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The S pipe between pump and filter accepts the same banjo bolt and fittings you use at the WUR, so it's an easy place to test for pump discharge pressure with nothing in between. It's a convenient place to put a gauge for pressure comparison with what you see under the hood during the WSM test.
The two-pumps setup expects some of the pressure from the in-tank pump. Generally, the main pump for single-pump cars has different capabilities than the one for two-pump cars. Pumps are rated for flow at a specific "total pump head", which is the difference between the pressure at the suction and at the outlet. In the two-pump cars, some of that capability is in the in-tank pump. If you eliminate that pump, the main pump needs to have the whole capacity. Double-check the main pump you have installed, and verify that it's correct for a single-pump car. There may be differences between the pumps for the non-S cars and your 300HP S car too.
The S pipe between pump and filter accepts the same banjo bolt and fittings you use at the WUR, so it's an easy place to test for pump discharge pressure with nothing in between. It's a convenient place to put a gauge for pressure comparison with what you see under the hood during the WSM test.
The two-pumps setup expects some of the pressure from the in-tank pump. Generally, the main pump for single-pump cars has different capabilities than the one for two-pump cars. Pumps are rated for flow at a specific "total pump head", which is the difference between the pressure at the suction and at the outlet. In the two-pump cars, some of that capability is in the in-tank pump. If you eliminate that pump, the main pump needs to have the whole capacity. Double-check the main pump you have installed, and verify that it's correct for a single-pump car. There may be differences between the pumps for the non-S cars and your 300HP S car too.
OK thanks. So I can put the pump directly at the inlet of my FD and check the pressure. And same pressure test to be done at the back at the tank.
As for the 2 pumps, the intank pump only serves for raising pressure in very hot climates...and pressure is only raised for about 0.3 - 0.4 bar.
Moreover, my Bosch pump is strong enough to deliver the amount of fuel needed. Specs are 228L /h @ 5bar, while according to WSM I will need 1120cc/30sec for 1 pump system , or 2,24L /min, or 135L /h. So pump is delivering twice the amount needed.
I could perhaps test my pump's flow via a hose by mounting a gauge and tap at the end of the line and closing the tap a bit so that pressure is built up till 5 bar and check my flow at the same time.
I thought I was reading that you are not able to get both the required flow and system pressure to happen at the same time. Was I not reading that correctly? My suggestions for diagnosing are based on that symptom.
The fuel pressure regulator controls system pressure by relieving a certain amount of pump flow back to the tank. The capability of the regulator itself determines how much it can bypass to the tank at target system pressure, and the sealing capability is a big part of its ability to retain pressure after the pump stops. There's interaction between the regulator and the pump, since the amount to fuel bypassed is the fraction that's beyond the pump's capability curve at target system pressure. That curve has flow on one axis and pressure on the other, and the two are inversely related. More pump backpressure equals less flow. More flow only when pump backpressure is lower. The regulator determines system and therefore pump discharge pressure, by bypassing fuel flow until the flow and pressure at the pump allow it to deliver the correct system pressure. With the engine stopped and no flow to the injectors, all pump flow is diverted to the tank by the fuel pressure regulator while maintaining the target system pressure. The amount of flow available at that condition is a product of the pump and any flow restrictions that might raise the outlet pressure at the pump and push the flow back up the capability curve.
Pump "capability" in your case seems to be the issue, but that can only be confirmed by testing to see if there's any significant restriction in the system between the pump and the pressure regulator. That restriction would cause the pump outlet pressure to be higher than the system pressure measured at the FPR and WUR. Restriction raises the pump outlet pressure and reduces available flow. If there's not much difference between pump outlet pressure and system pressure, the symptom is not related to a flow restriction, and the focus moves back to the pump itself, low voltage being delivered to the pump, etc.. For some reason the pump is underperforming, and the focus moves to that area.
I thought I was reading that you are not able to get both the required flow and system pressure to happen at the same time. Was I not reading that correctly? My suggestions for diagnosing are based on that symptom.
The fuel pressure regulator controls system pressure by relieving a certain amount of pump flow back to the tank. The capability of the regulator itself determines how much it can bypass to the tank at target system pressure, and the sealing capability is a big part of its ability to retain pressure after the pump stops. There's interaction between the regulator and the pump, since the amount to fuel bypassed is the fraction that's beyond the pump's capability curve at target system pressure. That curve has flow on one axis and pressure on the other, and the two are inversely related. More pump backpressure equals less flow. More flow only when pump backpressure is lower. The regulator determines system and therefore pump discharge pressure, by bypassing fuel flow until the flow and pressure at the pump allow it to deliver the correct system pressure. With the engine stopped and no flow to the injectors, all pump flow is diverted to the tank by the fuel pressure regulator while maintaining the target system pressure. The amount of flow available at that condition is a product of the pump and any flow restrictions that might raise the outlet pressure at the pump and push the flow back up the capability curve.
