Hello all I am new to the forum , just found it while doing a search for a little help. I have a 2003 4.6 auto transmission truck and when I get up to 45mph to 55mph the truck starts bucking or chugging . Its hard to describe it other than that. When it does that and I hit the gas hard it quits, or if I take my foot off the gas it quits or is not as bad. It is only when I maintain constant speed. Sorry that the description is not the greatest. I just want to have a idea what it might be before the dealer bleeds my pockets .
Thanks ,
Lou

 

Any check engine light?

 

My girlfriend is having the same problem with her 2001 4x4. when it gets to 55 it starts to feel like it wants to buck you out of it, or atleast mix you like a martini (shaken not stirred). Anyways replaced the coil packs and cleaned the air filter and got rid of two of the three things that her computer flashed when I plugged it in. No when i get back in two weeks I can see if it needs a new mass air flow sensor or if I just need to clean the carbon out. Anyways that seems to be what I have encountered so far. I don't know if after I do this it will stop but it is a start. Im glad to see its not just her truck doing it. but not glad to see someone else having the problem if you know what I mean.

 

No check engine light (ever). But the bucking is like stewballusn explained. It is rough.

 

This peticular condition is usually one or more bad coils with low voltage output causing missfires.
They won't set any codes.
Ask dealer to stress test all the coils and replace only those that fail.

 

Thanks for the replies , It will give me somewhere to start. Is this something I could do on my own? I am pretty handy and got a shop full of tools , I am just not a mechanic type other than oil changes , alternators and that sort of think. About the most complicated thing I have done on this truck was replace the u-joints with a friend. I am just afraid of messing under hood if i don't know exactly what I am doing. What will I need to stress test them ? Or is that better left to the dealer only.
Again Thanks,
Lou

 

Not sure if this helps or not but it seems to get worse in hotter humid weather than in the super cold.

 

Quickest way is to do exactly what Bluegrass suggests. Instruct the dealership to due just that.

You have a typical low grade misfire IMO.

If they replace a couple , plan on having 3 or 4 hundy on hand.

 

OK thanks guys, I will let you know how it turns out.

 

If you have more than 50k on the plugs, I'd replace them with Motorcraft or a quality aftermarket plug (NGK, Denso Iridium) and consider a set of COP's from Global.

 

LOU!!!!!
Stop do 1 thing first...
The only difference between your problem and mine is yours not showing codes, mine did.

I have basically the same problem with a vibration/miss and running rough at around 45 -50 mph. I am under the impression you have the same engine as I do: 4.2 efi? mines a 98 model
Go out and check the 90 degree vacuum hose that links up your ERG vacuum system to the intake plenuum and make shure it has not got any holes and is good shape. looking at the motor from the front of the truck, it is on the left side in the back. It's kinda hard to get to and partially hidden. Just a thought before you invest alot of money. That small hose cost me 500 in parts before I actually found out it was that small hose. I still have a very slight vibration but not as bad and am thinking it is a erg or regulator. Replacing that hose cured 95% of the problem. Also, you mentioned that it runs better in cold weather than hot, same thing here!! that maybe the egr and or regulator. Mine runs smooth in cold weather but when it warms up to operating temp it starts to vibrate when in overdrive just barely appling the throttle around 45-50 mph.
Hope this helps
Good luck,
Charlie

 

seems alot of us have this 45-55 "shudder" feeling.....i believe that some of these responses are correct....possible vaccum leaks , definitly some kinda misfiring going on.....and possible "convertor shudder" from a trans point of view....i have been looking into my own simmular problem with this . am going to start a "deductive reasoning" type of diagnosis as soon as the rain stops here this weekend.....will change the plugs , troubleshoot the coil pac's , do
a complete underhood inspection of relative components then take it to the next level if i dont complete a repair of this situation.

1. it only occurs at these speeds
2. it is the same type of shudder everytime
3. it goes away upon acceleration or de-celeration
4. is a little if not completely less noticable in colder mornings
5. does not happen at all (on mine) when the O.D. is off

it is also possible that each case could be a little different but i think we will soon discover that these trucks (cars) are all doing a shudder based on the design and use of the components they were built with.

good luck.

 

Lou, let us know what coils where bad . You've been instructed correctly BEFORE you last post in this thread - for your specific issue and COP'ed ignition system.

Thanx,

jbrew

 

Hmm, I seem to have the same problem, though it's not constant and not always very noticable. It seems that if the COP's were getting weak than the misfire would be more noticable either at idle or under heavy load, which isn't the case. NOTE: IMO, with no experience with COP configurations; just got my '99 5.4

Do the F150s have the same problem with the DPFE sensors that the Rangers had (mine was a '98)? It seems that they had some of the same symptoms.

 

Lou, I'm putting my money on the vacuum hose on the plenuum going to the EGR vacuum system. Very easy to check out. Your symtoms all five were "exactly" like the ones I had. After I replaced the 90 degree hose I plugged off the vacuum hose on the egr going to the EVR and "ALL" the vibs went away. That indicated a bad EVR either dirty or stopped up. I still have the vacuum line plugged off. Thanks to the help of the folks here especially "bluegrass" who directed me to the exact problem I was able to isolate the problem. Now to do the fix....GREAT WORK GUYS!!!
Good luck