Confused While Adjusting Idle

[ja17]

Also make sure your distributor timing retard is working properly. Then make sure your engine linkages are correct. IIf you still get over 200 rpms by loosening the air screw, then you mixture is too rich.

[Pawel66]

Joe, thank you!

Yes, I set and then checked timing and retard several times - I get the readings in line with what 051 distributor should have (I have 009 distributor). I did the linkage as well, including double checking if air flap is properly closing and both fuel and air controls go the same way from stop to stop. I am positive I am ok there.

Most likely I am still too rich on idle. I will fix the plugs and wires and then - I will look again in fine-tuning the mixture, as you say.

Thank you for your advise!

Pawel

[Pawel66]

Another update: have just replaced the plugs to recommended NGK with no resistor. It is a major difference! The car is flying now! Engine starts just by the sight of the key!

What I cannot get rid of fully is a bit of shaking on idle...

The next step is ignitioin wires replacement. No resistor on the distributor side, copper core, then Beru 1K connectors to the plugs. We will see what will happen.

[Tyler S]

Shaking at idle can be 1 or multiples of 4 things. Vacuum leak at the intake manifold, Poor fuel delivery at 1 or more cylinders (ie bad fuel injector), worn out motor mounts, or uneven compression on 1 or more cylinders.
Sometimes a bad front crank pulley can cause shaking as well but very unlikely.

[Pawel66]

Tyler, thank you!

Looking briefly (but not taking anything for granted):
1. Vacuum leak - likely. I know brake booster is leaking vacuum -when you press or release the brakes the rpm change 200-300rpms. I did not try, however, driving with booster disconnected and port plugged - need to try. I cannot find booster to replace. I am sending my other booster to PBE (Poland to California  ) for overhaul.
2. All injectors are brand new. Spark plugs look the same, but need to keep looking at them as I am driving very short distances and I need to see how the replaced NGK look like. Can the IP deliver unevenly to cylinders?
3. Motor mounts from MB - new.
4. Compression was confirmed even and ok after engine overhaul and then re-checked.

I will follow up on 1 and 2 - thank you!

What I also thought we might have had ignition issue on cylinders 5 and 6: when we were adjusting idle and we were taking rpm via induction connector (same as for ignition timing adjustment, the lamp has the function of showing the rpm), we were losing the signal on cylinders 5 and 6 when the connector was hooked up to wire more or less close to cylinder 5. That was when the engine was well wormed up. We were not sure if this is normal (you may lose strenght of the impulse over the length of the wire) or we have ignition wire issue. In any case I will replace the wires, I am just waiting for the components - connectors to distributor cap without the resistor.

Thank you!
Pawel

[Tyler S]

Keep in mind that these engines seem to idle smoother when on the richer end of the specs. 12.5- 13.5 to 1 Af seems to be the sweet spot.

[Pawel66]

Thank you - I will be testing this with proper tools, I understand to make them run on fairly rich mixture.

[ja17]

Sounds like your glove box spring is out of place, or came off.

[Benz Dr.]

Tyler, thank you!

Looking briefly (but not taking anything for granted):
1. Vacuum leak - likely. I know brake booster is leaking vacuum -when you press or release the brakes the rpm change 200-300rpms. I did not try, however, driving with booster disconnected and port plugged - need to try. I cannot find booster to replace. I am sending my other booster to PBE (Poland to California  ) for overhaul.
2. All injectors are brand new. Spark plugs look the same, but need to keep looking at them as I am driving very short distances and I need to see how the replaced NGK look like. Can the IP deliver unevenly to cylinders?
3. Motor mounts from MB - new.
4. Compression was confirmed even and ok after engine overhaul and then re-checked.

I will follow up on 1 and 2 - thank you!

