Car Clinic: Ignition Coil Failure

Car Clinic: Ignition Coil Failure
 

Question:

My 1991 Toyota Corolla 1.3 GL has done about 170 000km and is in good shape. But in September last year the engine suddenly started cutting out. The suspicion fell on the ignition coil. The coil was replaced and the problem disappeared.

But not for long. In the ensuing months, up until July this year, I’ve had three further coil failures. The symptoms always began with the engine cutting out. It would initially restart promptly, but soon become hard to start and then impossible to start. Every time a new coil was fitted, away I’d go until the next time. Along the line, new plug wires were installed, to no avail. What is going on here?

—RB

Answer:

RB, ignition coils (or coil packs on modern cars) are very often blamed, unfairly, for causing mysterious misfiring and stalling. But in your case there can be no doubt that the coil has been the culprit. The ignition system on Toyota’s 2E engines (used in the 1991 Corolla) was a transitional design in the evolution of ignition systems. It still has a distributor with a rotor twirling around inside it and four plug wires sprouting from little towers on the cap.

But the coil had been made smaller and fitted inside the distributor body. The electrical components on Japanese cars of that era had an unrivalled reputation for longevity, so when an original Toyota coil fails, except at very high mileage, the question arises as to what caused the failure. Two things that can shorten a coil’s life are:

  • Over-voltage from the alternator, which makes the coil run hotter than normal; and
  • Bad plug wires, or too big a plug gap — both things that push up the sparking voltages required from the coil, again increasing heat.

Whatever caused the failure of the coil (and it might simply have been age), I strongly suspect that the subsequent replacement coils were of inferior quality. I have had personal experience of no-name coils dying within a few weeks of being fitted. Unfortunately, no test or scrutiny can tell you how long a coil will last — you can test to see whether it’s working, but you don’t know whether it will keep working for 1000km or 200 000km. For that you are entirely dependent on the manufacturer’s reputation.

My advice to you, then, is to first make sure there’s no underlying problem responsible for the early demise of the Corolla’s coils, and then to decide, depending on finances, whether to opt for a genuine Toyota coil, costing about R1 830, or a coil from a reputable manufacturer (Sakura is one such, but there may be others) which can be bought for about R500. Don’t touch the no-name brands. Dud coils, I’m told, have been known to blow engine control units on late-model cars.

-For all your motoring queries, please contact Gerrit Burger: geb@mweb.co.za