spark plug #6 misfire

[mc30306]

My 1998 RR is currently in the shop and has been there several times for the past three week. About a week after having my water pump replaced the check engine light came on. According to the computer "spark plug #6 is misfiring." To date I've had the spark plug replaced, the spark plug cables replaced, the coil replaced, the fuel injector replaced and a valve job. Each time something is replaced the check engine light comes back on 1-2 days after being in the shop with the same fault code. Any ideas? Could this be related to the water pump replacement? This is becoming costly and frustrating.

[darkknight1999]

Have they done a leakdown test?

[mc30306]

Don't know but I will ask. What is a leakdown test?

[darkknight1999]

I didn't type this all out but it explains it better I would in my own words so here you go:

"A leak down or "cylinder leakage" test is similar to a compression test in that it tells you how well your engine's cylinders are sealing. But instead of measuring pressure, it measures pressure loss.

A leak down test requires the removal of all the spark plugs. The crankshaft is then turned so that each piston is at top dead center (both valves closed) when each cylinder is tested. Most people start with cylinder number one and follow the engine's firing order.

A threaded coupling attached to a leakage gauge is screwed into a spark plug hole. Compressed air (80 to 90 psi) is then fed into the cylinder.

An engine in great condition should generally show only 5 to 10% leakage. An engine that's still in pretty good condition may show up to 20% leakage. But more than 30% leakage indicates trouble.

The neat thing about a leakage test (as opposed to a compression test) is that it's faster and easier to figure out where the pressure is going. If you hear air coming out of the tailpipe, it indicates a leaky exhaust valve. Air coming out of the throttle body or carburetor would point to a leaky intake valve. Air coming out of the breather vent or PCV valve fitting would tell you the rings and/or cylinders are worn.

A leakage test can also be used in conjunction with a compression test to diagnose other kinds of problems.

A cylinder that has poor compression, but minimal leakage, usually has a valvetrain problem such as a worn cam lobe, broken valve spring, collapsed lifter, bent push rod, etc.

If all the cylinders have low compression, but show minimal leakage, the most likely cause is incorrect valve timing. The timing belt or chain may be off a notch or two.

If compression is good and leakage is minimal, but a cylinder is misfiring or shows up weak in a power balance test, it indicates a fuel delivery (bad injector) or ignition problem (fouled spark plug or bad plug wire)."

[98RRover]

you can check to see if the cylindor is cracked, or you might need a new pressure fitting ring around the spark plug and head.

[Paulo_Miguel]

Hello, at some time, my RR as misfiring and make some smoke, and also smells allot at petrol .... running the test book we get always an error code indicating an electric problem on Injector 1 and 4.
After changing and testing almoust everithing, Injector´s, coils, spark plugs, check wires, check ECU, including all engine sensor´s ....
They find the problem, bad CamShalf, timing chain and gear´s.
I thake the chance and order the RPI kit to repalce All on the head´s, since the engine nead to be opened ...
The conclusion as that we lost alot of time finding a electric or electronic problem, because the test book always pointing to a electric trouble, and at the end as a mecanic problem .......