Air in Injector Return Lines

[DieselScout]

I installed clear tubing on my injector return lines the other day.
All lines have lots of foaming/bubbles going back to the "out" port on the injection pump. Is this normal?

The car drives fine but it feels a bit sluggish and seems to require more "fuel" via the fuel enrichment screw to feel normal/peppy than I would think it needs, being a new engine. (My other, non-rebuilt engine requires less fuel and still feels peppy, even though that's an automatic) Currently, I'm about a quarter of a turn or less from maxing it out against the collar on the screw.

Doesn't really smoke when driving, but does blow some white-ish smoke on acceleration (not terribly visible if at all during day, but visible during night driving with another car's headlights behind) If I set the fuel screw low-enough so that I see no smoke at night, the car is uncomfortably slow on acceleration

Car takes about a second or two longer to start on a cold Morning than my other, non-rebuilt D24 (the older engine fires right up) and has some white smoke at cold idle (after cold start disengages, that is.......there is no smoke when the cold stat is engaged) that goes away after driving for a bit.

It has a loppy idle between 800 and 900rpm.

There is an inconsistent stutter (sometimes it's there, sometimes it not) on acceleration in low gears. I've rebuilt a few injector sets, all having some effect on this to a degree, but never getting rid of it entirely.

No air in the clear line from the fuel filter to the injection pump.
Mostly clear (some bubbles every now and then) from pump "out" to the tank (I spliced in a clear line for about the first foot)

I've checked the copper rings between the banjo bolts and inspected for fuel leaks. All appear to be stable

Fuel and air filters replaced.
Engine is 1mm overbore.
Pump timing set to .93mm.
I believe the head has 32mm pre-chambers
Injection Pump was rebuilt and calibrated last year.

Injectors are freshly rebuilt (DN0SD193 style) and set to 2000psi.
Engine is freshly rebuilt with compression averaging 480psi. (Lowest 460, Highest 520)

Some minor blow-by coming from the oil cap/dipstick (not sure what's normal for a rebuilt engine); I think oil consumption is about 1 quart every 2,600 miles, but need more time to verify that metric.

Thoughts on where/how I should start to investigate, or is all of this normal/acceptable?

Again, the car drives fine for all intents and purposes, but I just want to make sure it's 100% before I take this on a cross country trip to the higher elevations of Montana/Wyoming.

[ngoma]

Originally Posted by DieselScout

I installed clear tubing on my injector return lines the other day.
All lines have lots of foaming/bubbles going back to the "out" port on the injection pump. Is this normal?

It is normal for a few persistent bubbles to remain at the tops of the return tube arcs. Constantly forming small bubbles not so much. Where is that coming from?

The main problem with leaks in the fuel return tubing is that when the car is parked pointing uphill overnight, air can enter at a high point and allow fuel to drain out the IP back into the tank. Results in hard starting when the IP is full of air. I have had this problem with a leaky end cap on the #1 injector spill port and another time with a leaky fuel return tube at the IP out port.

A good troubleshooting method for you would be to splice in a low pressure (3-5 PSI) fuel pump before the fuel filter inlet. See if this changes your issues.

Originally Posted by DieselScout

I've rebuilt a few injector sets, all having some effect on this to a degree, but never getting rid of it entirely.

How close did you get them? Did you ensure no drips/moisture at the nozzle pintle when held for 10 seconds at just under POP?

Originally Posted by DieselScout

I've checked the copper rings between the banjo bolts and inspected for fuel leaks. All appear to be stable

Air can enter much easier than fuel can leak out.

Originally Posted by DieselScout

Injectors are freshly rebuilt (DN0SD193 style) and set to 2000psi.

Not familiar with that style.

Originally Posted by DieselScout

I think oil consumption is about 1 quart every 2,600 miles, but need more time to verify that metric.

Most excellent!

Originally Posted by DieselScout

Again, the car drives fine for all intents and purposes, but I just want to make sure it's 100% before I take this on a cross country trip to the higher elevations of Montana/Wyoming.

Take extra fuel filters and make sure your cooling system is in top condition. Hill climbing at high altitudes will stress it to the max. No cheating allowed there.