Pump "capability" in your case seems to be the issue, but that can only be confirmed by testing to see if there's any significant restriction in the system between the pump and the pressure regulator. That restriction would cause the pump outlet pressure to be higher than the system pressure measured at the FPR and WUR. Restriction raises the pump outlet pressure and reduces available flow. If there's not much difference between pump outlet pressure and system pressure, the symptom is not related to a flow restriction, and the focus moves back to the pump itself, low voltage being delivered to the pump, etc.. For some reason the pump is underperforming, and the focus moves to that area.
So when looking at the primary pressure regulator in my FD (for which I replaced the O-rings / shims some time ago), it could be that it restricts the backflow to the tank, making my flow too low (< 1120cc/30s).
Ofcourse, providing evidence that my pump is performing at the correct capacity.
This means I could already check 2 things :
1. verify my primary pressure regulator : plunger doesn't stick - O-ring is sealing - spring is OK
2. verify the pump's performance : put gauge in the lines at the back and under the hood to see whether flow is within range @ 5bar.
Once the issue is determined and solution is provided, I can recheck the flow again according to WSM
Remark : I will also receive a spare FD (not overhauled but in good state) for testing purposes to see if it makes any difference in my flow. This way I can also check whether my pump is performing correctly.
I thought I was reading that you are not able to get both the required flow and system pressure to happen at the same time. Was I not reading that correctly? My suggestions for diagnosing are based on that symptom.
The fuel pressure regulator controls system pressure by relieving a certain amount of pump flow back to the tank. The capability of the regulator itself determines how much it can bypass to the tank at target system pressure, and the sealing capability is a big part of its ability to retain pressure after the pump stops. There's interaction between the regulator and the pump, since the amount to fuel bypassed is the fraction that's beyond the pump's capability curve at target system pressure. That curve has flow on one axis and pressure on the other, and the two are inversely related. More pump backpressure equals less flow. More flow only when pump backpressure is lower. The regulator determines system and therefore pump discharge pressure, by bypassing fuel flow until the flow and pressure at the pump allow it to deliver the correct system pressure. With the engine stopped and no flow to the injectors, all pump flow is diverted to the tank by the fuel pressure regulator while maintaining the target system pressure. The amount of flow available at that condition is a product of the pump and any flow restrictions that might raise the outlet pressure at the pump and push the flow back up the capability curve.
Pump "capability" in your case seems to be the issue, but that can only be confirmed by testing to see if there's any significant restriction in the system between the pump and the pressure regulator. That restriction would cause the pump outlet pressure to be higher than the system pressure measured at the FPR and WUR. Restriction raises the pump outlet pressure and reduces available flow. If there's not much difference between pump outlet pressure and system pressure, the symptom is not related to a flow restriction, and the focus moves back to the pump itself, low voltage being delivered to the pump, etc.. For some reason the pump is underperforming, and the focus moves to that area.
first test done today of pump pressure & flow , directly after pump, so without any other components
test location = tank , Pump pressure (with closed outlet) = > 6 bar
Pump pressure (partially closed) @ 5 bar gives a flow of about 600 cc / 30 sec
test location = engine : Pump pressure ( with closed outlet) = > 6 bar
Pump pressure (partially closed) @ 5 bar gives a flow of about 500 cc / 30 sec
Looking at the pump specs @5bar : 228 liiter/ h or 1,9 litrr / 30 sec, this means that my pump is not delivering the needed amount under load of 5bar
What I also noticed is that after a while my pump pressure with closed outlet would not raise higher than 5 bar.
Your warm WUR control pressure is just a little to high.. That is what is causing the lean out between 1-2 k rpm... Been through all this mess before. I converted my WUR to adjustable. Then I set it up just on the edge of the low pressure side of the spec window... Test drive and if it still has a small lean spot then go even further under the spec window.. You will have to reset the air flow meter CO adjustment every time you change the WUR... It has taken me years to figure some of my cars out
Hi Gerrit, that is good news I think, well bad news for the fuel distributor…You could maybe send it to an expert to do the overhaul? Or do you want to go and try it yourself? Step by step you are getting closer to the solution 👍
Yesterday, I retested the fuel flow with the same fuel pump but by replacing my fuel distributor by another good second hand fuel distributor. And guess what, I had the same result : about 850cc fuel / 30secs. Voltage on fuel pump (directly powered via battery with charger ) while running was 12,9V
So now I will do the same test again, but with a new Bosch fuel pump.....fingers crossed...
