2002 Dakota Runs rough for the first mile then clears up


#1

My 2002 Dakota with a 3.9 (200,000 miles)has a problem that I cannot seem to cure.
When I start the engine it never hesitates…it starts without a problem. No excess cranking…it fires up as it always did.
It does run a bit rough as if ONE cylinder is missing every few revolutions. If I let it idle in the driveway for five minutes it will clear up and run fine. But if I take off right away the following will happen.
I put it in gear (automatic) and for the first mile or two it runs as though the plug wires (More than one) are wet and arcing. I can barely get above 25mph. it will spit and sputter for that first mile or two.Then suddenly it will clear up and surge…probably because I have loaded the system with excess fuel…and after it clears up , I have no other problems with it weather I’m on a long trip or a short one.
If I stop for more than 15minutes, I have to go thru all this again.
I’ve had vehicles that acted like this after a hard rain because the plug wires were old and arcing…that’s why I use that as a description.
I also noticed that the other day right at the end of a big downpour it took at least 5 miles to clear up.

Before this rainstorm I had replaced the plugs, wires, rotor and cap, while inside the shop so everything should have been bone dry except for all the humidity from the storm. After starting I checked for any arcing while in the dark shop and even moved a few wires that were touching and no arcing was seen from the cap, wires or coil.

FYI I also changed out all those parts 6 months ago when I did a major tune up, but it ran fine untill about two months ago.

When this started two months ago is was just a rare occurance and my mechanic thought that I had gotten some gas with water in it. He had me run a few bottles of injector cleaner it the next few fill-ups and I’ve run a few bottles of heet through it also. In the last two weeks it has been doing this every time I start up. When this did start showing up it would show a code of a random misfire and the engine light would come on even though I felt no signs of a misfire myself. The light would stay on for a day or two then go back off. A few days later it was back on.
I thought that I fixed the problem because the light stayed off for a month.
So it has been only the last two weeks that it bucks and kicks so bad at a startup, but you would think that an engine misfire would show up and the engine light come on. By the way the light does work.

Now, I never get a engine light on, and he found no codes in the history. I have my own scanner, but his can do so much more. I never find any codes also.

My mechanic ran some diagnostic’s and found an up-stream 0,2 sensor bad so we replaced that.

Yesterday I dropped the tank, pulled the pump and cleaned the tank real good. The only filter is the sock on the pump and that was clean. I refilled with fresh gas and I still have the same problem.

So I think that we can eliminate water in the fuel, plugs, wires, rotor, and cap.

My next thought is the cam sensor in the distributor.

Any sugestions


#2

@Yosemite

Here’s what I would do

Fuel pressure test
Fuel injector balance test
Compression test
Make sure you don’t have any obvious vacuum leaks and exhaust leaks in front of the O2 sensor
Monitor your fuel trims when it’s running rough . . . should be 0, plus or minus 10
Make sure the engine coolant temperature sensor is accurate


#3

When the engine is started cold, there are only four primary inputs into the computer.

These are the Crankshaft Position Sensor, the Throttle Position Sensor, the Coolant Temp Sensor, and the MAF/MAP Sensor.

I would look into those.

Tester


#4

An Update;

We had already replaced the upstream o2 sensor, on bank one a few weeks back. All sensors showed that they were working properly at that time.
(mechanics Diagnostics tool can show a graph and shows each sensor’s output as it’s working)

We finally decided to change out the o2 sensor on bank two. Even though we had no codes and it showed that it was running properly.

Changing out the one on bank two solved my problem and I have had no problems in the last week.

So much for computers.

Thank for everyones help.

Yosemite.