GerritD

Dear fellow 928 enthusiasts,

I have a simple question regarding the correct high flow external fuel pump for my 928S of 1980. (Euro does not have an internal pump)
I can choose between :
Bosch type 0 580 254 053 , 5 Bar (72 Psi), 175l/h (1458cc/30sec)
Pierburg type 7.21659.70.0, 6.5 Bar (94 Psi), 110l/h (916cc/30sec)

I currently have a Pierburg type 7.21659.70.0 of about 8 years old, providing 1100cc/30sec
Porsche advices the Bosch type 0 580 254 053

But my question is :

My current measured system pressure is 5,1Bar (74Psi) while Porsche WSM says it needs to be between 5,2 ..5,8 bar (with flow 1120cc/30sec)
Thus pressure is a little bit too low.

But if I would buy the original Bosch, the flow will be OK but pressure will never reach 5,8 bar with a pump of 5bar, correct ?
If I would buy the Pierburg, the pressure will be sufficient, but flow will be too low.

So I am a bit lost here.

Already thanks to Allan (from France) to provide me a working WUR and helping me out ! Great guy !

kr
Gerrit

FredR

Gerrit,

I am not too familiar with how your fuel management system actually works but I presume your system is the type K jetronic thus why the required fuel pressure is higher than most 928 models so as to drive the fuel through the system however that is not too important.

The fuel pump you are proposing to purchase is a modern generic Bosch item that is rated for 175 LPH at a differential pressure of 5 barg. The pressure actually developed will increase at lower flow rates and as you can see from the flow rate data needed to support your system, the dynamic flow requirement will be considerably lower than the rated flow of this pump. For your general information, for pumps of this type, the head developed at rated conditions will typically increase to about 121% of rated pressure when the pump is shut in [i.e. zero flow] which in this case would be 6.05 barg or 84 psig. To understand the actual pressure developed one really needs the pump characteristic curve but I would think that this pump should develop sufficient head to drop it into the Porsche specified operating range you quoted.

GerritD

ROG100

PET is a little ambiguous on the fuel pump for a 1980 4.7L ROW S car. Shows a 911 608 102 00 or a 911 608 102 02. I sell the 911 608 102 00 for the 4.5L CIS cars 78 to 82 and the 928 608 102 02 for the 4.7L CIS cars.
So following that the correct pump for your car is Bosch 0580 254 4967/ 0580 254 053 which both super to Bosch 69 466.
Pierburg make good pumps but did not supply for the 928. I would stick with the Bosch pump that Porsche specified for your car.

GerritD

drooman

Be sure to check pump voltage "at the pump" using your meter on the + and - at the pump. Low voltage will impact delivery volume, less so on pressure. There are no less than 5 connections from the 30 voltage supply to the pump, each one will lose some voltage. but it only takes one bad one to lose a few volts. See the diagram, start at the top, current track 20. Also just as important is the ground signal.. the notorious voltage robber from any 40 year old 928. if I remember right this ground point lives in front of the passenger tail light, inside the car.. and it's a pain in the *** to service. It is common to see 8-9 volts at the pump with engine off, increasing when alternator kicks in. The volume test was developed with a new car, where "normal" voltage drop at pump was probably around 11.

This may not be your problem, but you have to eliminate it before you chase volume problems. Also... some cars have 2 pumps ,one up in the RR wheel well. Do you? Is it working? if so check voltage there too.

allan29

The fuel pump ground is here .

GerritD

I think I found the problem of my flow issue : apparently there is a very small filter inside the entry of the fuelpump. This filter was clogged with debri/filth



Nevertheless, I will replace my fuel pump with the original Bosch and also replace the big fuel filter behind the fuel pump.
Strange, I never encountered any info on the net about this tiny filter ...

drooman

SwedeInSiam

I have 0580254053 on my 80 RoW S and it give the correct flow and pressure. Flowed 1230cc/30sec with new fuel filter.

GregBBRD

Those specifications for the pumps are what pressure they will generate at the flow they quote. Either one of those pumps will literally "explode" (non fire explosion, but severe swelling and splitting of the weld) your fuel filter, if they are dead headed. (Try switching the "feed" and "return" lines at the front of the car, if you don't believe me.)

