I have a Ledbury Maestro with an "A"+ 1275 engine. When it has been left sitting for more than a day or two it is very "three cylindery" for a good number of miles. Up to about 50 miles of my usual DC and motorway driving is usually needed to get rid of the problem completely. It is usually when it is under load but will also drop to three while sitting idling from time to time.
I put this down to dampness. Would this be a correct diagnosis? I have all the items needed for an engine service but with the weather (and personal circumstance at the moment) this will have to wait.
gazzafield ("gazzafield" ) gurgled happily, sounding much like they were saying:
OK, so that rules out an iffy injector.
Definitely a compression test, then. It's also worth spraying some easy- start, brake cleaner or similar over the inlet manifold gasket whilst it's on three - it may be sucking false air into one pot. If it runs smoother, you're lucky.
It _could_ be ignition, but it'd have to be one very knackered HT lead or plug to be THAT bad.
It's done less than 40k miles and has been very well looked after by it's previous owners. I shall further clear up my crappy posting information in the fact that it's not a continuous fifty miles, it just needs about fifty miles of running over continous days before it's fully sorted. The three cylinder-ing will also show itself while I'm pootling along the motorwway at say 65mph and I go to speed up to overtake, then it will pop and fart for a few seconds then go as normal.
The first check I'd do, is to wait until it's dark and then have a look under the bonnet while the engine's running. Look for any sparks tracking around the leads and distributor cap.
Dampness wouldn't cause a fault like that which lasts so long. My first instinct is a dud plug lead, which improves a bit with heat. My other possibility is a valve guide that is allowing oil down it to foul a plug. Final possibility is the condenser in the distributor might be getting weak, which might have enough in it to spark across a narrow plug gap but struggle with a wider one or a higher resistance lead. That is not easy to diagnose, but as they are cheap, you have the option of changing it regardless. You can always keep the old one as a spare if changing it makes no difference.
You can do some quick and easy diagnostics by moving things around - plugs first (and take a good look at the condition) which should tell you which cylinder as iffy, then leads if they are a convenient size to change over. If you can move the problem cylinder by swapping things, then it is plugs or leads; if it stays on the same cylinder it is distributor cap or valve guide.
But electronic ignition tends to operate the sparks at a higher voltage than a conventional condenser and coil, so have a look under the bonnet in the dark with the engine running and see if you can see any external sparks. (I knew someone who fitted electronic ignition to a HA viva, and that certainly showed up where the voltage leaks were when he tried to start it on a damp and foggy day when we spotted sparks across the outside of the distributor cap.)
The date being 31 Jan 2008, "gazzafield" decided to write:
It's unlikely to be just dampness. Is it just one cylinder misfiring or a general misfire? Have you checked the plug gaps and condition of the electrodes? Have you swapped ignition leads around (at both ends of course)? What's the condition of the distributor cap inside? Are all the HT leads properly seated? Have you checked the rocker clearances? Are the manifold nuts tight? Is it single carb, twin carb, SPI or MPI? (I'm familiar with A-series/A+ engines but not the Maestro.) There could be an imbalance here though that would be unlikely to go away with regular use.
You might not have time to do a full service at the moment but at least take the plugs out and have a look at them. If one plug is badly oiled up or sooted (or white for that matter) it will tell you where to start looking. Clean up all the plug and coil leads and the plug insulators and the dizzy cap (inside and out) and the rotor arm, then spray lightly with WD40 before putting everything back.
If it's one cylinder with a sooty plug suspect oil getting in via rings or valve guides. One cylinder with a wet plug probably means it's electrical. Two cylinders at one end with whitish plugs could mean weak mixture because of air getting in at the inlet manifold.
Basically if a cylinder isn't firing it means either wrong mixture or lack of compression or lack of spark or incorrect timing. If it's a timing problem it could be due to sticking centrifugal or vacuum advance on the dizzy, but that would affect all cylinders. If a plug gap is too wide it will require a higher voltage to spark so will encourage tracking.
Check all the plugs for any signs of fouling. It may be all of them or just one. If one doesn't match the rest, concentrate on that cylinder. It's a long shot but check the valve clearances as it's easy to do. While it's ticking over and misfiring, remove the plug leads in turn. You used to be able to get plastic pliers to do this but I've not seen any for ages so use insulated ones and be careful. That should tell you which cylinder's not working. If the engine's done so few miles and been looked after, it shouldn't have any serious internal problems but may be suffering from being driven too gently and may need a decoke. You can move some of this by hard driving for a number of miles. You want to get the cylinder temperatures as high as possible for as long as possible. Aim for high throttle opening for as long as possible. It's not unknown for sparks of burning coke to come out of the exhaust doing this. If this fails, remove the cylinder head and do it the old fashoined way. A series engines are easy to work on. I used to be able to change a valve and decoke mine in 2 hours but I did have a lot of practice. Even so. it's only a day's work.
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