The solenoid will magnetically lift the pintle valve needle from the seat of the injector, varying between 60 - 100microns.  While the valve is raised, the pressurised fuel is forced through the orifice gap in the bottom of the injector on to the pintle head or orifice plate and form a spray pattern shape as nominated by the head or plate design.

The injector will remain open for anywhere between 1 - 20 milliseconds, at a frequency of 3 - 125 Hz, depending on the engines requirements.  When the current stops, a small coil spring pushes the valve needle to the pintle seat and stops any further fuel from passing through.  This process is repeated many times a second.

Due to demands for various fuel quantity deliveries and spray formations, Robert Bosch alone, produce over 1100 different injector part numbers.

Even new injectors of the same type can often deliver slightly different amounts of fuel for a specific opening duration.  On an everyday road engine a tolerance of 6% is acceptable and this will usually not cause any running or emissions problems. On a race engine however injectors should have flow / delivery figures within 2% to ensure that each cylinder is getting exactly the same air fuel ratio for best performance and to avoid overheating of the piston due to a lean mixture.  For this reason we are often asked to match batches of injectors for professional engine builders.

Optimising injector performance is vital to get the best from your engine and we would always recommend at least checking injectors if your engine has suffered any form of mechanical failure.  If you are modifying or upgrading your engine set up with 2nd hand components then it is vital to check that the injectors are all performing properly.

Not only is flow rate important but spray pattern and solenoid response can affect injector performance.  During use, deposits build up on the pintle shaft and end plate that cause abnormal spray patterns and poor atomisation.  Each injector has a filter basket designed to be a last barrier to debris that can stop the injector working altogether.  The pintle shaft is only lifted by .06 mm and the  basket filters down to 30 microns.  Over a period of time these filter baskets become blocked reducing the injector’s capacity to flow fuel.

Our state of the art Asnu injector tester checks the injectors for leaks when the solenoid is closed and then pulses the injector at varying durations and rpm from 600 to 10,000 rpm.  The injectors are backlit so that the spray pattern can be easily assessed.  Once this has been tested the injectors are placed over the delivery tubes and injector flow is measured both with the injector wide open and at varied pulse widths to make sure the injectors perform correctly right through their operating envelope.

In the photo above number 1 has a weak pattern, 2 & 3 have split patterns, 4 is jetting to one side, 5 is good and 6 has a badly feathered pattern.

The delivery test shows the significant difference in these injectors.

As well as the test function, the Asnu machine has an inbuilt ultrasonic cleaning bath.  Once the filter baskets have been removed the injectors are placed in the bath and the solenoids pulsed.  The vibration of the cleaning fluid breaks down the baked on deposits left by modern unleaded fuels.

1.  The filter baskets are removed and the injectors are placed in the ultrasonic bath.  When the ultrasonic bath is switched on, the injectors will be pulsed simultaneously.

2 & 3.  The simultaneous pulsing of the injectors and the ultrasonic frequency in the ASNU Bio Clean Ultrasonic Cleaning Fluid begins to breakdown the baked on deposits left by un-leaded fuels.

4.  ASNU’s patented reverse flow programme begins to push the fluid back up inside the injectors and breaks down the baked on deposits left by the un-leaded fuels.

5.  During the 10 minute cycle, the fluid continues to flow back up the injector.

6.  The emulsified deposits eventually spill out of the top of the injector.

7.  The emulsified deposits continue to spill out of the top of the injector.

8.  The cleaning process must continue until the chemical have gone and the fluid is clear once again.

9.  The injector is cleaned and ready to be tested again to ensure performance has been restored.

Cheap Fuel and its effects

"You get what you pay for" it’s a well used phrase and just as applicable to fuel.  When it’s pumped out of the ground crude oil is in a tar like state and is almost completely unusable until it has gone through the refining process.  This involves heating the crude and bombarding it with superheated steam and other chemicals to break down the crude and draw off the various grades of base oil used to make everything from diesel, petrol and paraffin etc.  The majority of fuel suppliers will refine a batch of crude for around an hour which leaves the fuel 95% pure with 5% content of Olefins.  The cheaper fuels are only refined for around 3/4 of an hour leaving 85% fuel and 15% Olefins.  Race spec fuel is refined for up to 1 1/2 hours leaving it almost 99% pure and this is one of the reasons it costs £12 a litre.

These Olefins are the silicone, varnish and waxy deposits that you would normally see in the bottom of a carburettor when its been left with fuel in it for a long time. They are the chemicals that give off that horrible stale smell that you get from old fuel as the volatile/combustible elements evaporate off leaving the Olefins as a greater percentage.

These Olefins are also the cause of gradual degradation of injector performance as the gummy deposits build up in the pintle shaft and pintle plate causing the pintle shaft to rise and fall more slowly and less fuel to flow through the partially blocked hole in the plate.  Just 12,000 miles on the cheap fuel will see a 10 to 15% drop in injector performance with less flow and poorer atomisation.  The driver unconsciously is putting their foot down more and more to compensate hence emissions and fuel consumption actually increase.  The cost of an injector service can easily be recovered in half this distance in improved economy.

At the risk of being bombarded with solicitor’s letters I will let you work out for yourself where these cheaper fuels are sold.

• Injector testing and report is £5.00 per injector.
• Full injector service, including initial test, ultrasonic cleaning, retest, new filter, pintle cap and seals is £20.00 per injector. 
• Remove, clean, test and refit and rest emissions data in ECU on a typical 4 cylinder in line engine is £120.00. 

All prices are subject to VAT at 17.5%

With most injectors costing around £75.00 each, this represents a very cost effective method of maintaining your injector performance, protecting your engine and maximising power output.