Help! I'm stumped....

[n/a]

When decelorating (freeway offramp or slowing down for a light) in gear, I get a strong exhaust smell. It only happens when in gear.  I have no visible signs on an exhaust leak. Exhaust/intake manifolds are tight. (Gasket is clean, no missing or sputtering) Manifold to header pipes are both quiet and clean. My car is 70 280SL. Timing is correct, and the car runs great.  Any ideas? I'm stumped.

Michael

[Chad]

Is the top down at the time you are decellerating in gear?

-CD-
1967 230SL, 113.042 10
1983 300TDT, 123.193

[Tom]

Does the car also sputter/backfire when decelerating?  There is a deceleration solenoid on the back of the fuel injection pump.  Frequently, owners disconnect the wire that activates the solenoid as it sometimes cuts off fuel and stalls the car.  It is intended to reduce/cut fuel during deceleration and relates in some way to the emissions controls.  If you don't have a wire connected to the back of your FI pump, connecting that wire may solve your problem.

Car may also be set too rich.

1971 280sl Tunis Beige Metallic (restored & enhanced)
1971 280sl Tobacco Brown (low mileage stock)
1970 280sl Deep Red (Project Car)

[n/a]

Thanks for the response. I will answer the two questions in order.

1. I have tried with and without the fuel shutoff solenoid. I get the exhaust smell both with and with out it connected. All emissions systems test out to be working.

2. I get the smell both with the top up or down.

Iv'e been racking my brean over this.  Not to mention the headaches.

[Tom]

Ok, maybe it's the vapor condensation system-the black plastic box in the trunk.  Smell can migrate into the car.  Also, a good tight fitting gas cap is important.  Gas can leak from the cap, migrate down the pipe past the rubber boot and into the trunk area.

Also, check the vapor line that outlets into the crankcase.  If this is loose, vapor could escape and migrate into the passenger compartment.

As you can tell, I am just providing a "stream of thoughts" that might be your problem.

Have you checked the CO level when you tuned the car?

1971 280sl Tunis Beige Metallic (restored & enhanced)
1971 280sl Tobacco Brown (low mileage stock)
1970 280sl Deep Red (Project Car)

[Cees Klumper]

I don't recall this problem ever coming up before, it's always 'gas smell' rather than 'exhaust smell'.

Is your car automatic or manual?

There is no interaction between the exhaust system and any of the other systems, right? (I mean, all the vacuum connections are on the intake side). So the only thing I can think of is that it is an exhaust valve problem OR something amiss with the exhaust system after all. Although I don't know anything about the emission controls systems. Maybe studying the emission controls diagrams that I believe are in the BBB would produce some hints.

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[n/a]

Hey Tom,
Thanks for the reply.  I thought that the vapor tank may be the problem too.  So, last week I replaced the plastic line from the crank case back to the metal line.  As for the CO level. I keep it between 4.0 and 4.3

I have ordered a new rubber boot for the vent on the valve cover. (couldn't find fault with the old one but you never know)

Would the gases from the crankcase smell like exhaust?  Wouldn't that smell more like oil?

The only time I get the exhaust smell is deceloration "in gear" (4-speed car) Never during coasting, or acceloration.

I think I'm loosing hair over this....

Michael

[n/a]

Hey Cees,
I was thinking that maybe the valve timing/lap may be off causing exhaust to find it's way back through the intake.  But the car runs so darn well that I just can't emagine that being the case.  No kidding the car runs great.  I'm runnig a 327 rear and I can still spin the tires in first gear.  No kidding!

When decelorating could their be enough back pressure for the exhaust to find a way out?

Emissions system tests fine. As for vacuum.. only one outlet connected to the 2-way valve for the advance. I can check the hard plastic lines for splits and cracks again. I can't think there is enough back pressure to force it's way back to that little tubing.

[Chad]

You are trying to describe a perfect engine and mechanical gear, I think.  If that's the case I would look under the car and run through the exhaust system, but I really am not very mechanical. Has the car been up on a lift?

-CD-
1967 230SL, 113.042 10
1983 300TDT, 123.193

[n/a]

Thanks for the reply Chad,
I have a 4 post lift in my garage and have the the car in the air quite regularly.  I have acually change to a stainless system since this all started.  Their is a connector and clamp before the resonator that I will check out again today. I'm also going to inspect the manifold for a pin hole leak today.

Note* this car has been with this exhaust smell for a few years. I have since, Pulled the head, new valves and guides,new Timevalve exhaust (not that happy with the system) new vapor tank in the trunk (large style)and I still get headaches from the strong exhaust smell.  This car has been a great and reliable daily driver (I'm in California) for over 10 years.  My wife is tired of telling me that I smell like a garage after driving the car.