What I also thought we might have had ignition issue on cylinders 5 and 6: when we were adjusting idle and we were taking rpm via induction connector (same as for ignition timing adjustment, the lamp has the function of showing the rpm), we were losing the signal on cylinders 5 and 6 when the connector was hooked up to wire more or less close to cylinder 5. That was when the engine was well wormed up. We were not sure if this is normal (you may lose strenght of the impulse over the length of the wire) or we have ignition wire issue. In any case I will replace the wires, I am just waiting for the components - connectors to distributor cap without the resistor.

Thank you!
Pawel

I would not drive with the vacuum line to your booster disconnected! You will have almost no braking!

[Pawel66]

Yes, thank you for your concern! I did that already when I, by accident, connected the booster vacum line with check valve in the oposite direction. The worst was when I put in gear in the garage... thank God it was reverse and I had long clear distance behing me. It is a heavy exercise and you need shoes with hard soles . Well, when you know you do not have brakes, you just drive in the safe place and carefully.
It certainly will not give all the answers - with gear in, because of idle increase solenoid, you are not in the "idle mode" anyway, as the throttle is open and both levers are away from their stop positions. But the mixture richness is the same and you can experience idle in driving conditions, when you put selector on P, which may be different vs. when you do it in the garage.

[Pawel66]

Exactly - something must be wrong with this spring. I will remove the box (this, I guess is what you have to do with it ot fix it) and take a look.

Question of priorities - I have several things to correct/adjust in the car after complete re-built. Every day brings new topics  . Currently working on: ping noise when pressing down gently the right fender, strange noise from time to time when starting the car from a standstill (like a steering box sometimes when turnign the wheels to maximum), excess play in rear wheel bearings - have no idea why, they are all new and left/right are correct type....just to name the few.

But the list of things done starts being longer than the list of things to do  .

Thank you for your kind attention!

[Pawel66]

Just for an update again (I do this because I find that the stories here with an ending (happy or not happy) are of best value to me when I search topics.

On the leaking brake booster: before a major overhaul I decided to replace a simple oring between the booster and the master cyllinder. The symptom (rev change as brake pedal depressed) are gone. I read in Haynes "this oring is to be vacuum tight" so I decided to replace it - and it worked. before I read this, I had not think there was vacuum there....

As for the strange "ping noise" from suspension: found out that the king pin and upper outer pivot of the upper control arm were stuck. They were taking grease, but were stuck. This became evident when I went to MB to check wheel alignment. Disassembled, cleaned/replaced, reassembled - car drives great, no noises. I htink this is critical when the car stands for years being restored.

The issue I am left with is that the engine shakes a bit while idling. And I am begining to worry that the fuel pump may not be feeding the cylinders equally. From your advise above this is what I am still not sure about. Last chance is the thorough richness test - due to organizational limbo over the holidays I have not done that yet.

Pawel

[mbazinet]

How did things end up for you ? Were you able to get it all sorted ?

[Benz Dr.]

Just for an update again (I do this because I find that the stories here with an ending (happy or not happy) are of best value to me when I search topics.

On the leaking brake booster: before a major overhaul I decided to replace a simple oring between the booster and the master cyllinder. The symptom (rev change as brake pedal depressed) are gone. I read in Haynes "this oring is to be vacuum tight" so I decided to replace it - and it worked. before I read this, I had not think there was vacuum there....

As for the strange "ping noise" from suspension: found out that the king pin and upper outer pivot of the upper control arm were stuck. They were taking grease, but were stuck. This became evident when I went to MB to check wheel alignment. Disassembled, cleaned/replaced, reassembled - car drives great, no noises. I htink this is critical when the car stands for years being restored.

The issue I am left with is that the engine shakes a bit while idling. And I am begining to worry that the fuel pump may not be feeding the cylinders equally. From your advise above this is what I am still not sure about. Last chance is the thorough richness test - due to organizational limbo over the holidays I have not done that yet.

