Vacuum Diagram late 1970 280SL w113 / misfire question

[JSawyer]

Hi Lads, Wondered if anyone could share a Vacuum Diagram for a late 1970 280SL w113, manual transmission? Also curious if anyone has experienced this and what their resolve was: mild sputter, possibly a slight misfire, only at idle and after warming up a little. The slight sound/rumble seems timed. Have replaced spark plugs, plug wires, cap and rotor. No backfires, it does not get worse with time/warming, engine compression in each cylinder is good, power is strong in each gear and no hesitations upon acceleration. From what I have read it could be the condenser or vacuum. Planning on redoing vacuum lines. Also going to put a timing light on her to check ignition performance. She is a project still in the works but coming along well with her revival after a decade of dormancy. Thanks for any responses here. Julz

[Kevkeller]

Wondering if your misfire is caused by an injector that’s leaky or with a bad spray pattern. 

Can you locate the misfiring cylinder by pulling the spark plug wire one at a time?

[Benz Dr.]

Almost all new sets of plug wires come with a carbon core coil wire. Change that over to steel core and it will run much better. You can save the hardware from your old coil wire and reuse the ends and boots.

Until you have your ignition system working perfectly, everything else become an exercise in futility.

[rwmastel]

Have replaced spark plugs, plug wires, cap and rotor.

Julz,
Were those parts known to be bad?  If you don't know they are bad parts, then you don't know if you are fixing anything.  Don't just throw parts at a solution unless it is a last resort.

From what I have read it could be the condenser or vacuum. Planning on redoing vacuum lines.

Can't the vacuum lines be tested to see if they hold the required vacuum?  Can a condenser be tested to see if it has failed?

Also going to put a timing light on her to check ignition performance.

Good idea, and measure through the RPM ranges to make sure vacuum is manipulating the distributor properly.

Can you locate the misfiring cylinder by pulling the spark plug wire one at a time?

A good testing idea from Kevkeller.

Almost all new sets of plug wires come with a carbon core coil wire. Change that over to steel core and it will run much better.

I think he means copper, not steel, but Benz Dr. is right in that you should make sure you have the best type of wire.

[Benz Dr.]

Most modern plug wires are stainless steel. OK, let's call them metal.

[rwmastel]

Ok, news to me, Dan.  Thanks for correction/specifics.

[JSawyer]

Hi Lads thanks for the feedback.

Does anyone have a vacuum diagram they can share for a late 1970 280SL?

Going through each system to bring her back to life so was replacing plugs, wires, etc anyway. Injectors have been removed, professionally cleaned and tested; all good there. Am using properly spec'd MB equipment as appropriate too.

Hoping to get the vacuum diagram asap. Many thanks,

Julz

[Benz Dr.]

The vacuum system is really quite simple on the late 280.  Constant vacuum is connected at the throttle valve housing and a line runs from there to a vacuum switch over valve in the left side of the engine bay. The vacuum line is always connected to the central port on the switch over valve. A short vacuum line runs from the switch over valve to the vacuum cell on the distributor.   

[JSawyer]

Hello, Wondered if anyone has heard this before and can tell me if they think it is a misfire or other? She has no loss of power while driving. Video in link below (need to listen carefully for subtle tick sound recorded near exhaust). Plugs and wires are new, injectors are clean, rotor and cap are new. Pulled each plug while running and heard a distinct drop in sound.I welcome input. Thank you.

https://photos.app.goo.gl/dVyzb34dbsdy5aoU9

[ja17]

Not sure about that Dan, most solid wires are copper stranded and then tin plated. The tin gives them the silver color that looks like stainless and resists the copper "green oxidation. Copper is more conductive than stainless steel, and a lot more flexible . Try scraping of the tin plating and you might be surprised to find copper! Both stainless steel and copper are non-magnetic so the magnet test will not help to identify.

[rwmastel]

Julz,

I don't hear a problem in your short video, so maybe I need to see a audiologist.

Did you try the "pull one spark plug at a time" to see if pulling any specific one made no difference in "misfire"?  That would identify the cylinder, then you have to figure out if it is spark or fuel issue in that specific cylinder.

[JSawyer]

Thank you; I did pull each wire and I could hear the change in sound for each cylinder. My mechanic says that only tests for a dead miss. This misfire we are experiencing is intermittent. In the audio clip it is subtle but there is a change in sound. As a side note it corresponds with exhaust pressure as I could feel that changing when I tried taking a separate audio recording.

Before throwing out random ideas I have I am hoping someone might recognize the sound of the intermittent miss and have suggestions.

Many thanks, Julz