Backfiring through intake

[Amy McKenna]

It has taken just over 1 year to work on the kinks and bring back the '67 230SL which has been in the family for 30 years. My sister had it stored in the bottom of a barn for over 10 years. Yikes!  The work completed is too extensive to post but know that I have invested in its revitalization far more than its street value----I knew the inevitable costs associated with such a project but I must say I have loved every minute of it, besides my father would be happy to see his old car used again!  That all being said, my mechanic (who just rec'd an award from MB Classic Center for being their best customer---I am sure because of me! ) needs some assistance with a backfiring issue.  When warmed up, it backfires through the intake, it is more severe on decelaration, and will mildly and less frequently backfire at steady or under light accelerations.  Work performed has been: *complete tune-up, wires, cap, etc. * fuel injector pump rebuilt
* injectors checked and cleaned...all okay.  The throttle linkages relationships are in question.  He needs the degree setting MB tools to correct.  Also, timing has been set numerous times between 0-TDC and 10 degrees BTDC.
I appreciate all your postings, all the time.  Thank you in advance for any assistance on this subject.  We hope to take this car cross country on MB Lincoln Highway tour in September. I met Naj on the Route 66 MB tour in 2006 with our '58 220S. Thanks to Naj I learned about this site!

[Naj ✝︎]

Hello, Amy,

Good to 'see' you here.

 

quote:The throttle linkages relationships are in question. He needs the degree setting MB tools to correct. Also, timing has been set numerous times between 0-TDC and 10 degrees BTDC.

Joe Alexander's Linkage tour shoud help your mech. with the pump/throttle settings.

http://index.php?topic=5003

Need to know what distributor your car has! It's around a changeover period from vacuum advance to vacuum retard. Details are in the wiki:

http://www.sl113.org/wiki/pmwiki.php?n=Electrical.Distributor

Let us know how he gets on...

Good luck,
naj

68 280SL

[Amy McKenna]

Thanks Naj! I will pass on all of your good info to finish this project! Hope all is well with you!
Amy

[ja17]

Hello Amy,

The special MB degree tools are not normally needed to set the linkages.

Joe Alexander
Blacklick, Ohio

[ja17]

Hello Amy,

Backfiring through the intake is usually a result of a lean running condition which can be caused by incorrectly set linkages, or another fuel delivery problem. Yes start with the linkage tour first. Keep us up to date, we will help get it "dialed in" for you!

Joe Alexander
Blacklick, Ohio

[glennard]

Backfiring- Burnt valves??? valves out of adjustment?? compression OK??   valves(cam shaft) in sync with crankshaft??

[amys wrench]

Thanks to naj, glennard, Mr. Alexander for your valuable information.  I will check the websites mentioned.  
     A little additional info on Amy's sl.  It has the origional distributor.  Adjusting the fuel mixture has a small effect on the problem but does NOT clear it up.  Ign. timing has little or no effect.  Glennard's suggestions have all been checked and are within factory specs.  Having been trained by MB on this system, I am aware how important linkage adjustment is and will check Joe's linkage tour and other website mentioned by naj.  I would like to set linkage properly and then recheck my previous work, including all suggestions posted below, and check exhaust emissions to verify results, i.e. rich or lean condition. Currently, I feel that this is a lean backfire.  Fuel pump pressure and delivery rate are within specs.  Fuel filter has been replaced.  Fuel injectors cleaned and inj pump rebuilt by Bosch rep in New York.  Injector opening presures within specs.  Fuel lines have been blow clear from pump to injectors and pump to tank.  Tank filter checked for debris and is clear.  Tank is clean.  Tank vent is in working condition. All rubber fuel lines are new and all banjo bolts are clean. I have been looking for the factory degree tools for linkage setting.  In their absence, I will use Joe's tour.  After linkage is properly set, all other ign., tune up, and engine condition specs will be rechecked for possible errors or oversights on my part.  Any further ideas will be happily received, as thirty five years in the profession have proved that I do not have all the answers and I have learned to enjoy the taste of crow, no matter how it is prepared!

