Fuel Injection Conversion

Hi Karl,
Hope you find my little project amusing......
Engine spec:
1330 a+ piper 270/2 cam 9.5cr pistons mgmetro head with mild porting
mgmetro dizzy with slight curve adjustment LCB manifold and rc40 two box exhaust system 3.1 finaldrive duplex timing gear 95 ron petrol
Max power 87.5bhp at 5736rpm Max torque 87.3lb/ft at 4321rpm Not very highly tuned but the torque curve is like a diesel engine's! This engine wouldn't pull top gear below 40mph with an HIF carb and now it can plug along quite contentedly at 15mph! it even starts first time in the winter with no coughing or spluttering! Top speed was 125mph before I put the supercharger on.........
Bosch K-Jetronic Overview:
There are many books on the subject and I have gleaned most of the useful information from them so here are the basics, The Fuel injection system is pressurized by a high pressure fuel pump mounted by the tank, fuel then goes through an accumulator (pressure vessel) which damps out pressure fluctuations and holds a pressure in the system when the ignition is switched off. The fuel then gets pushed to the front of the car into a metering unit, this unit is about 150wx300dx200h, the metering unit has a built in pressure regulator which bleeds off excess fuel back to the tank, make sure this pipe is 8mm inner diameter minimum otherwise the restriction upsets the overall system pressure (I found out the hard way!) this return has to be drilled into the highest point of the tank (filler neck is good and epoxy resin is petrol resistant!)
The metering unit consists of an air filter, feed and return fuel outlets, 4 injector outlets, a cold start injector outlet, and two outlets for the warmup regulator (Choke equivalent)
As air enters the metering unit, it is filtered and then goes through a venturi with a disc in it that floats higher the more air is consumed, this metering unit works on the mass air flow principle, unlike carbs which meter fuel according to vacuum and a preset system of jets, when set up correctly, the unit will always give the correct air fuel ratio for normal running as it is measuring the weight of the air and not any vacuum that is being created by the engine. Idle mixture is adjusted by a small hex screw in the metering unit that is accessible through a little cap on the top of it, this screw adjusts the bottom end of the metering range and doesn't make a lot of difference to the top end(Full throttle), the mid and top end of the metering range are adjusted by the warmup regulator pressure, this is where you can adjust your full throttle mixture in the knowledge that it will be spot on at the midrange as well! The warm up regulator works the opposite to how you would expect, it has a bimetallic strip in it that when 12v is applied, it increases the pressure on the metering arm therefore leaning the fuel mixture, so to richen the mixture you need to shim it up to lower the pressure(simple but time consuming, I put a valve on mine so I could adjust the mixture from inside the car and view it on a lambda sensor display!)
The cold start injector is wired from the starter through a thermotimeswitch which can be plumbed into the cooling system to sense the overall temp, when the key is turned the timeswitch lets the cold start injector run for a short period and then stops to ensure no flooding if the engine doesn't start first time. I have to admit that I have never needed the cold start injector in sunny sussex so have just used it to block the hole in the manifold!
There is also an idle valve that bypasses the throttle butterfly when the engine is cold, this is fed by the ignition feed that also feeds the warmup regulator.
The injectors are activated by fuel pressure from the metering unit and only spray above about 40psi, they are constantly running which is why the system is sometimes referred to as CIS Constant Injection System.
I Used the golf manifold but cut off the four runners and had two runners tig welded on to the outer pair and used an old mini manifold as a JIG to bolt it to when it was being welded. I then got four tubes lathed up to accept the injectors and drilled the manifold diagonally (two in each runner) so that when the injector tubes were welded in they lined up with the back of the valves roughly, the injectors just push-fit into the tubes, always get new O-rings for them as the older ones tend to perish and the new ones are nitrile(green). Make sure that the injectors don't snag your exhaust manifold before you get them tigged in (I have used aluminium brazing rods and they have been fine for 30,000miles
Trev
If you have any questions then do ask them, as this is a nice conversion once set up correctly!!!
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