Rosin
Member
I've had my 99 Expedition for a little over a year now, and for most of that year, I've been trying to figure out why the SEL was on. I just wanted to share what I did in hopes that it might help someone else. Skip to the end if you just want the short version (marked with an *).
My truck has the 4.6L Windsor V8. The main problems I was having with it were rough idle, stalling when stopped, misfiring, and generally just being wimpy. The first thing I did was replace all the plugs and wires. This helped some, but the problems returned quickly. After some research, I found that the problems may have been caused by a vacuum leak. I looked for the leak for quite a while; I could even hear it, but I couldn't see it. Finally, I noticed a black hose way down in the engine compartment on the passenger side. It was the PCV hose. I examined it, and it fell apart in my hand. I then concluded that this was the source of the vacuum leak, and proceeded to cover the end of the hose with duct tape. The rough idling and stalling problems were completely resolved, but the engine still misfired. I replaced the PCV hose and valve properly before moving on to check something else.
Replacing the PCV hose had eliminated the "System Too Lean" trouble code, but the computer was still throwing misfire and EGR codes. I tried putting a couple of cans of Seafoam through it, and that didn't help. I replaced the EGR valve and solenoid, and tested the flow sensor, and that didn't help either. So I took off the throttle body and noticed that the two EGR ports at the back were completely blocked up with black gunk. Cleaning that out solved the EGR problem, but not the misfiring. I also cleaned out the EGR tube while I was in there.
Another thing I tried was replacing the fuel filter. It didn't fix anything, but it probably needed to be done anyway.
One day, while poking around under the hood, I noticed that the boot for the spark plug wire on cylinder 7 had come loose. I pushed it back on, and a few miles later, it had come loose again. What I ended up finding was that when I had replaced the spark plugs way back in the beginning, I had just not tightened them enough. My theory is that because the spark plugs were loose, exhaust gas was escaping through the treads and pushing the boot off of the plugs. To test the theory, I tightened the spark plug in #7, and the boot stayed on there. Next the boot came off #2; I tightened the plug, put the boot back on, and finally the SEL went off and stayed off. Now the truck runs smoothly, cruises at 75 without issue, and is generally fun to drive.
*Short version: if you're having misfires, rough idle, stalling when stopped, or EGR trouble codes, here are some things to check:
1. PCV hose may be disintegrating
2. EGR valve, solenoid, and sensor are prone to failure
3. EGR ports on throttle body tend to get clogged
4. Spark plugs and wires may need to be replaced
5. Spark plugs may be loose (be careful not to over-tighten them either)
6. Vacuum hoses may be disconnected or cracking
7. EGR tube may be clogged
8. Fuel filter may need to be replaced
Fortunately, none of these things are particularly expensive or difficult to repair.
My truck has the 4.6L Windsor V8. The main problems I was having with it were rough idle, stalling when stopped, misfiring, and generally just being wimpy. The first thing I did was replace all the plugs and wires. This helped some, but the problems returned quickly. After some research, I found that the problems may have been caused by a vacuum leak. I looked for the leak for quite a while; I could even hear it, but I couldn't see it. Finally, I noticed a black hose way down in the engine compartment on the passenger side. It was the PCV hose. I examined it, and it fell apart in my hand. I then concluded that this was the source of the vacuum leak, and proceeded to cover the end of the hose with duct tape. The rough idling and stalling problems were completely resolved, but the engine still misfired. I replaced the PCV hose and valve properly before moving on to check something else.
Replacing the PCV hose had eliminated the "System Too Lean" trouble code, but the computer was still throwing misfire and EGR codes. I tried putting a couple of cans of Seafoam through it, and that didn't help. I replaced the EGR valve and solenoid, and tested the flow sensor, and that didn't help either. So I took off the throttle body and noticed that the two EGR ports at the back were completely blocked up with black gunk. Cleaning that out solved the EGR problem, but not the misfiring. I also cleaned out the EGR tube while I was in there.
Another thing I tried was replacing the fuel filter. It didn't fix anything, but it probably needed to be done anyway.
One day, while poking around under the hood, I noticed that the boot for the spark plug wire on cylinder 7 had come loose. I pushed it back on, and a few miles later, it had come loose again. What I ended up finding was that when I had replaced the spark plugs way back in the beginning, I had just not tightened them enough. My theory is that because the spark plugs were loose, exhaust gas was escaping through the treads and pushing the boot off of the plugs. To test the theory, I tightened the spark plug in #7, and the boot stayed on there. Next the boot came off #2; I tightened the plug, put the boot back on, and finally the SEL went off and stayed off. Now the truck runs smoothly, cruises at 75 without issue, and is generally fun to drive.
*Short version: if you're having misfires, rough idle, stalling when stopped, or EGR trouble codes, here are some things to check:
1. PCV hose may be disintegrating
2. EGR valve, solenoid, and sensor are prone to failure
3. EGR ports on throttle body tend to get clogged
4. Spark plugs and wires may need to be replaced
5. Spark plugs may be loose (be careful not to over-tighten them either)
6. Vacuum hoses may be disconnected or cracking
7. EGR tube may be clogged
8. Fuel filter may need to be replaced
Fortunately, none of these things are particularly expensive or difficult to repair.
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