I have a 2000 dodge caravan 3.0L with 188,000 miles when I purchased the van it appeared to have a intermittent misfiring problem while driving it seemed to lack power at some takeoffs and would sputter or backfire at other take offs but ran fine for the better part of two out of three takeoffs.
after changing the distributer cap, rotor, plugs and wires the problem seemed to happen more frequently and more rythmically (if rythmically is a word) and now my misfire seems to be associated with a slight internal knocking sound from inside the engine.
i thought that maybe if one of my cams had jumped time then maybe with the firing gear up to par that maybe it had made the misfire more noticable.
i inspected the timing marks and noticed that crank timing mark was off about 30deg. From the timing marks on the cam sprokets. I thought I had it licked.
come to find out the harmonic balancer had sheered the woodruf key on the crankshaft. But had not affected the actual timing at all. The crank timing sproket wasnt affected.
so I did what any good mechanic would do I replaced the crank timing sproket for good measure, the harmonic balancer, timing belt and water pump along with the serp tensioner thermostat, valve cover gaskets and other misc items not related to my problem.
now with the engine all back together my small knock became a definate knock accuartly associated with the misfire of the engine. But still intermittent. At curb idle it seems to be fine with no problems at all. When reving the engine it will knock about every 2 out of 5 revs and hesitates and misfires every time the knock is present. I checked with a stethascope and found the noise to be located in the front head just above the #2 cyl.
when I had the engine apart I noticed that the discoloration under the valve covers was much darker under the front valve cover I dont know if that could be related to my problem or if its just temperature related due to the location difference between the front and back cyl heads. Or if one of my heads had been replaced at some point and if so ire the spesificatione the same for older and newer heads such as valve length and lash and so on?
so once I located the area of the problem I removed the front valve cover and visually inspected the rockers cam and lifters during cranking and while running and noted that there was no visual defects evident under any of those conditions.
i guess my question is this:
does this sound like I could have a broken wrist pin or a sticky valve? And if so is there any remedy other than replacing the valves? I have worked on several of these 3.0's and have dealt more with more burnt and antifreez eaten valves and have never seen a sticky valve in one of these engines but most of the ones ive worked on were pre 1995 engines that had the valve guide problems. Is this more common in the newer engines? And have you dealt with this problem before?
one other thing I noticed that may be of some help is that my front right plenum bolt has the bracket attached that was meant to hold the slack spring on the older non overdrive transmission linkage. But my van has the overdrive transmission. None of the older pre 1995 minivans ive owned or worked on have had this bracket attached if they did not have the non overdrive transmissions in them.
could this mean that my emgine was replaced at some point with an older engine? Or did this bracket become standard on the newer engines weather it was used or not. Any help or suggestions would be greatly appreciated thanks in advance.