96 Winstar 3.8V6 misses cylinder 3 only P0303 code

Any suggestions? My 96 Winstar has an intermittent miss only on cylinder 3. The mis will occure anywhere from 1 or 2 times a minute to nothing for 10 - 15 minutes. Misfire occures when cold (in open loop) and when the engine is at operating temp. Zero evidence of coolant into this cylinder. MIL on. My scanner gives P0303 Misfire #3. Vacume guage is steady at 21 inches hg, except for a down flick of less than 1 inch on a misfire. With the vacume guage attached, gooseing the engine up to around 2500RPM showed a quick drop to zero, a recovery to about 26 in hg and settle back to 21 in hg.
Swapped plug wires 2 /3 and 4/5. Swapped spark plugs 2/3 and 4/6, then replaced the year old Bosch w/ a set of Autolite Platinum's.
Checked the coil pack. Resistance was out of spec. Replaced it. No change. The new coil pack was with-in specs listed in the Haynes manual.
EGR ports are clean! I cleaned them last year when I replaced the intake manifold gaskets. (had a AF leek into the #1 intake valve). I checked them again to verify they were all clear.
Disconnected the EGR to see if a possible block in the passage. No difference.
Swapped fuel injectors #3 with #2. problem stays with #3. Checked the wiring to #3 injector. near 0 resistance and no deflections when I wiggle the connections, including the plug that passes from the main harness to the Intake wiring harness.
Compression test was somewhat high on all cyllinders. Minimum is 101 psi. All 6 tested between 200 and 215 on 4 cranks.
None of the changes listed above altered the misfire.

Except for the PCM, I don't know of anything that would affect just 1 cylinder.

I would expect a sticking valve to show a much larger down flick on the vacume gauge.

ruled out about everything but a possibly something mechanical... compression seems awfully high... sure it's not all full of carbon?

[tcvaughn]

Originally Posted by maypo7957

Any suggestions? My 96 Winstar has an intermittent miss only on cylinder 3. The mis will occure anywhere from 1 or 2 times a minute to nothing for 10 - 15 minutes. Misfire occures when cold (in open loop) and when the engine is at operating temp. Zero evidence of coolant into this cylinder. MIL on. My scanner gives P0303 Misfire #3. Vacume guage is steady at 21 inches hg, except for a down flick of less than 1 inch on a misfire. With the vacume guage attached, gooseing the engine up to around 2500RPM showed a quick drop to zero, a recovery to about 26 in hg and settle back to 21 in hg.
Swapped plug wires 2 /3 and 4/5. Swapped spark plugs 2/3 and 4/6, then replaced the year old Bosch w/ a set of Autolite Platinum's.
Checked the coil pack. Resistance was out of spec. Replaced it. No change. The new coil pack was with-in specs listed in the Haynes manual.
EGR ports are clean! I cleaned them last year when I replaced the intake manifold gaskets. (had a AF leek into the #1 intake valve). I checked them again to verify they were all clear.
Disconnected the EGR to see if a possible block in the passage. No difference.
Swapped fuel injectors #3 with #2. problem stays with #3. Checked the wiring to #3 injector. near 0 resistance and no deflections when I wiggle the connections, including the plug that passes from the main harness to the Intake wiring harness.
Compression test was somewhat high on all cyllinders. Minimum is 101 psi. All 6 tested between 200 and 215 on 4 cranks.
None of the changes listed above altered the misfire.

Except for the PCM, I don't know of anything that would affect just 1 cylinder.

I would expect a sticking valve to show a much larger down flick on the vacume gauge.

Did you ever find problem? I am have same problem. Have changed plugs, wires, and fuel
injector. Actually, it appeared to be fixed for a month or so. Maybe my new injector is bad. I have not swapped it yet.

[BryanF]

Originally Posted by tcvaughn

Did you ever find problem? I am have same problem. Have changed plugs, wires, and fuel
injector. Actually, it appeared to be fixed for a month or so. Maybe my new injector is bad. I have not swapped it yet.

try and swap the injector with another cylinder. if that other cylinder misses, you found your problem.

have you checked your ignition coils? i'm pretty sure you can check the resistance with a multimeter to make sure they're within spec.

[teemu]

My windstar catalytic converter was choked and given code P0303.

[eugeneford]

I got 96 windstar 3.8l and did have same problem with 4th cylinder missfire.
After changing all those plugs, wires, injectors between cylinders problem stayed at 4th!!! The problem was with carbon deposites in all 6 small holes in lower intake manifold from EGR. Just in 4th cylinder those deposites didn't block the entire hole and others did so all the return gasses were going to 4th cylinder and caused the missfire! 4th and 3rd cylinders are further from EGR and deposites there a lil less than in others so it could cause missfire in 3rd too for same reason. After cleaning all other holes exept 4th (deposites were very small there so I didn't even clean it first!) made problem dissappear right away till next cleaning in 30k mills.

[JohnWindstar]

How do you check coil pack for resistance? What should resisitance be?