How much vac on IP lines????

[derekp]

I did the vacuum gauge thing on the line from filter to IP. In addition to lots of air in line, I found a 5 inch vac. Traced this back to the inline checkvalve thats after the water separator. I removed it (for now, I believe its an anti drainback device myself so I'll put a new one in and vac check again) Removal of this valve dropped from 5 inch to under 1 inch vac, still a little bubbling in lines but tremendously reduced

In the process of eliminating the air problems, I temporarily disconnected and plugged the return line from the injectors, plugging it at the banjo on the IP - no change so the soft returns are ok.
I also replaced the "OUT" bolt with a new one, it was too hard to tell if that was restricted or not. Again no change.

Changing my fuel filter eliminated all air in lines. Strange as it was only 6 months old and I use conventional diesel fuel. Cutting the filter open I do see a little dirt in the element (unravel one of those sometime!) but not enough that I would consider the filter to be clogged.

My quesitions...
I still have about 1/2 inch vacuum - but no air - is this typical?

Are there alternative fuel filters than the bosch paper filter? 6 months on a fuel filter becoming restricted to the point of causing a vac is pretty bad by my thinking  (I have the so-called heated filter) Are there any cleanable mesh filters that might not offer the restrictions that a paper element does?

The power is up on the car - its smoother running - still too early to tell if my SMILAGE is back up to snuff or not after the  injector overhauls that led to discovering air bubbles and the timing woes encountered.

Thanks again to all who replied to my other posts about injector and timing questions its been a tremendous help!

[jtanguay]

you could get yourself one of those little facet fuel pumps to feed the pump... there will always be vacuum on the inlet due to the injection pump sucking the fuel.

you might as well just completely remove the water separator... that might help a bit too.

[Vincent Waldon]

The line is under suction... that's how fuel is drawn from the tank... so I would always expect vacuum... and 1 inch "sounds"reasonable to me.  For starters, the fuel has to be lifted out of the tank and that will account for some.

One thought:  track down Fatmobile over at www.vwdieselparts.net... he runs vacuum gauges full time on his various cars and can probably speak definitively about what "normal" looks like.

[autoholic]

1" is extremely low, you can run up to 10" just fine. Is that 1" at idle or under heavy load?

[derekp]

It was 5 inch at idle with loads of air (check valve back by water sep was sticking) now its under 1/2 inch at idle (removed valve) and no air

[smutts]

Are these inches of mercury? :?

[derekp]

Sorry, I still think in terms of non-metric units by default.
Its now down under 1/2 inch with no air bubbles.

[fatmobile]

Yeah a fuel pressure gauge is a great help when trying to figure out what is wrong,... or what isn't wrong.
 Mine usually run at 0" hg,..
sometimes gauges can be off by 1/2" so you might be running at 0 too.
 I get concerned at 5 and do something if it hits 7,...
 I've had it at 10 without noticing a big problem with how the engine runs; on it's way to the parts store for a new fuel filter.