I have a '99 E-150 with a 5.4L. It has 127,000 miles and in the last 2 months I've noticed a drastic reduction in power. You can feel it at all speeds, but it's much worse trying to accelerate from about 30 mph. If you just give it a little throttle it seems to bog, almost like the more throttle you give it the slower it goes. Once it downshifts, it accelerates ok but not great. Brought it to the mechanic and after 2 weeks of checking they decided that the knock sensor is picking up some noise in the bottom end that it's mistaking for a knock and retarding the timing in an attempt stop the knock. It's not the cat, they changed it and it didn't help. It's not the fuel filter or the air filter, both new. The answer seems to be an engine swap. I'm having a little trouble believing that, although I do trust this particular mechanic. I'm looking for alternatives before forking over the $$$. Anybody have any other ideas of other possible causes of the power loss?

 

Unplug the knock sensor,and see if it gets any better. IMO-there's no reason that the engine should be worn out already-Modulars are tough little engines. I'd bet it's a bad knock sensor.
JL

 

It does sound a lot liked a restricted exhaust.

Also, did they verify the cam(s) timing was still good?

 

Here's a bit of an update. First, they did change the cat but found that it wasn't clogged and the van didn't run any better so they put the old one back on and didn't charge me anything. Second, I picked the van up on Saturday and it drove just as badly as when I dropped it off. On Monday I decided to try locking out the OverDrive to keep in a lower gear to give me a better pick-up. Ever since I locked out the overdrive on Monday the van drives like normal, no hesitation. Could this be a transmission problem and locking out the overdrive that one time somehow changed something?

 

OD with the torque converter locked will show more defects because the engine has to work harder to accelerate with no converter slippage and the low rpm.

 

Did you ever find a solution? I also have a '99 with the same engine and mine just started acting like yours: no power. However, this happended right after a smog check (I passed). I replaced the fuel filter but it was only 20K miles old and it was not clogged. Air filter is fine. I can't stand it. I have 187K on mine. I thought I got some bad gas 'cause I filled up at a "cheapie" place but I've filled up there before (gas and diesel) and never had a problem. So, did you find a fix?
thanks

 

Yes, I did find the problem. It turned out to be a bad coil. After replacing the bad one and putting new plugs it ran great. I began having the same problem again, ended up changing all the coils and putting a fresh set of plugs. Runs great again. Hopefully I won't have to deal with this again.

 

did you buy aftermarket?

 

Willis65: Thanks for the follow up. How did you determine which COP was bad? I just replaced the plugs about 20K ago, so I'm hoping I wont need to. Also, my #4 plug got spit out and my mechanic repaired it. Again, thanks for the response.

 

I didn't actually determine which one was bad, my mechanic figured it out. They were aftermarket coils from NAPA.

 

Thanks. The funny thing is: My van is acting just like it did before my #4 plug was spit out. Sluggish. My mechanic/friend said that if it was another blown plug, i'd know about it. there would be no mistaking it. Maybe this old girl needs a new set of COP's. I'll update this thread with the solution.

 

Good luck equium. Changing those COP's did the trick for me.

 

I'm having a similar issue all of a sudden on my 02 Expedition. I'm hoping it's just a bad tank of gas. Plugs & COP's all done 12k ago. New PCV valve about 3k ago. New DPFE sensor & hoses 3 weeks ago. Engine runs great, but it just seems to be bogging down since the last fuel tank fill-up. Used a name brand fuel which I don't usually use, but was on the highway and had to stop for gas. This brand was at the exit. Going to go back to Sunoco next time - Expy runs great on it. Co-worker suggested I run a bottle of fuel system & injector cleaner through just prior to filling up the tank next time.

 

UPDATE ON MINE (EQUIUM):
I took it to my friends house. He drilled and tapped the exhaust just before the CAT. It read 6 Lbs of back pressure. He said it should read zero; 1 Lb might be acceptable. He tested the fuel pressure during idle and while driving and the fuel pressure was fine. We took the CAT off and turned it into a resonance chamber (if you know what i mean). Now there was zero back pressure. But, the van still ran like crap. But here's the kicker: Now the trouble is intermittent! It will start a trip running bad, and in the middle of a trip, she's back to (mostly) normal. I don't think it ever reaches 100% like it was, but it's much better than before. And something else that is puzzling us: Since the CAT is now "empty", the Check Engine light should have come on. Nope, not yet. even after a week of driving it this way, no light. I'll mention to my friend about the knock sensor and see if we can unplug it for testing.
In the meantime, since I just passed smog a few weeks ago, I can start to save up for the next two years for the $1900 CAT from my local Calif. dealer. Personally, I don't know if this van will make it; My wife is ready to kick it to the curb if we can't fix it.
Thanks for reading.

 

Update on my situation:

I added a bottle of fuel system & injector cleaner prior to my next fill-up. I went back to Sunoco, which the engine just seems to run 100% better on. About half-way through the tank, it's like the engine just came to life. Since then, gone through 4 more tanks of Sunoco (been away on vacation) and the engine runs like a champ again. Guessing it was just a bad tank of gas from the other brand fuel company.