[Diy_efi] direct injection

Phillip Kuhn pmkls1
Fri Sep 9 02:45:59 UTC 2011

I have been a tech at GM dealerships since 2001. I don't have the slightest clue about the other manufacturers using DI, but know a decent amount about the GM systems. So far I haven't seen any common issues at all with the GM stuff. I have seen a few injectors go bad and some issues with the high pressure pump leaking fuel into the crankcase ( just like the old mechanical pumps did), but nothing major or widespread overall. As far as the systems themselves go I will give a detailed description of how they work etc. Currently, only the Ecotec engines have DI versions, and all late model high feature v6 engines (2.8, 3.0, 3.6) are DI. They all use an in-tank electric pump running at ~60 psi to send fuel up to the high pressure pump.?The high pressure pump?is mounted on the engine, is driven off of a camshaft, and operates exactly like the regular old mechanical fuel pumps do ( save for the pressure output ). The entire system is a returnless system and
 like most newer vehicles has no serviceable fuel filter. The supply pressure is regulated by the ecm and a fuel pump flow control module via a pwm signal to the electric in-tank pump. The fuel pressure on the high pressure side of the system is also controlled by the ecm too via an actuator mounted inside the high pressure pump. The system operating pressures on the high pressure side are 500-800 psi at idle and around 2500 psi at max output iirc. From the high pressure pump forward they use heavy stainless lines with flare and ball connections and are supposed to be a one-time use deal. Anytime we take a line loose it is supposed to be replaced, although I have reused several without any leaks. There is also a fuel rail pressure sensor located on the fuel injector rail to send pressure readings back to the ecm and there is no other means of testing pressure on the high pressure side. The injectors look like normal injectors on the fuel rail side and
 use o-rings that appear to be the same size or similar to that of regular fuel injectors( I still can't figure out how the seals don't blow out at those pressures). The other end of the fuel injector is very long and narrow and uses special teflon seals to seal it into the cylinder head as they go directly into the combustion chamber?through the intake side of the cylinder head. Special tools are required to install and size the teflon seals similar to the tools used for non-cut teflon seals used in transmissions. There are also special tools required to remove the injectors?from the cylinder head as carbon will quickly cause them to get stuck in the close-tolerance bores. Every time the injectors are removed all of the seals have to be replaced. The injectors do require a special high voltage driver, but I do not know the specs right now. Overall, the systems operate like a regular sequential port system does and are designed similar to a diesel
 system. Both fuel economy and power are improved on the engines GM is using DI on currently. The latest 3.6 in the base camaro is up to something like 317hp now. As far as being able to fit DI to any other engine, I suppose it may be possible on some engines. Even then it would require significant cylinder head modification and some fabrication. You would also have to use an ECM designed for DI and be able to modify the calibrations and flash the ecm which I am unsure if that is possible currently. Hope this answers a few questions.


----- Original Message -----
From: Avery Nisbet <anisbet at gmail.com>
To: Fred Cooke <fred.cooke at gmail.com>
Cc: ScottyGrover at aol.com; diy_efi at diy-efi.org
Sent: Thursday, September 8, 2011 4:07 PM
Subject: Re: [Diy_efi] direct injection

I have heard from VAG mechanics that they still have trouble with
this. This is with the current TSFI engines found in the audi's and VW
in the US.

Though TDI engines have been around for years I only hear of them
clogging up the EGR system not the intake ports.

I think most of this is due to EGR issues and dirty air.? Where else
would any substance that would/could coke on the intake port/valve
come from if you have DI.? The washing action of Port injection
probably helped with badly designed EGR systems in the past.

For DIY at home "testing" of DI, EGR systems could probably be avoided.


On Thu, Sep 8, 2011 at 1:00 PM, Fred Cooke <fred.cooke at gmail.com> wrote:
> Early examples, from at least 1998, perhaps earlier, are to be avoided as
> they are usually prone to coking of the intake manifolds. Very bad coking -
> to the point of blockage! The earlier cars had a lot of trouble in many
> areas and were not reliable at all. If we're talking about DI. if we're
> talking about BMW Piezo DI, I have no idea.
> On Fri, Sep 9, 2011 at 7:18 AM, Avery Nisbet <anisbet at gmail.com> wrote:
>> A lot the current car have these.
>> GM has been using them in the eco-tec(FWD 4 cylinder) engine for a
>> while. ?Im sure there a few different injector styles.
>> The prices should come down in a few years. ?You may be able to find
>> specs by looking up after market replacements.
>> The cruze should have these depending on market. ? The later model
>> year US market cobalts had them too.
>> -Avery
>> 2011/9/8 Mike <niche at iinet.net.au>:
>> > All I know its pretty high pressure, the latest bmw twin turbos use this
>> > with piezo driven
>> > injectors that cost $2200+ (AUD) each !? But they do get pretty
>> > reasonable
>> > fuel consumption of
>> > around 6L/100Kms with sizable power on demand - straight six 2 to 3L,
>> > seems like the next tech step but geesh does it cost !
>> > regards
>> > Mike
>> >
>> > At 02:48 AM 9/9/2011, ScottyGrover at aol.com wrote:
>> >
>> > Has anyone done any work on this type of fuel injection? I can't get any
>> > data from Delphi, even as to the physical size (length, stem diameter.)
>> >
>> > Scotty from Hollyweird
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