Running like crap but may have made a discovery - please comment - 69 280 SL

[roadsterdude]

I research this forum a lot, but rarely post.  This is long, so bear with me.  My 69 280 SL has always run like a top.  Never any issues, but it has some miles (148K).  After getting it out for spring and doing some cosmetic work, I started it and suddenly it runs like crap.  It barely ran, got worse and I got it back in the garage before it died.  After this I was unable to start it at all.  Here is what I did initially:

New points (old ones looked fine)
New Condenser (old one was very old)
New rotor (old one looked fine)
New Dist Cap (old one had a chip out of it (figured this was the culprit)
New plugs last year < 1000 mi. (NGK non-resistor which made it run ever so good) left them in place

No change

Was low on gas, so I added non-ethanol petrol (always use non-ethanol) and cracked open the injectors to let them prime

It started, but runs like crap, can barely keep it running

Removed and cleaned WRD (Warm Running Device) to make sure it was not sticking

No change

Checked spark at coil & plugs - getting good spark. 

Checked fuel flow at return line going to tank: 1 litre in 15 sec as indicated.  Checked fuel flow at CSV on Intake.  nice floe there too.  All gas very clean.  Changed Fuel Filter. Inspected tank through sender hole.  Wow my tank is so clean and shiny, I was amazed.  Expected junk, but none found.  Did compressed air test back to the tank through the return line. "bubble bubble bubble"  Removed and cleaned lines on fuel tank venting system.  All clear.

CSV is clicking (engaging) when it should.  I was running out of easy stuff that I kind of understand, but researched the starting device tour and here is where I am right now.  I may have found something - Tell me if I did:

Removed three relays all with 4 pronged plugs with 30,85,86,87 poles.  they are in an L-shaped configuration near the washer bottle.  Tested the 87 prongs on the connectors by jumping from + bat terminal to 87.  The one nearest the firewall activated the CSV  The next seems to activate the solenoid on back of the injection pump.  The last one does NOTHING.  I get a spark but no click.  Do I have a eureka moment or a false positive.  Have no idea what it should activate, but no clunk.  Please tell me this is something.

While I have the relays on the bench I would like to clean the contacts, but I am not sure how to open the case, and I do not want to break something, so give me a hint on how to do that.  Also what do I need to do next?

It has to be something that failed because all of this is so sudden.  I love this forum and the resources, but my skills are limited so advice is welcomed. 

[Jonny B]

The relays just require some patience to open. A small flat blade screwdriver, with careful pries along the edge is usually enough to get it open. Just work it at each tab just a bit, and then to the next.

Did you check the transistor unit under the battery? Could there be an intermittent contact occurring that is giving you some fits?

[roadsterdude]

Thanks for the hint in opening.  Will do that as soon as I get back in the garage.  Mine is apparently earlier than the under-battery transistorized component.  I do not have one.  Thanks again. 

[Cees Klumper]

Somehow I don't think fixing the relay will solve your bad running issue, it sounds more serious than that. I would check the compression and the injection rod linkages

[wayne R]

Mike, you can test any relay ,especially fuel pump relay is critical.
just connect small  short piece of wire from  12 volts  to 85 and 86 to ground on
your relay, you will then here a click sound,  then all you have to do while that is connected
is use a continuity tester  across  30 and 87 on you relay, and it should be on.
Ask any Porsche 911 owner  re fuel pump relays, most carry a spare in the trunk all the time.

[mrfatboy]

You state that you put new plugs in last year.  Did you take a look at them after the engine died?

I would suggest pulling them and post a picture if you can.

Does your FIP have two solenoids on the back of it?  If so,  I believe your non working relay goes to the 2nd solenoid.

Top solenoid is for fuel enrichment
Bottom solenoid is fuel cut off.

You also mention that your CSV is activating correctly but did you check if it is leaking?

