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Hesitation at around 45 to 50 MPH when you go to accelerate
I started getting a hesitation/bucking in my 2001 F150 SCREW 5.4L 96,000 miles. It does it most often when you are barely on the gas at 45 to 50 MPH and then you press the gas to accelerate. It hesitates for a second and then takes off. I have replaced the fuel filter, cleaned MAS airflow sensor, changed transmission fluid and filter ( really don't think it was transmission related, was just time to change the fluid), and I still have the issue. My next thought was a COP and plugs. The problem is that it has not set off the check engine light, so how will I know what cylinder has the misfire? I really hate to change all the COP's because of the expense.
From what others have said the CEL is a little slow to throw a code for misfire. It will eventually. No expense things to look at would be to see if any moisture is in the plug area and that it has plenty of dielectric compound between coil and plug.
I have a 97 f150 and it did the exact same thing after it was up to the mirrors in mud. What happened was I pulled mud threw my intake and went into the third cylinder and it started missing. Its most likely a misfire. It wasnt a hard fix I just cleaned the sand and mud out and gave it a tune up right then while it was all apart. New plugs and aftermarket spark plus wire solved the problem.
I found my 02 beginning this same problem intermittently at about 37k. The older the truck gets, the more often it shows itself when feathering the gas between 45 and 55. Now at 67k, 2 visits to seperate mechanics, a trip on the dyno, nobody seems to be able to diagnose my issue. The check engine came on once but after turning the truck off, the issue cleared and never came back. The mechanic at the dealership said the code never showed in the history. Ocassionally this problem begins to show itself after idling for a few minutes. Turnoff the motor and restart it and the problem usually goes away. I noticed this issue is very prevalent in warmer weather. I was beginning to think I was losing my mind.
My neighbor's trick to get the CEL to go is to hold in the brake and give it gas (almost as if you were to do a brake stand) and the truck will start the missing under load so you can get the codes. Like Bill said the CEL isn't easily tripped with a slight miss, experienced this many times. You have to get it to start missing badly to throw the code.
Well, I broke down and went to Ford. I had two bad COP's (cylinder 2 and 3). No check engine light but they were able to find the misfires one at a time by looking in the memory. I actually picked the truck up after they fixed the first one and it still hesitated, so they went back in the memory and found the second fail. No more hesitation!!! Next time I am just going to buy the remaining six COP's and replace them myself, so that they will all be new. For what the dealer charges to diagnose and replace two I can buy the remaining six for anyway.
I had the dealership look at the plugs when they replaced the two bad COP's and they said they looked great. They said the previous owner had already replaced them, not to long ago, so there was no reason to replace them now. I have only owned the truck for 7 thousand miles. Next time I see the old owner I am going to check with him on when they were replaced.
Last edited by bbroe; 08-25-2009 at 10:17 AM.
Reason: Forgot one thing