Rough running Silver Shadow
Posted: Wed Feb 15, 2012 3:27 pm
I own a 1979 Rolls Royce Silver Shadow and am experiencing a very annoying rough running problem. At idling speed the car will rock somewhat and the exhaust makes a burbling noise (like a misfire). At speed performance seems normal but you can feel the engine is slightly rough, certainly not what a Rolls should feel like.
I am now in the middle of replacing the valve stem seals on my Shadow and used the opportunity to inspect the spark plugs.
I installed NGK Irridium GR4IX plugs about 2000 miles ago with an electrode gap of 0,6mm. Imagine my surprise when I remeasured them and found the gap to have grown to 0,8mm on all the spark plugs, as the central electrode had eroded. This kind of wear is of course abnormal, and I suppose it will have contributed to the increasing rough running. The strange thing is, it used to be running slightly better with the standard NGK plugs.
In the past I have had difficulty setting the ignition timing : when setting it at 25°BTDC at 1300rpm, it should be 12°BTDC at 650rpm (according to the workshop manual). However I can not get it under 17°BTDC. Absolutely every ignition component has been replaced (leads, electronic ignition, coil, plugs, cap, rotor, plugs, capacitator), with the exception of the distributor itself. Could it be that the distributor itself is faulty ? The weights and springs seem to be working OK, but look quite rusty to me.
I used a Colourtune kit, just to look at the combustion and found it to be very erratic. Somtimes it fired in quick succession and then nothing for a few seconds.
The fact that the plugs have eroded that much in only 2000 miles and the problem with the ignition timing lead me to believe it is an ignition problem and a new distributor might be needed.
If anyone has any ideas about this, I would very much appreciate them as I am getting increasingly frustrated about this ongoing problem and losing the pleasure the car used to give me.
I am now in the middle of replacing the valve stem seals on my Shadow and used the opportunity to inspect the spark plugs.
I installed NGK Irridium GR4IX plugs about 2000 miles ago with an electrode gap of 0,6mm. Imagine my surprise when I remeasured them and found the gap to have grown to 0,8mm on all the spark plugs, as the central electrode had eroded. This kind of wear is of course abnormal, and I suppose it will have contributed to the increasing rough running. The strange thing is, it used to be running slightly better with the standard NGK plugs.
In the past I have had difficulty setting the ignition timing : when setting it at 25°BTDC at 1300rpm, it should be 12°BTDC at 650rpm (according to the workshop manual). However I can not get it under 17°BTDC. Absolutely every ignition component has been replaced (leads, electronic ignition, coil, plugs, cap, rotor, plugs, capacitator), with the exception of the distributor itself. Could it be that the distributor itself is faulty ? The weights and springs seem to be working OK, but look quite rusty to me.
I used a Colourtune kit, just to look at the combustion and found it to be very erratic. Somtimes it fired in quick succession and then nothing for a few seconds.
The fact that the plugs have eroded that much in only 2000 miles and the problem with the ignition timing lead me to believe it is an ignition problem and a new distributor might be needed.
If anyone has any ideas about this, I would very much appreciate them as I am getting increasingly frustrated about this ongoing problem and losing the pleasure the car used to give me.