SO I think my 4.5 is running lean, now what (stupid question) - PeachParts Mercedes-Benz Forum

#1 11-27-2003, 02:58 AM

Is it probably just a vacuum leak? The door locks don't work. The spark plugs are white at the tips. Where would the vacuum leak most likely be? Could I find the engine vacuum leak with a hand pump? Do you just pump the hand pump and see if the needle drops any? Please elaborate on how I should go about this.
Thanks
Tim

wbain5280 · #2 11-27-2003, 05:34 AM

You could start by checking your manifold vacuum with the car running. Since you know the locks aren't working, find the main vacuum line and work from there. Don't forget the short hose sections between the intake manifold halves.

I don't think it's a stupid question.

Litton · #3 11-27-2003, 10:19 AM

On my 126 I finally gave up trying to find the vaccum leak myself. Just to many possibilies to explore. I took it to my merc guy and he hooked up his "smoke" machine and leak checked my entire system....you could see white smoke coming our wherever a leak was. In my case it was at the injector seals. I think he charged $35.00.

WANT '71 280SEL · #4 11-27-2003, 10:36 AM

When you are talking about the main line, are you speaking of the brake booster line or the main door lock line?
Thanks
David

ctaylor738 · #5 11-27-2003, 10:38 AM

There are a lot of posts on this. You can spray carb cleaner around the intake gaskets and injectors and look for an increase in RPM.

But before you determine that you have a vacuum leak, why don't you buy a guage (a Mityvac pump has one built in), and see how much vacuum you're pulling, if it's stable, etc. The Mityvac comes with pretty good diagnostic instructions.

You might simply be running lean and have no problem with vacuum.

Tomguy · #6 11-27-2003, 12:13 PM

Well, if your locks dont work, and even take a long time to work when the car is running, you have a problem there.
BUT I thought that made it run rich?

The main vac line for the door locks is yellow. It has a one-way valve on it right after it comes up (from the manifold I believe). It runs along the firewall starting about where the MAP is and over towards the driver's fender. Unplug it and see if it's "sucking" and if so, plug the line and see if it helps your running. If so, that's the issue.

#7 11-27-2003, 02:07 PM

So this does cause it to run rich, or does it cause it to run lean?
Thanks
Tim

Tomguy · #8 11-27-2003, 03:36 PM

Depending on conditions, it might cause EITHER or BOTH! It might make it lean at idle and rich at highway or vice-versa. It might make it lean cold and rich hot or vice-versa. I can't honestly tell you (and I don't think anyone can unless they know exactly HOW the MAP and the ECU control the mixture by vacuum).
It WILL cause it to run improperly, that's for sure.

Were the plugs beige or white? Beige is usually good... white is bad, and so is black.

Just plug that line and see what happens. I ASSUME your brakes work fine - if they seem weak (especially after repeated pressing and releasing of the pedal) it would mean a weak vacuum to the booster, and a leaking doorlock line might cause this. Same with a leaking line to the vac retard on the distributor.

WANT '71 280SEL · #9 11-27-2003, 04:17 PM

The plugs were BRIGHT white, and it was really built up badly. We didn't see anything right away. We are doing the valve seals tomorrow and maybe clean the injectors if we can figure out how to get them to open in carb cleaner. We think that psfred may drop by. We PM'ed him with numbers and he said he may drop by. Thanks everyone for the information so far. I am afraid to start touching the mixture because we would most likely set it off even more.
Thanks
David

#10 11-27-2003, 08:53 PM

What do you guys use to block vacuum lines?
Thanks
Tim

Tomguy · #11 11-28-2003, 12:29 AM

I went out and bought regular vacuum line (to cut to length and use as "the connectors to replace the dryrotted ones I had before). I cut a length of his hose about 3" and stuck a bolt with the perfect diameter into it and then plugged it on the plastic line.

ctaylor738 · #12 11-28-2003, 10:31 AM

You still need to get a Mityvac. It is an indispensable tool for messing with these cars. It comes in a case with all these cool connectors and plugs. Put it on your Christmas list!

psfred · #13 11-29-2003, 09:20 PM

Get the vac leaks fixed -- brake booster line, plug the line for the door locks until you can figure out what's wrong with them, etc.

Make sure the vac line to the distributor holds vac -- plug it if not and set the timing to 7 degrees BTDC rather than 5 ATDC.

Chances are it is the injector seals -- leaks here don't affect the manifold vac as much as leaks in other places, and it will run lean.

David:

How did the valve stem seal replacement end up?

Peter

WANT '71 280SEL · #14 11-30-2003, 12:08 AM

Well, the mechanic came at about 3:45, like he said he would. Brought the MB tool, we were all in shock and awe of course. He just went right down the line and had all the keepers, followers out, etc. He got to the third one, and said "we're done", we all looked at him and he showed us that he was pulling out the guide with the seal. He said that Monday he could sell us a guide and we would be able to put it in with the head on and valve in. He is also going to get the injector hoses Monday. The mechanic showed us how to cut a piece off the injector and use regular FI hose with 2 clamps instead of one. I managed to get all the old valve seals out, which is what came out on that one injector while you were there. They were hard plastic it seemed like, but the new ones were soft pliable rubber. Those were a pain, and small pieces of them did sometimes fall into the cylinder. I guess those will have to be burnt out. We of course cleaned the spot where the seals go into the head. We still have to do the speedometer and fuel guage. We also found a couple of other fuel hoses that were cracked so we are also replacing those. Some of them still looked pretty good, and we could tell some of them had already been replaced. I am right about the injector hoses, aren't I? It should go: aluminum head->injector seal->injector. There is no plastic that goes between the seal and the head is there? Also, the green caps on the injectors, how important are they? Several of the injectors had them broken off or completely missing. Can you buy just the cap piece? Oh yeah, we aren't going to do the seals on the right side, which wasn't opened when you left. We opened it when the mechanic told us to. Later we just put that side back together except for the valve cove and injector assembly (rails, etc.).
Once again, thank you so much for your help. You saved us a lot of time and guess work and it was interesting to get other useful information about the car. You are the only one so far from the forum that I have met in person, I hope they are all as friendly and polite as you are.
Thanks Again
David

Tomguy · #15 11-30-2003, 12:14 AM

The green caps are VITAL!
They fit snugly in the seals. Without them, the injectors will NOT seal properly. And I was unable to find just the cap myself - but my injector turned out to be bad anyway (it leaked).
The injectors go this way: Injector, metal ring, rubber ring, metal spring clip (to retain the rubber ring), and then a rubber seal (small one) that goes around the green tip and into the manifold.

You confused me about the valve seal coming out on the injector - did you mean the injector seal?

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