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#1
11-17-2005, 02:39 AM
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300 Sel 3.5 misfires during hard acceleration
Hello everyone, i am new to this forum.
i have been trying to slowly restore a 1970 300 sel 3.5. i had this car for the past 9 years, finally i have a little time to work on the mechanical side of it. i just put a new set of trigger points in it. it idles quite smoothly now. however, when i step on the throttle for a little of the travel and hold it, it misfires and vibrates quite a bit. but when i continure to step on the throttle, it smooths out a little. i have put new wire set, points, cap and rotors, and plugs in it. timing is at 2 degree +, i have not checked the dwell, but i have move the gap back and forth to get it to idel smoothly. i know there are many experts here, any advice will be greatly appreciated! 
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#2
11-17-2005, 07:58 AM
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timing
I'm not an expert. But, I would say setting the points by smooth idle is risky. Retarded timing (but not too so) will give easy start and smooth idle, but can also give you misfire/backfire at higher rpm's. If I misunderstood your post and you did set the points with a feeler guage I apologize. Point's change dwell and timing, but dwell does not change points. If you have the points set correctly, then dwell is automatically correct. Once points are correctly set, then set distributor timing with a timing light. Anyone, please correct me if I'm wrong.
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#3
11-17-2005, 08:11 AM
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IF every thing checks out!!... Timing . Dwell. Valve adjustment. Compression. Fuel mixture.
Then try disconnecting the electrical plug on the alternator. HAVE seen many of the 4.5's that produce too much A/C current due to diode problems!
__________________
MERCEDES Benz Master Guild Technician (6 TIMES) ASE Master Technician Mercedes Benz Star Technician (2 times) 44 years foreign automotive repair 27 Years M.B. Shop foreman (dealer) MB technical information Specialist (15 years) 190E 2.3 16V ITS SCCA race car (sold) 1986 190E 2.3 16V 2.5 (sold) Retired Moderator
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#4
11-17-2005, 10:00 PM
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thank you very much for all your help, i appreciate the prompt response.
i will try to set the points correctly, and then timing, see what happens. by the way, which electrical plug should i unplug at the alternator? thanks also, i have been trying to refill the A/c with some freeze 12, i think the freon has leaked out in the system already. when i try to refill the freon, the freon would not go into the system, i have tried both sides of the refill plugs.
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#5
11-17-2005, 11:15 PM
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mr obvious here
is the fuel fresh?
tom w
__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.  [SIGPIC]..I also have a 427 Cobra replica with an aluminum chassis.
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#6
11-18-2005, 12:19 AM
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[QUOTE=anthonyc1026]Hello everyone, i am new to this forum.
i have been trying to slowly restore a 1970 300 sel 3.5. i had this car for the past 9 years, finally i have a little time to work on the mechanical side of it. i just put a new set of trigger points in it. it idles quite smoothly now. however, when i step on the throttle for a little of the travel and hold it, it misfires and vibrates quite a bit. but when i continure to step on the throttle, it smooths out a little. i have put new wire set, points, cap and rotors, and plugs in it. timing is at 2 degree +, i have not checked the dwell, but i have move the gap back and forth to get it to idel smoothly. well, working on this car takes more the twiddling with the points. a good basic knowledge of how the fuel inj system and ignition system work would be a big first step. get yer dwell to to 32 deg. timing about 5 deg btdc. get yer c.o. adjusted. but to get to yer complaint it most likely is yer throttle switch. yer whole system needs to be checked by someone who knows those cars. good luck, george
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#7
11-18-2005, 02:05 AM
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if you do set all the dwell and timing where it should be that like mbshop sayes and it still does it it deffenetely could be the throutle body switch.Mark it and try and move it either way and test drive.
And Ralph yes you are paretly right about the points,but you have to be very accurate on adjusting them.Sometimes i could not read the dwell on the anylaiser i did the points adjustement from only the fieler guage.But you know how it is when dwell is out than the timming is out. Harald
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#8
11-19-2005, 01:41 AM
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You might want to try posting your question on the Vintage forum. I don't know why that forum isn't listed in the technical section since 99.99% of the posts there are technical!! Anyway check out the links at this site http://www.bmwcsregistry.org/Technical/D-jet.html
and the Djet section on this site: http://members.rennlist.com/pbanders/ for lots of good Djet info. Sounds to me like your MPS is not adjusted properly.
__________________
Bill Reimels Now down to one: 1972 300SE 3.5 W109 (Euro delivery)
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