Approximately up until 1994 mechanical fuel injection systems have been installed on certain Mercedes, Audi, Volkswagen, Ford etc. car models – starting with Bosch K-Jetronic, and after that – Bosch KE-Jetronic. These fuel injection systems were considered to be really reliable and trustworthy. Basically, such conclusion can be made based on a large number of cars that had such injection systems installed by the manufacturers during that time. However, the time has passed and all the automobiles with mechanical fuel injection systems are out of production. Nevertheless, they are still being used by the car owners, thus the older fuel injection systems still need to be diagnosed, serviced and repaired.
Experience has proven that those cars that are equipped with mechanical fuel injection systems are hardly welcomed by the car-care centers. Dealing with them is a pretty labor-consuming task that requires a lot of time and spare parts. Finally, such cars may not be fixed sometimes.
Now let us have a look how Bosch KE-Jetronic fuel injection system can be diagnosed and repaired on an example of Audi 100 2.3i AAR.
Examination and diagnosis
Detach the operational relay set from the relay block as well as from the safety appliance located under the steering tube.
Install a switch instead of the operational relay.
Detach the operational fuel pipes from the metering unit and from the fuel distributor that leads the fuel towards nozzles from the metering unit side.
Screw the fuel pipes you are going to use for testing purposes into the metering unit. Basically you can use the original pipes, but you will need to detach them from the nozzles first. Place the measuring glasses under the opposite ends of the fuel pipes.
Attach a manometer gage to the lower section of the differential valves.
Turn on the gasoline pump. Use the switch that has been installed instead of the gasoline pump operational relay set at the beginning.
Check the fuel pressure in the lower metering unit sections. The fuel pressure should not be above 5 atmospheres when the gasoline pump is on.
To check the gasoline pump pressure margin you can use common pliers. Use them to squeeze the fuel back leak pipe. The manometer gage readings should reach in such case 9 to 12 atmospheres which indicates that the gasoline pump operates well.
When the gasoline pump is on, the fuel should not leak out of the fuel pipes you use for testing purposes.
Carefully lift the pressure disk of the air metering unit. After that the fuel should leak out of the fuel pipes you are using for testing purposes.
Diagnosing the metering unit performance twice would be enough. Use different ladings and be sure to keep the pressure disk completely lifted for about 30 seconds.
Now make yourself a metering unit performance table and specify the amount of fuel separately for each of the metering unit sections.
The amount of fuel for each of the sections should be equal to any of the other ones.
When the disk is completely lifted, no less than 80 ml of fuel should leak out during 30 seconds.
Removing the fuel distributor metering unit
Removing the fuel distributor metering unit is actually not that difficult at all. Nevertheless you need to pay additional attention to the joint washers when detaching the pipes and the electric-hydraulic controller valve. Also there fuel in the system itself is under high pressure because of the petrol overstock. So be careful with your eyes.
Removing the three mounting screws may appear somewhat difficult. To make it easier it is suggested to slightly knock them with a hammer.
Please, pay additional attention to the sealing rubber under the fuel control unit in case you are dealing with a Mercedes-Benz automobile model.
Disassembling the fuel control unit (the fuel distributor).
You need to be especially careful and cautious here. The fuel control unit as well as the fuel distributor is a very expensive spare part and it is becoming more and more difficult to find it on a stand of a specialized shop or a market with each upcoming month.
The fuel distributor dismantling begins after you remove the captivating plate.
After that you will need to unscrew the slider valve screw. During this controlling the adjustment marks is obligatory.
Remove the plunger.
Unscrew the fixing screws.
The next operational step usually appears to be a really difficult one, so you need to take it easy and to be as careful and cautious as you can. Experience has proven that disassembling the top part of the metering unit from its bottom part is not an easy thing to do. There is a special mylar spacer and there is a pretty high probability that you can simply spoil it or break it into pieces. The latter, in its turn, means a complete breakdown, as the spacer cannot be neither repaired, nor renewed.
We suggest the following method that should be used in such case. Knock with a light hammer blows on the blunt edge of the knife, having the knife alternately putting on different sides of the dispenser. The usage of a sharp knife or any other sharp tool is strictly forbidden!
Thid, however, does not allow the penetration of the knife blade to a depth of 0.2 to 0.5 mm gap formed between the upper and lower parts of the dispenser. Once the entire circumference of the gap will do, without applying strong effort arms rotate the two halves of the dispenser in different planes, they gradually disunite. At the same time be sure to constantly monitor the condition of the membrane, to see that it would equally disconnected from the planes of the two halves of the dispenser. This is important and you need to be beware of it in order to be sure that the whole system operates properly.
Unplug the dispenser.
Carefully fold the diaphragm and all the other parts in a container of gasoline (noticed that a long stay in the air contributes to drying and cracking of the membrane, this is really important).
Note the color of the filter mesh. Bsically, as a rule, if 60.000 to 100.000 km of run have been done, they are dirty.
Use the depth gauge to measure the depth of planting adjusting screws and write down all the values.
Alternately, clean the dispenser halves in an ultrasonic bath (about 15 minutes for each of both of them).
After that be sure to start cleaning thoroughly and blow dry the remaining water with compressed air.
Assembling fuel dispenser-distributor
Be sure to be holding the sealing gum paste spool in the upper half of the dispenser. At the same time take care with adjusting the labels take it easy as they should coincide.
Elastic bands should be lightly greased with the engine oil itself before installing.
Adjust the depth gauge with screw planting depth so that all the secation are the same – this is important. The value of a selected planting depth should be equal to the average value measured and recorded immediately after the dismantling of the dispenser.
Be sure to make a dispenser assembly in reverse order of disassembly. Prior to assembly, the rubber parts should be lightly oiled with engine oil to ensure the whole system operates well.
Install the drawer and reconnect the fuel lines and electro-hydraulic valve, with the exception of the fuel from the dispenser to the injectors. Be sure not to forget, that the electrohydraulic valve fixing screws are made of special non-magnetic alloy and their replacement by non-specialist is prohibited. You also need to know that the fuel mounting screws are hollow, and when tightening them be sure not to exert excessive force. Sometimes it takes polishing aluminum sealing washers to prevent fuel leakage.
Be sure to check the dispenser after cleaning
Turn on the gasoline pump. When the fuel pump is on the fuel should not pass from the upper chambers of the dispenser. Be sure to check that.
Screw the fuel validation check dispenser as indicated above. All measurements should have been recorded by this time.
Repeat the same operations with connected nozzles.
When checking the whole system, special attention should be paid to the quality of fuel atomization nozzles. The nozzles that do not provide a uniform spray of small loads in operation and are idling should be replaced. Nozzles are subject to mechanical wear and are almost impossible to clean. Resource mechanical injector is about 70.000 to 100.000 km.
Removal and installation of the atomizers
On Audi engines removing injectors is a pretty complicated operation (yet the MErcedes ones are somewhat simplier). The nozzles are installed in special plastic “cups”. Removing the nozzle without those “cups” may be harmful – the damage may be very severe. For this reason, you should always have a spare landing “cups” and sealing gum for them to be applied.
When installing the cup with the injectors in the inlet manifold, it is sometimes necessary to gently lubricate the seat sealant to prevent air leaks. Be sure that there are no air leaks at the moment.
After installing the nozzles, it is necessary through the air supply channel to the “glasses” to check the tightness of the nozzles landing. This is important.
Push the nozzle and install the intake manifold.
Attach and connect everything back and start the engine – that’s it.