Recently my truck has been lacking power when accelerating and a few times has back fired. I put some BG 44K in the fuel, and it has helped, but it still is stumbling during acceleration. No codes have been thrown, and I had a similar problem back in May that a bottle of BG solved the problem. My question is how do you know if a valve is sticking? Also, what is the best stuff to use to free up sticking valves, CRC Intake valve cleaner, marvel mystery oil, ..... My thought was using an oil additive to clean up a stuck valve. Does anyone have past experiences to what works.

 

Truck details, please. We can't see it through the Internet.

Without that info, I can't help but think if BG44K helped, you may need new injectors.

 

98 F150 4.6 L with 191k miles.

 

Also changed the plugs and wires 30k miles ago, replaced fuel filter 6k miles ago.

 

Do a compression test, if it's good and the engine isn't making any strange noises, it's probably dirty injectors. There's a chance it's one or both of the coil packs but BG44K shouldn't have made a difference if that's the case.

What brand plugs and wires did you use?

 

Checking the fuel pressure is easy to do.

 

I used Autolight plugs (I have used before with no problems), and I believe Duralast gold wires (used before no problems). I checked the fuel pressure the last time I had this happen in May, and it was around 40 psi (low end of the fuel pressure range).
How much is a compression tester? I would then check each one, and if they were within spec., then I would know it's the fuel injectors. Would dirty fuel injectors cause a backfire though?
Thanks.

 

Fuel pressure was 30 psi, not 40 psi from last post, which is on the low end of the spec.

 

30psig is okay judging from my truck. That is the pressure I saw when I checked my 02 5.4 and it runs great and has for many miles after I checked it.

Put some more injector cleaner in it. I use Gumout for high mileage engines with PEA. On a recent 6k miles trip, my truck started missing at idle at the end of the day on two occasions and a couple bottles of that Gumout in a half tank of gas cleared it up. I must have been getting some poor quality gas on that trip.

 

The best injector cleaner is Techron. BG44K is no longer the best since they had to reformulate due to VOC regulations. There are reports of Autolite plugs not working well at all in these engines, on general principle I'd replace them with Motorcraft, and consider replacing the wires with Motorcraft. Remove, clean and inspect your coil packs, they may have cracks and/or carbon tracks. Ignition issues such as this can cause backfires. Make sure you use dielectric grease inside the plug wire boots at each end.

Motorcraft plugs and wires are a lot cheaper at Rock Auto than anywhere else.

Parts stores loan out compression testers.

Make sure you torque the plugs to 28 ft/lb to prevent loosening and blowout, if you use Motorcraft plugs antiseize is not needed.