Driving the other day and I hit 50mph and the truck starts bucking like crazy. It calmed down eventually as i powered through it but this is starting to get to me. After it gets nice and warm it will run excellent but until then it is a crap shoot. I could tell when it will do it as soon as i start the truck and it starts to idle very rough, like it is missing but no codes. The idle smooths out after a few minutes and i take off, then it starts to happen. If i drive it and park it for a bit and go for a ride agin it is fine, it only occurs after it sits for an extended period of time. My tach acts funny also until it warms up. It will jump a couple hundred rpms up and down until it warms up completely.
I searched and found it could be the DFPE or the IAC. I was able to pick them both up for next to nothing so I'll try them. The last time I cleaned them both it stopped the bucking until now and that was back in October. Also going to clean my K&N and throttle body. Thought it may be a head but I have 0 coolant loss. I have too much fluid in my tranny when i checked it the other day. Can that cause and issue like this? I'm changing the fluid out this weekend to rule that out. Any other suggestions?
Thanks all!

 

just make sure the engine is idleing while you check that tranny fluid, it will go down significantly when the engine is running.

 

I made sure of that. Seems like it always happens when we have weather changes. Like being warm during the day and cold at night or just really damp outside. The past 3 times i started it it has been consistently cold and the truck runs like a champ. No bucking, no weird idle, nothing. Don't know what to start with anymore. Will change the DFPE and IAC this weekend to see if that will help. Although i can't tell since it is not doing it anymore. Oh well, I'll just chock it up to Ford engineering.

 

Discovered that my coolant reservoir cap came off and spewed some coolant onto my filter. Cleaned it and put the cap back on. I then removed my radiator cap and the pressure blew the reservoir cap off. What could cause that? I believe this may be my issue but don't know what could cause all that presssure to blow the cap off. Reservoir cap is very loose so I need to find a way to keep it on.

 

Is your truck also getting hot? When you removed the radiator cap was the truck still warm? The coolant system is subject to around 13lbs of pressure when it's warm.


GB :)

 

I had the exact same problem minus the cooling stuff.
A screamin demon coil pack and quality spark plug wires(Taylor 8.2mm) with double platinum plugs fixed it.
I could never get it to throw a code because the problem wasn't originating with the coil pack so the engine will not see "engine missing" for just a weak spark.
I would recommend against Motorcraft spark plug wires.

 

if the cooling system was warm the cap will have pressure

when have you done a tune up last? plugs, wires, fuel filter

i think you just diagnosed it yourself when you said k&n filter...clean your maf and put a motorcraft (not fram or any other garbage with a thin gasket on it) filter in it and see if it makes a difference...disconnect the battery for 30 minutes for it to relearn fuel trim and idle

 

Truck not overheating and tune up was just done 2 months ago. The truck was still a bit warm.

Why would the cap come off while drivin inked it comes off by itself since it is really loose.

 

when you install the radiator cap, it will turn and stop, then you have to push down, and it will turn a little more...the middle position is to release the pressure before removing it...maybe you arent installing the cap properly...

 

It's not the radiator cap coming off it is the reservoir cap. It just gets pushed on and mine seems extremely lose. I have some duct tape on it for the time being until i could find a new reservoir with a good cap or just a new cap.

 

Make sure the plug wire connections are good. My brand new motorcraft wires went bad after a few months which I think is due to the crappy connections at the plug end. That is why I went with Taylor wires.

Just a random guess but your head gasket might be blown which could be fouling a plug and over pressurizing the cooling system.

 

there is no pressure in the reservoir so the cap is just there to keep birds and dirt out of there...if you have pressure in the reservoir, the radiator cap is defective or you have something (head gasket) pressurizing the system to the point that it is all blowing off into the reservoir

 

The overflow reservoir cap doesn't get blown off it shakes loose while driving because it is so loose.
Thanks guys.

 

So wrap some electrical tape on the tanks spout until the cap fits tightly. 99cent mod.


GB :)

 

you can leave the overflow cap home when you drive the truck and it wont make any difference...try the things suggested in the thread...especially the one about your K&N...i wasnt blowing smoke, thats a common thing i used to see at the dealer

 

i didn't know that. i always was told to only fill fluids when the engine was off. my tranny is full to the fill hole when the engine is hot. i did it about a year ago. should i turn on the truck and fill it to the fill hole again? can i get another confirmation on this. i don't want to over fill.

 

Yours is a manual trans. I always checked mine cold and made sure it was up to the fill hole. That's all you need to do. It sounds like he was talking about an automatic to me.


GB :)

 

PCV Valve working properly? Have you checked for vacuum leaks?

 

Just changed the PCV valce and there are no vacuum leaks. I'm starting to lean towards a cracked head or a head gasket. This will be the second one in 2 years. Possiibly my K&N as someone suggested before.
The only time it has been stumbling lately is at start-up. Once I start to drive the truck runs great. No issues.
Yesterday after i got home from work I let it sit for 2 hrs and went out and removed my radiator cap and my overflow reservoir started bubbling. The truck wasn't cooled down all the way yet as I still felt heat from the block but i think this may be a symptom of something majorly wrong. It seems everytime i remove the cap the next i start it it idles worse at start up.

 

Cool I do the same.

 

I had a 3.0 with the same bucking problem. Mine was the distributor itself. The bearing would get hot after the truck got warmed up and would hardly run.

 

No distributor on mine.

 

x2 thats what mine was

 

no one beleives me when i say that...im not blowing smoke or pulling it out of my ***. dealership experience is how i know

 

You're 100% correct when you told me to change it out. I can't get the airbox till this weekend since I picked up the wrong one this past weekend but I took out the K&N and cleaned my MAF really well and it has been running great since then. When I get the airbox if i could find one, cause i ditched mine 10yrs ago, I will be changing it out. I also took out my Diablo Sport chip.