Vacuum readings through your fuel system

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Jordan
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Location: Olympia, Washington

Vacuum readings through your fuel system

Post by Jordan »

Hi I was wondering what kind of vacuum those of you with a vacuum gauge are pulling. In the mornings at like 30 degrees Fahrenheit or so on cold diesel I'm pulling a solid 10 or so at idle and I wanted to see how high I could get it the other day and I got it up to 18 giving it quite a bit of the skinny pedal. Right when I switch to veggy when the engine is warmed up my vacuum goes right down to about 2psi max while my veggy oil temp gauge is still not reading over the 100 degree bottom reading on the gauge. I've even switched to veggy early a few times and still only 2 to maybe 4 psi depending on how much throttle. I have much larger fuel lines for my whole veggy system 3/8 aluminum od and 3/8 id clear rubber lines on my little N/A diesel 1.6. Diesel filter has maybe 5000 miles on it and haven't ran any bio through it at all.

I was thinking that I was pulling too much vacuum but my landlord just rebuilt his injection pump and he is also pulling 10 psi at idle on diesel with only about 1000 miles on his new diesel filter. With his old injection pump his vacuum gauge wouldn't move at all unless he had a restriction.

So what kind of vacuum are you all pulling at what temps? Thanks
Jordan
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Re: Vacuum readings through your fuel system

Post by Jordan »

Okay so its a blockage somewhere in my diesel system. It was pulling so much pressure that it was pulling wvo at startup and shut down somehow partially bypassing the pollack valve. I took out the valve and hooked it up to just diesel and it didn't want to run so I filled it with another 6 gallons of diesel thinking that it was just full of a mix of diesel and wvo and I got it to run but never was able to get it much below 20 psi of vacuum through diesel. Well unless I looped the return. I even threw my diesel line after the filter through my fphe to heat up the diesel/wvo mix to help it out and then tried warm the tank with the return but even though my fphe was getting it up to about 180 degrees it didn't seam to affect the vacuum so I just ran it for a while on the diesel tank and returned to my wvo tank. Switched out the lines to pull just from the wvo tank and I'm back down to 1 psi. Should start fine in the morning to get to work on the wvo and diesel mix I just hope that I have enough time to empty out my diesel tank and figure out where the blockage could be after work. Hope I didn't mess anything up driving around at 20psi of vacuum. Haha gotta love experimental fuels and old vehicles.
Fatmobile
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Re: Vacuum readings through your fuel system

Post by Fatmobile »

Hmmm, I wonder what kind of car you have.

Vacuum should be 0.
I worry at 5 and do something at 7,.. it will run at higher vacuum than that.
'91 Golf gasser converted to turbo diesel.
'83 Rabbit gasser, converted to diesel, then converted to run on vegetable oil.
2, '84 GTI projects cars
Jordan
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Re: Vacuum readings through your fuel system

Post by Jordan »

I'm running a vw rabbit truck with a 1.6 N/A diesel. My landlord has been running his rabbit truck for the last 3 years on wvo 2 tanks with a 1.6 diesel and has a freshly rebuilt injection pump. With his old injection pump he wouldn't pull any vacuum till he had a filter start to clog so maybe you have an older injection pump that isn't quite giving the performance that a fresh one does? Don't you have a vw as well? I thought thats what I remember but I could be wrong. Both my landlords and my rabbit trucks pull similar vacuum but my wvo setup has better flow than his and better heat too so I am pulling less vacuum on wvo than he is.

Before my diesel tank clogged I was pulling a pound or 2 or vacuum on diesel when it was warmer out and I pull a solid 1-2 psi of vacuum through my vegetable oil system which I just had drain to switch up to run diesel through it. Glad I have valves to turn off the coolant heat. I have a blockage in my diesel tank that I have to somehow get cleared. Dropped the tank tonight and it doesn't look too bad inside but the feed is definitely blocked. Now to just get this diesel tank flowing freely again.
Fatmobile
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Re: Vacuum readings through your fuel system

Post by Fatmobile »

I've had many VW diesels with vacuum gauges in them.
I started the idea back in 2000 when someone said you need a helper pump for vegy and found the pump pull no harder on vegy, when things are warmed up.

They all ride at 0 when lines, screen and filter are clear.
Except the messed-up gauge in my daily driver: it always reads high.
I have goten a few gauges that read wrong.

Sounds like you have a clogged intank screen,.. probably a little vegy made it's way to the diesel tank.
'91 Golf gasser converted to turbo diesel.
'83 Rabbit gasser, converted to diesel, then converted to run on vegetable oil.
2, '84 GTI projects cars
Jordan
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Location: Olympia, Washington

Re: Vacuum readings through your fuel system

Post by Jordan »

Interesting. Well maybe both my landlords and my vacuum gauges are inaccurate but I doubt that even though they are both the same cheap sunpro brand. Mine read vacuum on diesel even right when I first started it on diesel before ever running veggy oil. And now that I have my veggy system running just diesel I am still pulling 1 psi of vacuum. On warm veggy I pull about 2 if my memory serves me right.
I suppose it is a possibility that I could have gotten some veggy got in it with the pollack valves that I have been using to get this thing going. I have been really careful with my purging though to keep the fuels separate. I really want to upgrade now but am not sure which valves I want to get yet.
I figured it was a clogged intake pickup screen as well and am just planning on removing it. I have been trying to find a new fuel inlet hose for going between the tank and body though. I already threw away the factory one when I removed the tank as it had been leaking. I might end up having to use a piece of 3/8 stretched onto the tank and then on some 3/8" aluminum line that I have then shove 5/16 onto that to make it a nice fit on the fuel line up to the filter. Either that or I have a sight glass filter I might throw in that area so that I can monitor any sentiment that I might get out of the tank.

On a side note I picked up a 91 jetta eco diesel today. :D Its vacuum gauge reads the other way about 7psi of boost. Haha not much faster though.
VW cat
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Re: Vacuum readings through your fuel system

Post by VW cat »

I get concerned when I see about 5" on the gauge, 7" and it's definitely time to do something. Had my Rabbit truck up to 16" once, then it really started to slow down. Never have seen a vacuum gauge in psi. How many inches of mercury in one psi, is it about 2? Have to look that up.

I'm still using Pollacks. I believe that they can't have a pressurized inlet over 8 psi, if one is using an in-line pump, or they will shift. I just put a Carter P74021 pump near my heated filter on my Mercedes 617. One of many recommended on the Biodiesel forum, but this one only pumps up to 5.3psi. Working good and I have just left the vacuum gauge alone. When on veggie the pump comes on and my gauge goes back to 0. Now of 20 or so possible places for a dreaded vacuum leak(air) on veggie, not including all the injector return lines; I now have only 3. The Mercedes in-line injection pump is very intolerant of air. Phil
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