How to measure fuel flow on a 550?

Hi all,
I am trying to find out if my (new) pumps have enough flow, since the car is having driveability problems ( The electrical part of the diagnosis is already a 5 page post on the 550, no luck in finding the fault so far).

I can measure 55 psi pressure on the Schrader valve with the pumps directly fed on 12V, (engine off) but I want to know if the flow is enough .My pumps give 1.5 litre (each) in 30 seconds from the supply line directly, so that sounds good.
But: according to the WSM, the technique should be connecting to the return line, and the amount of fuel should be at least 1 litre (30 seconds).
But when I connect to the return line, I get 0.15 litre in 30 seconds, so only 10%, far off from that 1 litre.
Which is logical I think, as the return line means that only the pressure above the limit of the Fuel Pressure Regulator (=55psi) is used for measuring, limiting the flow enormously,
So is the WSM correct in saying the "overpressure" should flow 1 litre in 30 seconds, or is that a mistake in the WSM and are my pumps ok with 1.5 liter flow (each) directly?

Pumps (and rubber parts etc) have been purchased new by the garage from which I bought the car, so no clogging, but maybe they do not supply enough flow after all, wrong type?
Last time I opened the tank I forgot to look at the Bosch part numbers...so are there Bosch pumps that are not correct ? (I know of the check valve in the pump outlet, but I mean flow/capacity-wise)

Other question, does anybody know the spray pattern on the fuel injectors?

 

The occuring issue is that the car often has no power and it feels like one bank temporarily has shut down when you try to accelerate.
If I then shift up a gear (not down), I get normal acceleration for like 1000 -1500 rpm higher, until the car stumbles again, so for me it also felt like fuel.
(pressure building up again while shifting, then starting with a low fuel need at low rpm, so it works ok for a short period of time until the demands are higher again at higher rpm)

But as the pressure is a nice 55 psi on the schrader valve, and everything is new (pumps, rubber collars, hoses, filters) AND my MAF values are low, we started looking at the electrical side of the problem (and found a strange resistance on the MAF connector to ECU, but so far no reason for it has been unearthed, nor is it clear if it really is the problem. Qavion is helping me a lot in showing me what to test and how, but we have reached the end of the resistance and voltage measuring possibilities. So back to fuel pressure...

I bought the car with the condition that the selling garage would solve the broken fuel pumps the car had, after being in their private collection for 4 years.
But they took 10 weeks for that, and in the end I had to show them where to find the parts. Later it turned out they did not even buy it at Superformance, but somewhere cheap in Italy. When it then still took longer than the end date of our sale agreement, I wanted to get out of the deal, but the garage threatened me saying they would let their attorney make a case of it. And in Dutch law they even might have had a plausible cause.

So I had to buy the car, and did not make a long test drive, as I wanted the whole thing come to an (happy) end and leave that garage as soon as possible.
On my way home I got a SDL after 5 minutes, but when I got home it turned out one of the internal fuel hoses disconnected itself from the right pump, so I fixed that (and they also "forgot" to install the return lines and the check valves from the pump covers to the pumps, also fixed that)

The car was more or less ok for around 50 km, when the hesitating started to occur more often. It might even have had that right after my repair, but at that time I still had the SDL to get rid of (by driving/letting ECU cycle) so I contributed stumbling to that. And in that 50km I was driving very carefully, mostly in the low and mid range, where an incompetent pump system might still cope.

So do I understand correctly that the pump "overpressure" above 55 psi should flow 1 litre in stead of the 0.15 I measured?
With everything new, what could cause that?
It is the same for both banks, so the problem is not likely a clogged line, but maybe the new pumps are the wrong spec?
There is a Youtube video of a garage that changed the pumps of a 550 for Kia pumps, so is it a possibility? If even a Kia pump works...
Before I (again) drain the tank and remove the pumps for inspection...

 

Ok, thanks. So it sounds like my new pumps are not to the correct specs.
Time to drain the tank again, open it up and check the numbers!

 

So I drained the tanks,at least the pumps were able to do that fast with the fuel lines not connected to the rails.
Removed the pump covers, removed the whole assembly out of the tank, and took it apart on my work bench.
????? No Bosch pump? An M & D cheap rip off /look-a-like pump!
So there is hope, as the correct pump should be the Bosch 0580453443 pump (old number 433 is no longer made it seems).
I downloaded the specs, that Bosch is a 5-8.5 bar pump , and it should still flow 130 liters at 3.8 bar.
And then indeed the WSM is totally right (130 liter divided by 120 half minutes = 1-1.3 liters in 30 seconds)
Needless to say the M & D pumps are in the bin and I placed the order for 2 original Bosch pumps.
Finally I have found something that for sure is not correct, so I have good hopes this is the problem I have been chasing for over 2 months now.
(I only hope the M&D pump is a 3 bar type, and while that is fine for most cars, it is not for a fuel guzzling 550, ergo problem identified. )

I should have noticed it earlier by the way, as I had it apart before. But why would anybody buy a cheap 30 euro rip off when the original is only 60 euro. So I assumed it was the right pump, but as we all know, assumptions are the mother of...etc etc

 

New Bosch pumps came in, and were an easy install since I had everything out already.
As suggested by Ferraridriver I also bought some convoluted/corrugated fuel lines in the UK (nowhere to be found on the European mainland...)
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Installed everything, and now one pump gives 650 ml in 30 seconds through the FPR.
5 times as much as before, which sounds very good, but still only half of what the WSM says it should give.
Could it be that the WSM means 1 - 1.3 liter for both pumps together? That should make sense in my case...

(The weather was too awfull to make a testdrive, everything is wet and muddy now...)

 

Ok, so the weather is still cold, and wet and muddy, but I was tired of waiting so I took the 550 out for a test drive with the new pumps.
And even if the output is less than the WSM says, the car was fine.
I had two scanners connected, so I could compare values, and on accelerating firmly, bot S1 O2 sensors indicated rich. So there is enough fuel available it seems.
WOT with 2 degrees C on a wet road with 10 year old tires in third gear is not something I wished to try, ASR came on on half a pedal already.
(I did not drive faster than "slightly' above the speed limit, so I do not know what happens at 300 km/h , but for the speeds I am driving the car, the pumps are working well.)