Not even Gucci spark plugs will help...

Dear Car Talk

Dear Car Talk | Jul 01, 1991

Dear Tom and Ray:

I have a 1978 Cadillac with a 425 engine and one weak valve. A compression test showed that one of my cylinders has only 35 psi. Until I can afford to have it fixed are there any quick fixes? Home remedies? Recommendations? Suggestions? What about a hotter spark plug? What about a colder spark plug? Thanks.

RAY: Sorry, Carl, not even custom made Gucci spark plugs are going to make a difference at this point. With 35 psi, you're not going to get combustion in that cylinder no matter what you do.

TOM: The only solution is a valve job. But until you can afford that, you should take steps to prevent further engine damage. Since there's no combustion in one cylinder, unburned gasoline will leak down past the rings. Since gasoline is a lousy lubricant, that cylinder and piston will get scored and scratched, and then it'll take much more than a valve job to get you back on the road.

RAY: The easiest way to prevent that damage is to take a lesson from Cadillac themselves. Do you remember their 8-6-4 engine? That was an experimental fuel saving engine that switched from eight cylinders, to six, and then four depending on how much power was needed.

TOM: And you're about to invent the Cadillac 8-7-8. It's got eight cylinders now. After you disable one this weekend, it's going to have seven. And when you save up $1000 for a valve job, it's going to have eight again.

RAY: Assuming the bad valve is an exhaust valve, the best way to disable the bad cylinder is to have your mechanic remove (and save) both pushrods from that cylinder. That's essentially how the 8-6-4 worked. Disabling the pushrods stops the valves from opening and closing. That keeps unburned gas from ever getting into the cylinder in the first place.

TOM: The car will still run rough on seven cylinders. But the bright side is you may be pleasantly surprised at the increase in gas mileage. In fact, you may be so delighted, you'll want to go back and ask your mechanic to take out a few more pushrods!

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