IP input leaking under load?

[745 turbogreasel]

Long story short, helping a guy swap a D24TIC into an 83 LT28,  got it in and running, and I have an issue  I haven't run into before.
Teast ran the motor  before install, and it leaked out the pump input,  so I put a new seal in.
We've had some issue with  air suction upstream of the fuel filter, and blew a couple IC  hoses off, so  we were driving around with the  engine cover off , watching stuff   happen. 
Over 4000 RPM or so, it  starts  to pull air.
Turning on the 4PSI  electric lift pump stops the bubbles, but 3-5 seconds later fuel will leak out the input and sling off the pulley.
Lower speed, or  not running the lift  pump, it stops leaking.
Removing the lift pump, we still get air from something in the filtration setup.
I'm  confident of  fixing the air going through the filter,  they are new,  there are 2, with  a kind of inordinate number of lines/clamps ,etc.

Why does the new seal only leak at speed?

Anyway, here is what a  D24TIC looks like in  an LT

[fatmobile]

Air in the fuel isn't usually caused by a leak.
 High vacuum caused by a fuel line restriction will pull suspended air from the fuel, making small bubbles expand and appear.
Put a vacuum gauge on the fuel line. Some boost gauges read vacuum and pressure, since you have an auxiliary pump that might work best.

 Do you  have an "OUT" bolt in the output of the pump? Probably, because you'd see more air in the fuel without it.
 Normal input banjo bolt?

Clear fuel line coming from the pump?

[745 turbogreasel]

Clear line in and out, as well as pre- filter.  pre filter is always  air free, and does not suck shut despite being weak temporary tube, probably  fine.
Out bolt is 'out' bolt, didn't check the  in, but I doubt it's an 'out', power is  good, it hauls a 6000 LB van up step mtn road at 45, vs  20 the NA motor did,  gear limited speed on the freeway.

The bubbles are not small.
Bubbles show up between  filtration and pump inlet hose, Im pretty sure new rubber and full circle clamps should do it.

Only source of restriction is 2 brand new wix filters.  They have been on ~300 miles, and nothing has changed in that time.

The pump is definitely tampered,  free revs to at least 6K, and the  full fuel collar  was free floating.  must be from somewhere they inspect.  Strangely set for no smoke, and ~900 EGTs.

[fatmobile]

Air between the filter and pump usually means a clogged filter.
 Especially with no air in the filter before it.

If you think it's a leak where the hose joins the barb look for leaks there or move the hose around and see if it changes.
 A vacuum gauge on the fuel line will let you know for sure if the air bubbles are caused by a fuel line restriction you might be pulling 10"hg or more with bubbles like that.
 
 

[745 turbogreasel]

Most of it was sneaking in around a non  full circle hose clamp.
2 of the  hose  barbs on banjo fittings are a little small, I'm going to pick up  some different ones.
Air is 95% cured at this point, but the  leaking is  still a big

[92EcoDiesel Jetta]

Did you try plugging the return to tank port and Mityvac the input port, also plugging the input port and Mitybac the return to tank port? It should hold vacuum in both cases. If they don't, you still have a leak somewhere in the IP.

[745 turbogreasel]

A good test, but with the engine between the seats, it is real easy to see  bubbles in the clear lines on both ends of the pump.
Also,  the problem only occurs  at 4500 - 5000 RPM.
Its surprising how much  different it sounds with ear plugs, things like defuel  on engine braking  are very clear.

[92EcoDiesel Jetta]

"ran the motor  before install, and it leaked out the pump input,  so I put a new seal in."

Was that the input shaft seal? Was the mating surfaces clean with no gouges? Did you put grease on the lips? That seal see vacuum. Higher the rpm higher the vacuum. Could that seal be leaking?

[745 turbogreasel]

yes, yes, and it only leaks if I run the lift pump and  high RPM (leaks out, not in.)