Fuel Pump Blues, take TWO.

[ainarssems]

The amount is measured at the return after pressure regulator so it is flow at full working pressure whatever it is on these engines 3.5 or 4 bar.

[graynada]

I replaced mine with a new VDO pump but I am struggling to think of a way to get the old one out if the captive bolt is no longer captive, beyond what ainarssems has suggested in putting some tension on it. Plan B would be a replacement tank from A8 Parts, salvage whatever you need from the pump housing by brute force from the old one, fit you new pump in there, but given the 'saddle' nature of the tank I can't imagine they are much fun to change

[Goran]

I dont know if this is a rubbish suggestion as I dont know how the bolt set up looks, but would it work if you cut the head of the bolt off then somehow push the remaining threaded part through?

[ainarssems]

Originally Posted by Goran

I dont know if this is a rubbish suggestion as I dont know how the bolt set up looks, but would it work if you cut the head of the bolt off then somehow push the remaining threaded part through?

Unfortunately no. It's a long bolt that goes through fuel delivery unit and you cannot just pull delivery unit straight up as it's very tight fit and it needs to be tilted and twisted several ways and times as you pull it out.

[adjuster]

The long bolt has tapers on it that don't allow it to be removed either.

The solution to removing the bolt, is to make a custom hole saw, that's about 12" long, using a 1.25" hole saw, and arbor, and a 10" steel black pipe. You drill out the hole saw where the arbor normally threads in, to clear the bolt, weld it to the pipe, and then weld the arbor to the pipe on the other end, making a 12" long hole saw.

Then you drill down around the bolt, all the way down to the siphon cup where it's bolted to the fuel pump housing. This of course, destroys the fuel pump housing, and most likely, the sealing surface, and siphon cup unit.

The siphon cup unit is not attached to the tank in any way, but is held in place by the hoses attached to it. (And it can move around, making it difficult to align the two when you put it back together, even if you make marks prior to taking it all apart, assuming your bolt comes out.)

You might have to cut the bolt off anyway, just to get the siphon cup out too.(The guy who came up with this long hole saw idea had to cut the bolt off to just a nub, so it would allow the siphon cup to be removed.)

Good news is the hoses attach with quick disconnects, so they just snap on and off, but bad news is they can just snap off, and if any hose is loose, the siphon pumps and cup will not work correctly, and you will run out of gas before the tank is empty.

The problem I've run into is the cost of all this.

The tank is not cheap, even used.
The fuel pump housing is not cheap either, used or new.
And nobody seems to have the siphon cup used. (Or even know what I'm talking about, but of course the dealer would love to sell me all this stuff new.)

For this sort of money, I can BUILD a custom fuel system using the stock tank, that uses two pumps if need be, one for the fuel siphon system, and the other for the supply to the injector rail, and keep the existing fuel pressure regulator to return fuel to the tank/siphon system/cup. Many years ago, I built a custom system with three pumps, on a road racing car, so it would supply fuel to a central cup, where the main fuel pump was located that supplied the engine. It worked excellent with zero fuel starvation problems common to just a single pump setup. I can see why Audi did this, both for fuel tank design, and it works well if the car is driven hard, as fuel sloshes around, and the siphon system would pick up fuel from any point in the tank at any given moment. (Even better than the electric pumps I used, they ran the risk of being damaged when run "dry" as the fuel moved around the tank.) The tank we used had foam "baffles" in it to try and limit fuel slosh, but still the fuel would move around quite a bit.

So here is my take after all of this:

I'm going to try the cheap and easy route, and put the in-line 255lph Walbro pump just after the stock fuel filter, and have it supply the fuel rail/injectors. What's left of the stock fuel pump seems to be working the siphon system just fine, and it works fine as long as I don't try and go over 70mph. (I just did a nearly 500 mile day at 82mph, and while the engine ran like crap at that speed, just putting the car in neutral, shutting it off, and starting it again as we exited to re-set the ECU and fire all the injectors again, and the engine was smooth as normal around the towns, but would drop injectors again as soon as speeds exceeded 70mph for more than a few seconds.)

