A 2003 Mondeo found its way to us having already been to two different garages. The car was hard to start from cold and it was smoking, though when it did start, it ran without hesitation. The first garage replaced the knock sensor and the second garage had re-coded number 4 injector by using CYL 4 on the scan tool. When this didn’t work it was replaced. CYL 4 was again chosen on the scan tool to recode the injector and once again, it failed.
In my experience, this method of coding is where the problems can start. For example, do we code in cylinder order or in firing order? In this instance, re-coding CYL 4 made no difference so the garage fitted a new injector and again re-coded CYL 4. However, the glow plug light remained flashing, the management light remained on and the fault code still showed the fault to be on CYL 4.
Cylinder vs firing order
What the previous garage had actually done was re-coded injector 2, hence the warning light remaining on. Re-coding using CYL 2 on the scan tool cured the customer’s problem. To recap, you have to understand that the cylinder number and the firing order are not the same. For example, on the Mondeo, the orders are thus:
Cylinder order 1 2 3 4
Firing order 1 3 4 2
We have to code in new injectors due to them being ‘flow rated’ during manufacture and have very fine tolerances. Injectors can pass as little as 13mm of fuel – to get an idea of how small that is, a raindrop is about 303 mm. Of course, flow rating is nothing new. When early Ford Transit injectors needed to be replaced we had to order injectors with the same colour markings, as each colour denoted a different flow rate.
Contrary to popular belief, a car should still start even if the injectors are not coded. However, it will smoke and run rough until the ECU ‘adapts’, which could take a very long time. If all injectors are re-coded, the MIL will go out. Once the re-coding has been completed, the vehicle may be noisier than before. Sometimes, the pilot injection will have been turned off while the vehicle re-adapts to the new settings. To complete the re-adaption the vehicle has to be driven. Once driven, the vehicle will be smoother and pilot injection will be re-initiated.
Injector codes found on the rocker box might be incorrect if the injectors have been changed and can add to the confusion between cylinder order and firing order, so make sure you only use the codes that are on the injectors. Also be aware that some replacement injectors are narrower than the originals and will need the seal replacing on the camshaft cover, otherwise, an oil leak will develop.
A very clear performance indicator for common rail injectors is the diesel return-flow (spill rate). A defective injector has a significant higher or lower return-flow compared with a good injector. We must always re-check injectors whenever one injector has been replaced. This is in case a second injector is weak and can cause problems either at the time of diagnosis – which can make you think that the new injector is still faulty – or worse still, when a customer picks up the car, only to bring it straight back again.