Cylinder scoring from plug wire disconnection

Question

Cylinder scoring from plug wire disconnection

xcr800man (Automotive)

(OP)

29 Sep 03 09:36

Is it possible to score a cylinder from a plug wire being disconnected? Specifically, a plug wire that is NOT the cylinder that scores? This is in a medium duty truck applicaiton.

patprimmer (Publican) · Answer 1 · 2003-09-29 10:28:52

I don't see how.

If it was the one that the plug was off, it just could be unburned fuel washing the bores clean of oil, but only in the cylinder not fireing

Regards
pat

xcr800man (Automotive) · Answer 2 · 2003-09-29 11:15:22

I tend to agree but here is the Hypothesis:

The remaining 7 cylinders are subjected to increased stress building excessive heat causing the damage.

What else could cause a 4 year old motor, properly maintained with 50k miles to score a cylinder? The plug wire is the only "out of ordinary" issue.

franzh (Automotive) · Answer 3 · 2003-09-29 12:20:35

XCR:
What was the scoring? Foreign material? Was there just scratches or was there metal transferred? Were the rings or ring lands damaged? Was the cylinder completely dead or was the plug wire delivering a partial or weak spark? Was the scoring localized to one section or around the circumference? If the scoring was localized, I would guess that something worked its way into the the cylinder. If it is global, then the raw fuel washing theory makes sense. Also, it would have to be for a VERY long time, or a VERY high output engine, or a SEVERE case of cylinder washing. I have seen engines with one dead cylinder run for quite some time with minimal washing, but one cylinder on a racing engine crater on one race.
Franz

Metalguy (Materials) · Answer 4 · 2003-09-29 12:42:41

Here is a longshot possibility. IF the disconnected plug wire wasn't grounded, the high voltage within the dist. cap may have jumped to another cylinder terminal, causing that cyl. to fire 90 deg. early. Check the firing order and see if it fits-only the next cyl. to fire after the dead one could be affected. For example, on a Chevy, 18436572, was the scored cyl. the one right after the "dead" one?

xcr800man (Automotive) · Answer 5 · 2003-09-29 15:12:19

The disconnected wire was on the opposite side of the motor but that is an interesting theroy Metalguy.

There was no noted ring damage but there definately was no aluminum transfer. After reading franza's comments, I am of the mind that it was likely foreign material and not due to the disconnected plug wire. Particularly due to the localized damage.

Thanks for your help on this matter.

Metalguy (Materials) · Answer 6 · 2003-09-29 21:37:01

"The disconnected wire was on the opposite side of the motor but that is an interesting theroy Metalguy."

Doesn't matter where the cyl. is located. Just look at the firing order.

patprimmer (Publican) · Answer 7 · 2003-09-29 21:59:51

I'm with metal guy and Franz

The extra load theory doesnt stand up. If the engine is capable of operating at full throttle, as the stress in each cylinder is the maximum that each cylinder can make at full throttle. Disconect a cylinder, and you dont get more power from each remaining cylinder to maintain the engine power, you lose power.

At part throttle, you increase the throttle to make up, but you are still mostly less than full throttle power, and even at full throttle power, each cylinder is still at it's rated output.

A carbon track or crossfire from the voltage buildup from the disconected lead sounds most likely

Regards
pat

Come Join Us!

Posting Guidelines

Cylinder scoring from plug wire disconnection