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Simple and cheap EFI for the Murena

I bought an old Murena 2.2 manifold off eBay some time ago - it came with some useful items, but I started wondering about what to use it for - and an old idea of mine came up: Electronic Fuel Injection. These notes are thoughts about how to do it in a cost-effective way! EFI can be a complicated and expensive project, but using used parts, I beleive it can be done quite cheaply.

Ignition is not covered here, but could also be part of the project as described in my notes about that: Digital Ignition with MegaSquirt.

Manifold

The stock 2.2 manifold can be modified.

Murena 2.2 manifold
Murena 2.2 manifold as installed on the engine (ready to take the carb)

Four modifications must be done:

First the heating must be removed. It should not be heated as fuel injection will not take place in the throttle body, but in injectors fitted as close to the cylinder head as possible. Fuel condensation will therefore not be an issue. The heating can be disconnected, or the studs can be cut off completely if desired.

Second, Injector bosses must be welded or screwed into the manifold. They must be angled to spray fuel on the inlet valve. This will cool it down and ensure that a fuel mist is well built up before the valve opens.

Different options are available for different injector types, but most injectors (e.g. found at a car breaker) are top feed Bosch type injectors. This is a simple device which is normally fitted between the boss in the manifold and the fuel rail behind it. The fuel rail is screwed onto the manifold.

For a custom project like this, it is probably easier to buy ready made injector bosses with fuel studs on the top. This will eliminate the problem of making and fitting a suitable fuel rail.

Fuel supply system will be described below.

Third, a few extra vacuum studs must be fitted:

The Murena manifold has three vacuum studs, one for the cylinder head, and two for the brake servo and headlight vacuum system. The fuel injected manifold needs a few extra studs:

  • One for the fuel pressure regulator
  • A stud to run to the vacuum advance on the ignition (may not be necessary if digital ignition is implemented too)
  • One stud to a MAP (manifold absolute pressure) sensor.
Fourth, the manifold must be modified to take a suitable throttle body. A cover plate can be constructed to hold it.

Throttle body

The long/narrow cutout in the manifold doesn't mate well with a single throttle body. The simplest solution is to find a suitable carb and remove the jets and other internals, leaving only the throttle plates. If a single throttle body is to be fitted, it will probably be difficult to fit one larger than 40 mm. That's quite small for a 2.2 litre engine, so the carb option is probably better.

Temperature sensors

Two temperature sensors are needed: An inlet air temperature sensor and a water temperature sensor. The first must be fitted in the plastic inlet or rubber hose to ensure it is not influenced by the engine temperature. The other sensor is best fitted in the thermostat housing, which has a stud where a 10 mm threaded hole can be drilled.

MAP sensor

A MAP sensor reas the absolut manifold pressure and serves as an indication of the load of the engine. MegaSquirt has the sensor on the PCB and a vacuum hose must be connected to a suitable stud on the manifold.

Throttle potentiometer

On cams with high overlap, the throttle potentiometer is more reliable when determining the load of the engine than the MAP sensor. it is therefore not enough to have a simple idle/full throttle switch. Depending on the parts available, it is probably best to find a throttle body with pot already fitted.

High pressure fuel pump

Since the system will be tuned individually, choosing a fuel pump is not critical and should be done on availability and price rather than specifications. Experience with the Peugeot XU 1.9 litre fuel injected engine shows that good results can be obtained by fitting the fuel pump in the bottom of the right side of the engine room. Surge problems apparantly do not occur with the Murena fuel tank.

Budget

TBD!



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Page updated: 2008-01-20 21:01:14