'81 380SL running too rich - PeachParts Mercedes-Benz Forum

fischp · #1 05-17-2017, 09:55 AM

Hi all,

I have a 1981 380SL project car that will start every time on the first crank. The only problem is it seems to be dumping fuel into the intake manifold, because it's blowing rich smelling white smoke. I've checked the cooling system and I'm definitely not losing coolant.

I've rebuilt the fuel distributor and the warm up regulator and replaced the large black rubber bellows which connects the air metering value to the intake manifold. I've even purchased a Color Tune spark plug to look at the color of the flames in each cylinder while she's running. I see that the combustion chambers are running a tiny bit rich, but definitely not enough to cause what seems like white smoke/steam from unburned fuel. I've tried to go over all of the vacuum lines looking for holes with no luck. I've also done the squirt carb cleaner test, with no noticeable change in engine RPM. I've tested the fuel pressure in the system and I'm getting around 75psi out of the fuel pump. I do have trouble testing the control pressure from the WUR most likely due to a crappy gauge... But as I said, I rebuilt the WUR just in case.

Does anyone have any thoughts on this? I'm really at a loss where to start and/or look next... I'm going to pull the cold start injector today to see if its leaking...

Thanks!

meltedpanda · #2 05-17-2017, 11:31 AM

you have certainly covered your bases, the cold start injector is often the culprit , as might the other injectors, how old are they and have you checked their spray pattern?

They are simple devices but proper atomizing is important , as is closing off so they don't leak. What fuel pressure are you running?

fischp · #3 05-17-2017, 12:09 PM

Meltedpanda,

The fuel pressure out of the FD is around 78psi. I keep trying to reason through this. I'm used to electronic fuel injection and this is really stumping me...

I'm getting white smoke out of the exhaust pipe, so I'm "guessing" that the fuel is not being burned, otherwise it would be black smoke, correct? None of my plugs were fouled or wet, just lots of carbon. If I'm right in my guess, then I'm thinking its not getting burned and just going out the pipe. Could this be? Sorry so many questions...

Pulling the cold start valve now. Fingers crossed that it's bad...

Thanks!

fischp · #4 05-17-2017, 12:35 PM

Ok, good and bad news... The cold start injector does not leak. I started and ran the car for 10 minutes and not a drop seeped from the injector. When I started unbolting the injector from the manifold I did notice that the two bolts that secure it were barely finger tight, as in no effort to unscrew them. I put the injector back and tightened the bolts. The idle seemed smoother since the vacuum leak from the loose injector was gone but I still have the rich smelling white smoke.

Going back to an earlier question, I had originally replaced all 8 of the fuel injectors when I started doing my restoration, actually when I had to replace the black rubber boot under the FD. I bought a used set of injectors off of eBay. I did a cursory test and the pattern seemed good, nice mist as I recall. I didn't do a pressure test etc. Do you think they could be leaking? I'm new at this CIS stuff, but seems like the injectors are always pressurized, right? If so, then if one or more were bad they'd be squirting all the time...?

fischp · #5 05-17-2017, 12:55 PM

Please indulge me for a second and let me add a bit more info, in case I'm not conveying all of the details.

I live in Tampa and my garage is about 90 degrees right now, so I'm guessing there's not much cold about my engine even at first start. I've replaced or rebuilt lots of engine parts over the past months as time and money allowed. I'm not new at restoration, I've done dozens of cars over the years and I've gone through this car fairly well looking for vacuum leaks, broken things etc. I do have a vacuum leak in the interior, so I've capped the vacuum line at the fire wall where it splits and goes to the reservoir and then the interior. So, the interior vacuum gauge is not working right now, nor are the doors etc.

When I start my 380, it always starts the first time. When I walk around to the back of the car, I see what looks like smoke, with a white tint as far as I can tell, definitely not black. The smoke smells very rich and does not go away regardless of how long I run the engine. I've run her over an hour with no change. I am not losing coolant so the smoke isn't because of a head issue. The oil is fresh and does not smell like gas is washing into the crank case, I also have fresh anti-freeze. When I run the engine, I do so without the air cleaned attached.

I've only had one other CIS engine before and I don't remember any smoke or smell on that one, so I'm assuming there's an issue... I hope I'm not chasing shadows and these cars just normally run that way. I tried to take a video but the smoke didn't show well.

Frank Reiner · #6 05-17-2017, 02:17 PM

f:

Between the airflow sensor and the fuel distributor is a tower (that may or may not still have a plug installed) with a 3mm hex socket adjustment screw inside. That screw is spring loaded upwards, and can be pushed down with a hex key installed. When pushed down it engages a second screw in the arm between the airflow plate and the plunger of the fuel distributor. Try a CCW (lean) move of about 1/8 turn (with the engine off), and then proceed in steps of no more than 1/8 turn. Remove the adjusting tool each time before restarting the engine.

