dslwrench

Maybe I'm just expecting too much from the ole girl because I work in a diesel performance shop, but I've been chasing a "problem" with my 05 for a while that I'm beginning to think isn't a problem at all. It's got new motorcraft plugs and boots, a new cat, a new o2 sensor, new phasers and timing set. Even new rollers and tappets on the passenger side at which time I checked the screen on the vvt solenoid with no concerns. All of these repairs were based on actual diag and were truly failed parts, I'm not just throwing stuff at it. The fuel filter has 5k on it. Fuel pressure is good. I run 87 octane. Air filter is clean. I change the oil with motorcraft 5w20 blend and fl820s every 3000 miles. It's never thrown a check engine code, even in the ecm memory. now on to the issue. It's got good bottom end Torque, somewhat impressive actually, but once it gets over about 3700 Rpm it rapidly loses its power. And any Rpm over about 4300 feels like a waste. I understand peak Torque is supposed to be around 3700 in these, but peak hp is supposed to be around 5k. It feels to me like you're out of power at 4000 on this engine. Is this what all you other 5.4 guys experience and I should just settle in and accept the fact that passing someone on a hill is a thing of the past for me? It doesn't sputter, or hesitate, its just gutless. Sorry for the book, trying to answer questions ahead of time with information.

PerryB

You said it has a new cat. It has 4 cats. They are high on my suspect list. I have an '05 - 5.4 and it likes to make power well above 4000, in fact in the upper 4's it really gets with it.

SCORGE

Have you cleaned the throttle body and MAF?
If not, wouldn't hurt to try. I've 200k on my 5.4 and while it's no speed queen, she has a little bit of giddy-up to her. You've gone down the list of everything the rest of us would probably recommend. To truly open this engine up, you need a tuner. I'm no expert so I don't know RPM/Torque numbers and honestly...my motor only ever goes in that higher range if I'm passing or just playing around. Maybe another cat is on its way out?

dslwrench

I've only got two cats, one on each downpipe. The other seemed to flow fine when I had them off for replacement of the failed one. the o2 sensors are indicating its working like it should. I should add that I ran the fuel injector leak down test as well as reaction test and it passed.
I put an edge evolution on it last week, got it used from a customer where I work. I've tinkered with it a bit and to get the best acceleration and passing out of it, I set the wot shift to 4300. It falls on its face from there up. That's on extreme and a full tank of 91 as of 3 days ago.
I will get after the maf and throttle body today. I may also squirt a little ether along the intake Manifold while I'm in there just because.

SCORGE

Supposedly there's a throttle re-learn process that's supposed to help.
Turn key to on position
Slowly depress gas pedal all the way to the floor and let it bounce back up.
Do that three times
Then key to off and start engine.
I've no idea if it works, but hey....worth a shot right.

dslwrench

I did do that as well, and have monitored the app pid to be sure it's showing all the way from 0 to 100%. I'm really hoping I find something with the maf.

PerryB

What about the variable intake manifold runner door? Maybe its not shifting and is stuck in long runner/low RPM mode. I would expect that to throw a code, but who knows? Maybe.........

dslwrench

Now this is something I haven't heard of. I will definitely get into checking that out.

Eric Kleven

Disconnect the muffler and see if you get your top end back? Mine goes like a raped ape (a very heavy raped ape, but a raped ape nonetheless) above 4k, yours should, too.

I'd chase down Perry's suggestion first, though

dslwrench

It's got a mbrp muffler with less than 5k on it right now. I checked the intake runner rods and they seem to be attached. I'm gonna get IDS on it and see what it says about the runner control motor. Surely I can find a duty cycle pid for the motor. On a drive yesterday I passed a motor home on an uphill passing lane and hammer down 73 mph is all she would do. There's no way if it's making 300bhp it should ever stop accelerating on that sort of a climb.