Ok so I have a strange problem with my truck I am not sure what is the cause. Right about half throttle the sound of the engine has a rythmic surge and it is in time with the fp gauge bouncing between 10 and 13 psi. It is pretty fast the needle will go up and down just a little faster than once a second. The sound is hard to describe kinda like wawawawawawawawawa out the exhaust and it is in sync with the fp gauge. I do not know if it is the fluctuating fp that is causing the engine to fluctuate or if the engine or the ve is causing the fp to fluctuate. You can't really feel it in the power but can hear it pretty good. If I step on it harder or ease out of the throttle a little it will go away. Could it be timing??? Sorry for the long post but there is no good way to describe the sound.

 

Could be you have a baby under the hood. My 7-month old daughter sounds a lot like that!
Seriously though, have you checked voltage to your FASS or whatever it is you're running? If for some reason voltage isn't constant, could it be surging the fp?
... but just thinking about it, that wouldn't cause fuel pressure at the injectors to change. Mmm....
Is your governor hunting? No, that's not the term is it. Hunting is erratic, not rhythmical. What's the other phrase? Dang, can't remember!

 

Bill, what kind of turbo are you running?

Is it surging at a given engine RPM and the fluctuating boost is goofing with the AFC hence the fuel pressure jumping around?

How much timing are you running?

 

Bill has a stock h1c turbo with a 12cm housing on it

 

The boost and egt gauges hold steady just the fp gauge is fluctuating. I have the fass hooked directly to the battery and can't really check its voltage when the problem occurs. It won't do it if I just free rev the motor it needs to be under a load to do it. I think it could be timing but I don't want to back it off anymore cause it helps control the haze at idle. The timing is maybe 1/4" over stock I pushed it to the head and the problem was way worse.

 

Mine will kind of do that at a certain rpm if i just rev up the motor slowly in neutral. I need to get my fuel pressure gauge fixed and a snubber to see what the fuel pressure is doing though. I think its timing because if i give it a little more throttle or let off then it will go away, and I have it advanced so I'm just thinking its the timing at a certain rpm, I guess I could get it to that point and flip my KSB on and see

 

I guess you have pods just like I do so I think its just timing with those injectors at a certain rpm

 

My pickup has done that ever since I got it(35,xxx miles). If I let off the pedal, but not all the way I get a slight almost like a loping noise. I have a different IP now than when I got and it still does it. I quit worrying after a month or so. I am kinda curious as to what's causing it though.