Fuel pumps
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DeathBus
- Posts: 1176
- Joined: Mon Sep 30, 2002 1:01 am
Fuel pumps
Anyone had to buy a stock fuel pump for a 412 with FI? What are your thoughts of quality and where you got it? I have a friend thats into 914's and he has plenty of spare pumps, but if I had to buy one I was just wondering what Luck everyone has had.
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raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
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vwbill
- Posts: 970
- Joined: Sat Feb 15, 2003 12:01 am
Is that the return Line?
Is that the return line issue? On my brothers T3 wagen it had a flat circular valve near the pump in the out line to the fuel rail which was stopping the fuel flow. What is that for? Is that a pressure valve?
So what controls the run time? Is there different pressure valving in the t3/t4 cis pumps or does the regulator do that in the return? bill
So what controls the run time? Is there different pressure valving in the t3/t4 cis pumps or does the regulator do that in the return? bill
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Longbeach412
- Posts: 308
- Joined: Thu Aug 19, 2004 6:34 am
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raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
A feeder pump is needed, depending on the type of fuel pump you are using. The D-jet pump....compared to "most" that came after it, is rather unique. It has large, tight roller cells, that actually manages a good bit of suction. L-jet pumps were just a bit less good on suction. Later L and LH jet pumps, digijet, digifant, CIS and almost anything made for anything...these days....have little suction abilities at all. They are pusher pumps.
The reason for the change? The D-jet pump was a rather precise, expensive and hard to manufacture part. As long as you don't get rust in it...they tended to last for ages though. They also were only moderate in volume...and probably just barely adequate in volume for their application and only capable of generating so much pressure with that volume without pulling too much load and overheating. Thats the next reason for fuel pump design changes. The pusher type, straight through linear pumps like L-jet and CIS, were designed to get high volume past the non-return heck valve. Thats how they make pressure. But like any pump or compressor, the higher the pressure on the top side of the chamber, the less the ability to draw volume. So....they need to operate from a semi-pressurized vessel in order to keep the high speed pump from cavitating. Almost every thing after L-jet runs a feeder pump.
In fact...i have found that bothe L and D jet also get large benefits from running a feeder pump. The fuel pressure in the ring main is more stable. This allows closer adjustment of any injection system, better throttle response etc.
The disc shaped metal chamber in all D and some L-jet...with the offset inlet and outlet tube...is a fuel accumulator. It has nothing inside of it. It simply allows an area to damp turbulence and allows an easier and larger volume from which the pump can draw. Without it....you get a lot more pulses from the pump as it draws. Ray
The reason for the change? The D-jet pump was a rather precise, expensive and hard to manufacture part. As long as you don't get rust in it...they tended to last for ages though. They also were only moderate in volume...and probably just barely adequate in volume for their application and only capable of generating so much pressure with that volume without pulling too much load and overheating. Thats the next reason for fuel pump design changes. The pusher type, straight through linear pumps like L-jet and CIS, were designed to get high volume past the non-return heck valve. Thats how they make pressure. But like any pump or compressor, the higher the pressure on the top side of the chamber, the less the ability to draw volume. So....they need to operate from a semi-pressurized vessel in order to keep the high speed pump from cavitating. Almost every thing after L-jet runs a feeder pump.
In fact...i have found that bothe L and D jet also get large benefits from running a feeder pump. The fuel pressure in the ring main is more stable. This allows closer adjustment of any injection system, better throttle response etc.
The disc shaped metal chamber in all D and some L-jet...with the offset inlet and outlet tube...is a fuel accumulator. It has nothing inside of it. It simply allows an area to damp turbulence and allows an easier and larger volume from which the pump can draw. Without it....you get a lot more pulses from the pump as it draws. Ray
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MGVWfan
- Posts: 825
- Joined: Fri Jun 11, 2004 9:23 pm
The T4's fuel tank placement and pump placement also aid in providing a positive head for the D-Jet pump. Most other vehicle designs wouldn't lend themselves to having a fuel pump 4-6 inches below the tank.
Any experience with retrofit feeder pumps on our T4s? Since an in-tank pump is most likely not practical, it'd most likely be external (like on the '84 MoPar 2.2L turbos).
Any experience with retrofit feeder pumps on our T4s? Since an in-tank pump is most likely not practical, it'd most likely be external (like on the '84 MoPar 2.2L turbos).
