Ok, let me start off by saying I have been PMing back and forth with JBrew in an attempt to resolve this problem, but I'm at a wall now and wanted to post it here before I commit to bringing it to the dealership to let them diagnose the problem and hit me with a massive service charge.

The truck is a 2001 F150 Supercrew 5.4L 4x4 with right at 107k on the odometer. The plugs and coil boots were changed at 83k. I just changed the PCV valve last week. It's got a new fuel pump and fuel filter on it (less than 1000 miles on them). I just cleaned the MAFsensor and reset the PCM about two weeks ago. I also brought the truck to a local exhaust shop to have them check the cats for clogs - they listened, looked, and drove and decided that it wasn't the cats because top end seems totally unaffected.

The problem: the truck has no low end power under 2000rpm. It is extremely noticeable when I'm pulling either of my trailers. The truck isn't my daily driver, and only sees weekend use pulling my trailers. The power loss seems to really rear its head on hills, from dead stops, and when pulling trailers. It's also worse when the A/C is on. A few other things I have noticed since trying to resolve this issue - my fuel mileage has taken a dive. I'm getting around 9 mpg around town which is definitely down from my usual. The other thing that I'm seeing is the truck seems to idle very low. I thought I read on here somewhere that the truck should idle between 700-850? My truck idles in Park at just under 700. If I have the truck in gear, and keep my foot on the brake the truck idles at 600. This is when the truck is warm. I don't notice the idle fluctuating, but I guess it could be doing it slightly and I'm not realizing it.

The truck isn't throwing a CEL, starts fine, and seems to accelerate fine without a trailer behind me as long as I keep my foot in the pedal. I have noticed a slight exhaust leak that I'm pretty sure is a broken stud on the driver side manifold - I had my passenger manifold break a couple of studs a couple of years ago and it sounds about the same only on the driver's side this time.

This is a recent issue within the last couple of months - the truck just feels like a dog. It honestly feels like a 4 cylinder engine is under the hood when there is a trailer behind me.

Anyone out there have any suggestions? I've searched and searched for answers, but everything I have found always pointed to a dirty MAF or bad PCV and I've handled both of those possibilities with no change whatsoever. I didn't reset my PCM after changing the PCV valve - any chance that would affect anything?

 

Have you cleaned the IAC and throttle body?

This is a real stretch here - but it almost sounds like the timing is grossly retarding itself. MAYBE the knock sensor is sending bad info to the PCM......just a thought.

 

Transmission? Make sure the noise you are hearing is actually an exhaust leak. A bad lash adjuster can make the same noise and create a dead cyl. My truck idles at the same RPM's you discribe with no power problems. Also just because the MAF was cleaned doesn't mean it it is not the problem they go bad as well. Have you considered HEGO'S especially the two front ones? No codes tends to make me think it may not be engine related thats why I mention transmission as it appears to be a load/pulling problem but your fuel consumption has worsened as well. If you are towing a lot then its hard to tell if the consumption is worse overall or even lower 5-6 MPG while towing so it averages out to 9 mpg for all driving. No sticking brakes? I'm sure you have checked most of these but just kind of brainstorming here. I would suggest the trailer brakes but you are towing two different trailers unless your (if you have one) electric brake control unit went bad. Plus it sounds like you have the problem to a lesser degree even when not towing?

 

I don't suppose you noticed this right after you put the duals on it? Duals hammers low end torque.

 

It really doesn't. Maybe if you through on a 3" true dual with no cross over.

 

Idle's OK, should be 650 in N,P and 600 in D.

The exhaust effect is debatable... particularly if the low end loss came along right after the duals were added.... cause and effect.

 

I've got a '97 with a 5.4 and 3.55 gears and LT265/75/16 tires and been towing the same #5000 TT for 8 years and it performs the same today as it did way back then, (actually, it seems to tow better now) and I've got over 212,000 miles on the rig now...

What are you trying to do at 2000 rpms while towing?? I tow in third and cruise the hwy running about 2300 rpms going 60 mph.. Going up the grades, I'm in second and pulling around 3500 going 55 mph.. That's normal to me..

Are you saying that you can't get moving from a stop until you get over 2000 rpms? You do gotta put some pedal in it to get moving from a stop and 3.55 gears with 33" tires aren't helping... My tires are smaller then that, so that might be the difference? And, what kind of 'duals' do you have? That can reduce your low end, especially with your tire/gear combo..

