Help with fuel pump voltage (have I been misinformed?)

[fatjon]

Unless your pump is right on the borderline of what the engine needs this will make no difference. I think you are barking up the wrong tree. Unless you are also running injectors that are too small and hitting 100% duty cycle in which case a tiny drop in fuel pressure will matter. In that case the solution lies in fitting the right size injectors and addressing the fuel pump size/wiring so you have some overhead capacity without going lean.

[Butter Face]

fatjon said:

Unless your pump is right on the borderline of what the engine needs this will make no difference. I think you are barking up the wrong tree. Unless you are also running injectors that are too small and hitting 100% duty cycle in which case a tiny drop in fuel pressure will matter. In that case the solution lies in fitting the right size injectors and addressing the fuel pump size/wiring so you have some overhead capacity without going lean.

I have RC 650cc injectors, nowhere near the duty cycle unfortunately.

I believe that my issue is twofold.

The voltage is too low to the pump, hence it not flowing enough fuel
The original fuel line is too small, as above.

Cheers

[fatjon]

Yup, them are big injectors for a little OE fuel line. I have a twin injector setup and use a -6 for each bank but the fuel pumps share a 1.5mm cable without any problems. There is some volt drop so they usually see about 13.3 when running. If yours are pushing hard into a skinny fuel line they will take more current and consequently create more volt drop. Maybe the solution is in the fuel lines then? Quite easy to test just take a fat cable from the battery to the fuel pump and see if your problem goes away. If the pump is fed through a relay rather than directly switched by the ECU there's no chance of frying anything.

[Butter Face]

Thanks Jon, I think I will address both issues at the same time.

Might as well do a belts and braces, upgrade the wiring so the pump is running the best it cam whilst also making it's life easier with a larger fuel pipe.

[stevieturbo]

Butter Face said:

I have RC 650cc injectors, nowhere near the duty cycle unfortunately.

I believe that my issue is twofold.

The voltage is too low to the pump, hence it not flowing enough fuel
The original fuel line is too small, as above.

Cheers

Perhaps it might help if you explained what this supposed problem actually is ?

You seem to be blaming a voltage...but dont really understand how the system works in the first palce

You then say duty cycles are fine.....which implies there is no issue with fuel flow, voltage, line size or whatever

You make no indication there is a fuel pressure problem either.

So exactly what is the problem you're trying to fix even though all of what you are telling suggests no fuel flow problem ? Although there is a lack of proper information.

[Butter Face]

Hi mate.

The issue (as I understand it) is that the fuel pressure is dropping off at higher RPM, so at 5k+ RPM where my rising rate FPR should be upping the fuel pressure with the boost, the pressure is dropping off (I can't tell you exactly what it should be/is as TBH it's all been pretty confusing for me)

My understanding is that the engine is just not getting enough fuel at higher RPM, the pump is flat out but is restricted as to how much it can flow by the power it's getting/fuel pipe restriction.

I'm no technical expert at all, I am going by the information from various sources that tells me the pump isn't getting enough power and as such when the engine/injectors need it, it isn't there.

Hope that makes sense!

[stevieturbo]

Butter Face said:

Hi mate.

The issue (as I understand it) is that the fuel pressure is dropping off at higher RPM, so at 5k+ RPM where my rising rate FPR should be upping the fuel pressure with the boost, the pressure is dropping off (I can't tell you exactly what it should be/is as TBH it's all been pretty confusing for me)

My understanding is that the engine is just not getting enough fuel at higher RPM, the pump is flat out but is restricted as to how much it can flow by the power it's getting/fuel pipe restriction.

I'm no technical expert at all, I am going by the information from various sources that tells me the pump isn't getting enough power and as such when the engine/injectors need it, it isn't there.

Hope that makes sense!

Upload a datalog showing these items.

What base pressure are you running and how well does fuel pressure rise with manifold pressure, and when it deviates...by how much ?

You've stated duty cycles are fine....so almost regardless of fuel pressure there doesnt seem to be a lack of ability to feed fuel to the engine. Unless fuel pressure is dropping insanely...in which case in injector duties could not be behaving normally. So there has to be a red flag here somewhere.

