I am soooooo very happy! - PeachParts Mercedes-Benz Forum

Fisherman · #1 01-30-2003, 09:02 PM

Haven't figured out why the new/old 300D is running rough just above idle but I did figure out one thing today.

I have been dreading doiing a compression test and finally broke down to check it with one of those very nice KD combos that someone here found, (thank you whoever that was) at S&S Sales.

Anyway, my results:

#1 24.1
#2 24.4
#3 25.7
#4 25.7
#5 25.8

I was so sure that I had a bad hole but it is looking pretty bright in my eyes at the moment. Now to find out why it is running rough,,,, it's not injectors either..
Update:
At least I don't think it is injectors.
I had them tested and they came in at
(PSI)
1850
1850
1750
1900
1850

Is this enough of a variance to be concerned?

Who did the IP rebuild a while back? I'd like to get ahold of those booklets if they're any good!

Cheers,
Mitch

diesel don · #2 01-31-2003, 09:00 AM

Have you checked the following for rough idle:

1. rack dampner pin adjustment or replacement with gold model
2. banjo and hollow bolt cleanout at back of manifold

dp

Pete Burton · #3 01-31-2003, 12:57 PM

1750 is right at the wear limit recommended by mercedes, and they also suggest a max range spread of 5 bar and it seems like you are at 10

Fisherman · #4 01-31-2003, 08:30 PM

Thanks Pete.

diesel don,
I don't have the connection tot eh manifold in this old 1980. It is a non-throttle valve motor so there is no connection to teh manifold like the other cars that I have seen.

Thanks though for the thoughts. As for the rack damper I have to see if this IP has one....

I got into the vacuum system today and somebody had both of the vacuum tqanks connected to teh alda. Too weird...
I reconnected the lines correctly (I think) and now have working door locks. They even cycle an hour later!

Now I'm into the acc servo adn man this is a pain after tearing out all the parts to access everything according to the manul testing procedures and then I find that there is no test or funtional description of how this servo works. I'm pretty sure it's bad though because it leaks around the base.
I'm going to search the threads adn then find a replacement that hopefully works then tear this mother apart and find out what makes it such a pain...

Fisherman · #5 02-04-2003, 11:04 AM

After tearing the interior apart and testing al the cu\ircuits according to Hoyle i found that my vacuum system was working properly. The intersting thing is there is only one test in all the thrity pages that I printed from the CD that pertains to the actual ACC servo. It is a resistance test between two electrical connectors. I find that sooooo weird since this thing has all these connections in it.
I stole one off a friends dead car and low and behold I have regulated heat now.
One thing I did notice is that when the system is in park I can hear a faint whining (i.e. vacuum leaking) inside the car. I am going to assume that this is the control panel since everything else checked out in there.
Oh well it's a minor inconvenience for the moment.

Now it is on to the roughness of the motor. I have discobvered that it sems to be worse when the car is warm and it is consistant notjust above idle as I had thought.
The car seems to have plenty of power but I'm nowe thinking either it is the injector imbalance (as noted in a previous message) or the IP itself may have a problem and is not delivering full fuel to one cylinder.
As a test I have cracked the infection lines while running at the roughest speed I can set and when I do it is really noticeable that a cylinder goes offline.

Anyone ever had apartial fuel delivery problem? Could the one injector at 1750 be causing this due to not enough fuel delivery?

Thanks in advance for any insights......

Pete Burton · #6 02-04-2003, 12:23 PM

The injector @ 1750 will deliver fuel but the spray pattern could be less than ideal, as I think the idea of that pressure minimum is specified so as to ensure there is enough pressure to make a good spray pattern. I don't know if that difference in pressure alone is enough to cause a poor idle though. Is there any noticable difference when you crack the line to this injector compared to the others? Try running some Redline through that sucker!

Fisherman · #7 02-04-2003, 02:33 PM

Thanks Peter.
Naw there's no discernable differnece when I break this line loose as opposed to the others. That's what has me stumped here.

I did talk tot he dealer serice man today qand he believes that it is the one injector though because at a 1000 psi variance it is too far out of spec.
I think I will try another injector in the hole and see what happens.

I'll try to post the results when I make this conversion...

Pete Burton · #8 02-04-2003, 03:22 PM

I'll watch for your post

Fisherman · #9 02-05-2003, 12:24 AM

Changed out the injectors tonight one by one and then started the car to test and see if the rough spot was gone. When I changed number 2 Inoticed it seemed a little rougher than when I was running it after changing number 3.
Anyway, after changing all the injectors there was no differnece so I went back to number two and put in what I know to be a good injector. Huge difference.
it is still a little rough just above idle but when you hit the throttle it purrs now..........

Now for the stupid part:
You know the old saying that when you are going hunting look for sign? Anyway, take a look at the attached picture of the original sealing rings that I took out when taking the compression test last week. Notice any difference in number two? All the others have this nice sooty look to them except number two. Guess I found the bad cylinder now I need to put a completely balanced set of injectors in it and see if the final fix lies in the IP or the cylinder itself which would suprise me after the high compression readings that I got.

The second set of rings (smaller holes) are the ones that I just took out tonight when trying the different injectors.