1 just bought 2003 ram quad cab 1500 4.7l vin n.156000 miles a/t 4x4.when i drove it home i got p0172 code i found leaking injector so replaced all of them cleared codes and they havent come back but the truck misses and im getting neg 19 ltft.i checked compression all good checked fuel pressure good put in new plugs didnt make a difference.map is 11 at idle o2 sensors appear to be working correctly.could this be a dropped rocker arm?also did full seafoam treatment

 

If compression is good, it's not a valve train issue. Are the injectors hooked up properly? It's sequential fuel injection, so which connector to which injector matters. Also, sometimes the connectors just don't make good contact, so you get only a partial shot, or none at all....

 

ok i checked the injector hookups and their correct.when i changed the injectors number 6 plug was fouled so i replaced all plugs i just pulled the plugs and 6 was fouled again so i replaced it and switched coil packs around 6 fouled again.thanks for the help

 

Fouled with what? Gas? Oil? Other?

 

its black sooty and smells like gas.also i noticed if i rev to 2500 rpm let it drop to about 1000 rpm an stab the gas pedal it backfires

 

Put a noid light on the number six injector connector, and see what it does. It should blink, see if it is staying on solid.

 

i'll have to buy one any recommendation?

 

A rocker could certainly have fallen off. Compression would still be good because the valve would be stuck closed but it would run rough. Sounds like the #6 intake valve popped off. It's injecting fuel but the valve can't open to allow the fuel into the cylinder causing a dead cylinder and fouled injector. That's what I would check next if it was me. They usually don't cause any damage when they fall off. Just pop them back in using a wrench. If they fall off because of overheating then the seat could have fallen out causing valve damage. Since your compression is good, sounds like that's not what happened.

If they keep falling off, there's a guy that sells clips that fixes the problem.

If they keep falling off, running fully synthetic oil might help as well.

 

i dont have a noid light so i used a stethoscope and listened to all the injectors they all sound the same.if the intake valve isnt opening would it still foul the plug it seems like it wouldnt be getting any fuel.

 

If the intake valve isn't opening, on the downstroke, the piston will be sucking against two closed valves. They both will probably open just a little to allow some air and fuel in but the suction will also pull oil into the cylinder. This would cause fouling of the plug. That's my thoughts on what would happen in the intake valve isn't opening due to the rocker arm falling off or the lifter being fully collapsed..