Pawel

Pretty easy to short out each spark plug wire one at a time while the engine is running. I pull all of the wires loose before I start and then back each one away from the spark plugs to see if there's any change in engine sound or idle speed. If you have a dead cylinder at idle removing the plug wire won't make any difference on the one that's not firing. It's a very good idea to have an insulated tool of some sort to pull the wires away from the spark plugs or you'll find out quickly why you need this.

[Pawel66]

Thank you!

Yes, I know the insulated tool drill, learned it the hard way.
Did the exercise - the enginge is running more rough on each plug removed. Means all cylinders work. I think if it is misfiring, it happens occasionally on one of the cylinders, which makes it even more difficult to spot...

Pawel

[Benz Dr.]

Sounds like a mixture problem if shorting out each cylinder didn't change anything. It can be off a small amount and not show up as being rich as far as plug color is concerned. Split linkage test at hot idle should give you an indication.

 I agree with Joe. Idle speed should increase slightly when adding more air at the idle air screw. When you get it right on it should be a small increase. Set your timing to 38 - 40 degrees BTDC at 3,000 RPM. That will wake it up. Keep in mind that any timing increase or dwell angle changes will also increase/decrease your idle speed and you may need to reset your idle mixture accordingly.

280SL's are very smooth at idle when everything is working right.

[Pawel66]

Thank you! Look, I have the timing set at 30 BTDC, as per specs, now. How do I do that - just go and set it for 38-40 at 3000rpm and this is it? It will affect the other timings at lower speeds, I guess - shall I leave it like that?

Happy to follow your advise and ready to check anything  .

It feels like on idle, the engine has a little hick-ups form time to time...

[Benz Dr.]

Yes, that's pretty much what you need to do. Keep in mind that 30 degrees BTDC is the amount the distributor moves and that you need to add the initial idle timing of about 8 degrees for a total of 38 degrees. This will increase your idle speed and you will likely need to make a few adjustments to get it back to about 900 RPM.

 Idle speed is a combination of three things on our cars: timing, fuel and air. By triangulating those three things you can obtain a nice smooth idle.

[ja17]

Ignition contact points can cause a random miss.  Check them even if they are new. New ones sometimes "wear in" and can be off.  Use a dwell meter if possible. Also be sure to use Bosch brand.  Most other brands do not seem to hold up well. "Icor" brand ventilated contacts also seem to work well.

[Pawel66]

Gentlemen,

Thank you for kind help!

To recap:
1. I go and set the ignition timing at 38 BTDC at 3000rpm. Will check then at what points timing is for other rpm values, to note.
2. I keep the dwell as it is (spot on specs).
3. Work with air and fuel then (split linkage test, linkage tour procedure) ot get even idle

Let me try that, thank you. It will take some time as the weather "stabilzed" here and it is wet and not nice - with car right after restoration I am trying to avoid driving it in such weather.

I do use dwell meter to set the dwell. I use the gauge for gap initially, then fine tune the dwell using the dwell meter. I discovered that if I use 0,5mm gauge and I then I tighten the screw, I get ideal dwell.

As for the contact points (thank you for this comment) - it is the second set I have and I changed it for the reason you mentioned - not being sure if the new one is ok. I will look again for visible wear of points - so I hope this is what I can do to eliminate contact points as a cause. I do use Bosch. I am also aware that Bosch had a faulty production lot some time ago, but those contact points just stopped working after some time (Bosch guy said: it is for the oldtimers - how many miles can they do a year?). On high rpm my car runs very well.

Having said that - if the above does not work, I will look again at replacing contact points, because we also thought of contact points as a potential cause of trouble.

Thank you again for your kind advise!
Pawel

[ja17]

Contact points usually will last 12,000 miles or more for the std. ignition. Sometimes an adjustment between tune-ups is beneficial.  With the factory electronic ignition, the ignition points do not pit and may last longer. Improper coils, condensers, or ballast resistors may greatly shorten the life of you ignition points. 

[Pawel66]

Joe, thanks!
Well I made maybe 1500km since the overhaul. I will try the ignition setting as advised and mixture richness. I just need a bit better weather to drive...