I have a '06 expedition , runs great at normal driving speeds but if you get on the accelerator to pass another car it seems like it has no power. rpms will go up but no power increase. Plus I can hear what sounds like a spark knock. Just put new plugs, replaced 2 bad cops new air intake and breather box. Local mechanic can't find anything wrong with the motor. No codes. He thinks I might need my brain flashed at dealer. Any ideas? Thanks!

 

how are the codes being checked parts store or scanner was the truck running bad before tune up

 

Checked with scanner. Yes truck was running horrible before tune up. Runs better now but still not good. Check engine light came on last night on the way home from work. I didn't notice a change in the engine but light was flashing continuously for about a minute then stopped and went out. I'm going to have it scanned again tomorrow. I'm hoping it's just a bad coil. If not I'm thinking it may be a plugged cat?truck idols great and runs fine under normal conditions. It's just when you accelerate quickly or when it downshifts when I pass a car.

 

make sure you find out what the issue is dont through parts at it and find out what codes are like you said if any. a plugged converter will cause lack in power it sounds like something is still not right with the engine

 

I was also wondering if the intake was not properly installed would it make the engine do this. Intake was changed because of a small engine fire between the intake and air box. Melted a hole in top of intake so I had to put a new intake and air box on.

 

any leaks around the intake or mis assembly could give you lots of issues get the codes pulled and to get an idea at least as to weather or not the intake could be leaking or if someone caused a vacuum leak of some sort you could take carburetor cleaner and spray lightly around the intake not in but around it did you replace the intake

 

I didn't replace it mechanic did. They did the plugs and coil pack too. I usually do my own work put I figured since they where doing the work on intake through my insurance, I would have the do the plugs too. Glad I did as 7 of 8 plugs snapped off. Truck had 2 bad coil packs so it ran terrible before. Runs better now accept for the symptoms I posted. It does seem like it my be sucking to much air at high rpms. Hopefully scanner will tell me something today.

 

Well just had the shop scan my expedition. #5 cop is bad. Was missing under load. Picked up a new one and will put that on when I get out of work. I guess when they changed the 2 during tune up he changed out the wrong one. #5 was missing before so he changed it he thought. But turns out he had the cylinders backwards and replaced the wrong one.

 

good to hear hope the coil will fix your problems sorry that i could not come out right away with a answer but i i will never guess but if you still have issues and any more information let me know

 

Sorry it took so long to post back, I've been really busy with work. We'll after changing everything I stated in above posts the truck still had a miss and wasn't running right. After a few days the engine light came on. Catalytic converter bank 2. Changed it out with a new high flow cat and she runs like new. My guess is I ran it on bad plugs to long and the unburnt fuel dumping into cat ruined it. Just that I would let u know in case anyone else ever has this problem. The cat code never showed up until I had the plugs and coils changed. Thanks for the help !