Apologies for the lack of updates in here for the last while folks, the
finishing post was in sight and it was all steam ahead to avoid another
summer lost fu*king about in the garage. Now that theres some more
free time again I'll try and finish telling the story.
First part of the fuel system overhaul started many, many moon's ago
in a galaxy far, far away. The old fuel tank was kaput. She had started to
rust at the seams and once the rust gets in here theres not many viable options
So, new tank.......
and a fresh "in tank" lift pump to replace the old unit..........
The "in-tank" fuel pump shown above has one sole purpose and thats
to suck fuel out of the tank and pump it to the main high pressure fuel
pump shown below.........
Also included in the pic above is the fuel filter below the high pressure pump.
I think early cars had the filter mounted along side the high pressure pump like
shown above whereas later cars had the filter mounted separately up in the
As always seems to be the case, just after I'd coughed up the ransom
to replace the pair of fuel pumps I came across a forum thread detailing
how to junk the 2 pump setup and replace it with a single "in-tank" high
pressure pump instead, which works out a damn sight cheaper.
With the new pumps in place all the associated plumbing was freshened up aswell.
Actually, was a little frightening to see the condition some of the old fuel hoses
were in. Do yourself a favour, if your driving a twenty year old car and don't
know when the fuel hoses were last changed, put it on the top of the
"Shit to do" list. Unless your Michael J. Fox and driving a DeLorean
then flames don't look so good coming out from underneath a moving car.........
So, pumps and hoses in, the fuel can now get from the tank all the way up
to the engine bay where upon it fills this little item.......
Which is of course the fuel rail. When the engine is up and running the ecu opens
the injectors for a preprogrammed amount of time to squirt in just the right amount of
fuel thats needed. For this to work then the fuel present in the fuel rail has to be at a constant
pressure. For this engine that pressure is 3 bar. The ecu has no way of watching the fuel pressure
and will always presume the fuel pressure is 3 bar. If for some reason something went tits up and
the fuel pressure went higher than this in the rail, then the ecu still opens the injectors the same
length of time and more fuel will get squirted in leading to the engine running rich.
Likewise if the pressure dropped in the rail less fuel would be squirted in running the engine lean.
So, how the hell do we keep fuel at the right pressure in the fuel rail?
Well, it's all done by this little lad bolted on to the end of the fuel rail,
surprisingly known as the fuel pressure regulator.........
It's not a terribly complicated device and if your not familiar with the workings of one
then probably the best way of describing how it works is comparing it to placing your
finger over the end of a garden hose. When you block the water coming out of the hose the
pressure builds, let your finger off a little and some water squirts out and the pressure
drops off in the hose. The regulator shown above does basically the same thing.
The fuel pump pumps the fuel up to the fuel rail, fills the rail and try's to flow out the end of the
fuel rail where it meets the regulator. Inside the regulator there's a little valve held shut with a
spring. Once the fuel pressure builds up enough force to push the spring back the valve opens
and lets some fuel return back to the fuel tank. In this regulator the spring is just the
right tension to keep the fuel rail pressurised at 3 bar all the time and it's constantly open
to some degree returning fuel to the petrol tank.
Next up is the injectors.
As you may have seen previously during the build theres been a few mods done to the
engine to improve it's breathing capability with a view to finding some extra horse power.
And as the engine should hopefully now be fit to take in more air we're going to have to
mix some more fuel with this to find the extra bhp.
Unfortunately the standard injectors weren't going to be up to the task for this engine.
As mentioned earlier the Ecu opens and closes the injectors to allow the fuel to be squirted
into the engine. As the revs start to rise the amount of time the ecu has available to
open and close the injectors to get the fuel in before those inlet valves close and combustion starts
is getting smaller and smaller. With the increased amount of air now coming into this engine at high revs
the ecu simply hasn't enough time to keep the injectors open long enough to get enough fuel in.
So, the solution?
Bellow you can see a picture of the old standard injector and on the right the new
larger cc injectors I've bought............
Theres an absolute ton of waffle that can be written about selecting which
injectors for your engine and I'm not going to go in to the details of how I
came to my choice here, cause to be perfectly honest I think I just got
pissed off reading about them in the end and picked these.
If your in a similar position down the line then some things worth reading up
- injectors are basically split into two different groups,
high resistance and low resistance. The standard M3 injectors are low resistance
and most after market ecu's prefer high resistance. Fitting low resistance injectors
to an aftermarket ecu that needs high resistance one's can end up melting the ecu.
- injectors are usually listed for the amount of fuel they can flow
per minute at a given pressure. Usually you'll see them listed in cc/min (cubic centimeters per minute)
or lbs/hr (pounds per hour).
A standard 195bhp M3 injector flows 236cc of fuel per minute at 3 bar fuel pressure.
The new ones I've bought pictured above and below flow 370cc per minute at 3bar.
- a quick search around the interweb will show that injectors come in all different shapes
and sizes. The standard injectors in an M3 are usually referred to as a Bosch EV1 style.
As I wanted the new injectors to be a straight forward fit with the fuel rail and the electrical connector
rail I've choose to stick with the EV1 style body.
More details of the actual injectors I ended up buying can be found here.........
(just remember, they're high resistance injectors and unsuitable for the standard ecu).
One last vital modification to the injectors before they can be fitted was to paint em red.
This mod alone will add up 40 horse power and improve fuel economy,
remember where you heard it first...........
Now that everything was in place the next stage could begin, wiring things up
while holding a fire extinguisher.
Will try and have it up by the end of the week.