M110 - idles okay in P/N - dies in D ??
 

Hello All-

recently inherited my grandmother's W114 1976 280.
My grandma calls her 'The Handsome Old Gal' and with good reason: she is in outstanding shape as far as paint and interior goes. (Seen winters but no salt ) Starts all sorts of conversations, which is super fun, however, she stalls out when I move the automatic transmission gear shift from 'P' (or 'N') to 'D'.

Some background:

Drove her this past winter to the Bay Area from Montana (1500 miles) just fine, although she drank up a quart of oil every tank of gas (~250 miles). It pretty much went away about 1000 miles into the trip and then demanded 1 quart per 4 tanks or so. Didn't see any leaks below, so decided to ignore this ... Was having trouble with cold starts (my grandma did too), but had good MPG, at least 20 (60% highway/ 40% city). Then, the rainy season started, and she began to have trouble sometimes, stalling out in while in D while at a stop or just pulling out from a stop. Took her to a mechanic who turned up the idle. Seemed to help but still stalled out too frequently for my taste. Had the mechanic do a minor rebuild on the Solex (replacing gaskets + the carb mounting flange) after he insisted the carb was the problem. (He did the whole carb cleaner spray test). I got the car home, but just barely. He said he fixed a few vacuum leaks, yada yada, but now the car will only drive if the idle is turned WAY up. Said there was something wrong/leaking with the fuel pump vacuum or something but I was little inclined to believe him.

After reading around on these boards, I figured something I could first off do myself was change the plugs and wires. My grandpa insisted this is important, as bad plugs on this car once caused him a big headache. Pulled the old plugs, saw they were in bad shape, changed them out, turned the idle speed on the carb down to something that sounds nicer, and got some improvement with idling. The engine sounds smooth (with a tiny bit of 'puff'-ing occasionally), and the car drops down from the high cold idle to the warmed-up lower idle, but it immediately conks out when I shift into D. The funny thing is, the battery, which never gave me troubles before, now will not start the car...

So, the cold start problem is gone. Yay.
The car starts right away with a jump.
Idles just fine, no smoking out the back or leak-spots beneath.
Really Wants to keep running in Drive, but can't, and then won't restart w/o a jump.

Any suggestions of what I should do?
Does this sound like a timing problem?
A Carb problem?
An electrical problem?
A transmission problem?

I am more determined to fix this myself if I can, rather than pay someone else to make the car run even worse...Or a least have some idea from people who really know and care about these old cars before I venture out onto the 'mechanic market' again. ( I'm a student in the Bay Area, and mechanics around here want $100/hour at independent shops (!))

What do you all think?
Many Thanks-

CJ

I am more determined to fix this myself if I can, rather than pay someone else to make the car run even worse...Or a least have some idea from people who really know and care about these old cars before I venture out onto the 'mechanic market' again. ( I'm a student in the Bay Area, and mechanics around here want $100/hour at independent shops (!))

What do you all think?
Many Thanks-

CJ[/QUOTE]I know about but don't really care for those older cars, but I will offer some help. First off it was a mistake to let that mechanic rebuild that quadro jet. It is not the same as an American quadro jet. He probably cranked down on the four corner bolts which distorted the air horn and will now cause trouble with the secondaries. What's done is done. I would suggest a valve adjust if grandpa didn't want to spring for the expense. It should be done every 15,000 miles. Secondly I would set up the dash pot to factory specs. It is supposed to advance the idle when in gear or A/C is turned. Next I would be sure the vacuum box that sets pre throttle gap is functioning properly and also make sure the the pre thottle gap openning is correct. Keep me posted.

One thing to check is whether the idle valves are working.

You will see two conncectors at the base of the carb. With the igition off, loosen the connectors so you can pull them off easily, but leave them attached. Turn the ignition on, and unplug and re-plug each connector. Each time you do this, you should hear a "click." If you don't, then the valve is bad and needs to be replaced.

These valves are open when the ignition is on, closed when off. Their function is to stop fumes from escaping when the engine is off. If they don't open, the idle circuit does not get any gas.

