Totally lost about air in injection system, loosing mind!

[neo]

Hi folks, I recently built a 6.2 about the best I could afford. New pistons, IP ballanced, B/ped, custom girdle, heads redone, timing gears, etc. stuck it against a build 700R4 and Jeep NP208 and crammed it under the hood of my 89 Wagoneer. Military take out engine was started with. Starts fine and sounds pretty good at idle. Here is the issue: When under load and warmed up, you can hear what I believe is one injector popping . It is consistent, again as far as I can determine, with the cam timing/IP timing. There is some white smoke at idle and under load. Sometimes you can (for a very short time after accelerating, here the single injector popping noise at idle, but it goes away quickly. All injectors ahve been bled by crakcing them and the power test indicated nothing, all seem to affect idle.
I placed a section of clear Tygon hose on the exit to the IP and there are very slight, tiny little bubbles in the line exiting the IP. I placed a section of the same hose ahead of the IP and it is clear as it can be. I notice that it (the IP will "burb" more air bubbles when I either acclerate the engine and let off quickly, or at idle hold the return line clsoed and then let it go. The bubbles under either condition are much larger than the normal bubbles.
So I think there is a bad injector, just not able to locate it yet. Is it possible air can come back up into the IP to be expelled from the IP through the return line from an injector line? Can the IP simply have an issue and allow air in? I know it is not coming in the IP from the line cause as mentioned it is clear as it could be. The stream coming out of the IP return is normally very tiny and you have to look to see it, but changes signifcantly when you hit the throttle or bog the engine by closing it up.
Anyone have any ideas? It is driving me nuts:mad:!! Thanks!

[More Power]

It is somewhat normal for small-tiny bubbles to be seen leaving the fuel injection pump through a clear fuel return line with the engine running. The process of compressing and/or heating the fuel as it works its way through the pump will produce some amount of small bubbles. What you don't want to see are larger bubbles or lots of air. An air leak in an injector (when the engine is off) that allows air to migrate up through the fuel injection pump usually produces a hard to start and rough running problem shortly after starting. This sort of problem is made worse by a bad check-valve in the fuel lift pump, because any vacuum in the fuel tank can pull air back through the fuel system when the engine is off.

Jim

[JohnC]

The injectors are lubricated by a tiny amount of fuel that is allowed to leak around the needles on each injection event. I suppose if one injector was hanging up compression gasses could leak back into the return lines. This might explain what you are seeing and hearing.

You can isolate an injector by loosening the B-nut on the line on the injector. It will not fire when the nut is loose.

[neo]

Thanks for the replies.
What is the "B-nut?" Is this the end of the line at the injector (3/4"?)
SO if I hold the return line out of the IP closed - until the engine begins to bog, and then release it, larger bubbles shoot through the clear "return" tube.
Also, there is still a knock or pop that sounds like one cylinder on the cam timing. Am I correct in my presumption this type of knock is one injector not closing up after the injection squirt? I have had that same noise on my 89 Burb (6.2 NA) and I can usually floor it for a couple seconds, and it will go away. My suspicion is that was a particle stuck in the injector and by flooring it, it flushed out. Am I off base on this? Thanks!
Jeff

[jerry598]

Your knock could be injector lines touching each other or touching the engine itself.