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I am testing the fuel system pressure of my Euro 928S Kjet. This because I suspect that this is my issue during WOT : slight hesitation between idle and 1600 rpm
I noticed that the system pressure never goes higher than 5,2 Bar (75 Psi) , sometimes only 5 Bar (72 Psi)
Normally by adding extra shims to the primary pressure regulator of my FD, it should rise my fuel system pressure significantly...but it doesn't !
With all these shims (I added 0.6mm + 1mm) , system pressure still remains 5,2 bar I added 0,6mm but system pressure still doesn't go higher than 5,2 bar
My questions :
- why doesn't my system pressure rise with the extra shims ?
- could the spring of my primary pressure regulator encounter fatigue after 30 years ?
Remark :
I renewed my fuelpump 2 years ago by putting the original Bosch 0580 254 053 (and removed the intank pump)
I renewed my fuel accumulator also 2 years ago
Gerrit , did you check the voltage at the fuel pump ?
Don't know if it can make big difference , but i suppose the pump will work "better" on "12 V" instead of only "11 V " ??
Therefor was already here suggested to do the relay conversion , so that the hole oem circuit only has to trigger the relay.
And in favor, the fuel pump is close to the batterie ... so power wires are "short" .
Won't solve your problem, but why are you trying to give the car wide open throttle below 1600 rpm? Downshift at least one gear and things will likely go much better if you're not lugging the engine with full throttle that low in the range. A car bogging or hesitating under the conditions you describe is actually pretty normal.
Won't solve your problem, but why are you trying to give the car wide open throttle below 1600 rpm? Downshift at least one gear and things will likely go much better if you're not lugging the engine with full throttle that low in the range. A car bogging or hesitating under the conditions you describe is actually pretty normal.
I am not trying full throttle but when pushing pedal deeper between 1000 and 1600 rpm car must accelerate normal without hesitation (engine even cuts off almost . That is not normal)
As if I am not getting sufficient fuel at WOT
I am not trying full throttle but when pushing pedal deeper between 1000 and 1600 rpm car must accelerate normal without hesitation (engine even cuts off almost . That is not normal)
As if I am not getting sufficient fuel at WOT
Gotcha. As you do a lot of this work, it might really benefit you to install a wideband O2 sensor and gauge so you can see what your mixture is doing when you have these types of runnability issues. That hesitation can be caused by either a lack of fuel, like you mention, but also from too much fuel flooding out the cylinder, making the mixture too rich where it doesn't combust properly. A wideband O2 gauge would show you which way the needle is going during the running issues and also let you tune the motor for optimum fueling at different RPMs and driving scenarios.
Pinch the return line to the fuel cooler briefly to see if the pump itself is up to the pressure duty you demand. Do the pressure and fuel flow tests described in the WSM to make sure that your system is capable of delivering the correct fuel quantity at target pressure.
Know also that the two-pump system is spec'd on purpose, based on the total flow/pressure available from the pair of pumps working together. The pumps are designed with a flow capability at a specific net pump head, meaning it will deliver at a pressure that's a certain amount higher than the inlet pressure. Without the in-tank turbine pump, your available main pump outlet pressure will be reduced by the missing pressure from the in-tank pump. If you want to leave the in-tank pump out, it will be worthwhile finding a higher-spec main pump to make up the difference. There's normally no benefit to installing a higher-flow or higher-pressure pump as any excess will be bypassed by the fuel pressure regulator, meaning the pump will waster power and add heat to the fuel without any benefit. Regardless, you'll see the results of the pressure/flow testing and decide then if the pump you have isn't sufficient.
In my limited experience, the throttle response symptom you are seeing is almost always caused by the warm-up regulator and incorrect control pressures. The RPM range is low enough that total fuel flow demand is way less than the same throttle opening at higher RPM. Be sure that mixture adjustments are made with a CO meter in the raw exhaust rather than 'by feel'. Very tiny adjustments at the paddle can make big differences in mixture at different load points, and while tempting to use it to smooth out performance and drivability symptoms, those adjustments are just masking another system problem.
Gerrit , more info , i bought the same ( correct) fuel pump Bosch # for CIS cars ... and my car runs perfect again after problems with the ( not oem ) pump .
Gerrit , more info , i bought the same ( correct) fuel pump Bosch # for CIS cars ... and my car runs perfect again after problems with the ( not oem ) pump .
Thanks Barry. I will check the voltage of my pump, but I am almost sure it is at least 12 V.
If voltage is under 12V during running, I will try to boost voltage by charging my battery via chargecables to another car running 14,4V
Pinch the return line to the fuel cooler briefly to see if the pump itself is up to the pressure duty you demand. Do the pressure and fuel flow tests described in the WSM to make sure that your system is capable of delivering the correct fuel quantity at target pressure.
Know also that the two-pump system is spec'd on purpose, based on the total flow/pressure available from the pair of pumps working together. The pumps are designed with a flow capability at a specific net pump head, meaning it will deliver at a pressure that's a certain amount higher than the inlet pressure. Without the in-tank turbine pump, your available main pump outlet pressure will be reduced by the missing pressure from the in-tank pump. If you want to leave the in-tank pump out, it will be worthwhile finding a higher-spec main pump to make up the difference. There's normally no benefit to installing a higher-flow or higher-pressure pump as any excess will be bypassed by the fuel pressure regulator, meaning the pump will waster power and add heat to the fuel without any benefit. Regardless, you'll see the results of the pressure/flow testing and decide then if the pump you have isn't sufficient.
