79 450sl... chugging, sputtering, and problems accelerating! - Mercedes-Benz Forum

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post #1 of 22 (permalink) Old 05-02-2006, 04:14 PM Thread Starter
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Date registered: May 2006
Vehicle: 1979 450sl
Location: Rome, Georgia
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Unhappy 79 450sl... chugging, sputtering, and problems accelerating!

This is my first time posting anything, so hopefully im doing this right

ok I've been experiencing horrible sputtering, and hesitation problems with my 450sl. it has a new fuel pump and filter on it. After the engine is warmed up it will not accelerate when you press the pedal, when it gets like this you have to pull over because it will not go over 40 or so mph; and often when i come to a stop it just shuts off, and it esp. cant go up hills when it does this- which is a problem because i live on a mt. But the strange thing is that after you wait a few minutes it will crank back up and run strong for a few miles (sputtering still a little) and then it will do it again. My mechanic can't figure out the problem. so I am in desperate need of help from anyone who can help me find out what is happening! Another mechanic i took it to before this one, replaced the catalytic converter thinking it wasnt working properly; this fixed the problem somewhat but it continued to have the same problem esp at higher speeds when i went to pass someone. i have also been researching and i think it maybe the Mass Air Flow sensor or the Air guide housing, or the throttle valve housing. I was thinking this was a problem bc it started this problem again after i cleaned the flat metal plate thing that is on the Air Flow Sensor underneath the air cleaner, and manually pushed it down to clean around it better. Would I have caused the problem by me doing this?!?!?!?! If anyone could help me that would be GREATLY appreciated! Could i have clogged st?!?!

Brad D.
1979 450SL
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post #2 of 22 (permalink) Old 05-03-2006, 07:15 AM
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Binding airflow sensor plate or binding control plunger.Check the plate ensuring that it is centered. For more info,go to the W116 forum and read "D & K Jetronic Troubleshooting" for more detailed info.

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post #3 of 22 (permalink) Old 05-07-2006, 02:46 PM
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Fuel distributor valve,the one actuated by that plate you pushed,is gummed up.you can either remove the distributor and strip and clean it,or buy an exchange unit online.
And get a mechanic who uses a injection test guage to investigate fualts rather than someone who "guesses the fualt" at your expense.the Kjet is extremely simple in operation so it aint rocket science .
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post #4 of 22 (permalink) Old 05-10-2006, 06:24 PM
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Date registered: Apr 2005
Vehicle: 1974 450 SL
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Cool Trigger Points??

My girl didn't have as bad a symptoms as you are, but I chased my tail for 6 months with intermittent rough idle and rotten acceleration issues. Finally, the trigger points fixed my problems. Search the posts.

It is fairly simple to pull the distributor and inspect/clean them up if they happen to be gunked up. That might be an easy way to narrow it down. Mine looked great and had the "fantastic intermittent fault" in one of the 4 micro-switches that tell the computer what is happening inside her. THe only way i found it out was by trying another set loaned to me by a great mech in Seattle.

Good luck.
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post #5 of 22 (permalink) Old 05-15-2006, 10:36 AM
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Date registered: May 2006
Vehicle: 1973 Mercedes 350 SL (gray market)
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Had a similiar problem for years. Spent littlerally hundreds of dollars on mechanics until a found one that solved the problem. I had several vacuum leaks due to age. The car now runs like new. 1973 350 SL. Except for internals of engine, I believe it's the same car as yours.

Good luck!
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post #6 of 22 (permalink) Old 05-16-2006, 04:00 AM
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Drain some fuel and check it for contaminants, like rust or water. The check is almost free and can point out a problem, that no matter how much cash you throw at the engine or fuel injection, cannot be fixed unless you start at the source. It would have saved me $2200 if I had done this first. Unfortunately I replaced 2 fuel distributors due to rust in the tank.

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post #7 of 22 (permalink) Old 08-22-2006, 04:17 PM
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Hi Brad,

I have the identical problem on my 1983 380SL and have been unable to pinpoint the problem yet. The only difference is that my problem is intermittent which makes it worse since no one can ever diagnose it. The other slight difference is that it restarts immediately - no cool down is needed at all. It's gotten so that I don't pull over anymore, just throw it in neutral - restart - and I buy a few more miles before it happens again - or maybe it doesn't come back until the next ride. Such is the nature with the intermittent problem.

Anyway, I was wondering how you were doing so far with mechanics throwing parts at it. So far, I have a new cat, o2 sensor, fuel pump, fuel filter, and fuel distributor. Next is an OVP relay and ignition control unit. I may be able to keep Bosch in business all by myself!

Have you had any luck in curing the problem?

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post #8 of 22 (permalink) Old 09-16-2006, 07:05 AM
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chugging stopping problems

I'' having a similar intermittent problem with my 79 450 SL. I don't drive it much per year and take it out of storage for 3-4 months /year. I have always used a fuel conditioner and fill it up at storage time. This year lots of problems in first tank of gas treated and then no problems for a month then again episodic enginine stopping.The power stays on and if immediately shift to neutral will restart. It always restarts immediately. The mechanic kept it for a couple of weeks and as always is the case never did it once even though he'd drive it to and from work.
It has happened when the car is warm more often than when cold. More often when the fuel level is mid to low than full. No problems with acceleration or cruising. More likely at slower speeds but has occurred a couple of times at 55.
Currently thinking about pulling the gas Tank and have it refurbushed /replaced. Other automotive columns suggest the sensor.

Thanks for your thoughts.

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post #9 of 22 (permalink) Old 09-16-2006, 03:26 PM
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This may not be the case however it is worth checking your alternator. If the voltage applied to the sparkplugs is too low (as was in my case) the engine would sputter and symptoms similar to yours. When I went to check the enginge, found a small wire with insulation breakdown. Fixed it and works much better. Could also be the case if your alternator is bad or have too much electronics loaded in there. Worth a try to have a look if anything.
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post #10 of 22 (permalink) Old 09-22-2006, 05:30 PM
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Not the alternator for me at least. I have a new one in there.
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