If the stock pump FAILS at some point, the fuel tank will run empty as soon as the fuel pump cup falls below the fuel level. But to supply the fuel siphon system, I'm wondering if another smaller in-tank pump can be used, and hoooked up to the siphon supply line, and the pump placed in the left side tank somewhere? It's pretty tight down, there, but I can get a cheap Dodge Airtex pump that's pretty small, has it's own internal FPR, and intake sock, and just pull the fuel level sending unit, and use that access to hook up the hose that normally feeds the siphon system to the cheap small pump, and there you go. Two pumps, and all for about 150.00 USD complete. (And it should allow the system to work like stock again.)

As far as that goes, this idea would work fine if someone wanted to make their own custom two pump replacement setup for the stock pump. Use a Walbro pump with sock, and the cheaper Airtex pump with sock, turn them back to back, and fit them down where the stock pump used to reside. (And of course, you lose the stock fuel filter at the stock pump housing, but you KEEP the fuel cup design that's fed by the siphon cup fixture.) The Walbro feeds the fuel line to the engine, and the Airtex feeds the line that plugs into the siphon cup system.

Should run forever, and I'd think the existing power supply would handle the load of the two pumps just fine too.

For Toyota Supra's, we used to replace the stock pump with twin Walbro's on the over 650rwhp cars, and run them both on stock power supplies just fine. But even hooking up a seperate power supply, and use the stock one to just switch a relay would be no problem, especially since the battery is in the trunk. (Fuse, relay and some wires, and it's done.)

I don't want to spend 1500.00 on fuel pump/tank when I can spend 150.00.

I've got the less than 100.00 USD, all metal Walbro external pump on the way, and I'll install it just after the stock fuel filter this next week.

If it solves my random multiple misfire problem, I'll then have a stock VDO/Siemens pump for sale at the same price I paid for it, or I'll try and return it, since It's only been out of the box, and never used.

Greg

[Nollywood]

This will be an interesting set-up, one never knows when fuel pump failure is around the corner.

[adjuster]

Yep, I'm starting to wonder if adding an in-line fuel pump to the fuel system with the change out of a new fuel filter is not great insurance for anyone with a D2.

It should relieve the stock pump of most of it's job, and allow it to live a nice peaceful, and LONG life in the stock housing, just supplying fuel to the siphon system, and to the Walbro pump that's not only cheap, but most likely rated at a higher flow capacity as well. (No problem, as noted, any excess fuel just goes back past the pressure regulator, and into the stock fuel pump cup/assy in the tank.)

I will be thrilled if this adds a few more years of life to my ailing stock pump in it's never to be taken out alive housing... LOL

[adjuster]

Update: Have had the In Line Walbro, 255lph pump on the car for the better part of a week now, and it's running great around town.

1) The low speed engine performance is better. It used to "hesitate" and "ping" when I got on the gas off the line, not it does not do this at all, and the engine sounds, and pulls much stronger than it did before.

2) I can drive at highway speeds without the flashing CEL light, but ONLY if I don't use the cruise control? This has me confused, as clearly the engine is getting enough fuel from this setup, it's running great, but I have not cleared the codes yet, and wonder if that's resulting in the random misfire CEL flashing? (Or if that's what's making it flash, it does still drop injectors, so I'm guessing it is.)

So, crazy thing is I have plenty of fuel at the injectors/rail, but the engine ECU still sees a problem.

Any ideas?

I've been wondering if swapping out to another ECU would be possible. I know that the unit has to be coded to this vehicle, so it's not as easy as just unplugging one, and plugging in another.

But beyond that, I can't figure this out.

Plenty of fuel.
Injectors cleaned.
New fuel filter.

Still get the random misfire when the cruise control is used, and my fuel economy goes from about 20mpg to 16mpg as the engine runs like crap at 83mph.... But if I feather the gas, and slowing speed up, and down every few seconds, the CEL never flashes, and I can go as fast as I want....

ARGH! Love this car, but this fault issue is driving me nuts.

[ainarssems]

What are the fault codes?

[graynada]

Something restricting the air flow maybe?