Questions and Answers

Dead Cylinder In A Protege Q. Questions: I have a 1996 Mazda Protege 1.5 liter with 69,000 miles. She has been idling rough so I asked Merchants Auto to run a diagnostic on the car. The diagnostic system printout states that I have 90 psi in my number three cylinder and that the number three injector is not working.

When I pull off the number three plug wire the engine continues to run without disruption. When disconnecting the other three plug wires individually the engine stalls. Can I trust the diagnostics and what would your recommendations be? New engine? Rebuild? Replace the number three cylinder rings? Could I easily replace the fuel injector? Also should I run a compression test on my own or have another shop look at it? I've replaced the plugs, cap and rotor with no effect on the engine idle or performance.

Thanks,
Steve

A. The fact that there is no change in rpm when you unplug the number three plug wire indicates something is wrong in there. That would tend to substantiate the bad injector diagnosis.

Before I decide on any engine work, I would adjust the valves and redo the compression test. If the compression is still low, put two or three squirts of oil into the cylinder and retake the test. If there is little or no increase in compression, then you may have damaged intake valves in the cylinder head.

Mazda had a problem with the intake valves and came out with an improved intake valve. If this is indeed the case, and I think it is, then the best time to replace the injector is when the cylinder head is off.