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post #1 of 5 (permalink) Old 01-29-09, 01:12 PM Thread Starter
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2001 5.4 Expedition Engine running rough, Help!!

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I have a 2001 Expedition with a 5.4 that runs rough intermittantly. It almost seems like it's missing on a cylinder. This mostly occurs under load and in certain throttle positions. I'm not sure if I should be chasing a TPS or O2 sensor issue.

I went to Autozone today. The "service Engine Soon light is on. The codes they pulled are; PO303 and PO171. The "tech" said it needs a tune-up and it's misfiring on #3 cylinder. I realize codes just tell you what's wrong, not what is causing the problem in the first place. Also, the exhaust has a strong sulfer (egg) smell to it.

Any ideas?

Thanks, Steve.



Any ideas? Thanks guys.
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post #2 of 5 (permalink) Old 01-29-09, 02:30 PM
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Re: 2001 5.4 Expedition Engine running rough, Help!!

Steve, scanning for codes is the correct place to start troubleshooting. The codes you posted suggest faults detected by the system:
P0303 = cylinder #3 misfire
P0171 = fuel trim malfunction bank 2

Although the codes may not pin point the exact problem or component, they provide the tech with a starting point from which to diagnostically troubleshoot the problem. In some cases, a faulty component/sensor will be identified, and the solution is to simply replace that component. If you have access to a Ford factory service manual, you will appreciate what steps are required in diagnostically determining the source of fault codes. What may take us a weekend to solve, is solved by the tech in a few hours, but at $100/hour, the shop is the last place we want to be.

The service history (tunes, etc.) or mileage of the vehicle was not provided, so determining the need of tune-up can't be confirmed, although I am assuming the tech was aware of the mileage and maintenance history. To solve the first set of problems is to correct the conditions causing the LIGHT to appear. If you aren't mechanically inclined, then speak politely with the tech.

"Sulfur smell is usually generated by high temperatures in the catalytic converter caused by excess unburned fuel going through the exhaust. The converter oxidizes this fuel, which generates the heat, and the high heat generates the smell. An occasional whiff of this smell upon start-up or momentarily at idle isn't necessarily a problem. In fact, it indicates the catalytic converter is doing its job in preventing unburned fuel vapors from reaching the atmosphere. But of course, the concern is what's causing the higher percentage of unburned fuel from the engine." From article by Paul Brand.
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post #3 of 5 (permalink) Old 01-29-09, 02:55 PM Thread Starter
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Re: 2001 5.4 Expedition Engine running rough, Help!!

I am very mechanically inclined, but I do know my limitations. The trucks previous owner was a Retired Air Force Colonel. All his maintenence was done under warrenty at the dealer. They forgot to install the drain plug after an oil change, so..... the truck received a new short block at 90,000. Of course nothing started to go wrong untill the warrenty ran out at 100K.

I currently have 130,000. I changed the plugs at 115,000 and installed a coil and plug in the #4 cylinder at 121,000. I have less than 1000 miles on a new air filter and oil/filter change.

I will change the #3 coil and plug, if it's misfiring I assume that would cause the rich condition.

Thanks, Steve.
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post #4 of 5 (permalink) Old 01-30-09, 08:41 AM
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Re: 2001 5.4 Expedition Engine running rough, Help!!

Let's hope changing plug and coil solves the 'miss' problem, but you should also address code P0171 - fuel trim malfunction. That code could indicate a problem with the mass air flow sensor, which may require nothing more than cleaning. The MAF sensor is located in the air intake assembly.
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post #5 of 5 (permalink) Old 01-31-09, 12:23 PM Thread Starter
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Re: 2001 5.4 Expedition Engine running rough, Help!!

Guys, thanks for responding. I cleaned the MAF sensor then replaced the plug and COP on cylinder #3, $47 at Autozone. No more light and the engine runs smoother.

Thanks, Steve
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