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M103 CIS and Injector Health Question

778 views 4 replies 4 participants last post by  ianrandom 
#1 ·
I have a question regarding CIS related to the condition of fuel injectors on my M103:

I checked duty cycle and other related items today on the 300SEL. Duty cycle was pretty much on the numbers, maybe just a little low at 46.95 % at idle and 48.5 % at 2500 rpm, which according to the information I have is pretty good. Close enough that I see no reason to fiddle with any settings unless there’s an expert in the house that can tell me why I would need to change it.

However, I’m wondering how I could determine how well my injectors are doing by these values. That is, if I had a leaky or dribbly injector, or injectors that had a bad pattern, would that be reflected in the duty cycle, that is, would the system attempt to correct for overfueling, and if so, how that might manifest itself.

Drivability is fine with no performance issues whatsoever. Idle is not 100% smooth, as I can feel little “bumps” in the idle at a stop or just sitting parked out of gear. This is what has me wondering is I might have a injector or two that aren’t performing well. I’m assuming the injectors in the engine are at least 100k miles old, if not more. I know the head was redone at around 180k, but I have no idea if the injectors were replaced at that time.

TIA,

Dan
 
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#2 ·
hows the motor mounts ? also a few tanks of gas with the injector cleaner of choice (seafoam is mine ) might help, cant hurt .

at some point pulling the injectors changing their seals and having them cleaned and checked for flow pattern and volume is in the future of all these cars .
 
#3 ·
Engine and transmission mounts were replaced a couple of weeks ago. First tank of fuel got a full dose of Techron.

Understand that the car runs well, if anything it can have a little bot of a rough idle, but it's not anything significant. I suspect more than anything else there's a possibility that one or more of the injector sleeves are cracked or leaking.

I haven't gotten a full tank of fuel through it yet - that is, one that I didn't have an extended amount of idling or fuel removed through things like filter replacement, so I would definitely question the accuracy of the MPG values I have at present until I get a full tank run through it with normal driving.

I'm more concerned with fuel mileage that anything else. The occasional bump in the idle isn't an issue, nor is it probably perceptible to anyone but me.

I can get a set of new Bosch injectors for $125. For that kind of money I'm probably going to do it anyway.

Thanks!

Dan
 
#5 ·
Luckymike says what I was thinking. The only experience I have of new injectors is reading about them on here when members have bought a set and tested them before installing. There just seems to be quite a significant failure rate, one or two in each set seems to be happening commonly. And thats been Bosch mainly I think.

I was scared of that so I got mine 'cleaned and set to spec' by an injector place as my mate worked there and got on well with the boss. (Cost me a bottle of wine.) I was never able to find out what 'set to spec' meant but I would think they were just checked and must have been found to be fine. Its not like they are adjustable are they?

The car ran well but what with that and new MB ignition leads etc, you cant tell its idling most of the time, its very very smooth. It seemed to me that I got a slightly more even power delivery rather than a bit of a burst at higher revs.

The old injectors are such good quality, maybe worth giving them a clean or giving them to an injector place to check. The place I used was a diesel injector specialist really but they do all sorts. Although, if you can get new Bosch that cheap, you could buy them and check them until you have a good set, if necessary.
 
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