I have a 2002 T&C LXi with a 3.8L and 91000 mi. The problem I am having is that it seems to misfire at highway speed between 50 - 70 mph in overdrive unless I take out of overdrive its fine. I put new plugs and wires on about 6000 miles ago. I pulled one of the plugs and the white part right above where it fires was half brown. Is the plug not firing completely? I have noticed it has a little bit of a rough idle in gear and it will shift kind of hard under light accelaration and down shifting 2-1 once in a great while. No CEL either. My gas milage is in the low 20's and it still gets up and goes under hard accelaration. Any suggestions? I must add that the van only goes 2 miles a day during the week. Would it not getting in the normal operating temp daily have anything to do with it?

 

what plugs did u put in?? and was it there b4 u replaced them or only after?

 

The plugs I put in were Champions the same ones I pulled out. I was having a little bit of a rough idle and a similar issue at highway speed. Same thing with the trans it cured the hard upshifting and downshifting after replacing the plugs and wires.

 

if u had a real misfire there would be a check engine light along with codes do U have any?

 

No CEL. Could there be codes but no light? Also why would the plug look like it was partially firing?

 

misfire codes are a one time turn on which means if they are present the computer will turn the light on all because it is a federal emissions deal.

 

Have you checked your ignition coil ?

 

No I haven't. Whats involved checking the ignition coil?

 

Well the primitive way is to take all plugs out and then one by one place each into its respective HT socket place the earth of the plug (i.e. the part where the spanner goes) against a good earth e.g. the engine and get someone to crank the car over and you should see a big healthy blue spark. If you don't then the one that does not perform is the faulty lead.

However that is the old way and these days with integrated HAL effect CDI's not really practical. Best option is to take a trip to the local scrap yard and try and find one from a written off car that has done less milegae than yours. Test and see if the problem persist
If the ignition coil is breaking down under load or not delivering a sufficient spark you will see the problem you are experiencing. When in overdrive (depending on vehicle speed of course) you are placing the engine under more load. Hence if your spark is weak and all of a sudden you decide to accerate hard in overdrive more fuel enters the C/C than the given spark can deal with (i.e. ignite)

Couple of other things to conider

1. Have you checked the plug clearance. On modern platinum tipped plugs they claim these are not adjustable (b**s**t) An incorrect gap can give all sorts of issues. However adjustment of these type plugs must NOT be done by inserting anything between the cathode and the anode. Preferably use some long nose plies to adjust up the earth pin.

2. Have you done a compression check on all cylinders. A leaky or sticky valve will cause reduced compression and hence incomplete ignition. Even a spark plug that is not properly torqued up can cause blow pass.

Some modern cars have an igniter per plug. It is actually part of the HT lead. I do not know about your car though. I seem to think yours just has one for all cylinders. The last thing is the actual igniter itself. This is the unit that actually tells the HT coil to deliver the spark. Sometimes it too is integral with the HT box.

 

If I have a weak ignition, wouldn't it give a misfire code and turn the CEL on?