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Hi - I can’t find any info anywhere on this subject.
Can M278 fuel flow be increased with upgraded LPFP without changing the HPFP?
Somewhat related second question - is the M157 HPFP the same as the M278? The part numbers appear the same but that has fooled me in the past on other parts.
It would seem the answer should be yes. HPFPs are the same in both platforms, yet M157 engine calibrations show higher HPFP flow. So logically the M278 LPFP would be the limiting factor. I'm testing this theory and will report my results.
Hi - I can’t find any info anywhere on this subject.
Can M278 fuel flow be increased with upgraded LPFP without changing the HPFP?
Somewhat related second question - is the M157 HPFP the same as the M278? The part numbers appear the same but that has fooled me in the past on other parts.
Thank you!
Bill
Logically the answer would appear to be no.
LPFP is a lift pump to transport fuel to the HPFP.
HPFP, rail pressure sensor and injectors govern fuel delivery into the cylinder.
Injectors + tune = more fuel delivery
or simply tune alone = more fuel delivery
Spark and cam timing furthermore need adjustment to account for higher fuel dosage.
LPFP is a lift pump to transport fuel to the HPFP.
HPFP, rail pressure sensor and injectors govern fuel delivery into the cylinder.
Injectors + tune = more fuel delivery
or simply tune alone = more fuel delivery
Spark and cam timing furthermore need adjustment to account for higher fuel dosage.
But the question is: what happens first? The pumping flow capacity of the HPFPs outpaces the fuel delivered to them by the smaller M278 (vs M157) lift pump (my hypothesis), or the HPFPs reach maximum flow volume at normal rail pressure regardless of lift pump supply? We are discussing a fuel that requires higher flow even without tune modification. Clearly the HPFPs have a flow limit, but we're trying to determine if the M278 LPFP is reducing that limit. Maybe, maybe not.
Last edited by Siegmann; Dec 25, 2022 at 02:13 PM.
This says there are no return lines and that the HPFP has a quantity control valve. I conclude the HPFP governs fuel delivery to the extent the ECU controls the quantity control valve and the number and duration of injector pulses or “squirts”.
To increase fuel delivery first step is a tune then either injectors or HPFP. Read the W213 AMG E63 section as these guys seem to want to push hp.
This says there are no return lines and that the HPFP has a quantity control valve. I conclude the HPFP governs fuel delivery to the extent the ECU controls the quantity control valve and the number and duration of injector pulses or “squirts”.
To increase fuel delivery first step is a tune then either injectors or HPFP. Read the W213 AMG E63 section as these guys seem to want to push hp.
I'm familiar with the system and have serviced it. You're only considering the output side of the HPFPs. The input side may be limited by supply from the lift pump.
The factory injectors are capable of big power. No worries there.
Last edited by Siegmann; Dec 26, 2022 at 10:13 AM.
Not sure how much ethanol you want to run but I'm running 30% and the oem fuel system is fine with it. I'm not sure how much fuel I'm flowing but for comparo my Injector pulse width is ~5ms @ 3500 to ~2.5ms @ 6k. Maybe more because I only checked one data point, but at least that much for sure. I've never had a drop in fuel psi. So maybe compare to yours inj ms to get an idea? Mine is a '16 E550 and I'm 99% sure we have the exact same injectors.
Aside from that, I was curious what % ethanol you're running, plan on running in the future, and if you're doing anything to adjust for the ethanol? Because about 25% is my limit before I run into issues, and a little tweaking I'm at 30%.
I won't bore you with the details, but it's a software/programming issue. It causes the O2 to fault out at idle and ignore my richer ethanol setting. I were floor it like that who knows what risk there might be.
Our cars are almost identical but there are differences where I have this issue, so maybe yours won't do that? So fyi if you were unaware. If you are aware and know the fix, hook me up
Btw I tweak mine using HP Tuners. Which, btw, can apparently bump the fuel flow from the low pressure pump.
I'm familiar with the system and have serviced it. You're only considering the output side of the HPFPs. The input side may be limited by supply from the lift pump.
The factory injectors are capable of big power. No worries there.
Correct, the low pressure pump in the factory system can keep up with the high pressure pump. This necessarily means there is margin in the low pressure pump capacity. How much margin is an experiment to be found.
Increasing high pressure fuel pump flow guarantees more power because there is no fuel return. Increasing low pressure pump output may or may not increase power if the high pressure pump is a restriction.
It seems I finally got my fuel psi to drop a bit here and there under load. I'm now at 52% Ethanol btw. It seems to drop then recover, which I suppose may be the low pressure pump being unprepared for the sudden fuel flow? Just a guess.
Usually it does this but the drop is maybe 20-40psi, not it's as much as 300psi.
So with the ethanol, plus richer mix on top of that, I guess 45% more fuel vs oem? Then even more on top of that since my boost is higher. Hard to say because I never checked oem Inj pulse width, but compared to others I've seen I'm dumping a lot more than 45%. Stock, based on others, is ~2.0ms. Now that I've been looking, my Injector pulse width can exceed 6, and 6.44ms is the highest I've noticed. Maybe they have different injectors but I doubt it.
I've since fixed the 25% ethanol limit, more or less. If you don't adjust fuel delivery to match the ethanol then trims will do it for you. If so, then the 25% eth limit won't apply, but your trims are way off all the time and that seems risky to me.
So with my redneck fix I can push the ethanol content further, which I've been doing until I hit 52%. I've since reduced it to 46% and fuel psi seems fine.
Also, I have lower than normal voltage under load and that low psi pump is voltage driven. This may explain why my psi drop is inconsistent, because so it voltage. If I had normal voltage I could no doubt push Eth % higher.
I don't know what boost you're running but I'd imagine if I were at oem boost I just might be able to use straight E85? If I also leaned out to oem fuel mix I'm all but certain I could.
Hi - I can’t find any info anywhere on this subject.
Can M278 fuel flow be increased with upgraded LPFP without changing the HPFP?
Somewhat related second question - is the M157 HPFP the same as the M278? The part numbers appear the same but that has fooled me in the past on other parts.
Thank you!
Bill
hey not sure if you found your answer yet, but I see a lot of different info being throw around but to directly answer if the lpfp can keep up with the hpfp, and it’s quite tricky depending on the model. Eurocharge claims to have a tune for m157 100% stock e85 on my s550 the lpfp part # comes back to a w205 c63 fuel pump but I’m not sure that’s the same for every model
but from my research the lpfp will definitely give out before the hpfp. What happens is the lpfp can not lift enough to keep up with the amount of fuel the hpfp can actually handle
if you go on YouTube and type in “tasos moschatos hpfp” he breaks down the design while taking them apart showing there faults.
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