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Misfiring spark plugs

Question : Recently, I had my car engine transplanted with a similar BMW engine (E32) bought from some chop shop. After installing the engine, the car started to misfire.

I have changed the plugs. But they still misfire, and we found that the sixth plug cable is not firing consistently. I changed to a new distributor cap and rotor. It improved a bit.

But not satisfied with the performance, as it's still misfiring, I got a new set of plug cables. But the performance is still bad. It could hardly climb above 145km/hr.

When I rev the car in 'park', black smoke comes out. The spark coil was changed about six months ago. Sparks from the coil (with the cable removed from the distributor cap) are strong and consistent. But sparks coming out of the cable to the spark plugs are weak. I have also got a new timing sensor, but nothing seems to work.

I changed the old engine because it has a blown gasket. It needs daily bleeding of the water system to remove build-up of excess air trapped in the water system. Before the engine was removed, it could hit a top speed of 195km/h easily with good pick-up.

Answer : I think the problem lies in the distributor. Try to find someone with an engine analyser so that you can see the behaviour of each cylinder. You mention that you have replaced the rotor but I think you need to recheck the fitting of the rotor to ensure that it is seated properly on the shaft. Also the distributor cap has a notch to locate it in the correct position.

Sometimes if the cap is not fitted correctly, the engine will still start but misfire as the spark cannot jump the gap between the rotor and the contact inside the distributor for some cylinders. Your mechanic must also be aware that if the distributor is not put in correctly, you will not be able to adjust the advance properly and you may be run- ning with insufficient advance. All in all, look at the distributor and if necessary, send it to a specialist to check it out and confirm that the advance/retard functions are working and that there is no excessive wear on the rotor shaft.


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