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How to Set Points - Electronic Control Unit

Started by brettj, 20 August 2010, 07:43 PM

brettj

Hi All,

Started working on my 75 450SE again after taking a summer break. The car still has the warm stall issue and strange reving motor syndrome. I took Oscars advice and advanced the distributor setting. The motor is now set at 1000 RPM at standing idle, in drive the RPMs have increased to about 750-800 from 600. This was accomplished by advancing the distributor and adjusting the air idle screw.The motor now seems to have more pickup and does not  rough idle as much.

I've come to the conclusion that the warm start stall is caused by incorrect dwell. I put my dwell meter on the car today to find that the dwell was set to 65. The correct setting is between 30-34. So I replaced the points with a set I purchased from MB, the set with the black and white cable, put everything back together and the motor refused to turn over. I ended up putting the old point set back in, that set has a solid black cable, and the motor turned over. I rechecked the dwell and found the dwell is now set to 15.

I don't know what I did to the points to go from way too much dwell to too little. What is the proper method of adjusting the point set? I'm totally confused. Also why wouldn't the black and white cable set work in my car? I cleaned the contact points with denatured alcohol and greased the rubbing surface as instructed. Perhaps I shouldn't have used denatured alcohol or perhaps used too much grease? I also noticed that my car doesn't have a condenser near the points. My green distributor wire has a black ground wire which attaches to the outside of the distributor instead of the usual  attached condenser on the green wire.  Do you really need that condenser?


Thanks

koan

Quote from: brettj on 20 August 2010, 07:43 PM
I've come to the conclusion that the warm start stall is caused by incorrect dwell.

Sorry to disappoint but I very much doubt that incorrect dwell would be cause the warm stall problem.

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I put my dwell meter on the car today to find that the dwell was set to 65.

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I rechecked the dwell and found the dwell is now set to 15.

When you change the points are you just screwing them in or are you actually adjusting the point gap and then measuring dwell?

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Do you really need that condenser?

Some do, some don't. The condenser is there for more than ignition noise suppression.  I've had cars with standard ignition systems (not transistorised) that were gave big, fat sparks  without the condenser good spark but others gave only a very weak spark without it.

In a transistor assisted system the condenser is probably not needed for operation, just there for noise suppression.

koan
Boogity, Boogity, Boogity, Amen!

thysonsacclaim

Just a thought:

Have you checked your Auxiliary Air Valve? Oscar and a few others helped me out here.

I'm not sure what your exact symptoms are. Mine was that after driving for a while, the engine would die after being really warmed up. The air slide was not moving very well.

As far as the points, I wish I knew. I'm quite a novice when it comes to those things. Best left for those with more expertise; koan et al.

I can answer about the alcohol though I doubt alcohol would harm it. It dries fairly rapidly and is safe for most types of plastics. With as little exposure as you're talking about, it wouldn't have an effect on the metal, either. I would personally use 70-91% isopropanol, as it is pharmaceutical grade and has far less impurities.

You do want to ensure it is thoroughly dried. 100% pure alcohol is a very, very poor conductor of electricity. However, pure 100% alcohol is also fairly hard to come by. It usually will have water and some other things in it which can be fairly conductive. If its not dry, use canned air or dry air from a compressor to speed things up. If you don't have those, you can try using another volatile solvent with a lower boiling point, like ether. Be very, very judicious with its use. It only takes a small amount to speed up the evaporation of something like rubbing alcohol or denatured alcohol.

Hope you figure it out.

brettj

My car has the transistor starting system. So I guess that I do not need the condenser. I'm not concerned with correcting the warm start stall at the moment, rather I need to learn how to properly adjust the points. In attempting to change the set that was in my distributor I've messed up the point setting altogether. All I've been able to do  is screw the points back in. In doing so I noticed that if you move the point set hold down screw and move the points that the gap will open. Unfortunately all I can do is to get the set open and closed nothing in between. How do you get the points to set?

I do not think the warm stall is being caused by my air slide. I replaced my old one with a brand new slide from MB.

Thanks

koan

Quote from: brettj on 21 August 2010, 09:57 AM
My car has the transistor starting system. So I guess that I do not need the condenser.

Not really sure. I have the magnetic pickup so I don't have a condenser, maybe someone with the same setup as you can say yes or no.

There are a couple of jobs in the library in section 7.5 for your engine that are related to the ignition system. Worth a read if only to cover what I leave out.

Remove distributor cap, rotor arm and any protective cover.

Remove the old points and loosely screw in new points and connect the lead up as it was making sure any washers etc. go exactly where they were.

Mark the distributor body relative to the engine so it can be returned to the exact same position.

Loosen the clamping bolt at the base of the distributor so it can be rotated.

Rotate the distributor so the rubbing block on the points sits on one of the high points on the cam on the distributor shaft.

With a .020" feeler gauge (0.5mm) you need to adjust the position of the points so that the gap between the contacts will just accept the feeler gauge and tighten the points in that position. Check and recheck this a couple of times.

Return the distributor to its original position and tighten the clamping bolt.

Replace the previously removed cover etc. Make sure the rotor arm is is correctly oriented, there is notch, and it is pushed all the way onto the shaft. Replace cap.

At this stage the engine should run. If you wish you wish you can connect a dwell meter and refine the point gap adjustment to get the correct dwell. If dwell angle is too big point gap needs to be increased.

