Losing Power and "missing" at highway speeds

[brunnj]

I've had a problem with my 2002 Taurus with the 3.0L OHV V6 since I purchased it used. At highway speeds it often feels like it's losing power and misses. Here is the long list of components I have replaced. Ignition coil, wires, plugs, pcv valve, both upstream oxygen sensors, egr valve, egr vacuum solenoid and the DPFE sensor. The dealership recently checked it and said they saw nothing wrong with any of the cylinders but said the throttle body and upper intake manifold had alot of carbon buildup and needed cleaning. I pulled these items myself to clean them and this is what I found. The lower intake had blackish buildup in the first 5 ports but the 6th one had brownish, rusty looking buildup. I pulled it and cleaned as best I could, put new gaskets on the lower intake, upper intake and throttle body. The problem is still there. I'm thinking I might have a hairline crack in the lower intake or possibly something with the head gasket or head. Anyone have any ideas? BTW, the check engine light never comes on either. Thanks.

[shorod]

How did the plugs look when you pulled them? Did they all look the same, or was there some color variation between them? Does the PCV happen to vent in to the intake for port 6? Have you checked/replaced the PCV valve? Any chance you have access to a scan tool with the datastream mode so you can monitor the oxygen sensors, cylinder misfire counts, and short term fuel trims while driving on the highway and getting it to act up? When's the last time the fuel filter was changed? How does it act under hard acceleration in town with the engine cold versus hot?

-Rod

[brunnj]

Actually I didn't pull the plugs recently. I was getting a code for a misfire when I purchased the car and I pulled the plugs at that time. I will have a chance to pull them in the morning since I am at work now. I can post a pic of the lower intake if you think that may help.

[brunnj]

I've included links to photos of the lower intake manifold and two of the spark plugs. The port in question on the manifold feeds cylinder 6.

[IMG]<a href="http://s420.photobucket.com/albums/pp290/jabrunn/Taurus%20Photos/?action=view&current=DSCF2195.jpg" target="_blank"><img src="http://i420.photobucket.com/albums/pp290/jabrunn/Taurus%20Photos/DSCF2195.jpg" border="0" alt="Photobucket"></a>[/IMG]


<a href="http://s420.photobucket.com/albums/pp290/jabrunn/Taurus%20Photos/?action=view&current=DSCF2194.jpg" target="_blank"><img src="http://i420.photobucket.com/albums/pp290/jabrunn/Taurus%20Photos/DSCF2194.jpg" border="0" alt="Photobucket"></a>

[brunnj]

Here is a link to the entire album of photos on this topic.

http://s420.photobucket.com/albums/p...urus%20Photos/

Let me know if anyone has any suggestions. Thanks much.

[plymouthsrock]

It's old school, but if you can measure fuel pressure and engine vacuum that might point you in a direction (fuel delivery problem, weak valve springs, etc.).

[brunnj]

I've actually checked fuel pressure and it's in spec according to Ford's Emission Control Diagnostic Manual. I've also had the car checked at two dealerships and they have said nothing about the fuel pressure. I currently don't have a way to accurately measure engine vacuum.

[plymouthsrock]

As Rod says, it would be good to monitor the vehicle as it's acting up, or at least at high revs/speeds. Fuel pressure should remain pretty constant throughout, engine vacuum should not fluctuate much or drop more than 2"hg from the idle reading. Why were the egr parts replaced?

[shorod]

I don't really see anything I'd consider abnormal in the photos. I only saw photos of 4 spark plugs and they look pretty new. The right-most port actually seems to be the cleanest of the bunch, but I still wouldn't necessarily flag that. One thing you might consider is cutting back on the amount of anti-seize on the plug threads. The ground for the plugs happens through the threads and the seat and anti-seize will not be as conductive as the general metal-on-metal contact. You don't need anywhere near that much anti-seize to be effective.

-Rod

[brunnj]

I replaced the egr components just for the heck of it I guess lol. I've felt similar symptoms in ford's before with a bad dpfe sensor. When I went to remove the exhaust hoses from the old dpfe sensor the plastic ports on the sensor broke. Think the plastic was hard and brittle and possibly already fractured. Anyway, the problem is still there and I'm beginning to lose hope of fixing it, short of replacing the entire engine. I may go to a local self service yard this thursday and pull a lower intake manifold and head and replace those just for the heck of it. Thanks for your help guys. It is much appreciated.

[shorod]

For possibly less than the cost of the shotgunned parts you could pick up a decent scan tool with datastream capabilities and probably narrow down the issue as well as have another tool that you can use in the future.

-Rod

[brunnj]

I use the Actron cp9180 scan tool. I've actually driven the car with it connected and monitoring the pid's and never really saw anything out of the ordinary. The only thing I noticed was engine load was high at idle and my fuel pressure is actually low according to the Ford shop manual and in spec according to Ford's emissions diagnostic manual. I've had the vehicle checked by two dealerships and they never said anything about the fuel pressure.

[shorod]

It's pretty typical to see around 30% engine load even at idle. What fuel pressure is the scan tool reporting? Did you monitor the fuel trims while and immediately after experiencing a miss feeling? What did they show?

-Rod

[brunnj]

I think I found the problem. I decided to change my spark plugs yesterday and when I pulled them, one of the plugs on the back side of the engine had a split insulator. The car drove great to work this morning even though it was foggy and had lots of moisture in the air. It would always be most noticeable on wet days.

[shorod]

Yep, unless the insulator cracked as you were removing the spark plug, I'd say chances are very good you found the culprit! Congratulations.

-Rod