Loss of power

[rescuer3]

I'll try to keep this short. Truck started running and idling rough accompanied by a severe decrease in power and fuel milage. Pulled 3 codes: p0174,p0171 and misfire cylinder 1. Installed new COP and checked for and repaired 2 vacuum leaks. This smoothed out the idle but did nothing for power or milage. After 30 minutes of driving I now have a p0174 code but nothing else. While driving I can only get around 2800 rpm and truck will barely pull up a small hill. I have checked and rechecked for more leaks and cleaned the MAF. I am out of ideas, any help would be greatly appreciated.
Forgot to mention ths is a 2003 Expedition 5.4l 4x4 auto.

 

[JUST4FUN]

Whats the miles on the expy??

 

[rescuer3]

150,000

 

[JUST4FUN]

Have the plugs been changed?are they motocraft? was the truck running bad for a long time? if so i would say the cats are plugged

 

[Captain Morgan]

Spot on.

Be sure to read Rough idle? P0171, P0174? Here's what you need to check first!!!

If this is a 10 y'old vehicle and you haven't changed the plugs and cops it's time, esp at 150k. If the cats are plugged *i think* it should run slightly better when first started and at idle than while increased RPM by pushing the gas peddle, and less so under load while driving at any speed. Seperating the exhaust manifolds from the cats will relieve back pressure if that's the problem. The truck will be loud but not constipated.

FUEL - AIR - SPARK . . . check all the typical stuff related to these and do the maintenance. Replace the fuel filter, check\replace the PCV valve. Clean the throttle body and plate and inspect by hand. New COPS and injectors together run under $200.

Also, take a moment in particular to ensure that the tube between the MAS and the throttle body is on there TIGHT and has not wriggled out slightly letting air in. Is the air intake tube on the support arm, and does the support arm, have the bolt at the bottom holding it in place? SHAKE the air intake tube HARD like you mean it and see if it will move at all. If so use a 10mm socket, remove the three bolts that secure the cover over the throttle-body. Remove the hose clamps etc and disassemble to inspect the gasket material etc and make sure it hasnt warped sufficient to allow air in at that junction. Then reassemble while PUSHING the tube backwards as far as it can go and tightening the hose clamps. This is a 10 minute inspection.



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[rescuer3]

Thanks for the advice, I have picked up plugs and a fuel filter. I will change them out tomorrow and check the othe stuff,too. I will post on here if this fixes the problem or not. If the cats are bad, do I have any options other than installing new ones?

 

[FordandPolaris]

Hollow them out! However if you have emissions testing this is probably not a good idea.

 

[rescuer3]

No testing required here. How would that effect the ECM, wouldn't it throw a code and CEL?

 

[rescuer3]

Just drove it home after plugs and fuel filter change. Also checked and cleaned throttle body. Very little change at this time, a slight increase in power with cold engine on flat ground, back to where it was after engine warms up. Can't get codes at this time due to a blown fuse. Unless anyone has other ideas, I will see what I can do with the cats later this week.

 

[FordandPolaris]

I think you saw one of my earlier posts regarding the cats, but you should be able to hollow out the rear set as long as you leave the fronts in place. This allows the downstream O2's to detect some change in the exhaust from the upstream O2's, and therefore keeps the CEL off. I am only going with what I have read though, I still have all 4 of mine in place, however I will probably try hollowing mine out in the future.

One thing to be aware of is that by removing the cats, you will remove back pressure, and this may cause a slight loss in torque. Basically it will feel slightly slower off the line, but if it makes the truck run better than I would say it is a worthy trade-off. When I removed my muffler in favor of a glasspack, I noticed this symptom, but it since hasn't bothered me, and I do a fair amount of towing with my truck.

 

[rescuer3]

Thanks. I am going to try removing the O2 sensors and run it just to see if that helps before I actually cut into the exhaust. If it does, I will replace the front 2 and either hollow out or remove the 2 rear. It will be a while before I get the time to do this, but I will post what I find.

 

[FordandPolaris]

I would not remove the front O2's because the engine uses these to determine the fuel mixture that is injected into the cylinders.

 

[rescuer3]

Thanks, I guess I will get parts ordered then.

 

[rescuer3]

Update; Got the new cats installed today ( front only, deleted the back) and the differnce is amazing. Got the power back and fuel milage is as good or better than before. Thanks for the help.

 

[Captain Morgan]

Please keep us posted if you get more codes etc, and congrats on the fix!


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[gser425]

Hi rescuer did you replace front cats with oem or aftermarket. I am in nc as well and am interested in the rear cat delete. I just don't want to start chasing emission codes to get my 05 inspected. Thanks Stuart

 

[rescuer3]

It has been almost 2 months, no codes or other problems so far. Cats were replaced with high flow from Eastern. I did weld in a bung for the rear o2 sensor so it is still in place.