[captalex]

ok my 85 380SL has a strange problem that's driving me nuts. I dropped the car off at the local dealership for a week and they couldn't find anything wrong with it...

Here is the issue

I can start the car and it will drive like normal...no issues at all....when i slow down sometimes the car will start running very very rough and black smoke comes out the exhaust, vacuum gauge pegs to the right and brakes get spongy.

Car will barely make it back home...shifts hard and rough...black smoke out exhaust and no power at all I am basically flooring it to go 30 mph..

next day all is right in the world and car runs great.

I changed out O2 sensor and drove it an hour with no issues....next time out same issue..

I am thinking its a distributor / Timing issue but any other help would be appreciated.....its gotten to the point I don't trust or use the car anymore as even the dealership with a head mechanic who was there when the car was new could not get this problem to repeat

 

[reno4u2]

vacuum gauge pegs to the right and brakes get spongy.

I would start with checking that you don't have a vacuum leak somewhere.

 

[captalex]

That was the first route I went down....i can drive the car with no issues "Sometimes" and gauge stays to the left and only moves right during hard acceleration etc....Are there components in the vacuum system that are not used all the time that could possibly only malfunction occasionally?

 

[isthisdave]

I am thinking its a distributor / Timing issue but any other help would be appreciated.....its gotten to the point I don't trust or use the car anymore as even the dealership with a head mechanic who was there when the car was new could not get this problem to repeat

Black smoke indicate excessive fuel. Neither of those are likely culprits.

 

[captalex]

it does smell very rich when ever it has this issue.....The only cure i found that lasted more than a few miles was changing the O2 sensor but that did not last long.....

 

[Reichsrundfunk]

I wonder if something could be upping the rail pressure? Perhaps something going on in the fuel distributor??????????
-George-

 

[rockcrusher]

It could be your brake booster.

When you hit the brakes, the large brake booster comes into use. It is a BIG vacuum user.

 

[captalex]

Now that is an interesting thought.....as whenever this problem develops the brakes are almost useless....I have gone so far as to have the entire system bleed and new pads etc put on but no one has touched the booster..is there a viable way to get a good test on it

 

[rowdie]

Could it be the control unit that the O2 sensor connects to. Lamda control system. My understanding is that if it fails the system goes into a closed loop that enriches the fuel to allow the vehicle to be limped home. ProgRama 002 545 00 32 Mercedes Benz Engine control Unit
Just a thought.

 

[petesmga]

Instead of the booster, I would check the valve first, while it's running just move the valve a bit and see if the symptoms occur.

 

[rockcrusher]

Instead of the booster, I would check the valve first, while it's running just move the valve a bit and see if the symptoms occur.

You are referring to the check valve correct???

I was going to mention that, but just wanted to bring the attention to the booster system.

Rowdie, when he said the brakes went south, I figured it had to be a vacuum lead large enough for the car to run like shit, and effect the brakes. just throwing things out there....... I have not studied what happens when the car goes to the limp mode....

 

[rockcrusher]

I am on the crappy laptop. Does anyone have a pic of the booster and check valve to show him
I could change computers....

 

[captalex]

I am very interested in trying anything as so far i have not been able to recreate the problem

 

[isthisdave]

.



What does the tach do during these episodes, if you've had the chance to look? Are you losing any of the electrical function?

 

[captalex]

No electrical has given no issues......but I have to floor it to make any kinda of speed to get it back into the garage...I have had to tow it twice as it was too dangerous to drive and i was worried the black smoke was going to equal more costly repairs

 

[petesmga]

Remove the air cleaner lid and press down on the plate (car off). I am curious if it may be binding, it should have resistance down but return freely.

 

[roncallo]

I believe you have a valve hanging. Try some valve cleaner in the fuel tank before going too crazy.

 

[nobby]

It could be your brake booster.

When you hit the brakes, the large brake booster comes into use. It is a BIG vacuum user.

First thing I thought of too.

But usually the symptoms are hard grabby brakes.

 

[dgosh28]

Could it be the control unit that the O2 sensor connects to. Lamda control system. My understanding is that if it fails the system goes into a closed loop that enriches the fuel to allow the vehicle to be limped home. ProgRama 002 545 00 32 Mercedes Benz Engine control Unit
Just a thought.

This sounds similar to the experience I had recently with my 380 when the timing moved 25 degrees. You may be on to something.

 

[rowdie]

Spongy brakes is not a symptom I have heard in regard to booster failure. As Nobby said hard brake pedal is normal symptom of booster failure.

Replacing the O2 sensor seemed to help initially. That is what made me think of the emissions control module. I may be totally off but from what I have read the WUR controls the fuel system during warm up. Once the O2 sensor reaches operating temperature (could also be one of the engine temp sensors) control is transferred to the Electric Air Pollution Control unit. This operates the frequency valve MB calls it Timing Valve. Very simple explanation of what I have read.

Read the posts here by Pex
http://www.peachparts.com/shopforum...equency-valve-buzzing-among-other-things.html