Injectors on D7 17A

Before you go into it, cut each cylinder out by loosening each line in turn while it's missing at it's worst and see which cylinder if any doesn't affect the good running of the engine at all or as much as the others. Cracking the line on the bad one will eliminate most of the smoke from a bad injector since the fuel is no longer delivered into the cylinder so it can't smoke.

Once you identify the problem cylinder, swap that injector with another one from a good cylinder and see if the miss follows the injector or stays with the cylinder. If it moves, change the injector, if it stays put, there is a problem with the cylinder, the fuel pump, the line etc. The individual pumps can be swapped around as well to isolate the problem, but they must be timed to the rack as they are installed! There is a dot on each pump plunger and the rack that must be aligned. The plungers will also fall out of the pumps and could be damaged, so keep them in the pumps at all times if the pumps are removed.


Like every diesel, cleanliness is very important, so clean everything up before removing lines if possible. Then remove the lines and the hold down nuts. The injectors are a nonadjustable capsule type of "valve" as CAT calls them. They screw onto the "body" of the injector only finger tight. The loose thread allows the fuel to flow down to the tip and the joint is sealed when the hold down nut is tightened to 100 ft/pounds.

There are a couple of seals under the hold down nut and the fuel line that keep trash and water out of those areas that should be replaced each time. New "valves" aren't very expensive if the old ones don't check out on a tester. They should break at ~500 psi minimum and have good spray pattern with no drips etc.

If the injectors aren't the problem, having the lifters in the fuel pump housing set to spec will often times help the way the engine runs. As the parts wear, the injection timing usually becomes delayed and most of this can be adjusted out.

Just to follow up on this topic. The cat had been at my father in laws for the last couple of months. I just got a chance to move it home this weekend. When started it will idle a little rough and when it puffs smoke it is fairly irregular like it is not from one cylinder in particular. When you crank it open, it smooths out and runs fine. When one idles it back down after running her hard it runs fine.

Is it likely to be an injector that's giving the trouble at initial start up? Is it much to be concerned about?

Sorry about the delay ccjersey, and much thanks for the thorough post. If I ultimatley need to tear into it, it will tell me everything I need to know from the sounds of it.

Dan