HELP!! My Car Keeps Stalling At Idle!

[JPMOSE]

I have been plagued with the infamous 20-30 minute stalling problem at idle after the car is started and it won't go away.  Joe Alexander has been a tremendous help but all efforts to date have not eliminated the problem.  I refuse to keep taxing Joe's time and am now ready to ask for help on line.  I have spent hours reading through this forum (along with others).  Here are my steps taken:

1)    New fuel pump

2)    All new filters including tank

3)    Check fuel lines for clearance, including vent line

4)    New Red Coil & 1.8 Ballast Resistor

5)    New condenser, points and spark plugs

6)    Drain fuel tank twice and it is clear (just minimal particles)

7)    Removed fuel sender unit and observed "flower pot" with fuel
      low and engine running.  The flower put stays full.

   Confirmed correct operation of Starting, Fuel Shutoff and CSV
      solenoids (along with relays associated with them).

9)    Tested CSV for leaks

10)   Confirmed correct operation of Warm-up Thermostat and Thermo
      Time Switch.

11)   Replaced all rubber fuel lines.

Professionally: I had my injector pump tuned (pump has less than 750 miles on it)…it was running very lean in mid range…the car was shutter on strong accelation; valves adjusted; compression test and chain checked (both received an A+ score). Dwell angle checked.  Timing check.  Engine was run on a scope and exhaust analyzed.  I guess my mechanic didn't run the car for long periods or ignored the occasional stalls.

The car runs great (besides the stalling at idle)!  I have driven it up to 95 MPH for short distances and over 75 MPH for one hour.  Yet when I come to a stop it will suddenly sputter real quick and shut off.  Mostly, it just shuts off as if the key was turned off.  

The car usually starts back up.  I did observe that unless I shut off the key momentarily the car won't restart (if I turn the switch off for a few minutes the car will then run for a period before shutting off again….the long the key is off, the longer the period before it stalls again).

Here are some things I haven't checked:

1) Ignition Switch

2) Ground Straps (just a thought)

3) Fuel Pressure via instrument (I simply spent the big bucks and
   just put a new fuel pump on...yes it was dumb!)

4) Fuel return line between injector pump and point were rubber hose
   is (near the fuel pump).  I only checked between the rubber hose
   and tank. I assumed that if the flower pot is full with fuel
   below the walls of the flower pot that fuel must be flowing from
   the return line.

5) Wires between condenser, coil, ballast resistor and ignition
   switch (I assume they must be OK if I can drive the car in
   excess of 75MPH for an hour).



This weekend:

1)I will definitely remove the fuel return line at the injection pump, remove gas cap, and blow compressed air to assure it is flowing well into the tank.  WHAT IS THE ROUND DEVICE THAT IS IN THE RETURN LINE -- NEAR THE INJECTOR PUMP?  IT APPEARS TO BE A PRESSURE CONTROL VALVE.  DOES THIS NEED ADJUSTMENT....DOES IT EVER FAIL?

2) I will run a hot wire from the battery to the firewall side of the ballast resistor to by pass the ignition switch.

3) Check the ground straps.

4) Examine other wires and check with Ohm meter.

I KNOW THIS IS LONG WINDED BUT ALL MY EFFORTS SEEM TO HAVE FAILED.  I CAN CERTAINLY USE FURTHER SUGGESTIONS.  At this point I am stumped!  On a good note, I have learned so much about the mechanical operation of my car over the past two months.  I last reported to Joe Alexander that it appears that the new coil has solved the problem (but didn't have to heart to report my assessment was wrong).  My last resort was the fuel pump because the one I replaced didn't have many miles on it (but it had been replaced in 1978).  No change with the new pump!  I also disconnected the Fuel Shutoff Solenoid (in case I didn't check correctly)...no change.

HELP!!!


Best Regards,

J. P. Mose
1968 250SL

[mrfatboy]

Does the stalling have anything to do with how fast you come to a stop?  Try driving at different speeds and stopping.  If it does it might be another clue to help us diagnos it.  What that might be I don't know.

Also, just so I am clear, Is the stalling 100% of the time? or only after 20-30 minutes? And if it is only after 20-30 minutes is it 100% of the time.

[hands_aus]

Hey J P

If the fuel return line is blocked, the fuel will sit in the lines of the engine bay and boil. This is a problem in hot climates or traffic.
I am not sure if it will cause an instant (electrical type) shut off.

If it is like a bad electrical connection, check every connection including new components.
(I had a loose screw on the ballast resistor causing an intermittent shutoff while doing 100Km on the highway.... engine cutout and then came back on, a number of times, very worrying!)

If it was the ignition switch you probably would loose all electrical power.... do you loose the radio or lights or fuel pump at the same time?

The best place to test the whole fuel system flow is the return line to the tank at the tank end.
The correct flow should deliver 1 litre in 15 seconds.

The ignition switch 'should' be turned off before the car will restart.

If the car is an auto, is the constant speed solenoid working correctly?

Check the earth wire screw inside the distributor, also make sure there is the small insulating piece through the distributor side wall where the wires for the coil go.
Add 2 drops of oil to the wick in the top of the ditributor shaft while you are in there.

That 'thing' is a fuel flow pressure damper. I believe the diaphragm is replaceable, but is rarely done.

Have you checked the spark plug wires (plug end to distributor cap end) with your multimeter? Just to be 100% sure they have the same resistance and continuity? Max of 1K ohm recommended.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[JPMOSE]

I FOUND THE PROBLEM!!!  The first return line off the injector pump had a small metal ball plugged in the end!  

