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  #16  
Old 07-12-2009, 08:44 PM
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the dwell settings can be off unless you correctly connect the meter, something to do with the EFI, and CPU, cant put my hand on the link right now

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  #17  
Old 07-12-2009, 10:37 PM
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Dwell and other ideas

I suspect the "issue" is that you can't connect the dwell meter directly to the coil as in "normal" cars.
In order to get any reading you have to connect to the test terminal by the ballast resistor.
I need to try Barri's setting for the timing at 3000RPM.My car idles a bit fast even with the idle screw tuned all the way in but runs like crap if the timing is moved to slow down the idle.
I'm hoping to soon be able to put in on the CO meter at school and properly adjust the idle CO %.
You might also check out the vacuum hoses to the MAP sensor.Any loss there will be catastrophic!.Also check to see if the cap on the MAP is in place,If it's missing someone might have altered the settings to adjust for trouble elsewhere.If there are big differences in altitude from where you bought it to where you are now it might need to be adjusted.My indie adjusted mine as it was all screwed up by the PO!
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  #18  
Old 07-13-2009, 12:21 PM
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Well, I got readings by hooking to the coil as indicated by the dwell meter's instructions, so I suppose that the dwell may be way off now if it wasn't reading correctly. I also discovered yesterday that the vacuum retard on the distributor was only working sporadically when I set the timing, so that may have affected things as well. I'll poke around and see if I can find a thread on checking the dwell, then I'll reset it to spec and set the timing per the manual with the vacuum on (5 degrees ATDC, which seems odd, but I suppose it's right). It's still running like crap, so it probably won't make it any worse.....

If I get the dwell and timing perfect again and it still runs badly, I'm thinking I might just go ahead and take it in.

Just to be sure: there's no need to make any adjustments to or "set" the EFI points, is there? It seemed to me it was just an "install as delivered" part. I'd hate to spend tons of time on the ignition timing and find out the EFI points were out of adjustment....
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  #19  
Old 07-13-2009, 12:52 PM
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Be careful doing this, it can shock you. But here's what I would do.

It sounds like you have multiple missing cylinders vs having timing issues. This can be caused by an out of round distributor shaft, broken distributor cap, or bad wires.

While the engine is running, use long-nose needle nose pliers that the metal portion of is grounded to the body (with a long copper wire), and pull the wires off the distributor cap (NEVER off the spark plug!). Pull a wire off and see if the engine tone/rpm changes. Put the wire back on, of course, before going to the next. I assume you've ruled out all 8 injectors (all fire) as a possible cause, so this is the next logical step. What you describe sounds as multiple cylinders missing, and you can muck with timing and dwell, but if you have 2 or 3 cylinders missing you'll have rough running and a lot less power. The 4.5 can run with only 3 or 4 of the 8 cylinders actually firing.
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  #20  
Old 07-13-2009, 03:28 PM
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Well, the rotor, cap and wires are new (less than one month), and it ran basically OK (a little rough when cold) before I pulled the old EFI points out to clean them so I think we can rule that out. The only other thing I can think of other than the timing is possibly something with the new EFI points, but that seems unlikely....
E.
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  #21  
Old 07-13-2009, 04:06 PM
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When you put the points in, you must remove the distributor. That will, of course, affect timing. You also need to remove the distributor cap, that can affect the carbon brush in the cap and snap it if put in at an angle. It can also bend or break wires. Lots of variables that you need to just do basic troubleshooting steps on.
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  #22  
Old 07-14-2009, 01:08 AM
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Tom is right Ethan - check everything again even if you think its right! if you have a couple of missing cylinders you wont ever get it right. Even with a new cap its easy to knock the center carbon brush out etc etc. Also pull the spark plugs and test them for fouling if you were running rich and they foul they will misfire and unless everything is right these cars do foul plugs as they are not a very high energy spark. In case you need it here are the book values for timing as well.
good luck
Barri
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Cleaned EFI Points 1974 450 SEL - Won't run now!-timing.jpg  
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  #23  
Old 07-16-2009, 12:04 AM
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OK, so I finally threw in the towel and took it to the professionals. Not a setback, just a learning experience. I had to do it 2 or 3 times with my '64 Volvo 544 that I've owned since '99 and it hasn't been to a shop in almost 5 years. (Of course that B18 engine isn't much more complicated than a sewing machine.)

It was something to do with the timing/dwell/mixture/etc. No parts, just adjustments. I tried to quiz the tech about exactly what it was that they'd done, but no dice. Those techs are as tight-lipped as a priest just out of the confessional, but it's understandable. As a consultant, I make my living knowing more about a few specific things than most, and I imagine it's the same way with them. I'll catch up to them at some point...

Obviously I've got a lot to learn about these old MBs, but I'm looking forward to the challenge (and considering the good deal I got for the car, I can afford a stumble here and there...)
---E.


Last edited by EthanH; 07-16-2009 at 12:13 AM.
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