Just replace them. Bosch had intended for those to be a throw away item much the same as spark plugs and were cheaply made. At one time they were quite inexpensive. Less so now but they are no better made. Even when extensive cleaning seems to make them work well in a test environment they usually degrade quite quickly.
Which brings to mind this old discussion on the topic: https://www.ferrarichat.com/forum/threads/flow-testing-results-of-oem-cis-injectors.306357/
I have a lot of Bosch test equipment and have tested thousands of CIS injectors. Never experienced the issue. Easy to incorrectly use it to come up with a bad outcome. I believe you had some nature of bad experience with new injectors on one car. I have done hundreds of cars with no bad outcomes.
Don't I recall reading that the injector specs for new are not the same as the specs for used? I don't recall them now but a search should come up with that info. Used is lower all the way around BUT still acceptable. Another words the testing revealed a few that were off but most are fine by the "used" standard. YMMV
Thanks for the advice and the thread which was interesting reading. Right now I am waiting for new injectors to test on the bench and then in car with the three flow rates.
Tested the new injectors with good results. They open at about 4.2 and closes at 3.8. The variation is just +/- 0.1 bar. I can mention that one injector required almost 5 bar to open initially. After the first test it opened and closed normally. The others had similar behaviour with a higher initial open pressure. Now I just need to connect them to the FD and do the flow testing.
Ok .. now a question on max fuel delivery. With the old injectors I had a rather high fuel flow rate which may have been caused by bad injectors. However, the new injectors do not completely solve this. There is still a higher fuel delivery than the specified test case. The old vs new injectors in my system had not much to do with the actual fuel flow rate. This is not surprising since the FD should make sure the fuel flow rate is proportional to the sensor plate deflection. I guess the FD delivers more fuel than the specified test case or the end position (sensor plate pushed against the stop) is too far. The numbers according to the Mondial manual is in the range 140 .. 155 cm3 / minute. I typically get readings in the 170 to 200 region. According to the test procedure, one should find the injector with the low fuel delivery and calibrate the sensor plate against 140cm3/min. I guess I could do that. But I am still curious about acceptance level for the very maximum flow rate. At least in my system it is quite clear that the FD deviates more in flow rate between flow ports at full load than at mid/low load. Any ideas?
Said and done ... I tried to match the set point 140cc/min, but ended up a bit higher at 156cc/min. I pushed the air flow plate to the stop and raised it back a bit. The injectors were still "screaming" loudly at this new position. I really thought the flow rates would be about the same deviating results as with the maximum position. The result was much better this time with only 2% difference between the ports except one which was 7% off (also tried to switch injector, but no change). It is within spec, but I think the problem is with the FD on this port. It just don't deliver more fuel. My conclusion is that at the maximum flow rate, the problematic port is restricted more than the others which leads to that ports with higher flow capacity will get more fuel and the restricted port will get less. In this very high load case, the ports will differ much more than at the set point at 140cc/min. I am not sure if I should do anything about this since the low, mid and high flow rates are well within spec. It is just the very maximum flow rate which deviates. The question is how likely it is that the air flow plate deflects to the end position? and what could be the cause that only the very maximum flow rates will differ?
I just want you to know that what you are doing is GREAT! That's the kind of testing that REALLY lets you know what's going on. I'll be lucky to change out the injectors without screwing things up. Lester
I had a look at the fuel distributor function and it seems not many websites or even official sources has a good description of the exact function. Of course I might not get the whole picture either since I am more into electronics, but the mechanical analogy to electronics in the most simple model is pressure = voltage and current = current The FD is then no more than eight current generators with adjustable current. It consists of a spring in each generator that creates a constant "voltage" across an adjustable "resistor" which is the orifice/plunger which sets the resistance according to the plunger position. What this creates is a constant fuel flow independent of the system pressure and resistance in the injector, within operating limits of course. Just like in electronics, the current generator only works within certain limits. Hope this may assist in understanding the basic principle.
This is maybe not fuel system related but since most of the engine bay foam has lost its sponginess and starts to fall off, I decided to replace it with some new foam. Browsing through some manufacturers products I ended up with the Kaimann KK available on ebay. It is an NBR foam with closed cells a little more rigid than the original and darker gray colour. Curious about flammability and melting I burned some of the old foam and the new. The old foam which was still intact, melted quite easily with a lighter and produced some black smoke. The new foam did not melt that easily and produced a little less smoke. Neither material burned with flames. They just refused to ignite. Here is a photo of the foams side by side. Image Unavailable, Please Login
Time flies and it is now autumn. In a few weeks the winter may come and it is time for more fun rework, maybe the shift shaft seals and analysis of the gearbox issue I have. The fuel system rework went ok, I think. The occasional fuel smell I had is gone and it starts up much easier and runs smoother than before. I guess the combination of tighter joints for vacuum hoses and gaskets/seals, new injectors, new fuel accumulator and new fuel pump all contributed to this. I also think the time spent on carefully preparing the mating surfaces on the intake and other joints was well worth it. Thanks to all who replied in this thread!
