The Forum

Garage => Mechanicals => Topic started by: brettj on 20 August 2010, 09:43 PM

Title: How to Set Points - Electronic Control Unit
Post by: brettj on 20 August 2010, 09:43 PM
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
Title: Re: Confused - How to Set Points
Post by: koan on 20 August 2010, 10:53 PM
Quote from: brettj on 20 August 2010, 09:43 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.

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

Quote
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?

Quote
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
Title: Re: Confused - How to Set Points
Post by: thysonsacclaim on 20 August 2010, 11:22 PM
Just a thought:

Have you checked your Auxiliary Air Valve? Oscar and a few others helped me out here (http://forum.w116.org/mechanicals/a-bit-stumped/).

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.
Title: Re: Confused - How to Set Points
Post by: brettj on 21 August 2010, 11:57 AM
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
Title: Re: Confused - How to Set Points
Post by: koan on 21 August 2010, 02:31 PM
Quote from: brettj on 21 August 2010, 11:57 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   
Title: Re: Confused - How to Set Points
Post by: KenM on 21 August 2010, 07:29 PM
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,
Title: Re: Confused - How to Set Points
Post by: koan on 22 August 2010, 04:55 PM
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
Title: Re: Confused - How to Set Points
Post by: brettj on 22 August 2010, 05:00 PM
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?
Title: Re: Confused - How to Set Points
Post by: koan on 22 August 2010, 05:37 PM
Quote from: brettj on 22 August 2010, 05:00 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.

Quote
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

Title: Re: Confused - How to Set Points
Post by: brettj on 22 August 2010, 06:41 PM
Got it! Thanks!
Title: Re: Confused - How to Set Points
Post by: craigb on 22 August 2010, 07:37 PM
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.
Title: Re: Confused - How to Set Points
Post by: 13B on 22 August 2010, 08:55 PM
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.
Title: Re: Confused - How to Set Points
Post by: craigb on 23 August 2010, 07:15 AM
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.
Title: Re: Confused - How to Set Points
Post by: brettj on 25 August 2010, 09:44 AM
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?
Title: Re: How to Set Points - Electronic Control Unit
Post by: brettj on 27 August 2010, 09:25 PM
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.
Title: Re: How to Set Points - Electronic Control Unit
Post by: koan on 28 August 2010, 02:38 AM
Won't be the ignition control module, all that is working.

Don't know what idle assistance your engine has, often there's some sort of vacuum operated anti-stall setup on the throttle, maybe that needs looking at.

Are you supposed to set idle RPM in D or P?

Just sounds like the idle RPM needs to be increased a bit.

koan
Title: Re: How to Set Points - Electronic Control Unit
Post by: brettj on 28 August 2010, 11:55 AM
The only part linked to the throttle that I can think of is the throttle switch. Perhaps that should be adjusted?

I believe you set the RPM in P.

Just thought of another possibility in regard to the stalling issue, perhaps the timing isn't set right. Could incorrect timing cause stalling when shifting between gears?
Title: Re: How to Set Points - Electronic Control Unit
Post by: koan on 28 August 2010, 01:24 PM
Quote from: brettj on 28 August 2010, 11:55 AM
The only part linked to the throttle that I can think of is the throttle switch. Perhaps that should be adjusted?

Not unless you have logically deduced that the throttle switch is the problem (I doubt it is). All you are doing by playing with it stabbing in the dark which is not the sensible way to go about fixing the problem.

The timing should be adjusted to whatever the book says, there is (or should be) a sticker on the radiator support giving the conditions for timing setting, the RPM A/C on or off and any special needs like removing vacuum hoses.

Just sounds like the idle RPM needs to be increased a bit.

koan
Title: Re: How to Set Points - Electronic Control Unit
Post by: oscar on 28 August 2010, 05:51 PM
Quote from: brettj on 27 August 2010, 09:25 PM
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.

Quote from: koan on 28 August 2010, 01:24 PM
Just sounds like the idle RPM needs to be increased a bit.

I'd agree Brett. Needs a tad more air and I doubt the TPS is an issue too.  Although, I'm not sure of an anti-stall measure on these things as such, the TPS does have a fuel cut off switch which operates on a closing throttle.  So as revs drop there's no injector activity until the revs reach a point and the injectors kick in. I've no idea what that preset is or how it's determined.  It makes you wonder if the fuel cut off switch can get stuck or if it's over ridden.  To my mind it gets over ridden once a minimum RPM is reached, but either way to rule out the TPS as a problem I'd simply disconnect it and see if the car stalls under the same conditions, ie, same engine temp when attempting previous start when it stalled. 

Which brings me to ask if this stall happens only when you've attempted cold restarts and/or does the same thing happen when the engine is fully warmed up?

When you mention electronic control unit, I assume too you're referring to the ICM, ignition control module.  From what others say they tend to quit working without warning rather than degrade in performance so the one you've got has got to be ok.

Quote from: brettj on 28 August 2010, 11:55 AM
Could incorrect timing cause stalling when shifting between gears?
Yep.  If it's too retarded then it'll stall when under load.  More likely too whilst the engine is cold.  Koan's right, there's supposed to be a timing decal on the cross member in front of the radiator on a US d-jet with timing details.  If it's missing, manual says 7deg BTDC vacuum disconnected.  IMO that's conservative.  With vac connected and revs at 1500 it should rise to 10-14deg BTDC.  It's a balancing act but try to match the manual's figures and give a bit extra advance by a couple of degrees if need be.  You'll need to set the idle screw as well.  Although it's only supposed to be adjusted once the engine's fully warmed up, I'd wind it out a little if you can't maintain an idle whilst the engine's warming up.  Once again, it comes back to the suggestion that the idle RPM needs an increase.

