Hello everyone,

I have a 2004 F150 FX4 4WD 5.4L extended cab truck with 4 spd transmission 4R75W. It's got about 95k miles, bought used. I've been driving it with this problem since 77k miles, and cannot figure it out.

The truck drives fine through the gears, enters O/D, and locks out without issues. However, I've noticed that as I coast down in speed, say from 55MPH to 40 - 45 MPH, and start to moderately accelerate back up to 55 - 60MPH without changing gears, the truck will hesitate for about 1 - 2 seconds at around 2500 RPM. I don't see a drop in the tack, just a lag where the needle should be rising, then suddenly the needle will rise again. It's like I stopped accelerating, then immediately pressed the accelerator again. This has been driving me nuts for the last 1.5 years and I cannot find the problem. It is mostly apparent on highway exit ramps where there is a slight elevation at the end of the ramp to merge back into traffic, it does not tend to happen on a downhill slope. In fact, the problem seems to only happen when the truck is under slight load. Sometimes, it's worse in frequency than others, although it's been getting more frequent lately.

Here's what I've tried so far without success:
-Changed the plugs (the boots look fine, but I plan on changing them very soon anyway),
-Changed one coil-on-plug pack that I "thought" was giving me a bad reading when I tested it with a multimeter,
-Replaced the TPS
-Cleaned the MAF
-Cleaned the throttle body (although Ford recommends against it - I'm desperate),
-Reprogrammed the PCM with a SuperChips tune compatible with the K&N FIPK intake (I thought the intake might be making the truck run lean causing this problem),
-Made sure all the vacuum lines from the intake to the intake manifold were properly attached/sealed/clamped,
-Replaced the vacuum line from the purge valve on the driver's side firewall to the intake manifold (I thought the issue might be due to a vacuum problem).
Once it gets warmer out, I plan on checking the vacuum lines from the purge valve to the EVAP canister near the spare tire, but I'm not convinced that a leak there would be causing this problem (I do not have a lit service engine light, nor have I had any trouble codes - I wish I did!).

Has anyone had this problem and been able to fix it? Do you think it might be the transmission? Perhaps something to do with the tcc lockout or a solenoid? Any help would be very much appreciated.

Thanks all for your time!

 

is it like this?

https://www.ford-trucks.com/forums/1...-shudders.html

 

Blk150 - thanks for your reply! I'm not sure I have the same problem described by the shudder. I noticed this post before, but figured that I did not have a thud associated to the hesitation. Also, when it's happening, the tack doesn't bounce up and down. If anything, it drops just slightly, say from 2300 to 2100. It feels mostly like the truck is getting chocked for a second. Just to make sure, I will try driving around tomorrow in 3rd gear (O/D off), and see if it continues.

Thanks again!

 

I dont feel it when the O/D is off. Mine is getting worse, now it feels like the clutch is slipping. Ford already replaced the trans the last time they "fixed" it so we'll see what the future holds.

 

I feel the problem is getting worse. Just tonight I got a fluctuating idle. I took video of my tach, wish I could post it. It goes from a little above 500 down to around 300 intermittently. At one point, it stalled out while I was in park. Not sure if this problem is related with my description above. Does anyone have any other advise?

Thanks!