Well, I have had zero engine problems with my truck (97 F150 4.6L) up until now and I just hit 130,000 miles, so I have been lucky. I am having what I think is an engine problem but not sure. Here's the problem.
At about 1200-1400 RPM I get this surge or miss ( can't decide what it is doing) feeling in the truck. Best way I can describe it is to say it feels like a loaded trailer getting slack and then tightning back up. Kinda of a jerking feeling. No check engine or trans lights are coming on yet, and when the feeling of the surge hits the RPM's DO NOT change. It seems to only happen when I get up to 40-50 mph and overdrive kicks in and drops the RPM's down to the 1200-1500 range and I keep a steady throttle to stay within this speed/RPM range (kinda where the engine is bogged down a little, right before it should shift down), although I did feel it once with OD off at around 1800 RPM. I can let off the throttle and push back down and all is fine or I can just push down on the throttle a little harder and engine perks right up and runs fine.
I did a little full throttle test tonight on a long hill and the same problems appreared but a much worse rate along with the pinging nosie I am trying to figure out. I may be wrong but the two might be related. Another thing to point out is that my pinging really only happens in cold (below 50* or 40* weather) and that type of weather is when I noticed this problem also.
So far I am in the early stages of fixing this and have no real clue where to start. The plugs, wires, and fuel filter have about 22000 on them, so I wouldn't think it to be them misfiring as that would throw a code. I have been told that it could be the early stages of the fuel pump on it's way out (hope not). Any ideas out there because I really would like to get this figured out?

Sorry for the long post but I feel too much detail is better than not enough.

Sincerly,
Lost and confused

 

Could be a fuel pump, but they tend to cut out at higher rpms, not lower ones. I'd check your TPS.

Take care,
-Chris

 

Well to tell you the truth I have learned today that it does do it at other RPMS. Like today on the interstate I was running at 1900-2100 RPM and it would do it. If I pushed the engine just a little harder after the surge or miss (what ever it is) it will clear up and take off. Dad mentioned the TPS, might be bad like it was on his truck (94 F150 5.0). But his truck would not shift down right and had other symptoms when the TP was bad
If the fuel pump is bad say loose connection or more than likely low pressure, will it throw a code? Right now I am totally in the dark on this one. I am still driving it and waiting for a code to pop up any time, hope I'm not causing more damage but if so oh well I will just have to rebuild and move on. Right now I am kind of thinking towards the fuel pump or pressure regualtor or the trans itself.
Anymore replies are appreciated.Thanks

 

I had the same problem with a 1994 F150 and it ended up being the Mas Air Flow Sensor. It read within specs and did not give a fault code. The dealer could not figure it out for a while either, they had to call back to the factory to get the answer. They did a cleaning of the sensor and all the problems went away. That was 2 years ago and the truck is still running fine.

 

My 1998 F-150 4.6L does exactly the same thing, yet I have only 66k on it. I've taken it to the dealer twice and no codes were stored. They did drive it once and determined the #1 plug was misfiring. It was replaced and the problem came back after about 200 miles. I don't know if it could be a factor, but ever since I started using Amsoil my engine runs very cool. Physically the engine is quite cool and the guage only comes up 1/3 of the scale.

Could the temperature be so low that the computer trys to make the mixture rich???

I did change the TPS after it tested incorrect resistance on one side, this did help with a bit quicker response for the downshift from overdirive. I also had the transmission checked and flushed, it is not the problem.

I really like this truck but I am discouraged that this problem will not allow me to fix it.

 

I have a question for you. Does it run better when the engine is loaded, even a little, like running the AC, or do you ever notice it climbing a hill or accelerating, or only in a drift? I'm not seeing this in my 99Expedition 5.4 but have exactly what you are describing, in a Ford Tempo I run back and forth to work. Its driving me nuts, have replaced ignition wires, helped a little, and plugs, also helped a little, and the car passed smog with no problem, but still runs weird.

 

May be a combo of poor/diry gas and/or a dirty fuel filter--should be changed every 15,000 miles I think.

Dan

 

Well sort of happy now but at the same time still mad. On the interstate today the problem came up again and just kept on getting worse. I wanted to turn around and go back home but there was no where to do that and I was almost to my destination. About 2 miles before my exit ramp the MIL started blinking but the problem wasn't getting any worse so I kept on driving. At the exit ramp the MIL went from flashing to a steady light. I stopped at my destination (Flea market, was going to buy a set of decent used tires for 40 for winter use) and met up with my friend. We then took my truck over to Advance Auto and I bought a tester. Code 303 for cylinder #3 misfire. What gets me is the plugs and wires are only about 22-30K old. I thought they should last at least 50k, but I gues not. Now I have the headache of changing it all myself unless I want to have Ford put their crappy **** back on there. Anyways I used the erase function on the tester and pushed and twisted on the spark plug boots. I drove the truck home but the light did not some back on, the problem is still there but not as bad as the trip up was and performance is sluggish
Last question. I drove the truck for more than 3 days with this problem happening before I got the check engine light. Do you think that I could have harmed my engine in any way because of the misfire? Would it hurt to drive it a little more, this is my main mode of transportation?