The problem you are facing is that these carbs did not work very well even when they were new, and they are very difficult to repair as they age. They develop vacuum leaks from heat and over-tightenting and wear around the shaft bushings. With a 1976 car, you have the latest and best of the 4A1's but it is also in the middle of the most complicated emissions system, which has all sorts of pieces that can cause problems. You could well have a switch or relay failing causing the hot idle problem.

If you are going to try to troubleshoot, get a copy of the "Service Manual Engine M110" from Mercedes or eBay, which has great detail about the carb and its surrounding systems.

Chuck,
Good point. I forgot about the idle shut off valves. It has been years since I've woprked on one of these carbs. Also the o rings on the idle jets must be in good shape or they will cause idle prooblems. I always lubed them with silicone paste. Buying that carb, the Ford cruise control, and the Chrysler climate control were MBs biggest boon doggles.

I may have an extra copy of the manual I can sell. I'll have to check.

You may have to adjust the vacuum idle regulator (driver side of carb).
Unplug the hose and set the idle to 2000rpm (at lot) with the bold on the end.
Then reattach the hose and adjust the spring tension with the big nut.
With an automatic transmission there should be a 1mm between he bold and the linkage, if you have an airco, switch it on and adjust the spring until the car idles well.

An other thing to look at is the ignition. Set the points to 39-41 degrees, this is very important. One degree off and the car will not run as it should.

Maybe.

But the car should idle in P or N at about 800-900 and drop to 650-750 in gear without the vacuum assist. It is supposed to give a boost when the AC is turned on or the power steering is engaged at low RPM.

This are the adjustment instructions from my old German shop manual. I used it on both my carburettor M110’s and they always ran perfect.
The vacuum diaphragm pulls the screw back against the resistance of the spring. So you first have to set the speed without the vacuum line attached to get a standardised reading (2000rpm). Then set the spring preload.

If you put the car in gear you will get a temporary drop in vacuum, there is a slight delay in the carburettor reaction. Without the vacuum controlled idle the rpm will drop so much that engine will stall. M110 are a really high revving engines and bit sensitive on low rpm’s.

Rob,
You are absolutely correct about the adjustment procedure. It is the same procedure for the Zeniths.

According to my manual, it's 1700-1900 RPM (Job 7.2-100).

And I stand corrected. The manual adds in Step 11:

"[Re]-attach vacuum hose. Engage driving position on automatic transmission, set to specified speed [600-700] RPM by means of adjusting nut [on vacuum rod]. Turn power steering to full lock and engage AC system. Engine should still run smoothly. Re-adjust speed if required."

Both my German manuals say 2000rpm, maybe there is a difference between Euro and US.

What you say in step 11 only applies to cars with airco, as I wrote earlier. Without airco set the gap to 1mm. And of course test with car in drive, power steering at maximum and airco on.

Never put car in drive if you are not sitting in it and/or there is someone in front of the car. You would not be the first to be surprised by a car taking off while adjusting the idle. The parking brake is not that strong.

Hi guys,
I'm not trying to start a pi**in contest or trying to be top dog. I'm just interested in helping a guy get going. The way I was tought and the way it is illustrated in my MB training manual is to set the long screw to whatever specs are with vacuum disconnected. I will have to look it up down at the shop. Let's assume 1800, but I think that's too high. Reconnect vacuum and adjust the big nut until the spring keeps the screw about 1 mm away from contact. Then lock down the jam nut. The dash pot is not used to adjust idle. Idle is set with appropriate idle screws on whichever carb you are working on. Once idle is set, you adjust the dashpot. Rob pretty much has it right.

Thanks, Guys!
 

Autozen, Chuck and Rob-

first off, thanks for all of your feedback.
Autozen, you're right about my grandpa- things started breaking that should have been fixed on this car: I figure it stopped getting 'real' maintenance about 10 years ago. But, as I said before, the car is in relativley good shape, only 130k miles, and I do like tinkering around with things... My dad sent me his old tools he used to work on with his old home (a VW bus)- my spark plug puller and timing light are actually older then the Benz...What fun to try to figure out this old school engineering- no computers... I am also figuring out that if I want to keep this car around a while, I'm gonna have to be able to diagnose and fix most things myself....I do have the service manual, the service manual for engine 110 and the service manual for 114/115 in front of me. WOW. The section for job 7.2 is HUGE. The can of worms gets deeper.

