fuel pressure adjustment

herr_sparky · Post by **herr_sparky** » Sun Feb 22, 2009 11:29 am

i'm going to need to check/adjust my fuel pressure once i'm through replacing hose, any suggestions for a good tool? i see a very wide range of prices and styles, what do some of you use? any good low-pressure gauges out there?

raygreenwood · Post by **raygreenwood** » Sun Feb 22, 2009 1:01 pm

A couple of things. Personally, I have a very high quality gauge I use for tuning. It reads in 0.5 psi encrements and is accurate full scale. Its very nesessary for tuning on a fixed pressure system...because the system has no way of monitoring pressure...and makes its fuel decisions based around a "design" pressure. It assumes you have this pressure. A variance of 1 psi is 2.8% of your total fuel mixture.
I got into this frame of mind when over teh years...I discovered how much fluctuation D-jet fuel pressure has. New pumps have small issues, but as they age it gets stupid. It greatly decreases you ability to tune with mixtures that are optimum for power and throttle response.

All of that being said, if you are just setting basic range...a decent water pressure gauge in the 40 psi range with 1 psi grads will do fine. Go to any home improvement store and get one with a 1/4 NPT outlet, a 1/4 brass barbs, some teflon tape, three feet of fuel injecteion line and two clamps. You will then have a gauge good enough to make sure you set it at least to with in 1-2 psi of correct....and you can see what fluctuations you have.

Trust me.....once you get a good gauge...and see how much flucuation you have...the first thing you will do is install a feeder pump. That usually gets rid of 98% of fluctuations. Ray

herr_sparky · Post by **herr_sparky** » Sun Feb 22, 2009 2:29 pm

thanks, thats exactly the information i was looking for. i wouldnt be too surprised if my pump fluctuates, i've had issues with it in the past.

when you say "feeder pump" do you mean an entirely different unit or something to supplement? also, isnt the in-line damper supposed to iron out major pressure changes?

raygreenwood · Post by **raygreenwood** » Mon Feb 23, 2009 7:22 am

Something low pressure and high volume..similar to a feeder pump from a 90 model cabrio or gold for digifant. You can use a digifant style filter as an accumulator right out of the tank. This would take the place of your existing filter...or you can keep them both.

This may be a good filter. I have to check out whether its regulated internally or not.... http://www.shoptalkforums.com/viewtopic.php?t=123809

Like this:

Tank main feed-----(Filter center inlet)-------(feed pump)-----(main pump)
(filter inlet side goes to right "Y" fitting))
^
^
(Y fitting)------------(from return to left side "Y" fitting)
^
^
Tank return feed----^(Center prong on "Y")

Make sense? Ray

wshawn · Post by **wshawn** » Wed Apr 08, 2009 3:34 am

Can I just clarify a couple of things about the digifant fuel pumps please.

If used as a feeder pump do you power both pumps or just this one?

and would the Mk2 Golf GTi be a suitable source for such a pump?

The reason I'm asking is the replacement pump I had to source quickly last year has started to leak slightly and will need changing/overhauling soon to keep my D jet running.

raygreenwood · Post by **raygreenwood** » Wed Apr 08, 2009 7:56 am

In digifant, both pumps are powered. Since you won't be running an in tank pump for the feeder like digifant does, you should probably get a small high volume inline pump to fill a larger fuel filter right before the digifant main pump.

You could also use some of the intank digifant pumps externally as long as you can hook up a hose where the strainer used to go.
Check out walbro's website. There are a decent amount of inline external pumps that should do well.
Also...as others noted, you can use a high volume in-line pump from sonething liek a ford V-8 van...for pretty cheap. Ray