If you have a timing light the firing point could be adjusted next.

koan   
Boogity, Boogity, Boogity, Amen!

KenM

Koan just for the record, what's your method of checking dwell, or where do you connect your probes to? Or do you have a different way of doing it, through timing light etc?

Cheers,

koan

I've never really bothered about dwell much, I just set the point gap and leave it at that.

Dwell is good for a quick check of point gap without pulling things apart.

Connect one lead of the meter to ground and the other to the points connection on the coil and read the appropriate scale with the engine running.

koan
Boogity, Boogity, Boogity, Amen!

brettj

Hi Koan,

With a .020" feeler gauge (0.5mm) you need to adjust the position of the points so that the gap between the contacts will just accept the feeler gauge and tighten the points in that position. Check and recheck this a couple of times.

The above direction is where I get confused.  Is there a screw to play with to adjust the points or is it the same screw that you tighten to hold down the point set?

Rotate the distributor so the rubbing block on the points sits on one of the high points on the cam on the distributor shaft.

My distributor will only rotate a small distance with the clamping screw loosened. Do you just loosen the clamping screw or remove it all together to be able to completely rotate the distrubutor?

koan

Quote from: brettj on 22 August 2010, 03:00 PM
Is there a screw to play with to adjust the points or is it the same screw that you tighten to hold down the point set?

No separate screw. There is a elongated hole in the points for the mounting screw that allows them to be moved towards or away from the distributor shaft.

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My distributor will only rotate a small distance with the clamping screw loosened. Do you just loosen the clamping screw or remove it all together to be able to completely rotate the distrubutor?

Wouldn't have thought you would need to remove the mounting bolt but if it gives you more rotation it would be OK but just make sure the distributor doesn't rise up when rotated. An alternative is to give the engine a crank and hope it stops in a more convenient position.

koan

Boogity, Boogity, Boogity, Amen!

brettj


craigb

My understanding was that a bad condenser or none would shorten the life of the points or they will burn and get a lump on one side. My 113 burnt a new set of points really quickly (in the middle of our honeymoon road trip! - good way to start a marriage with the trials of an old car!) and wouldn't start on the next morning after the first night. I traced the problem quickly and filed the points up and in the next town with a little old benz dealer (looked up in my original 1969 service books - Warnambool I think - maybe Hamilton - and the place looked like it hadn't changed since then) they seemed to be of the opinion it was the condenser so bought one and a new set of points (in what looked like boxes that had been there since 1969!). Replaced the condenser quickly (without stuffing about with setting points gaps at the side of the road and further testing the new marriage) and it did another 1500km or so without missing a beat.
1980 280s

13B

My understanding, which has served me well for all my dealings with D-jet, is that the ignition points are more like an on-off switch to tell the ignition box when to charge the coil and when to stop and fire the spark, so there is very little voltage/current running through the D-jet points, and why they last so long.  When I put mine in the 450SE track car I set them by eyesight and then put on a dwell meter, then used feeler gauges to open or close the gap as needed to get the correct dwell.

Cars with a kettering ignition (like the 280S) have quite a high current going over the points which is why they pit and need a condensor to help control that.  The condensor also helps generate a big spark by cutting the charge field very quickly (I beleive thats what it does). 

On the D-jet cars I've wrecked I've never taken not of which have a condensor and which don't, i have bought distributors from wreckers (for the trigger points) and some have condensors and others didn't.  Wouldn't surprise me if it was something weird like if cars were ordered without the radio they left out the condensor...

I.
450SEL 6.9 #5440 = V MB 690 , 450SE # 43094 = 02010 H , 190E/turbo # 31548 = AOH 68K

craigb

I was definitely talking old style points and coil but thanks Ian, that explains what was going on! Didn't realise the d-jet had different ignition, my 280s has the optical thing in the dissy and every time I see one in upullit wonder if I should grab it for someone else so they don't need to touch points anymore. Is that a straight changeover with the ignition box? And is anyone like to be interested in one if I see one? Can't imagine upullit would want much for one.
1980 280s

brettj

That's what I thought on the condenser issue too. Because of the electronic switching unit the distributor is set up differently. I was also told that if you use a condenser you use solid black cabled point sets. If there is no condenser then you use black and white striped point sets. Anyone ever hear that as well?

brettj

OK- Not confused on point setting anymore. Installed the new Mercedes points with the black and white cable. The car starts right up and the dwell is now set to 31 degrees which is in the normal operating range between 30-34 degrees.  I used my new dwell meter to set the dwell and also the rpms which are now at 825 standing idle. I also advanced the motor by adjusting the distributor, the idle in drive now is roughly 750. The engine now runs smoother and has more pep. That's the good news.

The bad news is, now the car will sometimes stall when put in drive and  off and on the rpm's drop from 750 to 500, the battery light comes on on the dash and then the rpm's suddenly shoot back up to the normal range of 750 and the motor either stalls or returns to normal operating condition.  I can't figure this problem out. Could it be the electronic control unit? How does that unit actually work? Never really understood its purpose.

To test my electronic control unit I hooked up a couple of spares. One of these spares is the incorrect part number but I wanted to see what the motor did if I installed it. The other unit had the correct part number and came from a 280S. The result for both units was the car wouldn't turn over at all. So either these parts were just incorrect for my 450SE or are bad parts altogether.

I'm thinking that I should purchase a new electronic control unit.