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Chapter 5 of D-Jetronic article series by Dr-DJet describes the electrically operated injection valve. Do watch the hints for replacing their fuel hoses. If they leak you risk a fire in your engine!

 

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Late and early injector of a MB 350SLC
Late and early injector of a MB 350SLC

5.1 Injector function

These injectors do not open at a defined pressure but by electrical control. Still they have a needle that atomizes fuel in a cone. Injectors are controlled by trigger contacts, engine control unit (ECU) via drivers and power resistors on heat sinks in groups of 2 (4 and 8-cylinder) ,3 (6 cylinder) or 6 (12-cylinder). Opening times are in the range of 2 to 10 milliseconds. By constant fuel pressure of normally 2.0 +0.1 Bar (meaning 2.0 to 2.1 Bar) thus opening times and nominal flow rate of injectors determine injected fuel amount. Those injectors are part of Bosch's EV1 range and were also used later with different sealing and connectors e.g. in L-Jetronic. D-Jetronic injectors range from 0 280 150 001 to ...049. But D-Jetronic injector's production ceased in 2007. Very early injectors were all black and you had to differentiate by Bosch no. As this created a lot of confusion they were then marked with colour blots, finally their body was coloured to differentiate them. There are 3 basically different types plus a prototype for D-Jetronic:

D-Jetronic injector types
FarbeStatic flow rate at 2 BarRemark
black   very very early injectors are black, soon followed by black ones with colour blots. You have to check Bosch no. on black injectors.
blackyellow 265 cm³/min early versions black, later yellow
green 318 cm³/min  
blue 380 cm³/min  
white 480 cm³/min Prototype for MB 450SE 6.9, it was produced with KA-Jetronic

 

There are many variants of these 3 basic types with straiht and bent hoses, protective caps preventing needles from coking, and one or two sealing edges with appropriate bushings. But that does not change color coding and corresponding nominal flow rates. Only MB used all 3 flow rates, while most car manufacturers only used one or maximum two color types. A quick glance at your engine will tell you their color code and you can compare it with the component list of your car. Principally you can swap all injectors with same color (black and yellow mean one color), but you might have to change bent hoses to straight ones or vice versa, no matter what Bosch or your workshop tell you.

 

 

  Please watch out

  • Colour codes from original equipment list have to fit! They confirm correct flow rate.
  • Never operate injectors on 12V without power series resistors! They are operated at around 3V.
  • Never let them run in continuous operation! They are always operated in pulsed mode by ECU. A statical flow rate test of 1 minute is acceptable.
  • Immediately replace defective or porous fuel hoses, otherwise you risk a fire!
  • Watch the needle when inserting injectors into manifold! if it is bent, injector is broken.
  • Always replace rubber sealings between injectors and intake manifold! They are a weak point and a source of excess air.
  • Since 2007 Bosch does not manufacture injectors any more. But they can be cleaned easily.
  • Operating injectors vibrate during operation. If you do not fell vibration, they are gone or are not driven by ECU.
  • When storing injectors, close fuel hose and needle with caps. Otherwise they dry out and needle can hang. Never buy injectors without caps!

 

Injector in detail
Injector in detail

5.2 Injector in detail

The injector is connected via a few centimeters of standard 7 mm fuel hose to the main fule line. It is connected to that by a bushing. On early injectors the hose is pushed over the injectors single sealing edge and secured by a long bushing pressed onto it. As Bosch always had problems with fuel leakage, they introduced a double sealing edge on the fitting. You can recognize that by a short bushing that is not pressed onto the hose.

The upper part of the injector is made of plastics and has the mentioned color coding. Inside the fitting you find a small filter cap. Bosch recommends not to replace the filter. When replacing the filter you risk to let dirt enter and block the needle. You will however find replacement filters by the name pintle cap for EV1 injectors in the US, but I also do not replace them. In upper body there is a 2 pin connector. It connects to a coil with 2.4 Ω resistance, that will open the needle against a spring when 3V are applied. This coil is operated by ECU through power resitors mounted on a heat sink. Due to inductance and resistance opening and closing times are in the range of 1/10 of a millisecond. Without voltage the needle is kept close by a spring. Needle shape and spring determine the injectors nominal flow rate. As a later precaution a plastic cover was mounted on the lower part of the injector (not always in same color as injector). It is meant to prevent coking of the needle and helps a bit to prevent bent needles when mounting injectors. You can move this protective cap onto other needles. There are 2 big problems with these injectors. One is the rubber sealing to intake manifold that gets destroyed be engine heat and has been improved in L-Jetronic injectors. It is merely held down by a ring or holder that pushes down the whole injector without any sealing edge. Two is the fuel hose that will get porous over time. Never hesitate to replace them!

