Mercedes-Benz Forum - View Single Post - M103 Rough idle and vacuum leak
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post #117 of (permalink) Old 01-12-2018, 04:38 AM
KJZ78701
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Date registered: Apr 2011
Posts: 75
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Quoted: 19 Post(s)
Cody, The following is to H.D. I am hoping that he can teach me something as well.

>>Did you read posts 39, 41, 45, 49, 52, 82, 84, 86 and 91 ?<<

Habe ich. Sogar ein paar Mal.

>>Originally Posted by codycool55 Post 51
... Checking the zero position now I notice when I depress the meter slightly, (just before the resistance from the CP kicks in) the gap disappears, and both sides appear to sit within the "rim." ...
and H.D. replies in Post 52:
Sounds correct.<<


That Cody did not really understand this, you did have to ask several times, tells me that it could have been one of many items that was lost. You will note that I stated, "but I didn't see enough stress placed on making sure the plunger in the middle of the FD was NOT depressed while the motor idles."

As I did all of my tuning back in 2010 and 2011, I didn't remember it all that well. Once I reread my posts quite a bit came back, including the importance of the flapper not applying pressure to the plunger in the FD while the motor was at idle. It seemed to me that your tests with Cody were sometimes engine off and sometimes engine running. The AFM flapper tests seem like the former. Perhaps you could clarify?

As I recall there was a spring in there somewhere, perhaps in the FD above the plunger. Regardless, there was a reason for me to believe that nobody had ever been inside my AFM or FD or EHA (can't remember now what that was), and that lead me to believe that as these systems and parts age, they fall away from the original spec.

I love your approach, but I found that with my car, I needed to do it iteratively. I also decided to work from what I thought was the most important side, fuel delivery (the injectors) back. I pulled all of the injectors, checked their crack pressures, also found a bunch of hard seals needing love, and then checked the flow of all together. This is perhaps not a sight that would sit well with you, as the FD assembly was unbolted from the flapper assembly and the injectors and lines were up in the air with plastic bottles under all of the injectors. So, perhaps ugly, but very illustrative. Here is what I posted seven years ago.

To do this I pulled the fuel distributor (no wires connected) off the base (three Torx bolts-watch out for the o-ring around the plunger when you pull the distributor off the base) and put plastic water bottles over each injector. I weighed the bottles empty since I did not have seven (cold start injector-CSI) that matched and wrote the empty weights on the bottles. I then ran wires directly from a battery near the rear wheel to both pumps. I ran the pumps for about a minute as I pushed the plunger all the way up into the distributor (WOT). Wide Open Throttle

After removing the bottles and getting the fuel weights, the first run gave the following results.
60 – 65 – 68 – 62 – 64 – 72 with nothing from the CSI - 0

I then removed the cap screw on the bottom of the fuel distributor corresponding to injector 6 and turned the exposed set screw IN one turn and then recapped. Performing nearly the same flow test as above, but this time varying the amount that the plunger was pushed in (simulating varying throttle position), I got the following results.
70 – 75 – 79 – 72 – 73 – 66 (0 CSI) That told me that varied or fully depressed, the flows stayed about the same (relative).
Three runs later and a turn here and an 1/8 turn there (NEVER touching #4) I ended up with the following results after a longer run (plunger fully depressed since WOT was a bigger issue for me to match than idle).
123 – 122 – 123 – 121 – 123 – 121


Note the 20% difference between injectors 1 and 6 after the first test. Like Cody, I was chasing my tail for a while until I balanced the flow, then I was able to get meaningful results adjusting the EHA and the CO and the FD plunger.

Here was my follow up:

If I had to do it again on a running car I would:

-Make notes of fuel economy, idle mixture and fuel pressures at the top and bottom of the distributor (there are removable plugs on the top and bottom where you can attach your FP gauge) before I took anything apart. I would also remove the air filter and make a note of the position of the flapper when it just contacts the fuel distributor’s (FD's) plunger with the motor just turned off (residual fuel pressure in the distributor). This is a feel thing and a magnet helps to lift the flapper so you can let it drop just until you feel the point of greater resistance. Now mark that point on the aluminum housing around the flapper. Start the car and see if the flapper has moved down past the mark. If so, measure the drop. The ratio of flapper movement to plunger movement is 7 to 1. If I read the specs correctly, there should be from 0.1 to 2 mm of free play at the flapper at idle. That means 0.014 to 0.29 mm at the roller/plunger which you really can’t measure, but you can “feel”. Point is that the flapper should NOT push the roller into the plunger at idle. I do not know the thread pitch of the screw on the plunger but I assume it is a 1.0 mm pitch. If the flapper moves down 7 mm at idle from the resistance point you felt with the car off then you need to turn the plunger screw IN just over one turn. More likely you will need less. While you have it all taken apart, check the injectors for flow with plunger all the way out (idle) and all the way in and then adjust flow of up to five of the six injectors until all are matched. The min spec is 4-6 cc/min but suggested is 6.0 – 6.6 cc/min. A cc of water is a gram. Fuel is about 75% less massive, so 4.5 – 5 grams of fuel per minute is your target if you use a scale and plastic water bottles as I did. I flowed mine for three minutes at idle and was over the spec. Also check flow rates with the plunger pressed all the way in. There are two specs here: 100 – 109 cc/min (75 – 82 grams/min) and 140 cc/min. The 140 is a max. I just got the idle numbers in spec and then used the high flow to more precisely match the injectors. Since I removed the fuel distributor from the flapper assembly while flow matching I had no way to know how far the flapper was depressing the plunger so I could not check the “full” numbers. I saw mid 80 grams per minute with the plunger completely pressed into the distributor, so I concluded the fuel distributor was okay.

-Check the resistances of the air temp and water temp sensors at the computer’s connector. If out of spec (or more likely completely open or closed circuits), fix. Check the O2 sensor on the bench with a volt meter and torch.

-Put it all back together and go back to your notes. The differential pressure should be 3 – 4.5 Bar (difference between pressures at the top and bottom of the fuel distributor). If you are out of spec, remove the EHA and adjust the small Allen behind the cap screw. Be careful here. The lower pressure changes as the car warms up, so make notes of the ranges you see. If you can’t start the car after the EHA adjustment, you will need to adjust the idle/CO screw. If you turned the EHA CW a turn you will need to turn the idle/CO screw about turn CCW, or the other way and twice as much (roughly). Careful again. If you had to go CCW on the EHA and CW on the idle/CO too much you will/might have allowed the flapper roller to contact the FD’s plunger at idle….meaning another adjustment to the plunger screw, sorry it all comes apart again.


So, anything in there that you might incorporate into your current approach to help people in the future?
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