Lane
73 VW 412 (the Nomad, dropped valve seat land now, argh!)
67 MGB (Abingdon's Finest)
76 Plymouth Duster /6 (runs like a top)
99 New Beetle 2.0 (never gives any trouble)
04 Golf TDI (45 MPG)
09 JSW (love it, love it, love it!)
73 VW 412 (the Nomad, dropped valve seat land now, argh!)
67 MGB (Abingdon's Finest)
76 Plymouth Duster /6 (runs like a top)
99 New Beetle 2.0 (never gives any trouble)
04 Golf TDI (45 MPG)
09 JSW (love it, love it, love it!)
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raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
Yep...if you must use an in tank pump....go to the flaps store and ask for an AC delco pump from about a 1976-1980 starfire, Monza, skyhawk....and a hundred other cars that all used a two barrel holley carb. That is what my digifant injected rabbit uses as the in tank pump from the factory. Its a different brand...but identical in design. Its about 1-1/8" in diameter and about 3" long. It attaches to the fuel auge sending unit stalk. Or you can also use a less than high in spec D-jet pump (wjich will still last forever) to feed one or a pair of small digifant main pumps situated at the rear. This works superbly. Ray
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DeathBus
- Posts: 1176
- Joined: Mon Sep 30, 2002 1:01 am
Welp turns out all my friends pumps were crud!! I am at a crossroads, I am leaning to taking the FI off and going either 40mm KADS or 40IDF Webers. I really cant justify paying the amount for the pump, gas tank (which I am going to have to do anyway) and more than likely replacing most of the injection. Unfortunatly all my resources for known good OEM FI parts has pretty much been taken up by my 4 door, I am going to salvage what I can off the 2 door FI system to use to keep the 4 door FI alive (A FI system that works!). And run duals on the 2 door. I hate it, ripping FI off is just plain sick, but when you get to a certain point you just have to make decisions.
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Longbeach412
- Posts: 308
- Joined: Thu Aug 19, 2004 6:34 am
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raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
STOP!...Please do not get rid of your injection. This is really easy. I have a 5 gallon bucket full of pumps. I will be happy to send one to you...but it will be the end of the month before I can get to them.
But bear this in mind. There is nothing forcing you to use the D-jet pump. In fact...other than for originality sake...I reccommend getting away from them. They are just too expensive to replace. The only reason they have 3 connections, is that one has a spring loaded check valve to keep pressure even and help keep flow from being broken by loading up too fast. That goes right back to the tank return line with the "Y" fitting. If you used a two connection pump...like early L-jet, with only an inlet and outlet...it would run just fine. Simply remove the "y" in the return line and all will be well. Since pressure is pressure and volume is volume...any FI pump that provides the right pressure and volume will work. For instance...the digifant systems run with just slightly higher pressure...and the same volume. Yes, they generally run feeder pumps...but there is no law that says that cheesey feeder pump has to run inside the tank. It can be right outside, before either a digifant or L-jet pump.
Now.... 1 of 3 of my spare pumps have problems...like low volume, or weak relief valve. They were removed because they cause fuel pressure fluctuations due to lower volume. But...left in position in the front end....with their still good suction ability, they would be awesome feeder pumps for a digifant pump mounted in the rear about where the fuel line exits the body. They can be had by the pile from any Golf, Jetta etc...from the Junkyards. They are good pumps. This set-up will also make a weak D-jet pump last forever. In fact...it eases the load on both pumps. My personnal reccommentaion is a digifant pump on each rail at the rear on the forward side of the sheet metal outside the engine compartment. The coldstart valve can feed from one or the other...and be dead ended on one side...or you can swipe a single line cold start valve from a CIS or other car to use in its place....or with a pair of Y's...you can feed the cold start valve from both sides of the fuel ring for simple visual symmetry and balance sake. Use equal length fuel hoses from each pump to its injector pair. Then use equal length fuel hoses anda "y" to connect the downstream side of each injector rail together...right before the fuel regulator. This way they have identical fuel pressure regardless of volume. This is an outstanding set-up for reliability, fuel pressure stability, throttle response...and pump life. Ray
But bear this in mind. There is nothing forcing you to use the D-jet pump. In fact...other than for originality sake...I reccommend getting away from them. They are just too expensive to replace. The only reason they have 3 connections, is that one has a spring loaded check valve to keep pressure even and help keep flow from being broken by loading up too fast. That goes right back to the tank return line with the "Y" fitting. If you used a two connection pump...like early L-jet, with only an inlet and outlet...it would run just fine. Simply remove the "y" in the return line and all will be well. Since pressure is pressure and volume is volume...any FI pump that provides the right pressure and volume will work. For instance...the digifant systems run with just slightly higher pressure...and the same volume. Yes, they generally run feeder pumps...but there is no law that says that cheesey feeder pump has to run inside the tank. It can be right outside, before either a digifant or L-jet pump.
Now.... 1 of 3 of my spare pumps have problems...like low volume, or weak relief valve. They were removed because they cause fuel pressure fluctuations due to lower volume. But...left in position in the front end....with their still good suction ability, they would be awesome feeder pumps for a digifant pump mounted in the rear about where the fuel line exits the body. They can be had by the pile from any Golf, Jetta etc...from the Junkyards. They are good pumps. This set-up will also make a weak D-jet pump last forever. In fact...it eases the load on both pumps. My personnal reccommentaion is a digifant pump on each rail at the rear on the forward side of the sheet metal outside the engine compartment. The coldstart valve can feed from one or the other...and be dead ended on one side...or you can swipe a single line cold start valve from a CIS or other car to use in its place....or with a pair of Y's...you can feed the cold start valve from both sides of the fuel ring for simple visual symmetry and balance sake. Use equal length fuel hoses from each pump to its injector pair. Then use equal length fuel hoses anda "y" to connect the downstream side of each injector rail together...right before the fuel regulator. This way they have identical fuel pressure regardless of volume. This is an outstanding set-up for reliability, fuel pressure stability, throttle response...and pump life. Ray
Last edited by raygreenwood on Sat Feb 19, 2005 4:57 pm, edited 1 time in total.