my 98 f150 5.4 is missing when under 45 mpr. No check Engine Light or codes showing.

 

How long has it been since you've had a tune up? Sounds like you have a COP going bad. If you have or can get access to a scanner with mode6 you could track the misfires.

 

weve done all the stuff with the cops on mine and are leaning towards a new fuel pump now

 

You need to identify the cylinder that is missing. I would suspect a bad injector.

 

im waiting for the COPS to come in. The problem is that there is no CEL so cannot find out which one s acting up. It sounds fine at idle and at cruise but between them it is missing. Hopefully the new COPS will come in tomorrow

 

You are right to check the cops first. I read what Pete359a wrote and took that to be a post from you. I thought you had already covered that. Sorry, should pay more attention.
Let us know the results.

 

Whether you have a code or not, that does not stop the truck from doing a cylinder balance test. A full featured scanner should be able to get into the more advanced diagnostics.

A bad fuel pump will cause a lean condition and pinging, if it will even run at all.

 

Exactly how the miss is percived and under what conditions is important to the cause analysis.
This is a specific condition example;
If a miss occurrs in cruise under very light throttle application, the source is usually a COP with shorted turns.
It usually never causes a code to be set or a CEL lamp.
Reason;
The A/F mixtire at those times is very lean in the 20 to 1 range.
The voltage required to fire the mix goes up.
A coil with low output will cause the miss until more throttle and higher rpm occurrs with richer mixture that requires less coil reserve voltage and the miss goes away. When the sequence happens there is no code triggered because the fault has cleared until the next time the conditions occurr.
Finding the bad coil takes a dealer stress test or some means of testing coil output.
A simple resistance measurement will not find the fault because it is a dynamic operating fault.
If your miss fits this discription, consider finding the bad coil because if one of the new coils is also faulty you falsely think the issue is not a coil and end up confused.
I have been through this exersize from start to finish and found all the operating paramters that cause the peticular way it shows up.
Good luck.

 

I have the same truck but a 97 and its a dog from 35-45mph.. anything under and over that speed its a powerhouse. I have 187k and just replaced the cop's and plugs. next is the fuel filter hasnt been done sice it was new!

 

OK
the #4 cylinder spark plug blew out. So i had it fixed and all the coils, plugs and fuel filter changer. It still misses around 30 to 40 MPH. It seems fine under a load but at steady speed it has that miss. Where do i go from here?