-Idle Valves: I remember testing these with the aforementioned mechanic, L. I will re-do this test to double check.
-Dwell Angle + Valve Clearances: Found a friend with a tools to help me with this next week.
-Dash Pot : Is there another name for this? I see a fuel filter-type thing before the carb which is about half full of fuel which has the same shape as transmission dash-pots belonging to 123s I found on the internet...On the solex diagram on 7.2 900 - is the dash pot labeled here as something else?
ahhh, the Solex:
-Jobs 7-2 100 and 110: I know where I'll be on my next days off. Thanks for your comments on this.

Has anyone any experience with a 'new, un-over-tightened' Solex. Sounds like you have had good experiences with these Rob? Would it be worth it to buy one of these? I found a guy in Germany, Bob Taylor, who seems to know his stuff and has a 'new' Solex on hand. A bit pricy, but if it would solve the problem of the secondaries, at least give me fresh start from whatever happened to the car in MT....

"Never put car in drive if you are not sitting in it and/or there is someone in front of the car."

Yup. Figured this one out already. Have skid marks in my garage. ;-)

"Buying that carb, the Ford cruise control, and the Chrysler climate control were MBs biggest boon-doggles."
But there are so many of these 30+ year old cars still on the road, real workhorses. Longevity is a true test of quality, no?

May Many Many Thanks, Guys.
I'll report back with my progress.
-CJ

Just got back from the shop. Was going to install a nuthin safety switch on a 91 300E and decided not to waste my time moving 2 cars to get to the hoist on this beautiful sunny afternoon. There is always tomorrow.

Broke out the 75 qnd 76 yearbooks. Book says idle speed 800-900. Set vacuum pot to 1700-1900. In drive 600-700. Turn steering lock to lock with A/C on. Should idle smoothly. Book says to adjust big nut on vac pot to increase idle, but I disagree. Year books always come out the year of car and not really tested. Instructions usually change with time. After setting up hundreds of these carbs, I keep the 1 mm distance.

If you buy a carb, be sure to get a US 1976. There are 3 carbs for 3 years. Also since they changed the 20 year law in CA, you will always need to smog a 1976. IIRC you have a float bowl vent on that model than can give you grief at light throttle.

Since the carburettor was taken apart it is possible that the vacuum lines are mixed up.
On the carburettor you can find three vacuum lines, the one towards the centre of the engine should be attached to the idle delay of the distributor, the top one on the other side to the advance and the bottom one to the idle control and fuel valve.

I would also check the ignition, bad wires and rotor+cap, or wrong or points setting can give similar effects.

Do not buy a new carburettor without knowing what is wrong with the old one. Swapping expensive parts is a quick and practical way of diagnosing a problem if you have then lying around or can take them temporary from an other car. Not if you have to buy them.
My first 110 had a completely worn carburettor from running for 600.000 km with GLP poured in from the top. It still ran fine on gas.

If the ignition is OK, the next step could be to take the carburettor apart. Since you don’t have much faith in you mechanic it may be a good idea to do it yourself. It is not that hard.

Agree with that. Chances are the carb is fine. If you had a warped top plate from over-tightening or heat, you would have backfiring during warm-up.

You have accurately described the inline fuel filter.

The idle dashpot is on the fender side of the carb, in front. I you look to the rear of it, you will see the rod, that pushes out and contacts the throttle lever. The theory behind this, which we did not explain very well, is that as idle drops, so does the vacuum that hold the rod in. The spring then pushes the rod against the the throttle and opens it a bit so that the engine does not die. Then as vacuum increases, the rod is pulled back a bit. The trick is to get the rod adjusted so that it pushes just the right amount on the throttle lever.

One useful test is to get a MityVac, and test to make sure the dashpot holds vacuum.

But as Rob mentions, you should make sure that the vacuum lines are hooked up correctly, and that none are broken.

The thick gasket between the carb and the manifold is famous for leaking. I suggest getting a spray can of carb cleaner, and spraying it around the base of the carb - use the little red tube - with the enigne idling. If you get an increase in idle speed, then you need a new gasket.