Author Topic: easy way to reduce line pressure when dieselizing a gas car (Read 5305 times)

Dr. Diesel · « **on:** February 14, 2008, 11:02:54 pm »

Almost finished this diesel syncro passat project. (using the word 'finish' very loosely. Everything of mine seems to continually evolve!)
I kept the digifant system's in-tank fuel pump to act as a lift pump. Needless to say, the line pressure was very high. The local speed-ripoff-shop wanted $160 for an adjustable pressure regulator with the capabilities I needed.
Not.
So I made this little device.

The top is straight through, from the fuel pump to the filter.
The middle connecting pipe is filled in with solder.
The bottom comes from the pump return (left) and mates with the OE return line that used to attach to the gas engine's fuel pressure regulator.
When making such a unit, drill a very small bypass hole (1/16" is a good starting point) through the solder-filled connector and incrementally increase it's size until you reach the line pressure you want. This setup on mine holds a steady 3psi to the injection pump inlet at idle, and 7 psi when stopped.
Here's the installation:

This is on my syncro passat, which officially runs as of last night. It's been a drawn-out project, and I'm really looking forward to driving it. Should be in the next couple days. I've pretty well wrapped up the finicky little details, (including the unexpected need for a custom rad support! :roll: ) and now just need finish some basic reassembly steps. I'll probably put up a post with more details on it later.

burn_your_money · « **Reply #1 on:** February 14, 2008, 11:06:48 pm »

Right on, I was just thinking about doing a conversion (gas to diesel) but I don't think the gasser has a lift pump

Dr. Diesel · « **Reply #2 on:** February 14, 2008, 11:55:23 pm »

I meant if you want to use the gasser's fuel injection pressure pump AS a lift pump. Hence, the need to drastically reduce the pressure. In my application, the in-tank pump appears to be the actual pressure pump. (unless there's a second pump hidden between the tank and body that can't be seen without removing the tank.) Makes sense, why have two pumps?

burn_your_money · « **Reply #3 on:** February 15, 2008, 12:00:37 am »

yes sorry. I meant the car that I would be using does not have a lift pump. The lift pump on a gasser puts out about 30 PSI right?

somolovitch3 · « **Reply #4 on:** February 15, 2008, 05:30:16 am »

IIRC... the lift pump (in gas tank) puts out about 5 to 7 psi. The fuel pump (under car) puts out some 90 psi.

Neet little device there Dr. D.

Just what you ordered, no? :twisted:

the caveman · « **Reply #5 on:** February 15, 2008, 05:55:03 am »

why even bother with the lift pump at all. unless you want a *** load of power, and even then...

jimfoo · « **Reply #6 on:** February 15, 2008, 07:03:02 am »

Quote from: "the caveman"

why even bother with the lift pump at all. unless you want a *** load of power, and even then...

Easy priming any time you work on the fuel system, reduces the chance of air leaks and lets you find leaks easier as they are probably under pressure as opposed to suction.

burn_your_money · « **Reply #7 on:** February 15, 2008, 08:31:03 am »

It also reduces the amount of air in the lines, which is good for the pump. Air kills pumps

KTZed · « **Reply #8 on:** February 15, 2008, 10:50:24 am »

What about building a ball and spring type bypass similar to a boost controller. That way it would be adjustable and would maintain a constant supply pressure.
How would this tie in to the pump internal pressure mods everyone seems to be talking about lately?

fatmobile · « **Reply #9 on:** February 15, 2008, 09:53:11 pm »

I'm not sure about a syncro passat. Was there another pump under the car that you removed?
What kind of pressure were you getting with the tank transfer pump?
I was thinking about putting one back in the '91 gasser to diesel conversion and have been wanting to know how much PSI it puts out, this post might come in handy soon.

Turbinepowered · « **Reply #10 on:** February 16, 2008, 07:19:09 am »

Quote from: "libbybapa"

If it is supplying only a few psi at the pump it won't have a significant effect on internal pressure. It would if it were a high pressure pump and didn't have the bleed back to the return. Very nice setup. I think the ball and spring idea is also a good one. I was thinking that a simple needle valve between the two sides would work as well and make it easily adjustable with regards to pressure. Looks good, thanks for the post.

I like that needle valve idea. I'll have to remember that when it comes time to Diesel the Fox (CIS-E, in-tank low-pressure pump + external high pressure pump).

blkboostedtruck · « **Reply #11 on:** February 16, 2008, 08:17:39 am »

how about those dial fuel regulators that they used on old bugs when you switched to electric fuel pump ? made by FILT-O-REG ! I have one here from my old air-cooled days it adjust from 1psi to 5psi! do you guys remember those?
thanks Duane

Dr. Diesel · « **Reply #12 on:** February 19, 2008, 05:08:31 am »

Like I said, It appears the in-tank pump is the actual pressure pump. This is the simplest setup I could think of. Like many things, you can get pretty fancy if ya want. This setup serves my purpose perfectly, as did the less than $15 price!

lord_verminaard · « **Reply #13 on:** February 19, 2008, 09:01:43 am »

Quote from: "blkboostedtruck"

how about those dial fuel regulators that they used on old bugs when you switched to electric fuel pump ? made by FILT-O-REG ! I have one here from my old air-cooled days it adjust from 1psi to 5psi! do you guys remember those?
thanks Duane

I bet a CIS-fuel pump would probably blow one of those things to pieces!

I guess the question to ask is what kind of fuel system did it have while it was a gasser? If it was any variant of CIS, it could have had two pumps. The single-pump versions did not have a pump in-tank, just the primary pressure pump. Digifant cars had a single in-tank pump that was much less pressure, around 40 or so if I remember.

Brendan

RabbitJockey · « **Reply #14 on:** February 19, 2008, 05:05:50 pm »

yeah i believe most common rail injection cars run 30-60 psi