Changed the plugs...I gots questions.

Well I finally got around to changing the spark plugs in my JEEP today. The job went well and I had no real problems but I have a question. The odd cylinder sparkplugs were light brown in color and smelled fine. But the even cylinder sparkplugs were black and the #6 one was wet and smelled of gas. Why would this happen? I kept the old plugs and labeled which cylinder they came from to compare later. The electrodes on the old ones were a bit eroded. Now she runs stronger and smoother. Any thoughts? Thank you in advance.

 

Well, the even ones are running rich. Black usually means too rich of a mixture or excessive oil. You would notice the blue smoke from the exhaust pipe if it were oil. I am unfamiliar with the two barrell carborator on the V-6, but I think maybe the barrel of the carborator that feeds the even cylinders is adjusted too rich. Unless the float level in the carborator is set a bit too high? May we assume that the spark plug wires are good and the distributor cap is in good shape? If so are they in the correct order? It could be that the valve seals or the valve guides on these cylenders are worn. This is highly unlikely as they usually wear out evenly.
Alright how long have these plugs been in there? 6 years 2 weeks? What was the Jeeps last trip like? Did you just get back from a long trip? 400 miles or 40 feet? Did you drive two blocks to the corner store and back without warming it up?
Hmmmm..... Hey, have you done a compression test lately? If these cylinders have lower compression then the odd ones, the fuel/air mixture will not burn as completely, giving you the symtoms you have. Are all of the old spark plugs the same make and part number? If they are different numbers then they are of different heat ranges which could give you these symtems, as would 3 bad spark plugs. I am just thinking out loud here, tell you what why don't you check these thing and let us know what you find. I will check back tomorrow. Matt W.

 

The old plugs had been in there for at least two + years. As for the oil thing I was expirienceing blue smoke on start up. But this time it did not. Even when I changed the plugs. Oh well. I am not sure the timing is off. I thought of this yesterday. The engine started right up. The last trip was bombing through the snow a few weekends ago. Only about 5 miles though. I was in low range so there was enough power. I could tell it was not running on all cylinders though towards the end. Now it deffinately is running on all 6. I verified this upon start up after changing the plugs. The old ones were all Bosch plugs. The new ones are AC delco's. I think the old ones were the same heat range. I will ook at this today. I didn't do a compression test. I was going to but forgot the tester at my house. This is one problem with a JEEP not at your own house. Now it has more power and sounds smoother. I will check the condition of each plug and do a compression test once I get a few more trips under her belt. I will keep you posted. Thank you for the help sofar.

 

Well here is an update. I sarted the JEEP up after a few weeks of not doing anything to her. I had to persuade her with some cables. Started right up. Let the engine warm up a bit before I kicked the idle down. Put her into low range to break her free from the ground. Needless to say it broke off the ground and wnt through the foot and a half of snow well. I proceded to do some winter wheeling and she did very well. great power and drove well. Now it idles well and doesn't want to die when I decelerate to a stop. :? Bye the way I forgot to mention I have a hole in my muffler. It sounds cool but I can't think it is doing good for the back pressure. Any thoughts?

 

Replace that bad muffler, it can warp your exhaust valves. What happens is the valves are fairly hot, and on shutdown at least one of them is open, this prevents the heat from these valves from dissapaiting to the head. Then, especially in our colder states, the air is not heated by your exhaust system as it rushes into the engine thru the tail pipe. Now you have hot valves meeting very cold air, and unless the heads of your valves are fairly thick, they warp and do not seal as well as they used to. Do this many times and you can see the cumulative effect. While glass packs sound nice, I do not use them for this reason. They would be better then one with a hole thru it though.
BTW, a hole in the muffler reduces back pressure, the exhaust, like water, takes the path of least resiatence. In cold climes, on working engines, the longer exhaust system is necassary for the above stated reasons. So, IMHO you need a new muffler, Matt W.

 

I was wondering about the back pressure thing Matt. I think I will get a new muffler. How did you know I had a bad muffler though? :? Good call though. Maybe I will get a new one this weekend. Other than that I think I just need to clean my carb and do some repair to the PO "electrical" work. But I have to say at least they put inline fuses in. thanks for the help.