Hi, My truck recently developed a stumble/hesitation upon acceleration. If I try to accelerate from a steady speed(cruising along then give it more gas) it hesitates then goes ok. I stopped at Autozone today to see if they would plug a scanner in to see if any codes came up and he said if the check engine light is not on you will not get any codes. Is this true? Truck is an 04 5.4 with 66666 miles(well, yesterday coming from the mall but I thought the number was cool). I purchased a new fuel filter, figured it would'nt hurt. Any other suggestions?
Thanks, Sean:santa:

 

Change your plugs, clean your throttle body, change your air filter. The Autozone scanner won't pick up any codes if the check engine light isn't on, although there still might be some codes being thrown.

 

Is it just the Autozone scanner or all scanners that will not pick up a code if the check engine light is not on?

 

Pending codes will not set the check engine light. Go ahead and change the fuel filter and see if that makes any changes.

 

From my experience, with an '01 bought new and sold recently with 204k, the first hesitation I would notice came from worn/old plugs which was elimated with new motorcraft plugs.

 

my truck was doing the same thing. i replaced the front 6 plugs and its fine now. but i waited till i had a cylinder 1 misfire on the obd2

 

As whacko as this will sound, try replacing the gas cap. I've heard more stories about chasing stumbles on these engines and no codes but a change of the gas cap solves the issue on the 04 and newer trucks. It's a cheap fix if it works and if it don't you could always take it back.

 

FWIW, I had a Bosch spark plug go bad within 20,000 miles.

The engine was running bad for weeks before it would throw a code or an SES light. I scanned the codes several times after it started running bad - Nothing. Replaced fuel filter, cleaned the MAF and air filter, new PCV valve, etc...etc.... No improvements. I did not think it could be a spark plug, because I knew they had less than 20,000 miles.

When it started running REALLY bad (like losing a cylinder 100% of the time), FINALLY the SES light came on and I could pull a code. Misfire on #6. Put in a new Motorcraft plug and she ran like new. I could not believe how bad it had to run before that damn SES and code showed up.

As someone suggested earlier, replace your spark plugs (especially if they are not Motorcraft).

 

One or more of your COP is going bad. When it gets real bad, it will throw out a misfire code.

 

One or more bad coils will do this.
You may put new plugs in and seem to fix the problem but it will come back within a short time. The new plugs are easier to fire until they get some run time and degrade enough to be harder to fire, as well.
The coil develpes low output.
When in cruise and light load, the fuel is leaned and timing advanced as a normal function.
The coil can't fire this leaner mix.
As soon as you apply enough throttle, the fuel goes richer and the coil is just able to fire again until the next time those conditions are present.
The only way to find the offending coil/s is a dealer stress test or replace them all to get the bad one. BUT... if one new one is bad you still have the same problem again. Swapping cylinders is no help either since you still can't ID the bad coil.
Testing is the key to identifying the coil.
Since this is not a hard fault, no cylinder can be identified by code or CEL.