Hey all, I dont post here much, last time was for my old 95 play truck and I got some great information. My current daily is a 07 Lariat Supercrew with the 5.4 (vin v). I've had it a few months and have put 6000 miles on it. In that time I've had to replace the flexplate and the alternator. I drive a very hilly section of interstate going to and from work. The truck had been running perfectly fine then randomly it developed a major miss going uphill. I was practically flooring it to maintain 70, at that point the check engine light started flashing. When I crested the hill it shifted back into overdrive, the check engine light stopped flashing and went off, and pretty much drove like normal. At that point I got off the highway and limped it down backroads 30 miles to get it home. It gets the miss when accelerating starting between 30-50 mph (depending on how hard your accelerating) and keeps going until you stop accelerating. It is getting worse though. I checked the codes on it and all it had was a cylinder 3 misfire but this feels way worse than just one cylinder. it basically feels like your driving down an extremely rough road. I have access to a scanner with live data. I first thought it was a fuel issue because it feels like the engine is starving under load but I replaced the fuel filter along with an air filter and an oil change when I first got it. My scanner says that its staying right around 40psi on the fuel rail. Pretty lost right now and anyones input/help would be greatly appreciated. Thanks guys!

 

Did you check the FPDM under spare tire? Also pull #3 COP off and clean it...when were the spark plugs last changed out?

 

I had these exaxt symptoms on my 06' 5.4. It ended up being a crack on the porcelain on one spark plug after i'd installed new plugs.

 

Change the spark plugs...

 

I couldn’t tell ya for sure when the plugs were done last. The truck has 267,000 miles on it. The previous owner claimed he put an aftermarket set in recently and it does have msd coils. Changing the plugs is probably a good idea considering the mileage and the fact that I don’t know the history of the truck. I’m just hoping that won’t turn into a fiasco.

 

The fuel pump is providing a steady 40psi to the rail. I’m not sure if that’s an acceptable pressure or not though. Assuming that IS an acceptable pressure that would pretty much rule the FPDM out right?

 

You need new boots and springs on all cops . Use sp 546 plugs mc . Dielectric grease on boot ends only a small amount , keep it mostly off metal parts as it is an insulator .
You have the classic misfire due to improper sparkplug circuity .80 percent of the time its old boots or defective plugs .
This engine very fussy about sparkplug installation.
Clean your cop connectors they get corroded both input and high voltage tabs .
Torque wrench the plugs in 25 to 28 foot pounds not by feel . Loose plugs and blowby is common on these heads .

 

I erased the codes and switched the cylinder 3 and 5 coils. Still misfiring on cylinder 3. I suppose I’ll try plugs next. I’m sure it needs them. I’ll do those next Friday and check back with the results.

 

I have to agree with the above, coils/plugs etc.. I had a similar issue. Misfires and poor running up hills. I changed the COP's and plugs, runs fine afterwards.

 

It will barely maintain speed uphills. It feels like it’s gonna shake apart. I just assumed it was a bigger issue. Hopefully plugs fixes it.