System pressure and fuel pressure at not the same.

System pressure is regulated by shims under the pressure relief valve in the fuel distributor. Fuel pressure is much higher....about 8.0 bar, as I recall. Once you install your new pump, set the system pressure by adding whatever shim/shims are needed, under the spring of the pressure relief valve.

FredR

Gerrit,

No engineer worth his salt puts a filter into a pump suction- what you see is [presumably] intended to be a "strainer'. Folks commonly assume they are one and the same thing but they are not. A pump is vulnerable to particulate matter that is about the size of the clearance between the impeller and the casing- such particles can and will get stuck within the void and then the pump will jam up. Large particles cannot get through and smaller particles will cause no damage to the pump. This is a very common occurrence on later models like mine when the rubber pipe on the in tank pump discharge fails and bits of crud get into the main pump. That you have a strainer on your main [external] pump inlet is a little surprising but then you have a non stock pump. If a pump has a partial blockage on the suction it will invariably cause cavitation within the pump and such condition can destroy a pump in no time.

The first thing you need to do is pull the in tank strainer to find out how that crud got through to the pump suction. Chances are the stock in-tank strainer has failed and there is crud in the bottom of your fuel tank that needs to be cleaned out.

The fuel "filter" on the pump discharge is essential to eliminate fine particulate matter that if allowed to pass would block the fuel injectors. For this reason the filters have quite a sizable area of filter media so that they do not materially affect delivery pressure by blocking up every two minutes and thus why they need changing from time to time. They are always mounted on the fuel pump discharge.

The fuel filter has to withstand any pressure the pump can generate and I noted with interest Greg's comment that the fuel distributor in this particular mode specific system has a safety valve set around 8 barg. This is a recognised method of protecting the system if a dead head condition can generate a pressure that would cause any element of the system to fail. This is a common feature on systems that use positive displacement pumps which as far as I know is not the case with a 928 fuel pump. Nonetheless any system with such a protective device in them should ideally be tested from time to time to prove correct functionality at the specified set pressure for obvious safety reasons.

GerritD

I have another problem when installing my fuelpump. I cannot seal the leak with banjo and fuelpump. I used several copper shims but none of them sealed properly.
Any idea how to seal properly ?

GerritD

drooman

be sure to tighten the check valve onto the pump first... you need to grind down the outside edges of a good quality 17mm open end wrench so it fits between the pump electrical connectors and counter-holds the pump when you tighten the check valve. Needs to be tight to allow the copper seals to work. You also need another seal ring between the banjo pipe and the end cap. Then you need to counter-hold the check valve to tighten the end cap. Doing this in the wrong order allows leaks.

Regarding the garbage in your fuel pump inlet. You can inspect the bottom of your tank from the top.. but the view is limited. There's a baffle in the way. The fuel supply from the tank must be crystal clean (it is currently not) or you will be fighting it forever. If you find crud in the system, plan on cleaning everything out at the same time. You can clean your tank, but if a distant 40 year old hose in the return system is crumbling apart from within you just introduce crap into the tank. The fuel supply must be crystal clean all the way to the fuel distributor, through the injection system, and all the way back into the tank. the fuel circulates round and round over and over as the injection system uses it. Every section of rubber hose in the system is a suspect of crumbling apart from the inside. . CIS has no tolerance for dirt. The entire path should be checked , in this order :

Tank (can have dirt in it)
In tank strainer (holes in it or clogged)
tank to pump hose (interior crumbling)
Pump (gets junk in it from above list)
Filter (gets junk in it from above list)
pipe/ hose to accumulator (interior crumbling)
accumulator (junk from above list)
Accumulator to long supply pipe hose (interior crumbling)
Supply hose near passenger cam box (interior crumbling, sometimes burns car down too)
Injection system (usually will not "produce" contaminants)
Return hose near passenger cam box (interior crumbling, again, can burn car down)
Return hose going into top of tank (interior crumbling)

I'm to the point where if i see crap in the tank, I clean out the system and replace the filter and every rubber hose, minimum. Then i circulate the fuel with the return line going through a paint strainer and into a clear glass bottle. That return line does not go back into that tank until it runs crystal clean.