Good to hear your dwell's set.  FWIW, I read the black and white striped points superceeded the solid black wire type.  Couldn't find it in the manuals and it wasn't something someone else typed, it might have been written in a parts catalogue.
Title: Re: How to Set Points - Electronic Control Unit
Post by: brettj on 29 August 2010, 01:01 PM
OK - Yesterday, I drove my car  about 30 miles. Got home, parked the car for about a half hour, restarted, and the motor started to rev up and down uncontrollably all over again. It had not done this at all during the day.  I figured that the motor needed more air so I adjusted the idle screw. Nothing seemed to be happening so I turned the screw as far as it would go to see what would happen. The motor was also shaking as I adjusted the idle screw. The motor shaking stopped with the screw fully, opened but naturally the rpm's went way up. I've now adjusted the idle screw to the point where the motor does not shake and the engine does not want to stall between shifting gears. The only problem now is that in P the idle is very high, around 1600 but the timing seems to be set right with the idle in D at about 800. Is it safe to allow the engine in P to idle so high?  What is the normal setting in P for the 450SE?
Title: Re: How to Set Points - Electronic Control Unit
Post by: koan on 29 August 2010, 06:22 PM
Quote from: brettj on 29 August 2010, 01:01 PM
OK - Yesterday, I drove my car  about 30 miles. Got home, parked the car for about a half hour, restarted, and the motor started to rev up and down uncontrollably all over again

Think that's a classic D-Jet problem, maybe one of the D-Jet folks can help you.

Have you played with the throttle switch?

When you say "idle screw" you are referring to the air bypass screw and not the mixture adjustment?

koan
Title: Re: How to Set Points - Electronic Control Unit
Post by: brettj on 29 August 2010, 06:39 PM
The air bypass screw.

More strange stuff today, I drove the car another 30 miles, again parked it for about half an hour and then restarted. At the restart the idle speed in P went down to 1000. I drove the car about half a mile and parked it. Went to get some stuff at the market and again about 20 minutes later restarted. This time the motor dieseled at bit at start up and the idle speed in P went back up to 1500. Could the probelm be the vacuum box attached to the distributor? What does that part actually do?

Also, in the distributor there is a plate in which the points sit. There are 3 screws in the distributor that seem to hold down that plate. Should the screws be screwed down tight to the plate or left loose? The arm of the distributor vac box is connected to this plate. Does the vac box arm move this plate for some reason? I have the plate screwed down tight. Perhaps that's the issue.
Title: Re: How to Set Points - Electronic Control Unit
Post by: koan on 29 August 2010, 07:01 PM
Wait for D-Jet expert to clue you in on the idle problems.

The vacuum advance unit (vac box) rotates the plate in response to changes in vacuum from a port just below the throttle. You can test it by applying vacuum to the connection. In other words suck on it and the plate should rotate slightly.

The purpose of the advance unit is vary the amount of extra advance given under part throttle running but there should be no extra advance at idle with the throttle closed. Disconnect the line to the advance unit and block it with a finger, the ignition advance should not change with the throttle closed.

The screws have shoulders on them that allow the plate to rotate when they are screwed tight.

koan
Title: Re: How to Set Points - Electronic Control Unit
Post by: oscar on 29 August 2010, 09:44 PM
That up and down idle is caused by the ECU sensing the rpm is running away or too high after considering the input of all the other sensors and components.  Classic case is 13B's video http://www.youtube.com/watch?v=9a4WiAk9Ass . It was diagnosed for me by a guy from the NSWMBC a few years back and only occurs at idle and usually disappears once the engine has fully warmed up but does depend on the AAV working.  Without getting too technical the ECU shuts down the injectors till the revs drop then brings them online again.  It's a direct result of too much air but you don't necessarily have to have the idle screw way open for it to occur nor does the AAV have to be stuck open or faulty.  I've had it happen when I've thought everything was in good order and working normally.  Like koan said it's a common d-jet thing and it's not something to get too worried about.  However, you can reduce the chance of it occurring by placing a restriction in the "Y" air tube that goes to the AAV.  I've done that a couple of times during winter months but it's been a couple of years since I last did the mod.  I'm usually off and driving before the problem manifests.

The shaking motor is a misfire.  Anytime mine does that it's usually a fouled plug or two and disappears after I've revved it a bit and warmed it up.  Prolonged idling and short drives will increase the chance of plugs fouling with crud.  This is where an occasional spirited drive is beneficial.  If your misfire disappears after you go for a drive I'd put it down to fouled plugs rather than querying other ignition parts or d-jet bits.

The three screws in the distributor are supposed to be tight.  They're attached to arms that clamp the advance plate down.  Not sure what the effect would be if they're loose but they should be tight.

I don't think any of your problems have to do with the vac advance unit.  It only affects initial advance during acceleration whilst the throttle begins to open.  Once the revs are up and the throttle is opened up more the mechanical advance takes over and vac advance has no affect.  An extreme example, there's no difference between a full throttle take off with and without vacuum. I replaced my faulty leaking advance unit and the perceived difference was minimal at normal take offs.
However, if you want to check the integrity of the advance diaphragm, check the following vid.  Push the advance plate with your finger to full advance then occlude the vac hose attachment nipple with another finger.  Let go of the plate which will snap back (there's not enough vacuum generated to hold it there), wait for a while then take your finger off the nipple.  You should hear a pffft as the air is sucked back in.   You can push the plate the other way and do the same for the retard side.
http://www.youtube.com/watch?v=_ClKtjqsqrI

 

Title: Re: How to Set Points - Electronic Control Unit
Post by: brettj on 30 August 2010, 10:57 PM
Thanks for the info. I'll do the test you suggested.