I've got a 3" cat back single exhaust exiting behind the tire and it's helped my low in in my opinion...

I've had broken exhaust manifold studs on both sides for years and the only thing it's caused is the annoying 'tick' noise.... I do want to get them fixed, but only because of the noise they make...

What are you comparing your towing performance to? Were you able to do all that you want in the past with the same truck and the same trailers with the same mods on your truck?

Mitch

 

Ok let me try and answer some of these questions:

The duals have been on the truck for several years now with no noticeable loss in power - its a SIDO Flowmaster 40 series with stock cats all in place.

The noise I'm hearing is the ticking that I grew so familiar with when my passenger manifold studs broke so I'm 99% sure that's what it is - the exhaust shop owner (a wise old man) noticed the exact same thing without me mentioning it.

I haven't ruled out the MAF as a problem, but I didn't want to start throwing parts at the problem without narrowing it down a little more.

I haven't cleaned the IAC/Throttle body myself, but it was cleaned by the dealership about 23k miles ago - I realize they just run a special cleaner thru it or so I've read on here.

My tech mentioned the Knock sensor retarding the timing as well - so maybe it's a serious possibility.

The engine seems to be running smoothly, but the truck just takes a lot more pedal to move the same trailers I've been pulling for several years. Up a steep grade I can barely muster 55-60 mph with the trailer behind me when before I could cruise at 65-70 mph no problems. The brakes on the truck were just replaced about 1500 miles ago,both fronts and rears. The tires are the same size I have run on this truck for the last three years or so with no real problems. I keep 35-40 psi in them (currently 40).

I would think if it was missing I would hear it, or my Ford tech would hear it. He tried holding the brake and giving it gas in the shop to see what RPM it would start to break loose or try too and said the truck should have gone a couple hundred RPM higher than what it did. The truck doesn't seem/feel/sound like it's running bad - it's just running weak.

What's a HEGO?

I've avoiding cleaning the IAC because I don't feel confident enough in myself to pull the throttle body to get to it, plus everything I have found about the IAC says the idle would fluctuating or stalling out if it was clogged/bad.

Would the EGR have anything to do with this issue?

What could cause this and NOT throw a code/CEL? I've been trying to force it to throw a code by taking as long as possible to get up to speed so the truck has to work in the under 2k rpm zone, but no matter how many hills or dead stops I try it never throws a CEL.

And the problem is still noticeable when I am not towing - the 9 mpg figure came when I didn't pull any trailers a couple of weeks ago. I've been pulling my trailer this week so we will see how much worse it is.

 

Humm... Well, since you're experiencing this recently and AFTER your mods, then it's definitely something new!

If your EGR or IAC were 'really' acting up, then it would normally throw a code...

The theory about your knock sensor retarding your timing because it's sensing your exhaust leak might be something to look into... but, it would have to be a pretty loud 'tick' I would think? My 'tick' is pretty loud to me when I have the windows down, but I don't have any of the symptoms you are experiencing towing or not...

Or, maybe the sensor itself is faulty? It should throw a code if that was the case, but then, you have no codes!

Man, I wish I could be more help, but not having experienced it before, I'm not going to be much help....

Good luck with it and I hope you can resolve it!

Mitch

 

Did this start right after the brakes were changed?

 

I don't think so, but it's really hard to say for sure. I had some major fuel pump problems over the last six months so it's really hard to say when it started for sure.

What is your thinking in regards to the brake change?

 

HEGO = O2 sensor.

 

I would assume he is thinking maybe the brakes are dragging

 

O2 sensors can be fouled and not throw a code.

1. check brakes - adjust if needed
2. air filter? replace if needed
3. fuel brand? switch gas brands to chevron, shell or conoco try at least 3 - 5 tanks
4. running E10 or 100% gas?
5. tire pressure? truck and trailer
6. trailer brake?
7. trailer wheel bearings?

 

maybe a long shot...but are the pulleys turning freely? ive heard of issues with the bearings in the alternator, ac compressor, etc pulleys fouling up and causing the belt to drag. maybe pull the belt and turn them to see if theyre turning without any huge resistance.