As with any remote diagnosis, proper information is needed. At the minute there is to a degree conflicting information.
Fuel pressure dropping a little on it's own is no big deal. Not always ideal, but no big deal. But as it depends on many other factors...far more information is needed here.

Exactly how much power is the car making ? ( although that could be another dyno debate in itself ) and what fuel ?

[Butter Face]

stevieturbo said:

Butter Face said:

Hi mate.

The issue (as I understand it) is that the fuel pressure is dropping off at higher RPM, so at 5k+ RPM where my rising rate FPR should be upping the fuel pressure with the boost, the pressure is dropping off (I can't tell you exactly what it should be/is as TBH it's all been pretty confusing for me)

My understanding is that the engine is just not getting enough fuel at higher RPM, the pump is flat out but is restricted as to how much it can flow by the power it's getting/fuel pipe restriction.

I'm no technical expert at all, I am going by the information from various sources that tells me the pump isn't getting enough power and as such when the engine/injectors need it, it isn't there.

Hope that makes sense!

Upload a datalog showing these items.

What base pressure are you running and how well does fuel pressure rise with manifold pressure, and when it deviates...by how much ?

You've stated duty cycles are fine....so almost regardless of fuel pressure there doesnt seem to be a lack of ability to feed fuel to the engine. Unless fuel pressure is dropping insanely...in which case in injector duties could not be behaving normally. So there has to be a red flag here somewhere.

As with any remote diagnosis, proper information is needed. At the minute there is to a degree conflicting information.
Fuel pressure dropping a little on it's own is no big deal. Not always ideal, but no big deal. But as it depends on many other factors...far more information is needed here.

Exactly how much power is the car making ? ( although that could be another dyno debate in itself ) and what fuel ?

Power is 320bho using Tesco Momentum 99. The rest of the questions I will have to clarify and update at a later date but I will come back ASAP.

[stevieturbo]

Butter Face said:

Power is 320bho using Tesco Momentum 99. The rest of the questions I will have to clarify and update at a later date but I will come back ASAP.

Even at the lower voltage that pump should have no issue supplying only 320hp.

In injector duties are behaving fine, if fueling is fine when you are driving the car, and it behaves in a consistent manner at all times then there is no real issue to be concerned with.

If you feel pressure is abnormal or there is some other problem, detailed information/logs are needed to even attempt to diagnose.

[Steve_D]

I don't think I have seen in any of the posts any figures for what the fuel pressure is actually doing.
Seems the first job has to be running a pressure gauge and watch what happens.

Steve

[stevieturbo]

Steve_D said:

I don't think I have seen in any of the posts any figures for what the fuel pressure is actually doing.
Seems the first job has to be running a pressure gauge and watch what happens.

Steve

There has been no evidence given of an actual problem really.

[Butter Face]

Off the top of my head I believe that the anticipated fuel pressure at max RPM was wanting to be 4.5 bar but at the moment the pump is struggling to achieve 3.2 bar. I can't be sure and need to sit down with my guy and write it all down.

Appreciate the help so far!

[Markbarry1977]

Butter face, I have followed your build thread from start to finish. Might be worth putting a link to your build on here. It highlights a lot of the technical issues you have had/solved/having.

Just a suggestion. I'm no expert but am mainly following this thread as I want to know how you solve the problem.

Good luck

[Bollah]

I'd be also inclined to check the voltage when you have some load on the engine too. You may find that the voltage is dropping the more load you put on, which would be even more of a reason to run a feed from the battery through a relay as mentioned earlier

[stevieturbo]

Butter Face said:

Off the top of my head I believe that the anticipated fuel pressure at max RPM was wanting to be 4.5 bar but at the moment the pump is struggling to achieve 3.2 bar. I can't be sure and need to sit down with my guy and write it all down.

Appreciate the help so far!

Again, datalogs would be helpful.

If indeed there is a disparity of 1.3 bar....that is far from ideal. As to the cause, could be many things.

More detail on the fuel system needed. Size of lines, filters etc etc where is pressure being monitored and how ?

Bollah said:

I'd be also inclined to check the voltage when you have some load on the engine too. You may find that the voltage is dropping the more load you put on, which would be even more of a reason to run a feed from the battery through a relay as mentioned earlier

Some cars can do strange things under load, especially silly charge alternators on modern stuff. Again, datalogs of system voltage under load as you say would be helpful.