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  #1  
Old 09-07-2016, 06:39 PM
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Engine performance issue, 1985 Mercedes 500SEL

Hello,

As the title says, I have a 500SEL with some running problems.

She sat mostly dry for ~5 years, but ran fine before then. As far as the engine goes, I've only done the plugs, oil, and drained the fuel tank.
The problem is the engine runs rough at idle, throttle response is terrible, it's definitely not putting out full power, and she sometimes stalls out between gears at low speed. I think it's a vacuum leak somewhere, but a second opinion would be appreciated.

Bonus photos for reading this and helping me out. Your input is appreciated! I can't wait to have this thing running like a champ again.











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  #2  
Old 09-07-2016, 07:09 PM
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How old are the fuel injectors? It may be time to change them out...... also, how old are the spark plugs? I'd also install a new distributor cap and rotor and new plug wires. As far as vacuum leaks go, IMO, best to take the car to a shop that knows how to track them down. It will take them a few hours whereas it will take you six months!!!!
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  #3  
Old 09-07-2016, 08:21 PM
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need to find a mechani in his 60s a young one won't know anything
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  #4  
Old 09-27-2016, 02:37 PM
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Fuel injectors are high on my list of things to replace. At the very least, replacing the fuel injector cups and O-rings. Spark plugs and distributor cap are also a very good point that I had not initially thought of. What, specifically, is difficult about tracking vacuum leaks in these cars?

Taking it to a mechanic is not something I want to do from a cost standpoint. While I may be younger and with a low postcount here (lol), I'm also not totally dumb.

Last edited by Hdavis19; 09-27-2016 at 08:48 PM.
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  #5  
Old 09-27-2016, 10:55 PM
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The fuel injection system on this car is not something you are going to fix with the internet and with a car that has sat for years is suspect in its entirety. I don't mean to be insulting but it takes intimate knowledge of CIS injection and the proper diagnostic tools to diagnose and properly repair it. It is likely to be cheaper to do as HuskyMan suggested and get a competent shop to repair it. New parts can be astronomical and any used part of this vintage is suspect at best. Relying on forums will be akin to throwing hundred dollar bills at a dartboard in the mirror. Best to know that the money spent will return a proper running vehicle instead of an expensive collection of parts.
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  #6  
Old 09-28-2016, 12:11 PM
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I'm willing to bet this is all due to vacuum leaks. If our customer chooses to tackle the problem, we usually start by removing the intake manifold and replace all the gaskets including the plenum seals, all the hoses underneath, vacuum lines and all injectors and seals. 90% of the time we end up with a car that runs like new. I just did this to a 380 that was so bad that you couldn't get enough throttle response to make it around the block. Now, at idle, you can't even feel it running. I would spray carb cleaner where the intake mates to the head while the car is running. If you have a significant change in idle this may be your problem. I agree with duxthe1, if it's a fuel problem it can get very expensive and hard to diagnose on the old CIS systems.

Last edited by paul roberts; 09-28-2016 at 12:21 PM.
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  #7  
Old 09-28-2016, 02:42 PM
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Quote:
Originally Posted by paul roberts View Post
I'm willing to bet this is all due to vacuum leaks. If our customer chooses to tackle the problem, we usually start by removing the intake manifold and replace all the gaskets including the plenum seals, all the hoses underneath, vacuum lines and all injectors and seals. 90% of the time we end up with a car that runs like new. I just did this to a 380 that was so bad that you couldn't get enough throttle response to make it around the block. Now, at idle, you can't even feel it running. I would spray carb cleaner where the intake mates to the head while the car is running. If you have a significant change in idle this may be your problem. I agree with duxthe1, if it's a fuel problem it can get very expensive and hard to diagnose on the old CIS systems.
I think that this is a great place for a hobbiest mechanic to start. These are, for the most part, items that should be replaced on any car that's been sitting for this length of time, regardless of running issues (along with ignition systems that Husky mentioned above).

I've seen a lot of videos about the Bosch CIS system, and I certainly get how it works. But I understand that diagnostics are a totally different ball game. I'll perform the above items, and if nothing changes, I'll talk to a professional.

I plan on getting my hands on the car in late November. I'll let you all know how it goes!
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  #8  
Old 09-28-2016, 03:20 PM
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Quote:
Originally Posted by Hdavis19 View Post
I've only done the plugs, oil, and drained the fuel tank. The problem is the engine runs rough at idle, throttle response is terrible, it's definitely not putting out full power, and she sometimes stalls out between gears at low speed. .


Quote:
Originally Posted by Hdavis19 View Post
I plan on getting my hands on the car in late November. I'll let you all know how it goes!
Seems a bit of a conflict, Hdavis; If you are not getting the car until November, how did you do the items you claim in the highlight?
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  #9  
Old 09-28-2016, 06:30 PM
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This account is jointly operated by the vehicle owner and a friend who is helping to get it running. The vehicle owner made the original post, and the friend has been responding (that's me, making this post now).

I'm sorry for not mentioning that earlier. Does that change the circumstance for you?

Last edited by Hdavis19; 09-28-2016 at 07:06 PM.
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  #10  
Old 09-29-2016, 10:58 AM
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Sounds like you may need a fuel distributor and a warmup regulator but with your knowledge of the internet you can probably figure out how to modify or adjust them. Watch all the videos you want and when you are done then you can take it to the tech that knows what they are doing to fix it for you
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  #11  
Old 09-29-2016, 02:46 PM
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Why are people breaking balls on this guy for saying he's watched a few videos? I didn't see where he claimed they made him or were going to make him an expert. That strawman was brought up by someone else. He did say he wanted to avoid trooping off to a specialist but he didn't say he wouldn't. I thought that's what this forum was for, people who are smart enough to know what they can tackle themselves with a little bit of help. Find a mechanic in his 60s? I guess that means we've all got about 10 more years and then our MBs are finished.

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