Michael
70 280SL
04 C230 Kompressor
61 Maserati

[TheEngineer]

Check the gas tightness of the exhaust system by someone holding his/her gloved hand over the tailpipe, blocking off most of the gas flow at idle. Leaks become more observable that way. Check at the gasket between head and exhaust manifold. This is a dry seal gasket: It may have been omitted. There is also supposed to be a copper ring seal where the exhaust pipe meets the exhaust flanges. Because the flange of the aft exhaust manifold is close to the steering idler arm support, it may not have been installed properly, or the three bolts may not have been tightened unifomly. On my s/s exhaust system I found a one inch hole drilled and a pipe plug inserted. I have quizzed all previous owners, including the one who had the s/s exhaust installed, but no one recalls installing the pipe plug. I get no exhaust gas odor at all, with the top up or down, or the hard top installed. Didn't get any odor with my 230SL either. I'd be very sensitive about that. It's no good if you smell like a garage.

'69 280SL,Signal Red,007537,tired engineer, West-Seattle, WA

[Cees Klumper]

For what it's worth, I drove around for about 4 years with a significant leak between the manifolds and the downpipes of my old system: a design flaw would not allow the connection to be tight. It was an audible leak when the car was running (the car ran pretty good despite the leak). Finally cured it with a whole new exhaust system.
The point being that I never ever smelt any exhaust fumes from that very obvious leak.
Oh, and in the intermediate muffler there was another leak in that old system.

Bottom line I believe it would have to be a really BIG leak in the exhaust system before you would be able to really smell exhaust fumes inside the car.

Also, do the car's emissions smell so strong that, when they somehow manage to get inside the car, they make YOU smell 'like a garage'?

I can see why you would be stumped  :evil: This seems to be a tough one ...

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[Chad]

I think you'd be surprised to find how small an exhaust leak can result in fumes inside the car.  Had this problem on a 1991 Jeep Grand Wagoneer, old woody wagon, before I sold it during med school to pay for the insurance bill on it.  Anyway, it was a pretty small leak.

Being that it was a Jeep Grand Wagoneer, this experience is probably of very marginal application to the w113 chassis, and thank good ness for it!!

-CD-
1967 230SL, 113.042 10
1983 300TDT, 123.193

[Ricardo]

Michael
I think the exhaust smell is somewhat normal, if you decel in gear...a lot of partially burnt fuel is being expelled and the loss of road speed causes some backdrafting of this rich mix.
I wouldn't expect it to be noticable with the top on, but I sure smell it without, and my car is also running very well with nice tan colored plugs....as I mentioned in another post, I've taken to slipping into neutral on deceleration. I believe the second solnoid on the injection pump(after '69-70 US emissions) is supposed to cut fuel flow through the pump because of this unburnt fuel "pollution".
My opinion...it's from the tailpipe, not from leaks
Ricardo

[George Davis]

I agree with Cees and Ricardo.  I smell exhaust pretty strongly with top down and decelerating to a light and while at the light, and the exhaust system is tight and in good condition.

George Davis
'69 280 SL Euro manual

[waltklatt]

Ricardo,
You think having the 'diesel' friendly tailpipe extensions(chromed) will be better?  I have one of two for my diesel pagoda and think they will help tremendously by directing the exhaust down to the floor rather than straight back.
Walter
1967 230SL-diesel
1963 230SL-for sale

[Cees Klumper]

Even with the top down, I don't smell any exhaust fumes on deceleration.

Could this have something to do with the composition of fuel in our respective countries/states/areas?

I suppose differences in exhaust smell could also be caused by the "quality of combustion" and whether there is any oil being burned off as well? Before my engine rebuild, after deceleration I would always get a puff of blue smoke when accelerating again.

Cees ("Case") Klumper in Amsterdam
'69 white 280 SL automatic

[Ricardo]

Walt
I bet they will make a difference, though the backdrafting may still disturb the airflow around the pipes....do you mean the kind I've seen on ebay that look like the regular chrome extensions but are only open on the bottom rather than the end of the pipes?
Cees
I agree that different fuels have their own smell and probably Euro fuels have to meet higher standards...it's certainly true of diesel fuel. Here it seems each retailer/brand has their own additive package to "clean" your engine while you drive...yeah right, and I have noticed that "cheap" no name gas often smells bad. In Canada there has been some improvement in the sulfur content of diesel and I notice my wagon doesn't smell as much as it used to....
Richard

[George Davis]

Just for the heck of it I took my 280 SL to the local clean air testing station and had it run on the test dyno.  The results were shown in units that I don't recall right now, in a graphical form.  I really hoped the results would be in CO percent, but no such luck.

At any rate, one thing was very clear from the graph: when the throttle is shut and the car is coasting in gear, the mixture goes very rich until it gets back to idle.  I was really puzzled by that at first, but near as I can figure, it happens because the engine is still revving above idle rpm, thus causing the injection pump flyweights to swing out and move the internal linkage in the "more fuel" direction.  Meanwhile the throttle is closed and restricting the amount of air available for good combustion.  This phenomenon  explains the fuel cut solenoid used on the later US models, it eliminates this rich condition (and all those emissions) by shutting off the fuel until rpms are close to idle speed again.

And last but not least, this overrich condition on coast-down probably accounts for at least part of the lovely smell some of us experience.  I wouldn't expect the fuel to make much difference, but driving into the wind all the time should help .  Oh yeah, the test station had to compare the car to something, so they used the oldest standard they had available, the 1974 emissions standards.  We failed, but I think with a fuel cut solenoid we might have passed.

George Davis
'69 280 SL Euro manual