Due to a teenage son and a guardrail, I found myself one car short last week and had to take my 79' 280CE out of winter storage as a daily driver until I can replace the totaled vehicle. The first time this old Benz has ever seen snow and cold, she started and ran fine until a couple of days ago when an intermittent LOUD noise began like small pebbles rattling in a coffee can. The noise usually disappeared when the car warmed up, and so when I stopped at the mechanic to get a diagnosis, of course, no noise. He was surprised to see the polution stuff still hooked up, suggested that the noise was from the "air pump", and said to disconnect the belt as the source was probably a failing pump; that here in Minnesota on a car this old, the equipment was unneeded anyway. OK. Last night, the noise returned and was getting worse as I drove home, so in a suit, 15 degree weather and snowbank, I reached under the bumper and cut the belt off. Problem solved, noise went away, engine smoothed out and car seemed to have more power too. Later, I filled the tank with gas and took wife to dinner. COming home, we both smelled gasoline and this AM when I opened the garage door, the smell was potent! Driving to work with a window cracked, I thought the smell was being sucked into the compartment thru the vents but when I shut the window, it seemed better but maybe only because I was getting used to it. Help? Have I done something making it dangerous to drive? How do I get rid of this smell?

Well, my guess would be that disconnecting the emission control, in addition to the COLD weather (car running very rich) is that you're smelling the gas due to the car being too rich that otherwise would be better "processed." Does your oil ever smell of gas?

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Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

Check the fuel lines, it's possible you have a fuel leak brought on by very hard lines cracking in the cold. Look under the car, too, there is usually a short section of fuel line between the steel oned under the driver's seat. Also at the tank.

Fuel tank spillage or plugged tank vent is possible, too.

Cutting the belt to the air pump won't cause this, neither will running too rich -- that's plenty smelly, but of rank half burned fuel, not raw gas.

Peter

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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!

Cutting the airpump belt MAY cause an odor as air is no longer being pumped into the exhaust and exhaust fumes may back up through the airpump due to old/faulty control and check-valves in the air injection system. You should disconnect the air hose and plug the check-valve at the exhaust pipe or manifold if you plan on running permanently without the airpump.

Happy Motoring, Mark

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DrDKW

Ok, thanks for the guidance. Fred, I think it too coincidental that the smell started when I cut off the air pump belt to be fuel line related. I thought spillage because I filled the tank was a possibility, but with the miles I drove before parking it last nite, there wouldn't have been such a strong oder in the garage this am. The car has never idled down well from cold starts, so running rich may be a factor. But I think Mark's directive makes the best sense. I do not understand in more than theory how the pollution control system is supposed to function, nor what/where to plug off. What am I looking for?

I wouldn't park the old girl in any structure that I wouldn't want to see burn down until a leak and/or cracked fuel hose is ruled out.

I'm not familiar with the specific air-injection setup on the 280CE but generally, there is a belt-driven airpump forcing air into a 1 inch diameter air hose connected to a control valve (also known as a diverter valve or anti-backfire valve). The control valve will have another 1 inch diameter air hose connected to a kind of mushroom shaped item, called a check-valve or one-way valve connected to an air injection tube or air injection manifold. This air injection tube may be connected to the exhaust manifold or the cylinder head just upstream of the exhaust manifold or may even have an extension pipe connected down below, to the exhaust header pipe or catalyctic converter. You should disconnect the 1 inch diameter air hose from the check valve and get or fashion some sort of rubber plug to clamp over the check-valve nipple. Some auto parts stores stock large diameter rubber plugs for applications like this or you can make one from a short length of same-size rubber pcv hose or heater hose with one end plugged.

Also, as PaulC said, make sure you don't actually have a real fuel leak!

Happy Motoring, Mark

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DrDKW

Gotta be extreme degree of difficulty debunking your own emissions control sensors..... meanwhile you should consider every 20+ yr old fabric braided fuel line on the car as suspect of being porous.

This happened on my 116 - the car was getting crappy mileage with mild smell of fuel sometimes.... I threw the car on a lift and investigated several sections of original fabric braided fuel line. They looked dry - but became wet with leaky fuel just by poking them with finger....... and yes, there's probably 8-10 feet total length of flexible fuel line sections running from the tank to primary fuel pump to injector pump and also on return to the tank. If your 280CE is 123 body style then the tank is behind the rear seat...... hence the liklihood of fuel smell inside the car coming from time worn flexible fuel lines.

Personally, i think the idea of shut down vacuum system having anything to do with fuel smell is off the wall.

