Misfire help

Looking for a little diagnostic help for a 99 3.8L.

I have a misfire that occurs when the vehicle is trying to maintain a speed (eg: 65 on a highway, or 45 on a city road). The van will run rough for a couple seconds, then the CEL will flash for about 10-15 seconds and go steady and then repeat the cycle between flash and steady. I also had a busted spring in cylinder 1. That was repaired and new head gaskets were installed and the heads were resurfaced. The van still had the above misfire that is showing as P0302 cylinder 2 misfire. The spark plugs were replaced and it still had the above misfire. It was recomended to me to take it in and have the fuel system cleaned. Upon getting it back the mechanics note was "engine idles at 1100 rpm and still misfires, but misfire goes away while driving".

Any advice in what is causing this would be greatly appreciated.

There are a number of things that can cause a misfire including:
Fuel injector
Spark plug
Spark plug cable
coil pack
clogged egr ports

DRW1000, thank you for the reply. Would having the fuel system cleaned, clear up the ERG valves and the fuel injector? Is a coil pack difficult to change?

DRW1000, thank you for the reply. Would having the fuel system cleaned, clear up the ERG valves and the fuel injector? Is a coil pack difficult to change?

A fuel system cleaning would not clean up the EGR ports. If your injectors are dirty enough to cause a misfire then I doubt a fuel system cleaning would help. Keep in mind the injector could also be defective and not just dirty or the signal to the injector could be intermiitant. A coil pack is not difficult to change but I have to admit I haver not replaced mine so I don't know what is in the way.

I replaced the coil pack on my '96.
It is not a difficult repair...but is between the Upper intake manifold and the firewall. So it is not easy to see what you are doing. Main thing is to get the plug wires back into the correct place.
The coil pack can fail.....a hairline crack in the epoxy body (underside) through which the High Voltage arcs. If I was going to remove it....I would put a new one in.....but you might try plug wires / spark plugs first, as they are cheaper.

One would hope that the EGR ports were cleaned during the head gasket job....but that might be assuming too much. Removing each injector and spraying cleaner up into the cap over the spray end may clear gunk of the spray end.....I ended up having that problem...and it did not come clean with fuel system cleanings. I had to remove the upper intake manifold on my '96 to get at the fuel injectors. So I would do both...clean EGR ports and clean spray end of fuel injectors....in the same job. It does sound like EGR ports....but they usually do not cause the misfire on Cylinder 2....usually it will be cylinders 1 and /or 4....as the ports normally clog starting with the cylinders closest to the EGR valve.....leaving 1 and 4 open...getting all the EGR flow....causing the misfire.

The other thing.....is your antifreeze level in the overflow bottle dropping slightly?

The antifreeze level is staying the same.

Could it be a computer problem? The guy who did the repairs said his reader has having a hard time communicating with the vehicle.

My overflow bottle is dropping slowly.What does that mean?
My misfire seems to be a cracked tube which connect to the EGR valve.replaced, seems to work to date.

Just posted in another thread.....

I would get some Bar's Stop Leak......in the amount to treat the total capacity of your cooling system.

I found that the "original" pelleted product was hard to add.....as the transmission cooler that is inside the radiator seems to be right under the cap..... I have used the "Liquid Alluminum" and another Bar's product that was very similar (I drain and re-fill each year).

The 2 places that are common leaks.....lower intake manifold gasket.....and timing chain cover.
Timing chain cover is a MAJOR labor repair job.
I had seapage at both locations....and the Bar's product has been working great for several years.

For misfire help....I do not think that the computer is causing it. There are so many things that can cause a misfire. The GOOD thing is... that you have it narrowed down to a cylinder.
You can try the EGR port cleaning.....and the fuel injector spray end cleaning that I mentioned.....
I am mentioning it again....because I should have suggested.....that if you do clean the injectors.....move the injector from the cylinder that is giving you the misfire indication to another cylinder. If the problem moves....then the injector is bad. If you still have the misfire on the same cylinder....then at least you know that the injector is good....so you don't have to tear into there again.

One thing I remember reading was of someone having a electrical connection issue with an injector. Computer was good, injector was good....but there was a bad connection in between.

There is voltage to the injectors whenever the engine is ON. The PCM (computer) creates a path to ground to energize the injector.

Moving the spark plug from the cylinder that is giving a misfire to another cylinder is another suggestion.

If you are getting a misfire at idle.....in the dark.....lift the hood...and carefully look around under the hood......looking for ANY sparking. Look carefully along the spark plug wires (yes....even new wires can be bad...I've been there ).

DRW1000, thank you for the reply. Would having the fuel system cleaned, clear up the ERG valves and the fuel injector? Is a coil pack difficult to change?

remove passenger side wiper blade,the remove the plastic cover from the passenger side and up and out then unbolt the metal piece with the wiper motors and remove it then at the back of the motor it is easy to change the coil pack from the top.

Another thing(s) to add to the list of culprits of misfiring-causes: Camshaft position sensor, and the "synchronizer" that drives it.