[jeblack123]

May not be the same problem, but I experienced a similar event to me in my '68 280SL while in Amelia Island for the Concours. Car had been running wonderfully, but all of a sudden began sputtering, misfiring, and shutting off at every stop sign. With normal checks on most of the things you mentioned including changing my pertronix module. Pierre Hedary was kind enough to take a quick look as I was arranging to have it towed home. Turns out somehow, one of the ball pins on the linkage near the intake manifold "popped off". He noticed the throttle linkage was not connected, reattached it, made a minor adjustment to the linkage. Instant improvement and I have been driving since without a hitch.

James

[ja17]

The relays will not improve the running. They are mostly for starting. The third one may be the fuel shut-off solenoid. Did the engine problems start before or after you did all the listed work? What ignition are you using, factory non-transistorized or factory transistorized or aftermarket ?

[kampala]

I had a similar experience that I described in a post a couple years ago.  Bottomline, after trying many things, found that the thin wires going to the coil (+/-) were frayed and just barely making contact.  Did not see the wire damage as the tiny rubber covers hid them.  These are very easy to damage when working on the fuel filter from above rather than below.

[roadsterdude]

Thanks for the responses so far.  I will be back in the shop on Saturday to check out any suggestions thusfar.  Joe, I have the old non-transistorized points ignition.  Figured the non-responding relay was probably the fuel shut-off.  Would that cause any of these symptoms?  It started running badly all of a sudden, (on start-up) and that is when I started hunting and "fixin'" (or in this case not fixin')  I did change the oil while I had it on the lift and did not mention this, but it was thin and "gasoliney" smelling, so my guess is it is running way rich, which is what I am going to chase, but still could be spark or fuel, so please keep the responses coming.  I will update Saturday night.  Thanks guys!

[Benz Dr.]

If your engine is running rich then the spark plugs could be fouled. You can crank until the cows come home and it will never start. Try a set of new plugs.

[ja17]

Also, with the old std. ignition with contact points, make sure the condenser is grounded to the distributor. If it is loose you will have lots of problems. In addition double check your ignition points installation. Make sure the fork connector on the ignition points is not touching grounded metal. The ignition contact mounting bolt going through the distributor must not touch any metal ground. Lastly check the distributor cap center contact button to make sure you have not accidentally broke it off!

[roadsterdude]

Just to update the forum.  Thanks for all the responses and suggestions.  Had some time in the shop over the weekend, and went back to square one.  I had cleaned the plugs when this thing first started and yes they were carbon fouled, but when I ran it searching for the problem it was still running really badly.  So I had eliminated that.  Pulled the plugs again and yuk, they were carbon fouled again.  This time, I substituted an old set of Bosh plugs (that had always skipped at high rpm) and it came to life and ran OK.  took it our for a drive and lots of blue smoke but it ran.  They were black when removed.  Cleaned the NGKs and back on the road for an Itialian tune up.  Wow, it ran really good.  I think that because while it was in storage I would move it occasionally, and idle it to warm, but not drive it - it really loaded up the combustion chamber with gas over time (running very rich at idle) and that caused immediate fouling of my cleaned plugs initially.  Lesson learned.  If I crank it I need to drive it a while before putting it back up. (Of course I had also re-installed my points and fiddled with the Dizzy to be sure everything was grounded correctly and no errant wiring, so I cannot be absolutely sure that was not an issue)

Now I will go back over the injection system to lean it a touch and adjust my linkage accordingly.  I am sure the injection pump is tired and would like a rebuild, but that is not in my budget as long as it runs well and I can manage the rich idle.  I'll be researching the forum archives for rich running, but thought I would let you know it is alive again.  Thanks again for all the feedback.  Looks like Dr Benz gets the prize.

[Mechudo62]

Hi, it would be a good idea to check your distributor also, it may need to rebuilt. There is a nice article on the Technical Manual on how to do it and Mercedes-Benz Classic Center offers an inexpensive kit for this. I had a similar problem with almost the same symptoms you describe with a 1969, that were eliminated with the distributor rebuild and a tune up as per the Technical Manual. Best of Luck!