Monday 7 April 2014

Injector Testing and First Start

First of all, I am delighted to say that I have started the bike on injectors! Sticking to the timeline though:

As I was unable to get hold of a used fuel pump at short notice in Ireland, I decided to chance repairing the ZX10R pump I had. So late last week, I fully stripped all parts of the pump and cleaned all the contact points with wirebrush, fine emery paper and contact cleaner and reassembled the unit.
When I then tested the pump, it worked perfectly so I proceeded with testing.

As the CBR600RR injectors were designed for use with a fuel pressure of 50psi and the ZX10R fuel pump only delivers a fuel pressure of 44psi, I needed to test flow the injectors using 44psi fuel pressure. To do this, I mounted the injectors in the original CBR600RR secondary fuel rail and ran an extended section of fuel hose from the pump on the bike to the fuel rail. I also extended the wiring from the main bike loom out to one of the injectors on the test rail to provide power to the injector and a direct earth wire to the battery with a push to make switch between the injector and the battery to allow me to control the injector and operate it at 100% duty cycle. A graduated cylinder was used to catch and measure fuel discharge and the injector was run for several 30 & 35 second intervals to determine flow rate. Using the average of these tests, I was able to determine the actual flow rate of the injectors was 165cc/min.

Rudimentary injector test rig

 While the test rig was set up, I used the opportunity to test the injectors at various pulsewidths and speeds.

Once testing was complete, I re-installed the injectors in the throttle bodies and fitted them to the bike.

It took circa 5 mins of cranking and varying cranking pulsewidths before I got the bike to fire and sustain running. First start was even captured on film.

After first start, idle was very high (~4-5,000RPM) and the engine also sounded rough as if it was only running on 3 cylinders. Nevertheless, it ran and there was going to be some tweaking needed to refine it.

The next day, I was able to carry out more extensive testing and attempt to refine the idle. As it turns out, the roughness in running from the first start was due to one spark plug lead being unplugged! A quick fix. Idle was lowered significantly once I carried out a synchronisation of the throttle valves using a good set of vacuum guages. Once the throttle bodies were synchronised, I was able to get a steady idle around 2,000RPM.
Further adjustments of the idle pulsewidths meant I was able to get the engine to idle reliably and smoothly at 1,700-1,800RPM. I attempted to go down as far as 1,500RPM but the idle became slightly unstable and off-idle throttle response was not ideal. This is because the pulsewidths required at this engine speed were too low and most probably in the non-linear flow region of the injectors.

I adjusted the idle pulsewidths to achieve the lowest intake manifold pressure while still holding a stable idle. Ideally, I would have liked to know the air-fuel ratio also but my O2 sensor was not reading correctly. It consistently indicated extremely lean conditions even though I was able to bog the engine from introducing too much fuel. I was able to verify it worked correctly by inserting it in the exhaust of a known bike and getting a reading so I suspect the problem is caused by an exhaust leak between the headers and the cylinder head. This will need to be fixed before continuing with ride testing.

Even though the fuel VE table is still very basic and just a generic table generated by the software, the response off-idle is quite good and the engine appears to rev cleanly up to 6,000RPM. Ride testing will refine this even further and I am interested to see if this translates to a benefit in response when riding.