    On another subject, Amy has a 1958 220S Cab. with a Hydrac.  I am very familiar with the Hydrac having repaired many over the years. Thanks to Amy I have all factory Hydrac literature.  I believe that it is causing a vacuum leak, making it necessary to run the engine with the choke slightly out to prevent stalling.  This tactic, however, ruins the smooth operation of the Hydrac.  If I plug the vacuum tap at the manifold, the engine runs fine.  The vacuum diaghram, brake booster, and vacuum reservoir all hold vacuum overnight.  All vacuum lines have been replaced with the proper wire reinforced hose supplied by MB with new hose clamps, all tight.  It looks like the Hydrac vac. control valve is leaking to the atmosphere and needs rebuilding.  I needs parts or a new or used (any condition) valve.  MB has no spares for this valve.  Also, I want to rebuilt Amy's spare Hydrac fluid coupling and need bearings and seals, and one way clutch parts.  
     I also need suggestions about adjusting the shift linkage box at the base of the steering column unit. After installing new shafts, bearing and seals, and before installation this linkage assembly functioned smoothly.  After installation all gears engage smoothly except 2nd which takes extra effort.  2nd must be pulled in with some force, whereas the other gears glide smoothly into engagement.  I followed factory adjustment procedures and rechecked adjustment twice.  Gearbox has all new bearings, gears and synchros are in good condition.  What am I doing wrong?[/u] This linkage is the same as a standard manual transmission. Any info or suggestions more than welcome!

Thanks, Ted Rosenlund, 3706 Gap Newport Pike, West Grove, Pa 19390.  Actual location is on Rt 41, 1/4 mile north of the village of Chatham, Pa.

[ja17]

Hello Ted,

It is good to find a pro who is open to ideas from the masses. Often times ones ego can get in the way of learning.   I also learn from the members on this list. There is a lot of talent and knowledge here.

Yes, it sounds like a lean mixture situation. As previous, check the linkage first.  You can test the lean theory by adding an oval shim under the Warm Running Device on the injection pump. This will richen all speed ranges.  Read the "injection pump tour"  also if you need additional info on this.

As far as the ponton hydrac unit, you may not find much help on this list. The hydrac was never used on any of the W113 cars as you probably know. Try this good ponton site it is quite comprehensive

http://www.mbzponton.org/


and their question and answere forum on Yahoo
http://autos.groups.yahoo.com/group/ponton/

It sounds like you are on the right track. My father had a ponton 220SE cab with hydrac when I was growing up. At some point in its life the local dealer gave up on its complexities and converted it to a standard shift.  I am sure it is quite fixable but parts are scarce these days. It seems that I have an old used control valve around here somewhere.  You can probably get a lot of good advice from the ponton website also.

I have wrestled with the complex four speed column shifter assembly also in the past. Make sure the nylon bushing on the chrome ball of the shifter rod is in good shape before beginning. It seems that I finnally synchronized the linkages by getting them as close as possible on their splined shaft then disconnecting the shifter rods at the transmission and adjusting the ends until all the gears would engage easily and smoothly.

Keep us up to date!


Joe Alexander
Blacklick, Ohio

[amys wrench]

Hi, what are the chances of buying that hydrac control valve you might have?  Thx Ted

[glennard]

Ah, the 'Hydrak World'!  One of MB's nightmares.  Have a bunch of Hydrak parts in the back of the garage.  Might be a control valve there.

[ja17]

Hello Ted,

I'll see if I can find the control unit. Email me at ja17@worldnet.att.net.



Joe Alexander
Blacklick, Ohio

[amys wrench]

Hello Glenn, It would be great to purchase what ever hydrac parts you may have.  Actually, my feeling is that the hydrac was a good transitional system that US dealers and mechanics simply could not service.  Had MB supported the dealerships with parts, training, and info, things might have turned out differently.  I think the beginning of the end came when the chrome nut holding the shift lever in place wore out and/or the nylon washer at the top of the shifting shaft failed, problems with the system became tricky to diagnos.  It became hard to tell the difference between vacuum and electrical problems.  Anyway, let me know about your hydrac parts.  thx Ted

[glennard]

You're right about the 'electrical contact' on the column.  It was not a 'positive' logic of the desire to shift.  A pothole, knee, passenger, wear, etc would do it.  And, the contact in the trunk was the cherry on the sundae.

[ja17]

For those of you not familiar with the Mercedes hydrac transmission, it was a four speed standard with no clutch pedal!  the transmission  clutch was electronically/pneumatically actuated whenever the shifter lever was touched!  The transmission also had a fluid coupling so you did not have to disengage the clutch when you stopped, and you could avoid shifting altogether by leaving it in third gear even from a standstill!

Yes a good working hydrac worked amazingly well as long as you resisted the temptation of resting your hand on the shifter until you were ready to shift!

Joe Alexander
Blacklick, Ohio