Been researching the posts in here and have tried a few things. Lemme break it down:

I'm a merchandiser and the other day while going to a store my truck was running great. Went into the store, came out, headed to another store. Halfway there I heard what I thought was a backfire through the throttle body. But that was it...kept going. A few miles later it popped a few more times and started running rough. Pulled over, gave a visual and couldn't see anything wrong. Continued on with this roughness. Highway speeds were reduced to 50-55mph, anymore than that and she'd backfire real bad through the top. At some point in all this...my check engine light went out (it has been on for over a year now and it has continuously ran like a champ until the other day).

At first I just thought bad fuel (I'd filled up that morning), and then I thought the MAF sensor.

Since reading posts I've cleaned the IAC, but that didn't seem to help much. Still a little chilly here to undertake a plug change, even though it needs to be done regardless if that's the issue.

A few days later now, it is fairly smooth at idle. But you can still feel a roughness to it. A quick slap of the throttle and there is a hesitation and then pick up...but it's done that since I put on the Cold Air kit. Roughness increases with speed under load, and once you hit about 65mph, she pops.

Just tell me I didn't break something and it will be a load of my mind. But if someone can give me more ideas, or maybe have had similar issues and can help I'd really appreciate it.

My truck is a 98 F-150, 4.6L, 2WD, Automatic. 144,000 miles. (Incidentally when this happened...it was at 143,999) It's all stock for the XLT with the exception of a BBK Cold Air Induction kit and a Flowmaster exhaust. The only issue I've had with anything on this was last year my alternator went out.

Thanks in advance!!

 

What was the code that was on for a year?

 

Hi,
My 99 lightning with 70,000 mi just started doing that today!
It has a boost gauge, and it only happens when the boost is over 3psi (max is 10). It doesn''t matter what the engine speed is, just the boost. So if i keep OD off it runns fine, but load it up in OD and it boggs, and stumbles and eventurally will backfire (I only let it do that once.) otherwise it runns fine.
Any help would be most appricated.

Also, I've never had a code, and still don't.

 

Everything ran just fine, and there wasn't ever a drop in any mileage or things like that. So I never got it read.

 

Well there was a reason it was on, even if it felt like things were fine. If I'm not mistaken, an EFI vehicle with a lean condition can cause back-firing. And further more, can't the CAI cause it run lean too (or is that just on certain model years?). Either way, you should have the codes pulled. And maybe try cleaning the MAF. I was told to use brake cleaner and spray down the wire thingie inside. Use a can of compressed air to dry it.

But you should really get the codes pulled and then post them here....plenty of knowledgeable guys here to help!!!!

 

Yeah, NOW I know this. Didn't have this kind of access then either. But, I do now so I'm utilizing it. I got a code reader last night after some reading that just because the lights not on doesn't mean that there isn't something in there, so I ran one on it. And it told me there were 5 different diagnostic systems that hadn't ran their self-checks.
Those being:

Comprehensive Component Monitor
Catalyst Monitor
Evaporative System Monitor
Oxygen Sensor Monitor
Oxygen Sensor Heater Monitor

But no actual code was in the system, so it showed.

 

Just got done cleaning the throttle body and replacing a coil pack (unplugging wires on that side showed no difference, and it was easier to swap that then the plug, ). Now the backfire seems to be gone on a single road test, but it's still slightly rough....should I just chalk that up to all the new residue that's been broken loose, or do I still have some work ahead of me?

 

i hate to open old threads but i am having the same problem what ever did you find that was wrong with it?

 

It looks like he cleaned the throttle body which makes sense - Plugged Ports is a common problem in the 4.6L , it also happens in the 5.4L , just not as much..Cleaning the MAF would be the next step. If all that fails to solve the prob , you need to look towards the timing - make sure it didn't jump, there's marks which make it easy to check..

 

I had the same symptoms, turned out a plug wire boot was loose...

 

Plug wire caused it to backfire in a 97 or newer engine?