Very poor running

[Tomguy]

Within the last week, my car has begun to run horribly. I cannot find out why! Timing is right, dwell is right, mixture isn't that far off to cause it to run like this (I didn't touch it before this happened).

It seems to idle fine, without load. Idle in gear misses intermittently (it always did miss horribly when cold, but not hot). The engine doesn't want to go under load and even sounds wrong without load when giving throttle. It backfires, has no power, and full throttle seems to slow it rather than speed it up!

I've thought about checking valve clearances? Anyone have any ideas? I would like to replace the distributor cap but I don't want to blow over $50 if that isnt the cause - a few weeks ago, I started it and forgot to tighten the rear clip, and the cap came off, snapping the carbon brush inside - I went to the auto parts store and purchased the cheapest cap they had, and replaced my bushing with that one, and it's been fine until this. I don't think this would be the cause but it's possible.

edit: 280SE 4.5, if there's any confusion

[psfred]

New cap and rotor.

When the rotor hit the cap, it broke the resistor in the trace between the tip and the carbon button, so you have crappy spark.

You probably cracked the cap and got carbon dust in there, too and have carbon traking on top of everything else.

I did this too -- ruined my new cap and rotor, so and using the old ones, will get new ones now that I got a raise at work.

Your fuel system is just fine if you have backfires.

Peter

[Tomguy]

I'm worried that my rad leak may have gotten water into the ignition box... should I worry about this or not? Anything I can do to help "Dry it out" if so?

How would I hook up the ignition to use a condenser instead, just in case something goes wrong with the box?

[psfred]

Wouldn't run at all with the ignition box shorted out, and it's pretty well sealed -- gets sprayed by water every time you drive in the rain anyway.

New cap and rotor will fix it, most likely. However, if you DO have the condenor hooked up, disconnect it. Not required for trigger point type ignitions, and can cause poor running.

Do also check the condition of the points and the gap -- crap from a broken carbon contact will also insulate the points, so you get intermittant firing. Just pry the plastic cover up and off the points, pull them open with a fingernail, and put a slip of paper (a dollar bill or some cotton rag bond works well) and let the points close on the paper. Pull a short distance -- don't pull it out, fibers get pulled off the edge of the paper and keep the points from making contact). I'll bet you get a black smudge, and the car will run fine afterward. Open the points again with a fingernail and remove the paper. Put the plastic shield back on, too.

Rather than hooking up the points direct, I'd buy a Crane or Pertronix breakless conversion. Otherwise, you are going to be replacing points every 3000 miles and setting the timing once in between.

Peter

[Tomguy]

Peter: I don't have the condenser hooked up but the wire on the plug is cracking and fraying off and the only way to replace it is to purchase the condenser/wire assembly (whole).

Checked the points - they were clean, and I cleaned them more, regapped, etc, all to no avail.

I ordered a cheapie cap from parts america for about $31 including 2-day shipping. The rotor itself isn't bad from what I can tell, looks pretty clean and good, but I have one in my MB parts shopping cart and I'll probably order it Sunday or so, and just have it shipped to my apartment instead (Easter Break until Tues, starting after my Wed classes finish)

[Litton]

Tom, I just curious if you found your (cars) problem.

[Tomguy]

It was either the cap, "condenser" (the wire leading from the points to the ignition box) or the coil (I put on a new cap and wire, and my 2nd spare coil, I'll probably put the first spare on if the rad leak is fixed). It ran pretty near perfect after that (I can't say perfect because it does have 140K+ miles!). Reset dwell, timing, and thinned the mixture out a LOT - I guess the cap was going slowly the whole time, causing me to need to feed her more to keep her going. Probably a whole turn on the MAP! Gonna test mileage with this setup.

[dieseldiehard]

Once upon a time, I sent my old 230 to to an Indy because I was at wits end over an intermittently bad running engine. When cold it was OK. As it warmed up the thing would misfire and finally go kaput (dead in the water) - turned out to be the condensor.
I now run a Crane Cams ignition and NO CONDENSOR!
DDH

[Tomguy]

DDH: No condenser here either but the wire and condenser is one piece.... everyone cuts the wire for the condenser off!

[dieseldiehard]

I fashioned a rubber feedthrough, using silicone rubber from a Mil spec connector boot, and discarded the entire Condensor and its funky seal/plug.
DDH