Hey...just got my 2002 F150 4x4 4.6L. 68,000 miles. I love the truck, but it seems to just sit down by 4,000 rpm...it even feels like it misses slightly right at that point. If I stay in the floor it might get to 4,200 tops! Whats the deal? I am thinking maybe I need to put plugs it her? I just got it, but I wouldnt be suprised if the last person never changed the plugs. Any other ideas for me? I dont expect 6 or 7 grand but, this thing must have some more revs in it?... Thanks for all the help.... John

 

First step is to pull the codes.

 

what codes? I dont have any lights on right now...will it store any dtc's without the light coming on? Am I right in saying that I should rev past 4 easily?

 

Are there any other items I should look at replacing or cleaning when I go to do the plugs? Any special maintenance advice?

 

The 4.6L engine is know to have problems with the upper intake EGR ports clogging. That is one of the first things I would check since your truck has 68,000 miles on it.

 

When was the last time you replaced the fuel filter?

 

I havent replaced the fuel filter. I just bought the truck a month ago. I put new plugs in lastnight..(They looked due) but it didnt really help above 3,000 rpms. Would this fuel filter or the egr ports cause this problem?
(Here is a thought...I smashed my exhaust on some farm land and ended up cutting it off after the last cat....could such a lack of back-pressure be doing this to it? Just a thought. Also...where are those egr's? under the TB or in the Elbow? Thanks again guys

 

The fuel filters get dirty relatively fast on these trucks. A dirty filter CAN restrict flow which often shows up during high demand. It's just one possible area to examine.

 

Is the fuel filter relatively easy to replace? I know on my 96 F-150 I had a hell of a time with the special little tool. Also... do u think there is anything to the exhaust being a problem or no? This just baffles me because it runs so smooth before 3,500 rpm and then it just doesnt have anymore. It doesnt miss violently or anything...it just feels like the engine meets a soft wall that it cant push through. Thanks again.

 

There's a write-up in "Technical Articles" on replacing the fuel filter. There are dozens of posts you can search with tips, photos, and preferable tool selection. It's a simple procedure. Yes, having no exhaust can cause similar problems. I ran my 2000 5.4 with nothing after the cats when I modified the exhaust and it was gutless. Stock vehicles generally run like crap without the exhaust.

 

This is how my truck first began to act when the fuel pump started to go south. It kept losing power like that, eventually started to ping (lean condition) unless I used 92 octane fuel and then the check engine light came on eventually. Then it got really excited when the truck would lose all power at about 1500 to 2000 rpm.

 

Hey, today it all of a sudden started to get better..now it revs to a solid 4,500 or so strong on full accel. Could it be that the comp needed some time to re-calibrate itself after the exhaust got cut off? I still wonder about a fuel filter or pump....someone also said there is a valve on the underside of our intakes that open around 3 or 3.5rpms?? Anyone know more?...

 

Glad it got better, but it's a little early to celebrate. The learning process is almost all about idle and stopping gracefully in gear. I wouldn't think this would be related. max and nabbit are on the most likely track. Fuel demand is highest under high load and high RPM, trying to accelerate from 4000 RPM certainly qualifies. If you have a questionable pump or a filter starting to plug, you'll see it here first. Lean symptoms like pinging or surging often but not always accompany this. If you have a scan tool watch the pre cat O2 sensors when wide open. If they don't go rich (high mv or over 600mv) but instead go low (under 300mv), the pump or filter is indicated.

The MAF could also be related. The engine calculates fuel based solely on the O2 sensors after warmed up except when wide open throttle. Then it used the MAF. If the MAF is off, the fuel commanded will be off. This is far less likely but possible. If so, the fuel trim values will be off everywhere (again, requires a scan tool).

The other suspect under high load is secondary ignition (coil, wire, boot, and plug). Fuel is worse with load (throttle position) and RPM, in fact one times the other. Secondary is worse with load and is unaffected by RPM (dwell limitations are gone with multiple coils). So if the problem is just as bad at wide open throttle at low RPM, suspect the secondary. If you hold wide open throttle from say 1200 RPM up to 4000 and it gets worse with RPM, suspect fuel pump or filter.

EGR is commanded primarily (at least historically) for lowering NOx by keeping the combustion chambers cooler. Now they use it for increased fuel efficiency, to prevent knock, and several other minor uses. If you have EGR at low RPM or idle, it will cause roughness that goes away off idle. If you have individual cylinder ports blocked so all the flow goes to one, you can have a misfire. If all are plugged, you wouldn't have any drivability problems but your NOx emissions would go up and somewhat more likely to ping. Too much EGR can reduce power but the flow would be minor accelerating from 4000 RPM. And blocked ports wouldn't cause too much flow. If it were uneven flow, you would have rough idle also.

My guess from here is 50/50. You have a secondary ignition problem or a pump/filter issue. WOT from 1200 to 4000 and see where the problem starts.