96 Windstar Misfire

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 replaecd the year old Bosch w/ a set of Autolite Platinum's.
Checked the coil pack. Resistance was out of spec. The primary coil for 1/5 was low, .06 ohms and the other coils were high about 2.5 ohms. Replaced it. No change. The new coil pack was with-in specs listed in the Haynes manual for the primary and secondary coils.
EGR ports are clean! I cleaned them last year when I replaced the intake manifold gaskets. (had a AF leak 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. This was checked from the pin at harness pin at the PCM to the injector plug.
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 guage.

Mark
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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 replaecd the year old Bosch w/ a set of Autolite Platinum's.
Checked the coil pack. Resistance was out of spec. The primary coil for 1/5 was low, .06 ohms and the other coils were high about 2.5 ohms. Replaced it. No change. The new coil pack was with-in specs listed in the Haynes manual for the primary and secondary coils.
EGR ports are clean! I cleaned them last year when I replaced the intake manifold gaskets. (had a AF leak 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. This was checked from the pin at harness pin at the PCM to the injector plug.
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 guage.

Mark
http://www.automotiveforums.com/vbulletin/images/smilies/banghead.gif

Mark

Man...it sounds like you're doing everything right......switching injectors, sparkplugs, .....

Is the cylinder not providing power because it didn't get it's share of fuel on that cycle? Or is it getting fuel but not getting spark to ignite it. I don't think that the probem is a sticking valve. There is too much presure on the valve with the spring. Either it seals or it doesn't.

I'll keep thinking about this one for you. I'm sure there will be some good ideas coming.

Regards

Dan

Added 12/1/05

You know.....this sounds like some sort of interference with the PCM. I know manufactures go to great lengths so items don't interfere with each other. Items considered are: where components are placed on the printed circuit board where high voltage wires are ran....

Do you have any extra devices installed? CB? Tape deck? Radar detector?

Dan

That sounds like a tough one.
It may not help but.
You might want to pull valve covers and have a look at the valve springs. Check for a broken or weak spring and make sure a valve is not sticking open a little. Also look at cam lift and bent push rods and rocker arms.
Also make sure fuel prssure is at specs and check vacume hose to fuel pressure reg for gas in it.
Also condition of pcv valve.
Good Luck
MT

Mark

Man...it sounds like you're doing everything right......switching injectors, sparkplugs, .....

Is the cylinder not providing power because it didn't get it's share of fuel on that cycle? Or is it getting fuel but not getting spark to ignite it. I don't think that the probem is a sticking valve. There is too much presure on the valve with the spring. Either it seals or it doesn't.

I'll keep thinking about this one for you. I'm sure there will be some good ideas coming.

Regards

Dan

Added 12/1/05

You know.....this sounds like some sort of interference with the PCM. I know manufactures go to great lengths so items don't interfere with each other. Items considered are: where components are placed on the printed circuit board where high voltage wires are ran....

Do you have any extra devices installed? CB? Tape deck? Radar detector?

Dan

Dan, Thanks for the reply. I'm not sure how to prove the problem is lack of spark of lack of fuel. Since I swapped or changed plugs, wires, etc... and nothing changed....
I did research how OBDII detects a misfire. It looks at the Crancshaft Position Sensor and detects quick drops in speed. It can be falsely set in vehicles with lockup tourque converters and manual transmissions when tires slip.
Ford has a TSB on this issue, but I don't see that it applies to this situation.
I can feel and hear a miss when it is driven and that situation will appear on multiple cylinders.

There are no after market devices added to the vehicle of any kind.

PCM is about the only item remaining that can affect only 1 cyinder.

Dan, Thanks for the reply. I'm not sure how to prove the problem is lack of spark of lack of fuel. Since I swapped or changed plugs, wires, etc... and nothing changed....
I did research how OBDII detects a misfire. It looks at the Crancshaft Position Sensor and detects quick drops in speed. It can be falsely set in vehicles with lockup tourque converters and manual transmissions when tires slip.
Ford has a TSB on this issue, but I don't see that it applies to this situation.
I can feel and hear a miss when it is driven and that situation will appear on multiple cylinders.

There are no after market devices added to the vehicle of any kind.

PCM is about the only item remaining that can affect only 1 cyinder.

I would head to the local bone yard and pick up a used PCM. Put it in and give it a try.

Where did you find the info on the OBDII?

Regards

Dan

You can also look on ebay....if you cannot find one locally.
I have seen several parts online by salvage operations.....and sometimes they are pretty cheap.

Hang onto your original PCM in case a problem develops with your "new to you" PCM.

I would head to the local bone yard and pick up a used PCM. Put it in and give it a try.

Where did you find the info on the OBDII?

Regards

Dan
Dan, I found the information in 2 locations. 1 was a case study by Colorado State University. site is www.obdiicsu.com/Studies/2002CaseStudies/Misfire.Misfire.html (http://www.obdiicsu.com/Studies/2002CaseStudies/Misfire.Misfire.html)
The second location is an online document from Toyota Motor Sales that gives a good explanation of all of the OBD II major features. Unfortunately the web site did not print on the document.

Mark

maybe you can put a light or volt meter to monitor the pulse to injector to determine if the mis is due to injector not being energized.

And you can put a timing light on the wire to see if it skips a flash when the mis occures, this is how i found a bad coil on another car.

Dan, I found the information in 2 locations. 1 was a case study by Colorado State University. site is www.obdiicsu.com/Studies/2002CaseStudies/Misfire.Misfire.html (http://www.obdiicsu.com/Studies/2002CaseStudies/Misfire.Misfire.html)
The second location is an online document from Toyota Motor Sales that gives a good explanation of all of the OBD II major features. Unfortunately the web site did not print on the document.

Mark

Mark

Thanks for the reply! I'll check out the sites.

Regards

Dan

Where did you find the info on the OBDII?


Here's a site I recently found when doing a search on OBDII...

http://www.obdii.com

... I haven't explored the whole site yet but thought I'd mention it.

Dan, I found the information in 2 locations. 1 was a case study by Colorado State University. site is www.obdiicsu.com/Studies/2002CaseStudies/Misfire.Misfire.html (http://www.obdiicsu.com/Studies/2002CaseStudies/Misfire.Misfire.html)
The second location is an online document from Toyota Motor Sales that gives a good explanation of all of the OBD II major features. Unfortunately the web site did not print on the document.

Mark

Mark

Thanks for the reply! I'll check out the sites.

Regards

Dan