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MG MGB GT V8 Factory Originals Technical - Damp Electrics
|Following Sunday's downpour I had bad missing and a refusal to pull on the way back from this years Kimber Run in Derbyshire. I have experienced this once before on a very wet day but thought I had cured it with new plug leads. Yesterdays experience means I am back to the drawing board on this one and would appreciate any help. The car is a factory V8, with a Lumenition system fitted. On opening the bonnet when it had dried enough to tickover I found that where the coil is at the front nearside it was very wet and presumably this was wetting the base of the coil and thereby causing the missing. I cannot believe that the stock car wets this area habitually, even if road conditions are very bad, and so am at a loss to know why it should be so on my car. Could it be forward spray from the front tyres (195x70/14 on alloys) and if so can it be prevented? I could just turn the coil round so that the business end is uppermost to see if that stops it by lifting it out of the spray but surely this should not be necessary? It has crossed my mind that it could actually be a fuel problem as I have louvres in the bonnet next to the K&Ns but usually a bit of damp in the intake makes things work better not worse (water injection!). Has anybody experienced this before. Any comments welcome.|
|Not had any missing problems in my factory V8 in 10 years and 70k miles of all weathers - apart from when the bottom hose pin-holed and was spraying some plug leads. My coil is pointing down and has no protection. As well as water being splashed up I suppose it could be coming through the rad and getting flicked onto the coil by the fanbelt. When did the missing start? Suddenly after going through deep water? Gradually built up? If you suspect the coil connections you could try fitting the boot used on the Mini where the coil was immediately behind the grill. In my experience marginal components can fail under adverse conditions. I used to have to keep a set of plugs ready to fit in mine as all of a sudden it would fail to start, usually when we had to be somewhere so I didn't have time to diagnose it properly, and a new set of plugs always 'fixed' it even through the old ones looked perfectly good. Eventually it did it one day when I had some time and I diagnosed it to the distributor cap, which again showed no tracking or cracking. A new cap (which I happened to have) fired it up right away and I haven't had the 'plug' problem since.|
|HI Paul. The missing starts gradually as the road spray builds up. At first the engine just doesn't feel right but as the spray gets worse it can get so bad that I have to change down through the gears to keep going. I am sure that if I could see under the bonnet at that point everything would become clear. In fact I wish I could see under the bonnet as I was driving to see the spray pattern under there. Unfortunately when it's raining, the road is one which it is difficult to stop on and you are worried about getting home roadside fault diagnosis is not something you want to get into so I press on trying to keep away from the spray of the car in front. The really difficult thing is to keep the speed up enough to keep the engine running while driving slow enough to minimise the spray. Stopping for a few minutes when it gets really bad allows things to dry out enough for me to continue but even this is only done as a last resort as by that time even getting it to tick over is difficult - and worrying if a long way from home. On arriving home last night and immediately opening the bonnet it was noticeable how much water there was in the area below the coil, not that you could miss if from the steam coming off the wet back of the radiator. I had thought of the Mini part but I never really did trust them as although they exclude direct spray I suspect that they also trap any water which does find its way in - with precictable long term results. I haven't started it since but I know it will be fine.|
|As a test to eliminate or not I'd tape a polythene bag around the business end of the coil and see what happened next time. The distributor is close by, like I say it could be the cap. If it still happened with the coil bagged I'd remove that and bag the distributor next.|
I think the Mini boots were effective. Mine never had one, but then I never had any problem with the ignition either even when driving through floods with gusto in my youth.
If you do find it is the coil getting wet and causing the misfire you could try looking around a motorcycle breakers as several m/c's have a protective rubber sleve that goes over the bottom of the coil (with a hole for the HT lead).
|Thanks for the advice Richard and Paul. I have had a new Dist cap and leads since the last time I had this problem (which was some time ago but still the last time I had it out in such weather). What really puzzles me is why a basically original setup should display this problem. This would suggest that I am actually looking in the wrong place. I will take steps to shield the electrics though and wait for a rainy day - shouldn't be too long!|
This thread was discussed between 19/04/2004 and 21/04/2004
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