Another Wayne type question

[GPster]

Just trying to make things run forever I had my neighbor change the spark plugs in my 2004 Jeep Grand Cheroke (?) at 70,000 miles He used NKG plugs and everything appeared OK. Everything was OK but the other day it started running rough and I had a chance to take it to Advance right away to have the scanned and it said mis-fire cylinder 6. It is a six cylinder and there are only 10,000 miles on those plugs. The neighbor is changing the oil for me and checking the for mis-fire that of course wasn't there when I started it up after it had been setting for 3 days and was cold. NKG recomended the plug's porcelin be coated with di-electric grease,which the neighbor did. When he pulled the spark plugs cover and wiring boots the di-electric grease has become a white powder on all six of the plugs. He has never seen this before but he probably has never had to change a set of plugs the second time in any customer's car. The di-electric grease that he uses is a reputable brand not some dime store imitation. Is this normal? He hasn't even got the plug pulled yet because he wants to get the area clean before he pulls those plugs. GPster

[wayne petty]

i have seen similar effects when the spark plug wire terminals are too deep in the boot.... they don't snap down....  there is a gap...  the arcing going on in there creates high levels of trapped Ozone..      the high temps caused by the arcing and the ozone cause changes in the silicone dielectric compound.. it dries it out.. turns it back into sand...

this is one of the reasons NOT to use it to lube spark plug threads with.. or lug nuts...    under high heat... it drys out.. and becomes a solid...


i have always wanted to know if the ford tridons that has locked in spark plugs might have gotten some of the dielectric silicone lube on the threads instead of the insulator..


on a 4.0 jeep,.,,, i would also pull the distributer cap...   grab the rotor and see if the shaft is loose in the distributer housing..  they have a problem with that..  wears to one side...   warning.. don't turn in your core till you make sure the reman unit works...   they don't always replace the cam sensor.. thats what is in the housing.. the timing is set by the crank sensor on the back of the motor...  signaled off the flywheel or flex plate..


i have also had to replace the coils on a few.. they just would not pass a coil spark output test.. using a GAP style tool... not a neon light..

[GPster]

He got the 6th cylinder' s plug pulled and he pulled the 5th cylinder's also. The 5th looked good but the 6th was a little black like it was burning rich so we changed that on out. All six cylinders had that powder from the di-electric grease so maybe the harness hadn't been pushed down far enough when the plugs were changed. I don't think this engine has a distributor but is crank sensered. To me all of these plug wires are like a harness that includes the coils and he said it's all one piece. When I took it to him for this problem the check engine light wasn't on but after changing the plug and putting it back together we now have the light, no misfire but the light. I'll give him this information in the morning and will probably take it to advance and have it scanned again. when he got the light on start--up he shut it off and dis-connected the battery terminal hoping that the computer just needed to reset itself,but no such luck. This is actually the wife's daily driver and i'd rather not have it that we'll wait till it quits to find the problem. GPster

[wayne petty]

i want to know...  are the new spark plugs the same length as the originals...

that is a one piece coil...  i missed that it was a 2004..

some brands vary in length of the insulators above the threads...

it will take a scan tool to read and erase the codes..

be sure to write them down before erasing them..

if you have other than a p0300 -p0306...  please don't erase them...   you will want to view the snap shot of engine data taken when the trouble code set...  

p0300 is a random misfire...   p0301 through p0312 is individual cylinders.. depending upon how many you have..

[GPster]

Well I drove it over to Advance. They scanned it and nothing showed up but the light is still on. I talked to them about it and they said that liability doesn't allow them to delete anything. For that I would have to go to a dealer or a repair place that has all that equipment. Thinking about this I didn't have to delete anything when I changed the throttle position sensor a while back. Maybe there's something else wrong. Talked to my neighbor/mechanic about the plug boot thing and for as well as he described the way it goes together I don't believe that it was not put together right the last time. Of course the plugs only have 10,000 miles ago but that was a year ago and it would be impossible to find the old plugs he took out. He said he normally replaces plugs with the same brand unless the customer specifies a Brand or cheap. I'll think about this more. It seems to run OK and the seat position I normally drive in the check engine light is blocked from my line of sight by the steering wheel. GPster

[Carnut]

Black electrical tape always worked on my check engine light.

[wayne petty]

one thing... that most people don't know about the  check engine light being on....

it rolls back power and fuel economy so it does not hurt the motor... or melt the converter...    getting the problems fixed can restore fuel mileage..  i have seen some cars loose 30%  with the check engine light on...

HF has the 98614 obd2 scan tool for 119.99 this week online...

it will turn off any  OBD2 check engine light.. except possibly a mercedes or VW product..  but it still might..


the 40 buck OBD2 code  readers will usually clear a check engine light  if the tool is left plugged in for a few minutes... some others have push buttons..

did you get the codes??  from the autoparts store?

if the misfire goes away.. the check engine light will turn out in a few starts...  if it is one of the codes i listed..  and the problem is fixed..




this chart does show gm TBI/TPI/PFI sensor values.. but other cars have almost identical values..

one might want to copy this cart to there computer... when a car comes in with the check engine light on... plug in the scan tool... run through the trouble codes... then write the cars scanned values on the chart .. this way i can sit and examine the data to see what does not look right..