I've been having problems with my truck, rough idle, intermittent hesitation during a WOT launch, and fuel mileage went to ****. It hadn't thrown any codes.

I checked the following:
fuel pressure - normal
vacuum - normal
cleaned throttle body
changed plugs
changed wires
checked Cats with a temp gun - normal
cleaned MAF - It was dirty and seemed to have a film on the parts inside the MAF
fuel rails and the filters in the injectors looked clean but the spray tips were dirty which was cleaned with TB cleaner

This morning when I started my truck it was idling really rough and the engine light started flashing. The light ended up going off. I brought it to a friend shop and did a scan. There was a P0300 code and cylinders 2,3,7, and 8 showed a few misfires. Cylinder 4 had almost 300 misfires and Cylinder 5 had over 300 misfires.

I'm thinking it is either the MAF or the injectors need to be serviced or replaced.

Any suggestions on which is most likely to be causing the problem or how I can figure out which is causing the problem? This has been driving me crazy since it started back in May.

 

get a spark test light, that'll eliminate the pcm as an issue. If you have an honest missfire (not a false code like I had) I would work backwards from the plugs. make sure the ceramic isn't cracked, switch the wires with a good cylinder, see if the misfire moves, switch coils with a good cylinder, see if the misfire moves, clean all the connections to the individual coils and the main connection to the coil banks. See if that helps. Sometimes we have a tendency to get wrapped up in the electronics of it all and forget that this is still a SBC at heart. Let us know what happens.

 

I spoke to the mechanic that did a scan for me back in July. He reminded me that the misfires were on cylinders 7 and 8. Yesterday the scan showed the bulk of the misfires are occuring on cylinders 4 and 5. The only thing that was done to the engine was the fuel rails and injectors were taken off to see if there was trash in the rails or on the filters at the top of the injectors.

So it seems that the misfires followed the fuel injectors. I checked around and autozone has injectors for $95 per injectors, dealership were $125 per injector. Jegs has some for $44.99 per injector.

There is a local shop that does fuel injector cleaning for $25 per injector. Has anyone had their injectors cleaned and did it get them back in "like new" condition?

 

My Truck was running bad at one time caused from my MAF sensor. I unplugged it and drove it around and it drove a lot better. You can give it a try, might get a MAF code when doing it.

 

I don't believe it's a MAF problem. I'd rather think you have a clogged injector. Look for a shop in your area that has a Motorvac fuel system cleaner machine. Around here it costs about $100. It cleans everything that fuel touches. Fuel rails, injectors, intake tracts, tops of the valves, combustion chamber & top of piston, etc. It does work very well.

 

+1 seems like clogged injectors are fairly common on our trucks