2003 Isuzu Rodeo Question Engine makes loud knocking sound a

ANDREW.ZEMA

MEMBER
2003 ISUZU RODEO
6 CYL
2WD
AUTOMATIC
92,000 MILES

About a year ago my #4 spark plug exploded and shot out through the ignition coil gasket; leaving only the threaded portion in the head. I asked around and could not find a good explanation as to why this would happen. I double checked that all my spark plug sizes were correct and changed all of them. I also replaced the valve cover gaskets because there was a small hole on the the #4 gasket, but I'm not sure if that happened before or after. Ever since the engine makes a knocking sound when winding down after releasing the accelerator. There is also oil on the electrode side of all six spark plugs, but mostly on the #4 side. I have been keeping an eye on it, but also driving it ever since. It doesn't seem to be getting any worse. There is heavy carbon deposit in tailpipe. There is no water in the oil. Any ideas?

3 Replies

SERVICE WRITER

MECHANIC
9,123 POSTS

Regarding the oil on the electrodes, I would think since the valve cover gasket was replaced that would leave worn rings or stem seals. Aside from a manufacturer's defect such as with a few of the ford engines, I would suspect that the threads were compromised when the plugs were changed. Might want to compression test the engine and see where the #4 cylinder compares.

IT may be good to stick a boroscope into the cylinder to see if any damage internally on the piston occured.

I'm assuming the noise is from that cylinder. If you can use a stethescope to listen closer to see if it is closest to the cylinder.

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Tuesday, May 18th, 2010 AT 8:14 PM

ANDREW.ZEMA

MEMBER
2 POSTS

I replaced the stem seals when I replaced the valve cover seals. I'm not sure where to get a hold of a boroscope, but that would be nice. The compression test had #4 at about 90 and the rest in range.

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Tuesday, May 18th, 2010 AT 8:40 PM

SERVICE WRITER

MECHANIC
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Good on the testing!

The spec is 145 psi. If any one cylinder is lower than 10% of the others there is a problem on that cylinder.

What I would do next is squirt a little 30 wt oil into the cylinder #4 and recheck compression. If compression comes up, I would suspect a ring problem or a worn/damaged cylinder.
If the compression does not come up, then I would lean towards a bad valve or leakage through the plug hole threads.

A cylinder leakage test can also be done. Air escaping through and into tailpipe would indicate exhaust valve, through the throttle body would be intake valve and leakage into the pcv would be rings.

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Wednesday, May 19th, 2010 AT 7:08 AM