2001-F150 5.4 Eng. bucking/stumble help!!!

Hello,

I am new to this forum, but have spent hours reading many of your great posts. Thanks, it is really helping with my education. But, I think my problem is slightly different than what I am reading about. Here is what I get (125k miles):

* Engine only bucks/stumbles intermittenly and not at idle or at harder acceleration (this bucking is really harsh and makes the truck feel like a learner trying to drive a manual transmission and it is jumping down the street). The engine stumble is not a regular timing such as a cylinder going out and staying out for a period of time. It is quite a random pattern to the jumping

* Originally thought it was humidity related, but now I realize it happens in any climate

* No stumble in neutral at any rpm... only at a stop if I put it in a power brake load.

* When the stumble shows up, it seems like the throttle is around 10-25% (my best guess)

* Sometimes goes days without issue, but sometimes every ride and virtually every acceleration.

* Normally no stumbling at highway speeds, unless going up a hill.

* Everytime it stumbles, it can be eliminated by either backing off on the accelerator some, or hitting the accelerator harder.

* No engine codes or CEL has ever come on

* Fuel mileage appears to be the same before and after the trouble started

Here is what I have done to try to correct it:

-> Fuel related (bad gas)... tried to run the tank as close to empty and fill it with fuel from different stations... when this didn't work, I have added HEET to it to dry up any water in tank.

-> Fuel delivery... replaced the fuel filter... seemed to work for one day, but then the gremlins came back.

-> Fuel delivery... ran multiple injector cleaners through tanks of gas.

-> Intake... replaced the filter.

-> Electrical... I don't believe this is related, but my battery died... parts store tested the system and stated the alternator was bad... replaced it, and took the old one to the parts store for bench testing and it was 100% OK... even thought the old showed OK, I left in the new one as a precaution. Only other item was a set of plug changes around 30k miles ago... I think I put in the super duper Bosch plugs with a lifetime warranty.

Current thinking and items I don't understand:

A) The bucking is so severe, it appears to be a random harsh loss of either fuel or ignition. A component that has failed electrically should give me a fault code with this level of severity. No trouble codes or indicators to electrically sense this disturbance...

B) For the fuel path, the most likely item is bad gas and I emptied my tank by running it as close to empty as possible and then used different gas and HEET to eliminate water. THIS MIGHT STILL BE THE CAUSE???

C) Another one for the fuel path is an intermittent fuel pump electrical connection or a weak pump from a pressure point. But if this is the cause, then why does it dissappear upon harder acceleration?

D) One last fuel thought is injectors... perhaps one or more have a range of delivery that they don't work properly... but this doesn't make much sense as at idle and harder accels are fine

E) From an ignition standpoint, perhaps I have failing COP's. I have not just gone out an replaced them due to my limited budget and the difficulty I read about changing them. Again, if one of these is failing in an either open or short condition, the computer should set a code for a miss-fire for the related cylinders. I get nothing. Hense my hesitation in making this change so far. ONE THING I DON'T UNDERSTAND FROM THE VARIOUS POSTS IS THAT THE COPS CAN FAIL UNDER LOADING. WHAT MAKES THIS HAPPEN AS ELECTRICALLY, I DON'T THINK THEY CAN DETECT A LOAD OR NOT? IT IS HARD FOR ME TO ALSO UNDERSTAND WHY MY TRUCK WOULD ALLOW ME TO BACK OFF ON THE THROTTLE OR HIT IT HARDER AND THE ISSUE DISAPPEARS.

If anyone has ideas on what I should do next, it would greatly be appreciated. I would also like to know why, with the severity of the jumping, the computer can not detect something is wrong. Finally, what causes COP's to die under heavier loading conditions?

Sorry my 1st post is so long, but I have tried all kinds of things... excluding the costly ones... and, before I take this route, I would like to have more assurance that what I am doing will actually correct the issue.

Thanks,

Brett

 

check the coil packs. i had a 4.6 that did it and the truck would have like no power...

 

i would say the cops. make it run rough accellerating and slowing down over and over, you WILL get the light to come on then you can have computer read. a cop failing the truck will feel like it is falling apart. change them yourself or expect to pay 200 bucks to change one. I would also advice to go ahead and change them all

 

I would also guess a COP is going out, have you tried to pull a code..does your check engine light work? I know that seems like a silly question but I drove mine (2 days) with a bad COP waiting for the light to come on and then realized the bulb was burned out.

 

I have a functioning CEL (check engine light) and I have tried to run the truck for longer periods of time with it bucking, but no code has been set. Even with no CEL, I have connected to a scanner to find the computer has not been able to detect any malfunction.

Does anyone know how long the bucking must go on for the computer to detect a misfire code? Perhaps my 1-2 minute rodeo is not long enough... my problem is that I feel like I am destroying the life of the engine when I do this.

I still don't understand the WHY of how a COP can fail under loading, but work well at other times. It has no intelligence, so how can it fail only under these certain conditions?

Thanks, Brett

 

When I had water in one of the spark plug holes it took a whole day of driving for the CEL to come on. Mine just felt a little rougher then normal with a loss of power.

 

Wow... a whole day to set a code... I don't think the truck would last if it shook this hard for a day. Is it normal to take this long to set a code?

 

I don't know if it's normal, but thats how long mine took.

 

Have you changed your plugs lately? If those are original plugs they are due,motorcraft plugs only please. It would also be a good idea to change all of the coil boots. If you still have problems, then I would look at the coils for problems.

 

Is it a good idea to change ll the coil packs when one goes?
I have seen these packs on ebay for a good price, has anyone used them?
Dan

 

Plugs were changed around 30,000 miles or so ago. I changed them with the lifetime BOSCH type from Autozone. I see from this site that many recommend changing them with Motorcraft parts. I suspect if I have to change any of the ignition coils (COP's) then I will change the plugs back to Motorcraft at the same time.

I see that you can get a full set of COP's on Ebay with a lifetime warranty for $75 plus $11 in shipping. For this price, I suspect I should just change the whole lot. My personal issue is that, as an engineer, I really want to understand the what and why of the failures vs just changing parts to see if the problem goes away.

The location of these are at: http://cgi.ebay.com/ebaymotors/NEW-I...em180223319317

Would love to hear someone confirm these are good parts to use.

Thanks, Brett

Brett

 

If its happening at the same throttle position ( you said 10 to 25 %) maybe TPS?

 

If you want some cheap COPs, then go to Summit, and get some ACCEL COPs.

 

As for the throttle position sensor, I don't really think it is this as I can have the throttle at the same positions other times (non load times for instance) and not have a problem. Plus, this is one of the easiest items for the computer to set a code for... it is an easy algorithm to detect this fault.

I will also look at Summit for Accel COP's. Thanks for the advice.

Brett

 

As spark plugs wear, the spark plug gap increases which makes the voltage required to fire them to go up. The gap eventually gets wide enough to cause the coil to be stressed when engine loads are very high. The stressed coil will get overheated and turns of the coil will short out, which limits the voltage output of the coil.

With the voltage output of the coil down and the engine load high, the bucking comes in. The misfire is not repetative enough to set a code in the computer. The only way to identify the problem is for the dealer to do a COP stress test to find the one that is bad.

My truck by the way has started this same thing. I am on my original plugs with 78k miles. Good luck!