Yesterday, I retested the fuel flow with the same fuel pump but by replacing my fuel distributor by another good second hand fuel distributor. And guess what, I had the same result : about 850cc fuel / 30secs. Voltage on fuel pump (directly powered via battery with charger ) while running was 12,9V
So now I will do the same test again, but with a new Bosch fuel pump.....fingers crossed...
Wow, another potential problem off the list. So curious if the pump will be it in the end…good luck!
Wow, another potential problem off the list. So curious if the pump will be it in the end…good luck!
Bad luck, I replaced my fuelpump and filter but same result 700cc/30 sec :-(
So last test that I will do is bypassing my fuel accumulator. If that doesn’t solve my issue, I will overhaul my fuel distributor …I am out of other ideas
WoW @GerritD i know how it feels….you are basically working your way through the system like I did…I changed the fuel accumulator at some point too…that was not the solution for me but I think you are right to try this…looking at the bright site: you almost have a complete overhauled fuelsystem…on the longer run that will only be more and more expensive to replace…good luck!
WoW @GerritD i know how it feels….you are basically working your way through the system like I did…I changed the fuel accumulator at some point too…that was not the solution for me but I think you are right to try this…looking at the bright site: you almost have a complete overhauled fuelsystem…on the longer run that will only be more and more expensive to replace…good luck!
Putting fuel pump directly at the entry of my fuel distributor doesn’t change anything 😩
So I need to send my FD for overhauling
My intuition says there is something wrong with the primary pressure valve inside the FD, because adding shims did not raise my system pressure
Where are you going to send it to? And yes that would be the last step I think?
Originally Posted by GerritD
Putting fuel pump directly at the entry of my fuel distributor doesn’t change anything 😩
So I need to send my FD for overhauling
My intuition says there is something wrong with the primary pressure valve inside the FD, because adding shims did not raise my system pressure
Where are you going to send it to? And yes that would be the last step I think?
Well I was thinking to send it to Allan in France, who helped me with my WUR and is a really nice and reliable guy.
But he told me that he was involved in familial worries so he has less time…but I still hope he can find some time in overhauling my FD.
Could the primary pressure regulator be the culprit of
- too low backflow from FD to tank ?
- too low system pressure ?
What can I verify, measure at my primary pressure regulator inside the FD ?
I suspect bad O-rings, sticky plunger: I added 0,6mm but system pressure still doesn't go higher than 5,2 bar
Where are you going to send it to? And yes that would be the last step I think?
Originally Posted by dr bob
Gerrit --
I'd start by making sure that the pump can deliver the required pressure while dead-headed (outlet completely blocked briefly, no flow at all). Then move to making sure that it has the ability to maintain that pressure at rated flow (the WSM test...). If it makes plenty of pressure at zero flow but fails the WSM test, I'd put a gauge in the line at pump discharge (the S pipe fittings...) and compare that to the under-hood system pressure reading while performing the WSM test. If the pump discharge pressure is significantly higher than under-hood system pressure, there's a restriction in the filter, hoses or piping between the pump and the engine bay. If they are close (within 5PSI or so, guessing) and it still fails the WSM test (not enough pressure at test flow or not enough flow at test pressure), you may need to replace the pump(s). Many cars came with two pumps -- one small priming pump in the tank, feeding the main pump mounted on the tank. Inside the tank there's a suction screen on the end of the pump itself, with a short connecting hose from the pump discharge to the fitting in the bottom of the tank. If you look at the fitting at the tank outlet, the ones for in-tank pump have connections for wiring passing through. A telltale that there's a pump inside. If that pump fails or gets clogged with debris or the little connecting hose disintegrates (common with "modern" fuels here) there's a risk of it limiting suction flow to the main pump. If you do have that in-tank pump, it's worthwhile removing and inspecting it completely. Replace the short rubber connecting hose with modern plastic-lined injection tubing and proper clamps. Verify that it does in fact run and pump, maybe with some paint thinner/mineral spirits in a closed container.
Originally Posted by jpitman2
Forgot to mention - my car ran fine for years with an S4 pump on it , delivering pressure and flow. If you have access to such a pump, try it.
jp 83 Euro S AT 57k
After waiting a couple of months for my FD to be overhauled, I finally re-tested my fuel flow with the overhauled FD and guess what : problem is still not solved
I only get 500 cc / 30 sec fuel when priming my pump (directly connected on my battery and with charger on the batterie)....
So in the meantime I replaced : FD, fuelpump, fuelfilter, WUR,.Hotstart valve..
06-21-2021, 09:22 PM
