USA Emission controls

[reggie]

My 1970 280SL has all that emissions stuff , is it worthwhile disconecting it all, if so which bits, i would like to leave it all there, but diconected, i went to MOT it yeasterday, and asked the guy to check the co, it was around 6, so a bit rich on tickover, I knocked it back two notches when i got home, i havnt been out in it since, there is something just not quiet right when driving it, not always but its like the throttle is a switch, you know-on or off, it dosnt come on smoothley, very strange, ive checked points, cap, rotar, all look new. The car hasnt always done this, just lately, Every thing i look at is ok or new, I changed the fuel filter, that was new by the look of things, I imported this car last year, it lived in palm springs, Underneath is like new, well so is the outside now, it really is WOW, So chaps what do i disconect, or do i leave it,
Thank you,
Reg

[ja17]

Hello Reggie,

The emission system on these cars is not that radical compared to US cars made after 1974.  Most likely your problem is some other tune up or injection adjustment.

[reggie]

Hello Reggie,

The emission system on these cars is not that radical compared to US cars made after 1974.  Most likely your problem is some other tune up or injection adjustment.

Thanks Joe, just what i didnt want to hear, I noticed one side of the coil go's to ground ?(earth) I have points ? my understanding was points switched the coil, the other side was power, (live), Whats that all about. Where to start, mmmm,

[ja17]

Hello reggoie,

Start with the linkage tour. Then do a split linkage test.

 You have points even if you have the factory electronic ignition. One side of the points is grounded to the distributor. The circuit is open until the points close, then the circuit goes to ground.

If you have the factory electronic ignition, the "box" is under the battery.

[reggie]

Hello reggoie,

Start with the linkage tour. Then do a split linkage test.

 You have points even if you have the factory electronic ignition. One side of the points is grounded to the distributor. The circuit is open until the points close, then the circuit goes to ground.

If you have the factory electronic ignition, the "box" is under the battery.

Thank you Joe, I did the linkage tour to sort my gear change, which is spot on now,Its intermitent so i dont suppose that can come and go ? Its not a permanent fault, seems to come on when ive been driving a bit, its like the throttle becomes a switch, if i'm just touching it, on  off, I stop open the hood, and bring the power on slow, acts normal, just when driving, dosnt need to be under load, just cruising even down hill, on off, drives me crazy.

Reg

[Raymond]

At what RPM does the "switching" occur?  Is this only from idle? 

[ja17]

Hello Reggie,

If you have the deceleration solenoid  on your IP disconect the wire going to it.

[reggie]

Hello
Ray, yes its just from idle, 

Joe, I will have a look to see if i have one, i suppose there will be a picture of it, in the technical ,
Thanks Guys.

[Naj ✝︎]

Hi, Reggie,

I suggest you check the points gap and timing.
There is a vacuum cell on the left of the throttle body. It is supposed to behave like a constant speed solenoid, so that when you engage gear, it opens the throttle slightly to maintain idle speed.
If the idle speed  (and therefore manifold vacuum) is erratic, the problem will be amplified by the vacuum cell operation.
I think this is where your on/off effect is coming from.

I think the new points have a stronger spring causing premature wear on the rubbing pad and closing the point gap.

Worth a try anyway...

Naj

[reggie]

Hi Naj
The idle speed has never been erratic, The motor runs like a swiss watch, just recently this on off business started,
Joe said disconect what he called a deaccelerating valve, Looking in technical its called a fuel shut off valve,
Anyway whatever it is, its cured the problem, when you think about it, it is the only switch on the pump so it has to be that,
I have just been out in it, and alls well with the world,
Thank you for taking the time to answer,
My car looks a million dollars, and now drives a million dollars,
Thank you all
Reg

[Naj ✝︎]

Hi, Reggie,

Nice result!!

Good to know its sorted.

Shows there's still a whole bunch to learn from the master.

Naj

[reggie]

Perhaps we should rename the technical manual, The Joe Alexander, Your none too shabby with the idea's also Naj.
Thank you for the help
Reg

[Benz Dr.]

The later emission control system may not be all that radical but you can't simply disconnect everything and expect the engine to run properly. The system works well if everything is working.
If you disconnect everything all you will have is about 10 degrees of ignition advance - try that for performance and mileage. Everything is dependant upon all of the systems working - take one out and it won't work right.

Some vacuum cells on the late system have over 20 degrees of advance, so much so that they will go into ATDC at idle. When they switch over to advance the distributor will still give you 30 degrees at 3,000 RPM. The mechanical portion is about 10 degrees and the vacuum portion can be as much as 25 degrees because this system idles ATDC.

If you decide not to use the later CD ignition system then you will need a 051 distributor or equivalent and possibly a different throttle valve assembly depending on which type you have. You can not use the constant speed type. It has to be a vacuum retard air control valve. You could also use a vacuum advance unit if the distributor you're using is that type.
You will also need to use the correct coil.

[reggie]

Thank you Doctor.
I think i will leave well alone now,disconnecting the fuel shut off valve cured the problem, just been up around the lake distrct. 180 miles in total, the car ran great, I'm happy with it,
Thank you everybody
Reg