Disassembled injector
Disassembled injector
Broken injector sealing
Broken injector sealing
Injector with 1 (left) and 2 sealing edges (right)
Injector with 1 (left) and 2 sealing edges (right)

5.3 Replacing fuel hoses

When replacing fuel hoses on injectors we have to differentiate bewteen early versions with 1 sealing edge and a high bushing pressed onto the fitting or a late version with 2 sealing edges and just a loose low bushing. The low bushing is not pressed onto the injector fitting, it just guides the hose which is purely sealed by 2 sealing edges.

Injectors with 1 sealing edge and high bushing pressed onto fitting

First you have to cut off the old bushing with a side-cutting plier or a tool like a Dremel. Be sure not to cut into the sealing edge! I did buy these bushings in new and an expensive tool to press them onto the fitting. However I could not use it as the electrical connector prevents me from using it. That is why in such cases I replace the old hose with a new one and use nut and bolt hose clamps with rolled band edges (I use ABA Mini 13 in stainless steel). When using a new hose, do not use the ones with a textile covering on the outside. Use the ones where there is a reinfocement inside the rubber and pull your clamp tight.

Injectors with 2 sealing edges and short bushing

This makes life much easier. Keep the bushing in place and just cut down the old hose with a knife. Remember not ro cut into the sealing edges! Then get a new hose ready and push it from above over both sealing edges into the old bushing which is just guiding the hose. I created a tool for easier pressing. READY !

Some manufacturers even offer repair kits for replacing these fuel hoses on injectors. But they are only short standard fuel hoses and clamps. That you can do yourself! I prefer stainless steel clamp jaws ABA Mini 13. They build up enough pressure to seal and they have round edges that do not cut into the hose. Do not use weak clamps, it will never seal the injector. As a fule hose you can use any standard 7 mm fule hose with 13 mm outside diameter. Cut it to proper lenght and that is it. You should even be able to do that for bent fule hoses like you have them on Porsche 914. While you are replacing those fuel hoses, don't forget to replace the rest connected to main fuel line and the hose from intake manifold to MAP sensor.

When using Dremel be sure that no chips fall into injector. Purists will ask someone to press on a new sleeve on early injectors. While you have your injectors out, it is a nice opportunity to do spray test with them. Some people also pull out the fuel hose without opeining the sleeve and then try to insert the new fule hose with oil into the old sleeve. Don't forget the importance of a proper sealing and that is why I do not recommend this method.

5.4 Injector spray test

When you e.g look at your spark plugs color and are suspicious about injector spray and leakage or when you discounted injecors anyhow, it is time for a spray test. Of course you could send them in for a professional test, but you can still do that when this test shows an injecot failure. For this test, remove all injectors from intake manifold but let them connected to main fule line. Then put small but equal glasses underneath each injector. Now remove pin 15 of ignition coil (to avoid burning it). A second person now operates the starter while you look at each glass whether you have a fine cone type spray and no leakage when starter stops. Now collect a bit of fuel in each glass. What is it we want to see during spray test?

Spray test on 8-cylinder
Spray test on 8-cylinder

 

  Injector spray test

  • Do you see drops of leakage after valve should be closed?
  • Does the spray show a nice cone?
  • Do all injectors spray the same amount of fuel?

 

Now you put all glasses on a board in front of a white background and compare whether you see the same level in each glass. If you see a difference, it is still time to send injectors for cleaning. I prefer this test over measuring static flow rates. Injector verification on a test stand is done same way, of course glasses are replaced by graduated measuring glasses and deviatiosn between injectors can be measured and documented more easily. If you want ou can use a new injector as reference. But that is not necessary for a short test las probability is little that all injectors show the same deviation.  I operate all injectors while hanging them into an ultrasonic cleaner and let them run there. Cleaning without operation is not recommended as dirt under the needle can only be removed when the needle is operated. This way you can normally restore your injectors. It does not help if needle are bent or coils are buned.

 

Your Dr-DJet (Volker)


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