Poor cold running - PeachParts Mercedes-Benz Forum

Tomguy · #1 11-11-2003, 10:54 PM

Well, the cold has come, and my car doesn't like it one bit...

It starts right up, but idles very rough. It accelerates very slowly and hesistantly, and backfires (or fires through the intake manifold, not sure which, think a little (a lot) of both). Once it warms up it does run a bit better, but it takes quite a while. It still runs a bit funky even then. But if I park it somewhere for at least 5 mins, and go back to it, it fires right up and runs perfectly. I have no idea if my mixture is set right, or close-to-right. But it runs great and seems powerful when warm.

Any ideas? *stumped*

Tomguy · #2 11-13-2003, 01:44 PM

Well, adjusting the mixture leaner didnt help. Have to wait till she cools to see if richer does. Any ideas out there?

Fuel filter is about 3 mos old. Newer plugs, wires, cap, rotor and points. Timing dead on 4* ATDC (I wanted to be a degree more "Agressive" but don't think it changes anything, really). Dwell was 30 last time I checked (1 week ago?). Points are clean. *still stumped*

psfred · #3 11-13-2003, 08:10 PM

Tom:

Check for condensation in the distributor cap -- this will short out the rotor and cause misfires (wrong cylinder firing) and surging, all of which Big Blue exhibits when started cold. Goes away with a quick squirt of carb cleaner and a wipe. Will also short the points.

Take a look at the rubber plug the point wire goes through -- chances are it is rock hard and floating around in the slot, allowing damp air to get in at night. If it is, do what I'm going to do soon -- get some RTV sealant and glue it back in to eliminate the leak. Probably best to do with engine hot to reduce the amount of water vapor in there to start with.

Peter

Jim Anderson · #4 11-13-2003, 08:31 PM

I think they should be maintance items. If it's any more than a couple of years old, change it.

Tomguy · #5 11-13-2003, 08:50 PM

I KNOW I need a new thermo. But this I don't think is related to it: If I run it, shut it off and come back to it, it'll be fine. Even a short run where the temp barely rises.

I'll try that, Peter. Sounds like it's very likely - I didn't even KNOW that was rubber, thought it was bakelite!

zambo · #6 11-13-2003, 11:22 PM

Hi Tom

I had similar behaviour a couple of weeks after I bought my 3.5. I did a couple of things (because they obviously needed doing) and thus do not know which fixed the symptoms specifically but here goes;

Installed a set of german ignition leads because it came with a cheap set of Champions

Trigger points serviced because they had some gunk on them and adjusted.

Had one fouled spark plug - it was replaced.

Re-set timing and normal idle adjusting stuff

After this stuff, it has run (touching wood at my end) flawlessly from an engine viewpoint.

My MB trained mechanic said that anyone of the above can manifest the symptoms I had - which are very similar to yours. Hope this helps.

Regards

Richard

Tomguy · #7 11-14-2003, 07:18 PM

WOW. It's amazing that my car was running at all! The bottom 2 trigger points were COMPLETELY gunked up with oil! After cleaning them out and reinstalling my distributor, my car seemed like it didnt want to run at all! But I held the pedal to the floor and (while it was running about 1K RPM) it blew out a TON of smoke and then ran so clean and well I couldn't believe it! Thanks for the advice!

psfred · #8 11-14-2003, 10:40 PM

Tom:

I cleaned mine when I fixed the stuck mechanical advance. Made a big difference! I probably need to get the distributor apart someday and replace the bushing and seal to keep the oil out, cleaning is only a temporary fix for oily trigger points -- the oil will come back so long as the dizzy leaks...

I'd going to go out and try to start Big Blue in a bit -- haven't driven it all week after cleaning up the rotor -- ran great after that, no stagger or surge cold. Need a new cap and rotor, but money is tight right now, as per usual.

Peter

Tomguy · #9 11-15-2003, 01:59 AM

Peter: What ticked ME off the MOST was finding out that my mechanical advance doesn't work (AGAIN)! It wasn't 100% before (probably 50%) but now it's 0%! It doesn't move at all unless I force it. I NEED to find out how to get that pin out of the gear!

psfred · #10 11-15-2003, 10:50 AM

Or you can do the cheap and cheerful fix like I did:

The problem is the rotating section at the top is gunked up, so pull the felt pad out from under the rotor and apply liberal amounts of PB Blaster overnight. Liberal means enough to partially fill the cavity. Next morning, should be empty again, add some AFT, just a couple drops, then with the distribultor in a vise, start working the rotor shaft back and forth. You can see the weights through the trigger point hole, so you can soak them down with carb cleaner to de-gunk then some PB Blaster as well if you want. Weights are almost never the problem on Benz, though. Leave the assembly completely dry when finished, it will get plenty of oil from the top.

The shaft will eventually free up considerably. At this point, add some synthetic oil, just a couple drops, and wipe up. I actaully sprayed it out with carb cleaner first to get all the oil and stuff out to prevent spraying it around the dizzy, only partially successful.

I'd also oil it again in a couple weeks, just a drop or two off the dipstick will work. Oil again every 3-5K miles.

Mine still isn't as free as I'd like, but it does actually move now, much better than before.

Peter

Tomguy · #11 11-15-2003, 03:36 PM

Erm... felt pad under the rotor? I think mine is rock-hard... I don't recall exactly.
It (when well greased) moves with a LOT of resistance - I think that there is something amiss in the weight mechanism )The weight is off its pivot I believe).

psfred · #12 11-15-2003, 08:16 PM

It will flop around with the weight off, since the weight and return spring are what move the rotor in relation to the drive shaft.

Most likely is is gunked up -- if it is like the Ford distributors I've gotten rather too got at over the years, the upper part fits over an extention of the lower shaft, and any dead oil or dust makes it very difficult to turn the upper part. Best thing, of course, is to take it apart, but failing that, you must dissolve all the gum in there to free it up. Hopefully it's not rust from never being lubed.

You are supposed to lubricate the rotor shaft on this dizzy each oil change, two or three drops of oil on the felt pad. No one does, of course, so they lock up.

Mine did exactly what your's did -- worked fine when I got it, was stuck next time I checked.

Ruins gas milage and seriouly reduces top end power when stuck, but mine is now free and works fine.

Peter