xyxuhy Posted June 9, 2011 Report Share Posted June 9, 2011 I have a 2000 Cadillac Seville SLS. 32 Valve NorthStar. It is running rough and making some noise. The check engine light is on. The code is misfire on cylinder # 6 and misfire on cylinder # 6 pending. I changed the coil pack and no change. I pulled the #6 spark plug out and found that the piston is hitting the plug closing the gap. Thus the tapping noise also. I bought a shorter plug and nothing changed. this cylinder is still not firing and there is raw gas in this cylinder. Why would the piston be hitting the spark plug? Reply With Quote Link to comment Share on other sites More sharing options...
BodybyFisher Posted June 9, 2011 Report Share Posted June 9, 2011 I have a 2000 Cadillac Seville SLS. 32 Valve NorthStar. It is running rough and making some noise. The check engine light is on. The code is misfire on cylinder # 6 and misfire on cylinder # 6 pending. I changed the coil pack and no change. I pulled the #6 spark plug out and found that the piston is hitting the plug closing the gap. Thus the tapping noise also. I bought a shorter plug and nothing changed. this cylinder is still not firing and there is raw gas in this cylinder. Why would the piston be hitting the spark plug? Reply With Quote Itis possible that you have carbon on top of the piston, but if that is the case and you are hitting the spark plug, you must be hitting the valves also. I would have a compression test done to see if you have any valve damage and that you are holding compression. This is a problem we have never hear of happening before, in all my time here, never heard of the plug gap being closed by the piston. There must be something on the top of the cylinder a carbon buildup causing this. I would bring this cylinder up to the top, pull the plug and take a long screw driver and try to clear the top of the piston and put the stock plug back. Check for spark Are these stock AC DELCO plugs with the correct model number? Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
CoupeDTS Posted June 10, 2011 Report Share Posted June 10, 2011 Are these stock AC DELCO plugs with the correct model number? x2, im guessing no. Plus you said you got a shorter plug and same problem. Shorter how? The plug is the only variable I see here which from what you have said and not said I can draw a conclusion. * 1966 Deville Convertible * 2007 Escalade ESV Black on Black * 1996 Fleetwood Brougham Black on Black V4P -Gone* 1983 Coupe Deville Street/Show Lowrider -Gone* 1970 Calais 4dr Hardtop GONE* 2000 Deville DTS - Silver with Black Leather and SE grille GONE* 1999 Seville STS - Pearl Red GONE Link to comment Share on other sites More sharing options...
Texas Jim Posted June 10, 2011 Report Share Posted June 10, 2011 I have had detonation close the gaps on plugs before. It is rare...but it can happen... Link to comment Share on other sites More sharing options...
Ranger Posted June 12, 2011 Report Share Posted June 12, 2011 My money is on wrong plugs and/or carbon build up on the piston. I can't imagine anything else causing this. Link to comment Share on other sites More sharing options...
rockfangd Posted June 12, 2011 Report Share Posted June 12, 2011 I also must add I have never heard of this on a N*. Pull a plug frrom another cylinder and compare it with the one from the #6 cylinder. post here GM FAN FOREVER Nice, clean, luxury= fine automobile Link to comment Share on other sites More sharing options...
lyev Posted August 2, 2011 Report Share Posted August 2, 2011 Im thinking that the either the main bearing or rod bearing in that cylinder is damaged. A worn bearing would allow the piston to move higher up than it should allowing the piston to hit the spark plug. That would explain the piston hitting the spark plug. And the tapping noise is the piston moving slightly up and down while the engine is turning. But bearings usually fail catastrophically. If it is the a bearing it will only get worse, the bearing will completely fail, rings will be destroyed and the rod will break. Or the engine will just lock up. Remove the spark plug on that cylinder and tap on the top of the piston with something that fits through the spark plug hole. And listen for a rattling sound when you tap it. And look for movement. There should be no movement possible unless a bearing is worn. I have a 2000 Cadillac Seville SLS. 32 Valve NorthStar. It is running rough and making some noise. The check engine light is on. The code is misfire on cylinder # 6 and misfire on cylinder # 6 pending. I changed the coil pack and no change. I pulled the #6 spark plug out and found that the piston is hitting the plug closing the gap. Thus the tapping noise also. I bought a shorter plug and nothing changed. this cylinder is still not firing and there is raw gas in this cylinder. Why would the piston be hitting the spark plug? Reply With Quote Link to comment Share on other sites More sharing options...
Texas Jim Posted August 2, 2011 Report Share Posted August 2, 2011 If a rod bearing was worn bad enough to have enough clearance to let the piston move THAT FAR... you would be hearing a REALLY LOUD KNOCKING... not a slight tapping... Link to comment Share on other sites More sharing options...
cdgrinci Posted August 2, 2011 Report Share Posted August 2, 2011 I think I would do a compression test on that cylinder; carbon deposits 'could' close the gap and cause the plug's gap to be closed but it sounds as something else is going on (in there) that doesn't sound very good. Chuck '19 CT6, '04 Bravada........but still lusting for that '69 Z-28 Link to comment Share on other sites More sharing options...
Ranger Posted August 3, 2011 Report Share Posted August 3, 2011 If a rod bearing was worn bad enough to have enough clearance to let the piston move THAT FAR... you would be hearing a REALLY LOUD KNOCKING... not a slight tapping... Not to mention that the engine would probably tear itself apart before too long. Link to comment Share on other sites More sharing options...
Texas Jim Posted August 3, 2011 Report Share Posted August 3, 2011 If a rod bearing was worn bad enough to have enough clearance to let the piston move THAT FAR... you would be hearing a REALLY LOUD KNOCKING... not a slight tapping... Not to mention that the engine would probably tear itself apart before too long. And if a rod or crank bearing was really bad... you would have almost no oil pressure... Link to comment Share on other sites More sharing options...
airmike Posted August 3, 2011 Report Share Posted August 3, 2011 just to rule it out-what plugs do you have in it? Link to comment Share on other sites More sharing options...
airmike Posted August 3, 2011 Report Share Posted August 3, 2011 just to rule it out-what plugs do you have in it? Sorry i just read that you put a shorter plug in it. So what was the result? it didn't still hit did it? Continued to miss, or did it run ok for a short time? Link to comment Share on other sites More sharing options...
CoupeDTS Posted August 3, 2011 Report Share Posted August 3, 2011 old topic. Youll probably never hear the findings or solution. * 1966 Deville Convertible * 2007 Escalade ESV Black on Black * 1996 Fleetwood Brougham Black on Black V4P -Gone* 1983 Coupe Deville Street/Show Lowrider -Gone* 1970 Calais 4dr Hardtop GONE* 2000 Deville DTS - Silver with Black Leather and SE grille GONE* 1999 Seville STS - Pearl Red GONE Link to comment Share on other sites More sharing options...
lyev Posted August 3, 2011 Report Share Posted August 3, 2011 But it doesnt make sense that the piston just suddenly starts making contact with the plug! Unless he changed the plugs and got some with a longer threaded part, that would make sense. And the guy didnt say it was slight tapping anyway. Could be anywhere from slight tapping to loud knocking. It just depends on who is listening to it. In any event, im curious about what the actual problem turned out to be. But we may never know as this post is kinda old. Probably long forgotten about by the poster. If a rod bearing was worn bad enough to have enough clearance to let the piston move THAT FAR... you would be hearing a REALLY LOUD KNOCKING... not a slight tapping... Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.