Diseasel300 · #7 05-17-2017, 02:31 PM

A rich running gasoline engine will be producing BLACK smoke, not white. White smoke is coolant, condensation, or oil which is actually blue but often mistaken for white.

If you have vacuum leaks, you can expect to have mixture problems. Don't touch a THING until you know the vacuum system is 100%.

fischp · #8 05-17-2017, 03:43 PM

Frank and Diseasel,

Thanks for your replies.

Frank, I've tweaked the mixture screw in the tower several times now but never in a scientific manner. You say back it off, CCW and eighth of a turn then start the car, until it doesn't start or what? I'm assuming this is like an old carb adjustment for the mixture... get it to where it runs reasonably well then add a quarter turn for good luck. Sorry, not being flippant. How do I know when I've adjusted to the "right" place on the metering screw?

Diseasel, I've done a smoke test, that's what found the bad rubber bellows. I've also sprayed carb cleaner on different parts of the engine listening for RPM changes. Is there another way to see if anything is leaking? I've also measured the engine vacuum at idle and it seems good, but I honestly don't remember the reading. Do you know what it should be?

Thanks to both of you!

Diseasel300 · #9 05-17-2017, 04:05 PM

When I adjusted the metering screw in my SL, I would back it off, then start the engine and listen to it. Blip the throttle and see how the engine responded. If it sputters or hesitates, you've gone too lean. Make sure the engine is at operating temperature before adjusting anything. If the cold-start injector is still running it will throw off any adjustments you try to make.

I backed mine off to the point where it would sputter on throttle blip, then 1/8 turn CW. Go for a ride and romp on it. If you get hesitation, sputtering, or pinging, pull over and shut the engine off and go 1/8 turn CW again. Wash, rinse, repeat until you have the engine running properly as lean as it will go. Take it out and do some 50-60mph driving for a while and watch the temperature gauge. If it starts climbing, you may need to go slightly richer still.

Mine had misrouted vacuum lines. Mine is a Euro model and someone tried to plumb it like a US spec 380. There are enough differences that it didn't work out well. To compensate, there were several lines disconnected under the hood and the mixture was turned very rich. Once I corrected all the lines and installed new rubber boots on everything, it was so rich it was blowing black clouds. Once adjusted it runs like a top. No cat on mine, so it always has a smell of gas when cold.

fischp · #10 05-18-2017, 04:58 AM

Diseasel,

Perfect, thank you. I'll tweak the mixture as you suggest and take her for a ride.

I'll also do a compression test this weekend to try and rule out burning oil.

Thanks!

Diseasel300 · #11 05-18-2017, 09:36 AM

A compression test won't tell you much about oil burning. If the oil is coming from valve stem seals, the compression test won't tell you squat. It won't tell you much about the rings either, unless they're REALLY bad, at which point I doubt you'd need a compression tester to tell you about the state of your engine.

meltedpanda · #12 05-18-2017, 11:40 AM

I will send you a file that may help, as mentioned here, one step at a time, don't throw too many fixes at it all at once , EVERTHING in the CIS system is related

fischp · #13 05-18-2017, 12:04 PM

Diseasel,

I've begun to notice that same "white smoke" coming in what looks like a stream of steam out of my valve cover vent tube, the one that is supposed to go into the air cleaner. It does increase in volume of the "stream" as the engine heats more. So I'm thinking ring blow by...

The white smoke from the exhaust pipe starts immediately when I start the engine and does not stop no matter how long I run the engine. If it was the valve seals I'm thinking it would more or less just be at startup and then go away since the oil that leaks through the seals when the car is standing usually doesn't continue leaking in sufficient quantities when its running.

My theory on the compression test is not the actual cylinder compression values but the deviation between cylinders. I'm starting to suspect one or more bad rings, valves or whatever. Yes the car still runs a bit rich, but the smoke is an indication of a bigger issue.

Again, just me fishing right now but I'm getting past my apprehension on the CIS fuel system and getting back to plain 'ol mechanics.

Thoughts?

fischp · #14 05-18-2017, 12:06 PM

Thank you in advance meltedpanda. I really don't want to tear into this engine but I will if I need to...

fischp · #15 05-18-2017, 04:16 PM

Silly question, where is the coolant temperature sensor located? The one that controls the mixture, not the temperature gauge, which I assume is on the thermostat housing. Thinking its on the right cylinder head by the firewall. Red/yellow, red/blue wires on it?

Does anyone have an anatomically correct diagram showing where things like sensors are on the engine?

Thanks!