I’m new to the world of vintage Mercedes and new to this message board. I'm enjoying the car and really appreciating the quality of the engineering and workmanship. It's slow at the bottom end, but amazing at the top end.

Here's the problem: It starts fine when cold and runs well. 15 ~ 20 minutes into the drive, it starts to run bad, idles rough, and stalls at stops. I can park the car for just a few minutes, and then it purrs at idles and runs well again.

Any ideas? Thank you in advance for your tips, knowledge, and insights.

i would start by checking all of the fuel lines,and replace the fuel filter.fuel filters are cheap and easy to replace.

Without more to go on, the fuel filter is always a good place to start. That something is affecting fuel flow is the most logical culprit. Crud in the lines or carbon buildup somewhere can often be cleaned this way: When down to 1/2 tank or less of gas, pour a full tank's worth of injector cleaner in and run the tank dry and keep using cleaner with the next few tanks. The 280 gas engine seems to run better when driven hard too. Remember when Dad used to "blow the carbon" out of the family Chevy? Same applies here. Sometimes something as simple as a high speed highway drive solves the problem...The Italian Tune Up its called.

Next possible cause with a simple fix is to look at the plug wires. Pretty common that the brackets that hold the wires away from the hot engine are broken off. If old wires, lying directly on the hot engine can limit the juice getting to the sparkplugs

Thanks you Guys!

* I've installed new plugs, new cap & rotor, new K&N air filter, run injector cleaner through the gas tank once, checked for vacuum leaks and it still does the same.

I'll replace the fuel filter and check the plug wires to confirm they aren't sitting on the engine and let you know the results.

Any other ideas? Please post!

Thanks!!!

Fuel filter? Ditto!!!!

I am sure that this is your culprit. Blockage just builds up over ride time and under system pressure.

Had the same thing in my 450 sEL. Started strong, then got weaker and ehsitated.

New filter will help much. Have it done right.

You may not notice difference immediately upon installation. Srive it gingerly for about 2-3 days, slowly increasing acceleration.

Let us know.

Make sure you don't have condensation in the distributor cap -- dampness here will cause all sort of trouble. If it runs fine below freezing and gets rough as it warms up, suspect water vapor frozen on the cap.

Usually culprit is a loose point wire rubber grommet. Can be fixed with some RTV sealant to eliminate the air leak.

It's probably not cold enough for the strange problem I had on the Audi Fox with CIS injection -- when it got really cold, the blowby (ported into the intake in front of the fuel distributor) would freeze on the venturi, causing the velocity of the air to increase and the flap to be forced further and further down until the engine flooded out. Stopping for a few minutes would allow the fuel distributor to thaw and it would start right up. Took a while to figure this one out, only happened when it was 10F or colder on the highway. I finally caught on when I had to floor it to keep the engine running and saw black smoke rolling out the back -- stopped at a garage and had them pull hose on the fuel distributor, and it was full of ice!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I've gone back and reviewed the records from the previous owner. The fuel filter was replaced 2 years ago and approx. 20 thousand miles.

No condensation in the cap and because I'm in Southern California, very cold temps aren't really a factor. Also, the plug wires still have the guides keeping them off the hot engine.

If you guys still think it's prudent to change the fuel filter, I'll do it this weekend.

Thanks for your assistance on this topic.

BTW: that's an amazing story and a wonder that you located the culpret for that problem!

You tend to get creative when you are stranded on the side of the road in 4F weather!

I figured it had to be fuel related from the smoke, and I knew enough about the FI by then to take a look.

The blowby hose had been disconnected when I got the car, I surmise this is why. I hooked it back up (but not the EGR or the coast idle bypass -- the EGR cooler was rusted out and the bypass stuck open -- 2000 rpm with your foot off the gas is kinda scary....)

I managed to get 135,000 miles out of that car before the floor pan rusted out, along with everything else. Great car to drive, but I've not seen one for at least 15 years now. Fenders rusted out from the inside, the frame had holes in it big enough to put your hand through, and the tailgate wouldn't latch because the frame had rusted so much it flexed away from the door when you closed it. Interior, engine, and tranny were in nearly perfect shape. Sad. I liked it MUCH better than the Dodge Aries I replaced it with.

Your running problem sure sounds like a progressivly plugging fuel filter. If a new filter fixes it, you should consider getting the tank cleaned, it may have lots of crud or rust in it. If a new filter doesn't fix the problem, you need to check the tank screen, especially if the problem is worse when the fuel level in the tank is low!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Checking fuel delivery when running poorly may help with diagnosis

I had similar problems……..see my ‘Italian Tune’ thread……………. that wasn’t helped with fuel filter replacement……..but was cured by cleaning out the tank and replacing the in tank screen

Couldn’t believe the crud……….but my ’78 280CE hadn’t been used for 5yrs……..or perhaps we have particularly cruddy fuel in Australia !

In any case, if fuel delivery is good when playing up you can save yourself pulling the tank ……..which for my w123 was the easiest way to clean the crud & replace the strainer

The crud was a couple of inches deep around the screen…….my theory is that a few corners shook up this crud which plugged the screen……..I noted pump ‘zinging’ as it tried to suck against the blocked screen……………turning the motor off for a few minutes allowed the crud to float off the screen and everything ran well again………I also noted it ran for longer in a straight line………..died on corners & hills

If fuel delivery is shown to be the problem……..bite the bullet and pull the tank……start at the top and work down stream to clear all the supply system

Good Luck

David

Link to 'Italian Tune' thread

Thanks to all of you for your replies.

I'll follow your recommendations and I'm confident they'll take care of the problem.

It might be a few weeks before I can get these done. I'll report back and let you know!

Really appreciate your help!

Check for fouled injector points

No trigger points on K-Jet, as a '77 280 would be.

Possible that you have a loose or warped intake manifold, too, that opens up and causes a big vac leak with a hot engine -- another poster had this problem in the earlier L6 engine.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

After reading many of the threads on various topics ... this is the fix that has worked so far.

I lubricated the top of the distributor's shaft with ATF fluid a couple of times over a 3 week period. It seemed to break-loose a sticking advance mechanism.

Now the car doesn't stall or run bad after freeway driving like it has since I got it.

Thanks to this forum, I'm enjoying the world of "Vintage Mercedes".

Thanks to all!

Richard

you should still replace your fuel filter,if i read it right it was replaced 2 years ago.a least once a year or more,theses are older cars and unless you have a brand new fuel tank in there,you'll have some kind of junk in your tank.just my opinion..