In my limited experience, the throttle response symptom you are seeing is almost always caused by the warm-up regulator and incorrect control pressures. The RPM range is low enough that total fuel flow demand is way less than the same throttle opening at higher RPM. Be sure that mixture adjustments are made with a CO meter in the raw exhaust rather than 'by feel'. Very tiny adjustments at the paddle can make big differences in mixture at different load points, and while tempting to use it to smooth out performance and drivability symptoms, those adjustments are just masking another system problem.
Hi Dr Bob, I agree what you are saying. Normally the original Bosch pump delivers more than 5bar. I will first check this by hooking up
a gauge with a tap so that I can close the line to build pressure.
My WUR is OK because warm control pressure is 3,4 bar within specs.
I also fine tuned my mixture via a CO meter. It was 2.0% , so within specs.
Gotcha. As you do a lot of this work, it might really benefit you to install a wideband O2 sensor and gauge so you can see what your mixture is doing when you have these types of runnability issues. That hesitation can be caused by either a lack of fuel, like you mention, but also from too much fuel flooding out the cylinder, making the mixture too rich where it doesn't combust properly. A wideband O2 gauge would show you which way the needle is going during the running issues and also let you tune the motor for optimum fueling at different RPMs and driving scenarios.
I am thinking about a wideband O2 but here in Europe, I do not know which one would be a good complete kit ?
Pinch the return line to the fuel cooler briefly to see if the pump itself is up to the pressure duty you demand. Do the pressure and fuel flow tests described in the WSM to make sure that your system is capable of delivering the correct fuel quantity at target pressure.
Know also that the two-pump system is spec'd on purpose, based on the total flow/pressure available from the pair of pumps working together. The pumps are designed with a flow capability at a specific net pump head, meaning it will deliver at a pressure that's a certain amount higher than the inlet pressure. Without the in-tank turbine pump, your available main pump outlet pressure will be reduced by the missing pressure from the in-tank pump. If you want to leave the in-tank pump out, it will be worthwhile finding a higher-spec main pump to make up the difference. There's normally no benefit to installing a higher-flow or higher-pressure pump as any excess will be bypassed by the fuel pressure regulator, meaning the pump will waster power and add heat to the fuel without any benefit. Regardless, you'll see the results of the pressure/flow testing and decide then if the pump you have isn't sufficient.
In my limited experience, the throttle response symptom you are seeing is almost always caused by the warm-up regulator and incorrect control pressures. The RPM range is low enough that total fuel flow demand is way less than the same throttle opening at higher RPM. Be sure that mixture adjustments are made with a CO meter in the raw exhaust rather than 'by feel'. Very tiny adjustments at the paddle can make big differences in mixture at different load points, and while tempting to use it to smooth out performance and drivability symptoms, those adjustments are just masking another system problem.
You are obviously "in the dark".
It was found that Porsche had extra money and Bosch had some extra fuel pumps laying around, resulting in them building an overly complex system where an in tank pump (or a suction pump immediately outside of the tank) feeds the main pressure pump (which is terrible at suction, but great at pumping.)
Totally unnecessary!
Ignore those stupid engineers who designed and tested these cars....what could have they possibly known?
Much better to run whatever suits your fancy....and then ask why it doesn't work.
Gerrit , i bought some sets from Innovate for my cars , single and dual gauges. Being a V8 , it's better to have a sensor on each bank , but not needed if you thrust both banks are running "equal" ....
You will have to weld thread nippel(s) on the exhaust , and that on the upper side so no water condens can flow into the sensor(s).
I ruined several ( expensive ) sensors switching the gauge with ignition..... now , i only switch the gauge on when the exhaust is a bit warm. That seems to work. I suspect that the gauge preheats the sensor to quickly in a "wet" cold exhaust ... thermoshock kills it.
I "heard" that the wideband gauges form Stack would better control the sensor heating.... but no experience myself.
Also know what you see , those gauges measure O2 in the exhaust. So , in case of misfire(s),( fouled plug ? ) that cilinder is dumping a lot of unburned O2 in the exhaust . The sensor will see it and show a probably false "lean" condition. It doesn't see the unburned fuel . So be sure all cilinders are firing from the group exhaust ports the sensor is mounted . ( exhaust gasses from 4 or all 8 )
For that we shoot the temperature of the exhaust ports with a laser gun to be sure all are "hot" at approx the same level , so firing is OK.
Bad news : my system pressure even dropped till almost 4 bar after multiple testing with shims.....as if the primary pressure regulator doesn't seal ....
However I did replace the O-rings one year ago....
I also checked my pump pressure and it will pump 6bar and more, so it is not pump related...
Gerrit , did you check the voltage at the fuel pump ?
Don't know if it can make big difference , but i suppose the pump will work "better" on "12 V" instead of only "11 V " ??
Therefor was already here suggested to do the relay conversion , so that the hole oem circuit only has to trigger the relay.
And in favor, the fuel pump is close to the batterie ... so power wires are "short" .
It is definitely not my fuel pump : I can get pressures easily at 6bar and more when testing it separately.
However, I am almost sure the low system pressure is related to my primary pressure regulator (today I tested again and I only get 4 - 4,5 bar ! )
I dismantled my primary pressure regulator several times for adding shims...without result...it even got worse. So perhaps the O-rings are leaking and not tight enough anymore, although I placed them new last year.
Could these O-rings fit my primary pressure regulator :
Were you able to use fuel-rated o-rings last time? I think you are on the right track looking at the FPR o-rings, but... The original o-rings are pretty durable. Some generic replacements not so much. Verify that the o-rings you used are truly modern fuel proof.
Also, verify for me that you were able to pinch the return hose from the regulator and see that 6bar pump pressure. If that's the way you tested, the ONLY option for the low pressure is the fuel pressure regulator.
01-11-2021, 06:47 PM
CIS System Pressure vs Primary Pressure Regulator
