OM642 injector replacement - Mercedes-Benz Forum
 
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post #1 of 10 (permalink) Old 01-20-2019, 05:54 PM Thread Starter
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OM642 injector replacement

I figured this might be the best place to post my experience with replacing an injector on the OM642. I know official guidelines call for coding the new injector with DAS/Xentry into the ECM, however I took the gamble of replacing a bad injector with a rebuilt unit and not coding it in. Car has been running great for more than half a year now. Of course I'm cautioning everyone with "proceed at own risk", but so far nothing bad has happened, and now that I don't have a fuel injector dumping fuel into a cylinder, the car is much happier.

My reasoning is as follows:

The injectors probably need to be coded in order to immediately fall within emissions requirements, as every single injector will flow a tiny bit differently than another. The injectors get flow tested and the code gets printed to the injectors so they can be scanned in, and the engine immediately gets the correct trim for that injector. This poses a few problems however, rebuilt injectors will not flow the same amount as they did when new, so unless they are re-tested and a new code printed on them, the code on them is irrelevant. Also, if you need to fix your car, replacing an injector is quite easy and a miscoded injector is certainly better than a stuck injector washing down your cylinder. I can tell the rebuilt injector in my case eventually got trimmmed correctly as that cylinder is no longer louder than the others. The initial difference was audible, especially at idle, the rebuilt injector's cylinder was louder. The most affected part of the injection cycle is probably the pilot injection phase, where tiny differences in fuel flow will change how loud that cylinder will be. This has gone away with some driving though.

If anything bad happens I will certainly post back here to let everyone know.
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post #2 of 10 (permalink) Old 01-21-2019, 08:20 AM
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Do you notice difference in mpg, or any other symptoms?
I really wonder if all that coding is really needed for engine performance, or it is simply another way to scam owners from their money.
I had similar experience with replacing air filters on 642 engine, who suppose to be reset.
I did not have scanner at the time, so drove without reset just fine for few months.
Did it change anything? Heck no, when I bought the car, the filters were clog to add 2 seconds to acceleration time. Would car read the filter status I would expect red light somewhere. That never happen.


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post #3 of 10 (permalink) Old 01-21-2019, 07:24 PM Thread Starter
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If we don't assume the worse, that it's not just a quick cash grab, I think my explanation about immediate correct fuel trims is possible, but I also honestly believe that's really all there is too it. Any other claim that this is absolutely mandatory would indeed be a cash grab. So if you are time pressured, then you don't have any way around it (like you've already failed an emissions test because of a faulty injector). Otherwise, if you can drive around a little bit, in varying conditions like city and highway driving, the fuel injector will get trimmed correctly.

Of course the side effects were all good, fuel economy came back down to normal, and the DPF resumed normal regen intervals. We mostly drive long highway trips with the ML, in summer we rarely get a regen, in winter of course they are much more frequent, but that's expected.

It's interesting you bring up the air filters, but that's a totally separate issue. If you look at the air filters on the OM642, they are pathetically small, especially for a diesel engine. By the time you reach the 40k change interval, they would completely clogged, which means various engine trims would be completely messed up. In order to immediately restore power, you would have to reset the adaptations, but they would also self correct after a little bit of driving. The real solution is to half the change interval for the air filters, if you do them every 20k then you will not have this problem.
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post #4 of 10 (permalink) Old 01-22-2019, 08:11 AM
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I am long time diesels owner and this is the first generation of diesels that have injectors coding. Injector are extremely high-precision pieces of machinery, so they can't have significant differences in performance.
Coding would mean that microscopic differences can be still catch by ECU.
I am skeptic by birth and will doubt it.
same was when Fss come in MB in late 1990's. MB claim the system has oil quality sensor.
20 years later and nobody found it on the car
Now with air filters, all big diesels I had were equipped with filter minders.
I install 1 in W210 and driving on CA freeways for 80,000 miles it was still showing green.
Changing air filters by mileage is playing Russian roulette and since those cars already have bunch of sensors on intake, it might be a matter of small adjustment to show a gauge on dashboard. Why MB is not doing it?
The mentioned 642 I bought come from Tennessee and filters were packed with insects I have never seen in California.


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post #5 of 10 (permalink) Old 01-25-2019, 03:20 PM
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Has anyone installed air filter minder on their W211 with OM642? Pictures would be nice to see. Thanks

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post #6 of 10 (permalink) Old 01-25-2019, 10:38 PM
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There are several models of filter minder.
The most common, used on trucks use rubber grommet, so you need to drill big hole.
On my MB in the past I had smaller minder, commonly used on generators. It had 1/8" pipe thread and the ducting coming from filter in the car had enough thickness to tap it and thread the minder.
I also have seen minders with rubber hose, what probably would be the best for this engine due to top cover.


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post #7 of 10 (permalink) Old 02-03-2019, 04:39 PM
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i have used diff model injectors and they have workd
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post #8 of 10 (permalink) Old 02-03-2019, 04:41 PM
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i had a wash sealing problem but sorted now
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post #9 of 10 (permalink) Old 02-03-2019, 04:41 PM
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so happy now could seal then for longitme
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post #10 of 10 (permalink) Old 05-14-2019, 09:28 PM
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Hey Patman how could you tell you had a bad injector? Just by listening closely? How easy are replacing these fuel injectors are any special tools needed? I got a 2008 e320 bluetec with 190000 miles. No codes , I’m getting slight then heavy vibration at idle. Seems like the vibration gets heavy when car is hot.
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