Thanks Mark, I'll figure it out, but first, and with due appology to PSFRED, I DO have a fuel leak, a huge one. And really need someone's help now to figure out what to do about it. When I went out to the car after work tonight and opened the door, the gas fumes from inside hit me. On the way home I called the MB wrench who advised me to remove the air pump belt, this was right at 5pm as he was closing up for the weekend. He opined that cutting the belt wouldn't cause such a smell, that I should look to see if the gas cap was on. When I got home, I chose not to pull into the garage, but took a look at the garage floor. About right behind where the right rear tire would sit, there was evidence of about a 3foot diameter evaporated gas spill. Expecting to find evidence of a leak elsewhere if there was one, I first thought maybe one of the family had spilled gas when filling the snowblower. I walked back to the car in the driveway and noticed a puddle on the cement about the size of a softball behind and to the inside of the right rear tire. Could it be? Or did another car drip something there? Changed clothes and came back out with a flashlight. In 20 minutes, the puddle was now the size of a bushel basket, and looking under with a flashlight, it was still dripping from a drain hole in the undercarriage between the right wheelwell and the tank. Is the connection from the filler pipe to the tank rubber? I'm guessing thats where the leak is. But even at 25 years old, the undercoating on the car is all there, and for the life of me I can't figure out how to get to it. No access from underneath. Nothing from the trunk either. Do I somehow have to pull the inner fender lining with the tire off the car? Help, help? If this is a bigger job than I can tackle this weekend, I need to know as I'll have to buy another car tomorrow just to get to work. And sorry guys, but it will be a toyota I've been eying.

I took a quick look in the parts book and the tank and filler are one piece. The filler seems to be the only connection on the right side. I wonder if it has cracked and is leaking because of the full tank. Or perhaps the tank has sprung a leak on the right side. If it is the filler, I would expect it to stop as the fuel level drops.

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

I think there are some vapor control hoses there too, that go up to the neck of the filler.

You could have a bad gas cap, allowing fuel to splash out. This will happen even with fairly low fuel in the tank on turns.

The tank is, I believe, behind a sheet metal shield. Pull the trunk lining and take a look for retaiing screws. I'd also pull the first aid tray and take a look at the top of the tank, you may have a bad hose up there, too.

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!

Almost sure it's leaking rotted dryed-out fuel line hoses.

Replace all rubber in fuel lines. With proper hose, of course.

I'll bet smell disappears after residual gas evaporates completely!!

I recently had, what I thought, a minor gas leak.

I removed the tank for inspection and found one or two small holes on the top of the tank (made sense of why I could only fill half the tank). 50 bucks at a radiator shop and I figured the problem would be solved. Well, they flushed the tank over night and were getting ready to seal it when they notice thousands of tiny holes, which made my gas tank resemble a spaghetti strainer. I ended up purchasing a gas tank form a local junkyard for $175. A little expensive but it was the cheapest local place I could find.

Well, I'm stumped. It was surprisingly easy to uncover the tank re psfred's directions, although the cardboard trunk lining I pulled to expose the sheet metal cover shredded coming out. The sheet metal cover was held in by only 4 8mm bolts. (Which BTW were all loose, and so could be the source of a rattle I've been looking for a long time) But I could find no leak! As I described (poorly) before, gas was dripping from a weep hole under the right side of the trunk, but the hole is a good 2 feet from the filler pipe and tank. To get there a lot of gas had to have run from somewhere else. Of course after sitting all night, all gas had evaporated, and I couldn't detect where it had come from. The tank and welded filler pipe appears solid. And as this car is from Florida, it has never had rust anywhere in or out. (Ok, a tank can rust from the inside, but follow with me.) What hoses I could see were either metal with still fresh looking black paint on them or rubber. All I found was that the vent hose that goes from the tank to a nipple on the inside of the filler opening was off the nipple and so venting into the trunk. But it was too short to reach, and so clearly has not been attached in some time. (previous owner told me that at some time in the car's past before he owned it, it had a fender bender near the gas cap, and my sense is when the repair was done, or the tank has been out of the car for some other reason, the vent hose wasn't routed as original and stuck between tank and chassis, rather than re-loosen the tank bolts, was just left that way.) Had gas somehow splashed back out of the vent line? I drove the car around some and couldn't get the problem to re-occur. Ok, maybe because the tank wasn't full. So I went to the same gas station as when I filled up and the problem started, topped off all the way up the filler pipe and then retraced my exact driving route that night I first smelled gas. Nothing! Bone dry. No leak. Ok, since the trunk still smelled of gas I stopped at the auto supply for some killer freshener and a short piece of fuel line to splice onto the too short vent hose. I'm typing this while I wait a bit to check again, but my best guess is that I somehow didn't get the gas cap on tight enough...it has always been a tight fit and the rubber ring in the cap is ok...and that gas blew or splashed out of the cap, and with the hose off the vent hole, the hole became a drain, funneling the gas into the trunk and eventually out the weep hole. I can't come up with any other explanation, so I'll make the splice tomorrow to make the vent hose reach and put the shield, sans cardboard cover/trunk liner plus the plastic side trunk liner back in. BTW, I still think I'll get the Toyota this coming week and re-park the Benz till Spring, but geez is this old engine running well with the pollution control belt off. 172K now, and she still burns not a drop of oil.

The 280 used to reek of gasoline once in a while til I discovered that the filler cap had a bad gasker. Replaced it with an oil filler cap (same fitting) and the problem dissapeared. Gas milage went up a bit, too.

You could have had fuel spilling due to expansion in the tank, too. I don't know what the temps involved are, but it's possible that the garage is warmer than the fuel at the filling station was, so that it expanded and overflowed out the vent line overnight. Driving with a full tank could have splashed it out, too, although I would expect it to happen this time was well.

Get the line fixed and be careful -- some idiot flips a ciggy butt under your car while it's dripping fuel and you could have WAY too much fun!!!

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!