HPFPs, DI, and FI

[JB_Vert]

I've read lots of posts on this site over the past few years, and there seems to be confusion (for some) about high pressure fuel pumps (HPFPs), which in turn creates confusion for readers. I often see posters treating HPFPs as though they are turbo-related, or FI-related technology. My understanding is that this is not the case, and someone please correct me if I'm wrong. The need for HPFPs is driven by direct injection (DI), which does two things: 1) it requires the fuel to be injected into a higher-pressure environment; and most importantly 2) it requires the fuel to be injected more quickly during only a certain portion of the cylinder cycle, while port injection allows fuel to be injected during almost the entire cylinder cycle.

This topic seems especially relevant these days, given all the talk about the next-gen turbo M3. In reality, it will also be direct injected, therefore needing an HPFP, but I thought it might be useful to clear up why an HPFP is needed. It's not the turbo, it's the DI.

There's been at least one thread discussing why the S65 wasn't DI. For myself, I will say that was part of its appeal to me, even though I understand DI allows a lot of tuning flexibility for both power and fuel economy. I don't trust the technology yet. My other vehicle has an iron-block, push-rod HEMI for reasons other than horsepower and torque. Call me old school.

JB

[mkoesel]

Yeah, without taking the time to fact-check you, I will say off the cuff that everything you say sounds reasonably correct.

Keep in mind BMW does have the N53 direct injected naturally aspirated I6 in non-North American markets, and as far as I know there are no HPFP issues there. For that matter though, it seems that the BMW HPFP failure rate is particularly high in the US anyway, which leads to a lot of speculation that our gasoline is the culprit. Oddly, it also seems to effect the N54 and N55 much more than the N63 V8. And I haven't heard anything about S63 HPFP failures at all. Doesn't mean they don't happpen (not too many X5/X6 M out there after all), but that could be a good sign for the future M5/M6 and M3.

There was also the last generation BMW V12 - the N73 - that was direct injected and not turbocharged and used in the US. Though that was sort of a first generation GDI with no lean burn cycle. Still used by Rolls Royce, in fact.

[dexx]

DI is a godsend for high-detonation prone combustion, i.e. High compression/forced induction. Also there's much better control in low fuel and lean burn situations, which means better mileage.

BMW's fuel pump failures are there own. They made a shitty part and for some likely corporate reason haven't gotten the right people to fix it. Or they frankly don't give a shit about you discussing it and they have decided replacing the current parts as they fail costs less than replacing every single sold HPFP with a much better one.