Hi,
I'm new to the forum and thought some of you real mechanics can help me figure out what is causing power issues with my wife's 2005 Lincoln Navigator. It has the 5.4 motor with 118,000 miles.

About a year ago, it was running a little sluggish so I checked one of the spark plugs and saw they were the original plugs and in dire need of a change. I replaced the plugs with Motorcraft plugs from Autozone for $12 a piece and it ran better for quite a while. Then about 3 months ago, it began to run really sluggish again especially in 2nd gear. If I floor it, the RPM's seem to struggle, the A/C continues to blow but not cold anymore, and it threw misfire codes. Initially, it was a misfire for cylinder 5 so I changed the coil pack for cylinder 5 and it ran fine for about 5 minutes and then the same problem returned with a misfire in cylinder 4. I changed out that coil pack and again it ran fine for a couple minutes and then threw a random misfire code. I decided to slowly change out all the coil packs one by one because my wife works 2 miles away from home and drives 30 miles a week so the power problem wasn't unbearable. Every time I changed a coil pack, I checked each spark plug to ensure it was tight because I've heard of spark plugs coming loose in the 5.4. So now I've changed all the plugs and coil packs and still have the power problem. It seemed to run fine for the first couple minutes and then the power problem returned and sometimes I would have to wait a few days for a code to show up.

It does sound like it has an exhaust leak or it could be a lifter (I doubt it's a lifter by the sound) but that sound has been there since we bought it 4 years ago when it had 95,000 miles. I would think the exhaust leak would be constant no matter whether plugs or coil packs have been changed and I would have the problem all the time.

So does anyone have any ideas? I figure it is either Air, Fuel, or Spark so I've changed out the fuel pump, ran injector cleaner, changed the plugs, and the coil packs. My logic tells me something is affecting a sensor that is changing the fuel ratio after a couple minutes and that's what is causing the power problems. Could an exhaust leak change the Oxygen sensor readings enough to do this? Not sure where to go next.

I apologize if this isn't well written, it's late and I'm zapped.

Any help is greatly appreciated,

Thanks,
Steve

 

Hi Steve, thanks for the detailed explanation of what has been happening and what you've done so far to try to remedy it. I'm no mechanic, but I do all of my own work, and first thing that comes to mind is after changing the plugs and now most recently the coil packs, after clearing the codes, what are you now seeing for codes? Can you provide the specific DTC's you see?

Another thing worth checking is the spark plugs. Try to remove a few of the easier ones to get to, being sure to remove them while the engine is still nice and warm. Even with the revised plugs, the heat of the cylinder head will help them turn loose. Looking at the plugs will tell you if the engine is running lean, rich, or just right. However, if you're running rich or lean to an extreme you should be getting O2 sensor DTC's telling you this. But I would still look at the plugs. For instance, if you were getting bad blow-by in the cylinders oil will start to coat the electrode on the spark plug and you will surely lose power. That's likely not your issue, as you'd also be consuming a bit of oil if you've been keeping an eye on the oil level, but that's just an idea of something you may not always see a misfire DTC for but a look at the plugs would tell you.

What are you using for a scan tool? If you can look at the PID's for things such as your O2 sensors TPS voltages, accelerator pedal position sensor, throttle body position, etc., you can confirm that the voltages are within range and the percentages on the TPS, APPS, and throttle body position all seem to jive with how far you are pressing the accelerator pedal with the key on and engine off. You'd typically see DTC's for these too, so that may not be the problem, but it's worth checking out of you have a scan tool capable of viewing these PID's. If you don't have anything capable of viewing PID's, want to try to troubleshoot this issue (and other future issues) yourself, but don't want to spend a lot of money... I recommend a decent Bluetooth OBDII dongle and the paid version of the FORscan smartphone app. You can easily view DTC's on the go; clear them on the go; view PID's in chart, table, and graph for, and much more. Can easily go that route for $100 or less between the dongle and app.

Another few easy things worth checking are the air filter and throttle body (physically). Only 4 bolts on the upper intake manifold need to be removed along with a hose or two and some sensor connectors in order to move the intake manifold out of the way and get to the throttle body. If there's buildup on the throttle body, get some throttle body cleaner (not carb cleaner, nor brake parts cleaner), remove the TB, and clean it up. Go through the TB relearn procedure after re-installing and see how things go. Also wouldn't hurt to buy some MAF cleaner (again, not carb cleaner, nor brake parts cleaner), remove the MAF, and clean it off.

But let's start with the current DTC's. Again, make sure you've cleared the existing ones since the coil pack install, and read us your current and pending DTC's. If we need to go the route of troubleshooting anything difficult I can get you the documents from the Ford PC/ED DVD that I now have and they will give you complete steps on diagnosing whatever you may need to look at.

-Andrew

 

Before you dig too deep into replacing parts first change your fuel filter, then if that doesn't fix the issue take a fuel pressure reading and post it here.

 

The A/C probably is a coincidence and just needs to be topped off.
Is the sound from above the engine or below? Maybe you have a vacuum leak. Check the PCV hose in particular and any other vacuum lines.
Clean the MAF.
Test the TPS - Throttle Position Sensor.
I don't think an exhaust leak would affect power that much. I had a loose pipe to manifold connection which was throwing a P0171 - Bank 1 Lean code, but it still ran fine.

 

For the AC, I think the PCM disengages the AC compressor if it detects severe misfires in an attempt to remedy the situation. Check fuel pressure after replacing fuel filter as Alloro said, if you have a scan tool it would also be nice if you posted what your long term fuel trims are. Since it runs fine initially, in order to diagnose either MAF or O2 sensors, disconnecting them will make the PCM use an approximation for the missing sensors (and throw a check engine light), but the engine should run fine.
If you disconnect either the MAF or the O2 sensors, disconnect one, test, then reconnect and disconnect next, test, and so on, and it suddenly clears up, chances are that you have a bad sensor with a bias.

 

Thanks for the replies, I didn't realize I could disconnect those sensors and check them that way.

I am using a basic scan tool that just gives me the trouble code which I then look up online or in the manual. One code was left bank running lean, the rest were misfire codes. All have since been cleared after I changed the coil packs and no codes have reappeared in about a month and a half but the power issue remains.

It definitely sounds like an exhaust leak on the left side of the engine but I have had an exhaust leak before and noticed some power loss but that was constant no matter the rpm or gear, this problem seems to come under heavy load.

I will double check all the vacuum lines and test the sensors later. Thanks again for the help.