Hey everyone. It has been quite a while since I have posted, which is good because that means I haven't had issues in a while. That means I have an issue now, with my newest addition to my F-Series collection.

About 2 months ago I picked up a 2006 F-150 Supercrew. The truck has the 5.4 V8, and is a 2wd automatic. The truck now has 105,000 miles on it, so it is only just now getting broken in. I was looking at a 2010 F-150, and decided on this truck because it was in almost brand new condition, plus the dealer did the entire 100,000 maintenance including plugs resetting the timing. Now I am seeing a small bug with the truck, and this is where I need some information.

Since picking this truck up, I installed a Dynomax 39450 2.5" catback dual exhaust, and this is where I am noticing the issue. Since I have installed the system I notice that there are times that when I start the truck and let it idle, it will start idling up and then idling down, almost at times like it can't control itself. When the idle starts doing this up and down, the A/C starts blowing warm air too, so I am starting to wonder. As soon as I take off and start driving the truck runs smooth, and the A/C freezes you out of the truck. My first thought was maybe an exhaust leak, but after going over every single clamp, I can't find any leaks. I will say next time I am skipping the Dynomax system, and going over MBRP just because I think I like the design better after installing this system.

Any help anyone can offer would be appreciated, this is my first time with the 5.4, my other F-150's have the 4.2. I hope to get this straightened out easily because I am loving this truck.

 

Maybe the new system messes with the back pressure in a way it causes the truck to do this. If you went from a 2" system to a 2.5" system that could be something(not sure of the stock size). Could be the quality of the system that causes the truck to act weird at idle and then normal when gases begin to really flow through it. No clue. Just throwing stuff out there. Good luck broseph.

 

Thanks for throwing out the ideas. Stock size is 2.5", so it was simple bolt on. I talked to one mechanic and he said the computer would need to be tuned, but when I talked to ford about having it done they said that an exhaust would not require any retuning to the computer.

 

You could try disconnecting the battery for 20 minutes to put the computer in the relearn mode.

 

I have a 2wd 2006 5.4 and didn't notice any problems like this when I put my Roush (Borla) catback on, for what that's worth. Exhaust was installed at 78k miles or so. I agree with disconnecting the battery, just because it's free and easy, and could work. But I think you really shouldn't be having any issues as a result of installing the exhaust

 

If you disconnect the battery to reset the computer, the following is from my 04 owner's manual on reteaching the idle after replacing the battery.

Because your vehicle’s engine is also electronically controlled by a
computer, some control conditions are maintained by power from the
battery. When the battery is disconnected or a new battery is installed,
the engine must relearn its idle and fuel trim strategy for optimum
driveability and performance. To begin this process:
1. With the vehicle at a complete stop, set the parking brake.
2. Put the gearshift in P (Park) (automatic transmission) or the neutral
position (manual transmission), turn off all accessories and start the
engine.
3. Run the engine until it reaches normal operating temperature.
4. Allow the engine to idle for at least one minute.
5. Turn the A/C on and allow the engine to idle for at least one minute.
6. Drive the vehicle to complete the relearning process.
• The vehicle may need to be driven 10 miles (16 km) or more to
relearn the idle and fuel trim strategy.
• If you do not allow the engine to relearn its idle trim, the idle
quality of your vehicle may be adversely affected until the idle
trim is eventually relearned.

 

I just wanted to say thanks for the advise. I have been away the last couple of days, but I am going to try and reset the idle and computer this weekend. I am just happy the truck is finally coming together the way I want. Got the exhaust done, just installed factory 18" from a 2011 F-150 today, and got to finish installing my stereo over the weekend. I will post how the computer and idle reset go. Thanks again.

 

I have to say that so far disconnecting the battery and following the idle reset instructions have made a world of difference. It seems like the truck is gaining back some of its power and has evened out its idle. Thanks for all of the help everyone!

 

Glad to hear it!