109 4.5 distributor setting - PeachParts Mercedes-Benz Forum

tosbt · #1 10-16-2004, 11:06 AM

Hello all, long time no see.

My 109 4.5 may be displaying symptoms of faulty distributor. I THINK I may be having problems with my vacume advance, car still runs hotter than should may be a little under powered and on occasion has a misterious miss real quick like and then the problem stops and runs ok again. I had the Crain unit installed a while back. I intend to take to the Mech Monday. Would someone please give me the proper advice on how to tell him to set the timing on this car correctly, correct setting ect. step by step please. As always, thanks in advance.

psfred · #2 10-16-2004, 12:43 PM

Tobst:

First, you must determine if the vac retard (it's not an advance!) is working, and verify that the mechanical advance works.

With engine running and timing light in use, timing must advance 12 degrees when the line to the retard on the dizzy is pulled. Not a terrible problem if it doesn't work, but you cannot set the timing correctly unless you know.

Stop car, pull cap, and turn rotor clockwise til it stops and let go. It must snap back immediately to the original position, without binding and without "help". If not, you need to take the upper hollow shaft off and clean the insides and oil it so that it moves properly, otherwise the timing will be goofy.

Once you are at this point (vac retard either works or doesn't and the mechanical advance does), you can set timing:

If the retard works, set timing to 5 degrees ATDC -- you can go as high as ten degrees for better preformance and better milage, but you MUST then use premium only, it will knock otherwise).

If the retard is stuck, set timing to 7 degrees BTDC and it will run fine. You won't get advance under heavy throttle and won't get an idle increase with AC use or high engine temp, but it will work. Replace it if you want.

A sticking mechanical advance will cause the engine to run hot from late ignition timing at speed, and will often cause it to knock on hot starts. GAs milage will stink, too.

Rough cold idle, surging cold, and intermittant missing or sluggishness until up to full heat is likely bad trigger points. When they get really old and worn, some of them will fail to open until the dizzy heats up because the rubbing blocks are worn off (like mine...).

Peter

#3 10-16-2004, 07:41 PM

Wow...this sounds like what mine was doing too. I took it back to the shop and they adjusted it and it's definately better. But mine is sluggish when cold and then much better after it's warmed up and I stop and start the next time. My idle seems to be all over the place too. Either way too high or normal. Also I get some smoking when it's cold at intersections. Then the rest of the time I drove it around today, none. Since the old shop has had it twice and it's still not right I'm thinking I should try a different mechanic. Really frustrating.

psfred · #4 10-16-2004, 11:35 PM

Cold idle is 1500 rpm, more or less. If too high, it will surge badly as the closed throttle fuel cutoff will kick in above 1500 -- cure by reducing the idle speed a bit at the idle speed screw.

Rotten running cold that dramatically improves once warmed up is almost always bad trigger points. Get ready, they aren't cheap....

Peter

Tomguy · #5 10-17-2004, 04:35 AM

I don't have bad trigger points but it ran very, very poorly cold last winter until I pulled the dizzy and cleaned them out. Lots of gunk in between the points that must've been conductive when cold, causing way too much fuel to dump into the engine, and ran off the points when warm (or thinned out so that it no longer remained between the points when they were open). Fixed cold running problems like a charm!

And Peter, when you say "Snap" back "without help" - mine is absolutely clean (I took the entire thing apart, cleaned and greased it) and it doesn't snap back into position. It'll return nearly all the way and I need to push it slightly for it to go the rest of the way. However, I think this is right? If not, PLEASE let me know, I would NOT mind even MORE top-end performance (My top end is great but, due to timing chain stretch, low end suffers to the point where I can't squeal the tires from a stop on dry, level pavement when not making a turn)

psfred · #6 10-17-2004, 12:33 PM

There is a bit of play in the advance mechanism, made worse by wear on the spring and weight pivots by now. As long as it goes back to the same spot each time you are OK.

You are lubricating the felt pad, right?

Oil on the trigger points will prevent them from opening and closing cold -- the oil is stiff enough that the closing is delayed or prevented. Real cure there is to rebuild the dizzy, and that is a PITA or expensive. The bushing at the bottom is leaking, and the o-ring seal long dead, so too much oil accumulates in the lower section. Good for the mechanical advance, but bad for the trigger points.

New points work better because the springs go weak on the old ones and the rubbing blocks wear off, resulting in less movement of the points themselves. They usually don't quit conducting (no current flow to speak of), but will fail to open and close reliably.

Get the new chain and roll it in -- milage will improve, too!

Peter

tosbt · #7 10-27-2004, 09:42 PM

Not having much luck with this problem. Mech took dizzy apart and checked trigger points which were fine no oil in the lower part,cleaned and reinstalled.

Drove the car for several miles and then " bup bup bup" cut out and in a flash was driving again with no problem.

Said he pulled plugs and was some carbon but thinks it was running to rich.

I have the Crain unit in the dizzy, could this be the problem?

Weeks ago I check the alternator which tested fine.

What should I look for?

tosbt · #8 10-29-2004, 09:10 AM

Any Ideas? Anyone.

j9fd3s · #9 10-31-2004, 11:35 AM

maybe bypass the crane? see if the problem goes away?

psfred · #10 10-31-2004, 02:19 PM

Intermittant problems can drive you nuts.

This can be dirty or worn trigger points, intermittant fuel pump or relay, or intermittant ignition.

Check the Crane unit for dust or buildup on the optical sensor -- this is the only problem with the Crane, anything in there can reduce the sensitivity of the triggering sensor and cause the ignition to fail or a second or two.

Also check all the ignition wiring for loose connections or corrosion, same problem. Dampness will short of the cap, too -- make sure it's sealed properly and in good condition, no dust or carbon inside.

Verify that you don't have a vac leak cold, too!

Peter

Tomguy · #11 10-31-2004, 07:57 PM

What is your CO % in the exhaust?

If it's too high, the engine will missfire every so often due to carbon buildup in the combustion chamber, and it can also preignite if these deposits get hot enough, causing a hot engine and power/rough running issues.

If it's too low, the engine will missfire every so often as the chamber is starved for fuel. The lower amount of fuel means that combustion happens slower, as it is less dense in the chamber - the combustion will still be ongoing when the exhaust valve opens, leading to red valves as the gas is exiting. This also causes preignition where the hot valve rather than the hot deposits ignites the fuel prematurely - also leading to rough running.

However your problem sounds more like the "Too rich" one because you say it stops - indicating that once the carbon is blown out of the chamber, the preignition no longer occurs.

Of course, it could be neither of these, and a loose connection somewhere in the EFI system and/or ignition system, or even a dying ECU. Check the ground wires for the injectors, make sure your cold start valve doesnt leak. If it runs poorly when cold but not warm and your trigger points dont have oil on them, it could be your aux. air valve...