 ohms which will read as a shortcircuit on any normal mukltimeter - even the better ones.

The secondary is some 6K ohms - BUT BEWARE !
Any ohm meter / multimeter checking of the secondary will induce a back EMF of high voltage.

My workshop method of testing an ignition coil any type - early round or later square transformer type :
Fit a HT cable to the coil HT terminal. Arrange for the end of the HT cable to have a pretty precise gap of 12mm to earth.
(do not use a spark plug with the standard 0.8-1.0 mm gap - this will always make a solid spark in free air even with a very weak coil)
Connect the coil + terminal to a +12V source.
Connect a free ended wire to the coil Breaker (Rupteur) terminal.
Now slide the free end of this wire across an earthed surface. This will produce lots of sparking from a sound coil.
C U / Anders - '90red16riBreak - '91GrisDolment16meteor - Project'88red19trsBreak
dead cars : '89white 16RS - '89antrasitTRDturboEst - '90white19triBreak

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Baldbazza
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Post by Baldbazza » Sat Sep 23, 2006 11:08 pm

jeremy wrote:Haven't seen one of those for years! Do you think its original? - Looks like a British substitute for the original as continental ones seem to be square and look more like transformers (electrical ones rather than toys or C4 ones)
Ah the joys of classic car motoring!!! My old 1960 Austin A40 had one just like that when I were running round in short pants!

I have a fair amount of history from 1991 and there's no receipt for a coil - probably unlikely it was replaced before then, as it would have been less than 6 years old, so could well be the original. 21 years is a pretty good mean time between failure!
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Post by adamskibx » Sat Sep 23, 2006 11:50 pm

Its an original coil altright. My GT has one identical to that. My GT cuts out only if I have been in a stupidly high gear and then let the enigne idle, but I think this is normal for any engine. My car was a bit lumpy until I checked the plug gaps. If youve sorted the HT side of things, then chech the LT wires, and also the carb solenoid connections have given these symptoms on mine before. Check the solenoid by disconecting the battery, turn the ignition on, then reconect battery and listen for a click from the carb. Then squeeze the spade connector to make a tighter connection and lube it up with WD40.

The engine I fitted to mine had the later type coil, bolted to the engine (its still there actually, I havent got round to removing it), and I wanted to use that as well as the distributor, but had to revert to the GT ignition system in the end.

Good luck with curing that. Check the carb solenoid conmnection first.

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Coil.

Post by Geoffrey Gould » Mon Sep 25, 2006 8:20 pm

Hi replaceing the coil would be a good move anyway, I had a very hot 998 mini once and stopped for some lunch on a journey, there had been no problems, went to start it and it wouldnt fire. It had fuel and what I thought was a good enough spark BUT it was in strong sunlight. Very lucky enough to find a coil as it was a small villiage on a sunday. It was the coil. Started and ran no problem. I notice it has in the picture what looks like a ignition amp, the connector and amp are not above suspiction, remove the amp and clean the back of it and the face of the mounting plate and put a thin smear of heat conductive compound on to the face/s, this will make sure that the amp does not suffer from overheating. Compound available from MAPLINS etc.
Cheers.
Geoff.
1991 BX 1-7 td Auto.


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Re: Coil.

Post by Baldbazza » Mon Sep 25, 2006 9:05 pm

Geoffrey Gould wrote:Hi replaceing the coil would be a good move anyway, I had a very hot 998 mini once and stopped for some lunch on a journey, there had been no problems, went to start it and it wouldnt fire. It had fuel and what I thought was a good enough spark BUT it was in strong sunlight. Very lucky enough to find a coil as it was a small villiage on a sunday. It was the coil. Started and ran no problem. I notice it has in the picture what looks like a ignition amp, the connector and amp are not above suspiction, remove the amp and clean the back of it and the face of the mounting plate and put a thin smear of heat conductive compound on to the face/s, this will make sure that the amp does not suffer from overheating. Compound available from MAPLINS etc.
Cheers.
Geoff.
Thanks Geoff - is the amp the little grey-black thingy to the bottom left of the coil?
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Post by adamskibx » Mon Sep 25, 2006 9:35 pm

Yes thats the amp Bazza. Funnilty enough, my car started missing on entry to the motorway today, was fine at speed, but not when gently cruising, and a press of the acclerator when ghently cruising bought about a massive power hickup followed by a very sudden jump to full power. A bit of Italian style driving soon sorted that so I imagine it was dirt in the carb.

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Carb.

Post by Geoffrey Gould » Mon Sep 25, 2006 10:47 pm

Hi jonkw you could well have got it, your memory of a filter jogged mine of a same thing, only on a transit.Nylon filter inside the float needle valve with a piece of "fluff" or something in it brought the top speed down to 30 to 40 mph with no guts.
Cheers.
Geoff.
1991 BX 1-7 td Auto.


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Re: Carb.

Post by Baldbazza » Mon Sep 25, 2006 11:59 pm

Geoffrey Gould wrote:Hi jonkw you could well have got it, your memory of a filter jogged mine of a same thing, only on a transit.Nylon filter inside the float needle valve with a piece of "fluff" or something in it brought the top speed down to 30 to 40 mph with no guts.
Cheers.
Geoff.
In this case though, the car quite happily accelerates to and travels at, ahem, the legal limit - that's what makes me think it's not fuel-related (although I haven't yet changed the fuel filter so I'll do that anyway). The problem only happens when it's engine braking or idling, or rather trying to - it revs nicely when I press the loud pedal ..... which makes me think it's not electrical either... :?

I think I'll have a session cleaning / replacing low tension contacts on the coil, cleaning the amp and using heat conductive compound - anyone know if that's the same stuff that you use between a computer CPU and motherboard? (I've got some of that). If needs be, GSF sell the coils and they're just down the road from work, so that's probably the next step.

However, the investigation will have to wait a while until we can sort out a couple of 16 valves and get them out of the way of the garage where the GT is snugly lurking..... :roll:
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Post by jeremy » Tue Sep 26, 2006 12:10 am

If the problem does not happen when the engine is under load its always possible that its an electrical connection or wire that's stressed or shaken on the overrun or at idle but not under load.

Filter problems sometimes occur under load - ie when demand is not high the system can keep the float chamber full - but when demand is high it can't keep up - so you accelerate and the thing responds normally until the level drops in the float chamber and you loose power.