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Old 03-17-2007, 11:00 AM
Registered User
Join Date: Aug 2006
Location: Chesapeake,VA
Posts: 23
Hesitation problems

I have been having hesitation problems with my 1995 SL320 since the new gas started (Ethanol) I am not sure if it is the culprit or just a coincidence.

I have changed , spark plug wires, spark plugs and the fuel filter so far. The car starts hesitating (seems like it is missing) and runs very rough. If I shut off the car and turn it back on it runs fine.

This problem is getting worse. It seems to improve if I run Octane boost in the fuel. But also seems worse when it is raining.

Anyone have any ideas? I have thought about Oxygen sensors, fuel injectors or one of the ignition coils, but I have no idea how to trouble shoot this. I don't want to randomly start replacing some of this stuff without some idea of what the probable problem is.
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Old 03-17-2007, 12:45 PM
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Join Date: Mar 2003
Location: Milwaukee Wisconsin
Posts: 1,149
I found this info doing a search on "sl320 harness". It was posted my another member. The harness has been an issue on some models.

I have a 96 SL320, and it has some little gremlins too. Everytime I wash the engine it goes into limp mode, I am told that it is from the moisture causing an arc in the ignition, the computer sees this and then set it to limp. I correct by shutting it down and re-starting.
I have friends in the MB club that have problems with the big black box that sits between the firewall and the passenger side windshield. When I got my car it had a crack in it, 2 others told me the same. This crack lets moisture into the computer box, that is where all the "brains" are for everything. Make sure there is no moisture getting inside, that it is sealed properly. When they put some of these together the harness connector inside was too high and caused the top to crack when bolted down.
Another problem with these cars is the wiring harness. MB made the harness bio-degradeable, so it is already weak, if you get it wet it makes it worse. Usually the engine harness will go first. Because of the heat and exposure to weather conditions. With your Top controls goofing up and your braking systems, I would recommend that you take it to a dealer and have them hook it up for a diagnostic. It seems like the harness between your firewall and your windshield could have problems, you will see where they all meet up at that black box. The engine control, the soft top, the cruise, everything is in that box. Be careful when checking these out, some have said all it takes is a little twist and the wires arc/ they don't break, just the insulation around them, causing them to arc or ground out. This makes it fun when trying to find a problem. Overall this is a great car, so don't rush out and sell it. If you are not an MBCA member join, you will get free tech advice and you also will get discount at dealers. goto Good Luck.
Resistance is Futile.
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Old 03-18-2007, 12:15 PM
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Join Date: Nov 2006
Location: Minneapolis
Posts: 51
possible options

I had a similar situation with my 91 500. Not sure if yours has points and rotors but changing both solved my problem. You may also try running a bottle of injector cleaner though as well..

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Old 03-18-2007, 01:47 PM
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Join Date: Nov 2003
Location: Hella NorCal
Posts: 3,301
Are you running E85 or gasoline that has the ethanol mtbe substitute?

07 MB ML320 CDI
12 Trek 2.1 Triple
16 Nike Free 4.0

it's automatic.
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Old 03-19-2007, 12:18 AM
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Join Date: Aug 2006
Location: Chesapeake,VA
Posts: 23
I have been running Premium Gas. I have already run injector cleaner on a regular basis through. (Good Quality not cheap stuff). Anybody think it could be a vacuum line or something along that lines?
This is getting real bad now. It is taking a very short time between when I have to turn off the engine and turn it back on. It used to do it sporadically, now it is almost constant.
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Old 03-19-2007, 12:29 PM
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Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
This is almost certainly something in the injection electronics or the wiring harness is going, or both. You should take it to someone who can pull the codes, or you'll just continue guessing.
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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Old 03-21-2007, 07:40 PM
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Join Date: Oct 2002
Location: Columbus, Ohio
Posts: 155
Had similar problem with 1991 300 SL. Looked to be an injection system issue but was actually an ignition system issue. The ignition coil was the cause of the problem.

Car has run perfectly for many miles on new coil, new distributor cap and rotor, and new NGK plugs.

Hope you get your problem solved.

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Old 03-22-2007, 07:56 AM
Registered User
Join Date: Aug 2006
Location: Chesapeake,VA
Posts: 23
Car is in the shop as I write this. They have some codes that showed up (they did not tell me which ones) but the only thing they have done so far is replace a fuel line. I will post the results of what they found.

Got the car back today. It runs GREAT!!! Solution was:
1-new fuel line
2-another new fuel filter
3- all three Ignition coils replaced

total of $ well spent. Thanks

Last edited by RSWoodley; 03-24-2007 at 12:19 AM.
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