QuestionHello
Van running great the out of the blue started jerking/bucking at speeds over 40 -my regular mechanic changed fuel filter, then it started setting off codes PO300 -he said take to a specialist, i took it to the best around -they found scanned and sets PO300 at times for random misfires. tried plugs, O2 sensor and other major components including PCM, check engine light was in-op. foung missing bulb and replaces same. tried crankshaft position sensor and throttle position sensor even though tested good with lab scope suspect possible transmission problems starting also they told me that the tensioner arm was bent and serpentine belt needed replaced (was not done) parts replaced were O2 sensor plugwire set, dis rotor, gasket set, fuelpump, $800.00 later they sent it home said it was only bucking at 60mph + and at a slight downgrade 1 to 2% and they could drive thru it -said take it home and maybe have a tranny shop check it out -drove great for about 16 miles then lost power 4 blocks from home! would start and move slightly then die! i know this is long but wanted to provide all info i would appreciate any insight you might have on this problem! Thanks so much for you time and help
Catherine
AnswerI'll need a bit more information from you on this, specifically the engine. You said they replaced the distributor rotor so to me that screams 3.0L v6 but before I go any further with trying to help I'll need to know EXACTLY which engine it has. Also, I really appreciate all the info but if you can break it up some with some spacing that really makes it easier to follow. At the end of the day everything is harder on the eyes. Thanks.
To give you some idea as to what I think right off is this. The people working on your car are going off the deep end for a simple mis-fire code. They are not that difficult to diagnose and CERTAINLY should not have replaced: plugs, wires, PCM, rotor, fuel pump, o2 and whatever else only to have the problem still present.
The diagnostic steps I would run through would be very involved. So I don't know that I could talk you through everything but if you have the ability to get someone on your end to chat with me through here then together I could help rule out alot of possibilities.
Multiple cylinder misfires are either random or multiple. Randoms are kind of hard because they are indeed random and finding the exact cylinder in question may change from day to day. Multiple cylinders on the other hand are somewhat easier because they frequently affect the same cylinders, repeatedly thus making reproducing the problem eaiser.
Random misfires would point to common components such as intake manifold gaskets, oxygen sensors, or even trash in the fuel lines. Trash in the fuel lines can come from a number of places including bad gas, liners of fuel tanks deteriorating (Your's isn't known for this problem), or metal lines rusting from the inside. There are other conditions but that's ball-park info there.
A cylinder misfire occurs because of a condition present frequently and in the same cylinder. This is anything that is cylinder specific like 1 injector that has trash in it, 1 injector pintle that is stuck, 1 plug wire, 1 spark plug, 1 or a pair of damaged valves in that cylinder, damaged cylinder walls, or worn out piston rings for that cylinder. It's something that is distinctive to that particular cylinder.
Throw in a multiple cylinder mis-fire code and you multiple the chances for all of the above "1" cylinder problems to multiple times as many cylinders as you have. But there are some things that can make life easier to diagnose.
For instance you have a 4 or a 6 cylinder. The easy part here is that the "coil pack" is broken down in pairs of cylinders. If you've got a 4 cylinder engine then cylinders 1 and 4 work as a pair and share one half of the coil. Cylinders 2 and 3 share the other half. So... if you've got misfires on "companion" cylinders then I would suspect (note I did not say replace) the coil pack or circuits related to it.
If you've got a 6 cylinder then you've got a single block referred to as a coil pack. In it there are 3 coils. So two cylinders share a coil. If you find two cylinders misfire that share a single portion of the coil pack then obviously... then should allow someone to focus their diagnostic time on that particular area.
There's alot of if's as you can tell here. It's really difficult to diagnose a driveability problem without the car in front of me and the diagnostic tools I use on a regular basis to try and fix cars just like yours. But, if you're able to get someone willing to spend some time with me through this site and who has access to diagnostic tools then hopefully together we can stop the rapid flow of money out of your pocket and actually get the car fixed.
Doug