This is really making me feel like a stupid ass!  First and foremost, Rodd contacted me before I even took delivery of the car and warned me of all the problems associated with fuel delivery and return, if not correct.  I followed his lead with one exception...I NEVER checked the return line from IP to the rubber hose back near the fuel pump.

FIRST LESSION...WHEN RODD TELLS YOU TO DO SOMETHING YOU DO IT!!!

What is even more annoying is the fuel hose itself.  The first thing I did when I obtained the car was brakes then replacing all the fuel lines.  I noticed they were all in good condition but since I had already purchased them I figured it was good insurance.  So today, when I noticed the ball in the line I thought it must had been there and I didn't notice it.  Then I realized that is ONE line didn't appear to be as new looking as the others.  Sure enough, it was sitting in my car parts closet! The day that I replaced all the lines, I received a call from Lockheed Martin and was called out of town suddenly.  I had forgotten to change that one line upon return!

The moral of the story is don't do anything half assed!  Also, WHEN RODD TELLS YOU TO DO SOMETHING YOU LISTEN!

I can't thank Joe Alexander enough for all of his time.  

Some more questions first?  How could I drive at 95MPH w/o a problem?
Why would someone have blocked that line to begin with?

Best Regards,

J. P. Mose
1968 250SL

[J. Huber]

Well, yes. We all know to listen to Rodd (and Joe, and Dan, and Geo and Naj and AD and ....)

Glad you discovered that -- but, what the heck are you talking about with a metal ball? I don't quite get it.

James
63 230SL

[jeffc280sl]

JP,

I'm glad you found the problem.  Could the ball as you call it be part of a check valve that only allows fuel to flow one way?  I'm not too familiar with the fuel system.

Jeff C.
1970 280SL 4-speed

[ja17]

Hello JP,
Sounds like the ignition by pass could prove worthwhile. The ignition switch could possibly be going bad.

Keep at it and good luck!

Joe Alexander
Blacklick, Ohio

[JPMOSE]

James...the ball was similar to a bearing ball.  I have a feeling that it was placed on the end of the hose with a cap when the injector pump was replaced several years ago.  The mechanic must have forgotten the remove the ball before he reinstalled the line.  Perhaps the ball was placed there to prevent fuel from leaking.  The prior owner told me she only drove the car a few times after that and mainly just started the car in her driveway for 15 minutes.  She may have never noticed the stalling.

In any event, the car now runs fine.  I drove it yesterday afternoon after I left the last message.  Not a single problem.

On a bright note, I did learn how to test all the solenoids and discovered one of the relays was bad.  Didn't need the new fuel pump but now I have the other as a spare.  The red coil was an upgrade, as the car still had the original.  Now I on the the cooling system...finally!

Best Regards,

J. P. Mose
1968 250SL

[J. Huber]

Glad you found it JP. Good news is your chase resulted in you doing a lot of maintenance items. Should be an enjoyable summer of driving for you. Have fun!

James
63 230SL

[ja17]

Congratulations JP,

A roundabout fix, but the knowledge gained along the way is invaluable!

Let's hypothesise here:
If the fuel return line is plugged, the pressure in the fuel system will rise to around 40 psi (way too much high for this system).  The problem may not be noticeable when fuel demands were high (highway speeds, cold engine, acceleration ). However during low fuel demand , especially hot idle, the injection mixture would be too rich, thus a stalling after warm-up problem could arise!

A fuel pressure check would have shown excessive fuel pressure and pointed to such a problem early in the process!

Happy motoring!


Joe Alexander
Blacklick, Ohio

[rwmastel]

quote:Originally posted by JPMOSE

FIRST LESSION...WHEN RODD TELLS YOU TO DO SOMETHING YOU DO IT!!!

J.P.
Thanks, but all I do is repeat what other smart people have said before me.  I really don't have much experience working on these cars, I just read a heck of a lot and repeat what the experts say.

You say, "it was placed on the end of the hose with a cap when the injector pump was replaced several years ago."  I don't understand the purpose of this task by a mechanic.  Can you elaborate on why an obstruction would be placed on a fuel line?  Is it to keep moisture out during long-term parts storage?  Are fuel lines normally capped when shipped?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[WILL2614]

hi  jp  i am having the same problem  help

[WILL2614]

help  jp  please

bill

[WILL2614]

amazing  car runs on highway fine  no problem even when hot  as soon as there is traffic  or car is idling  it will stall  i start it up and after about  3-4 minutes  all the time  the car  stalls   was your problem similar  as mine   my  injection pump was recently gone thru  and checked out to be  good 

[tel76]

I suggest you read the above thoroughly and then go through each item methodically,you will eventualy get there.

[J. Huber]

Bill, I would start with the more basic things first (as opposed to targeting the Injection Pump)... Plugs and points first. Then timing. If then the car is idling too low, you can then play with air and fuel mixture. At the same time, be sure your Constant Speed Solenoid (CSS) is doing its job. It can be adjusted. Good luck, its a common malady that can usually be cured.

[stickandrudderman]

As well as the basics listed above, I urge all of you to consider fuel delivery and pressure as a "basic" item.

[pj]

Hi James,
what's the "constant speed solenoid"? I couldn't find it in the TM and I can't imagine what it might be called by any other name.

[Benz Dr.]

PJ ( also known as Peter ) I looked at your car today and it doesn't have a CSS. The reason why is because your car is a standard, and they don't use that part.

The constant speed solenoid is designed to move the throttle linkage a small amount on automatic transmission cars so that the engine maintains the same RPM in drive or reverse as it would have at idle or while in park.

[pj]

I should have known the answer would be simple like that. Another reason to be glad not to have an automatic 

[WILL2614]

New  fuel pump was put in  the specs are 17psi  at  50gph  as called for by an original Bosch.    Everything was done  points  plug  condenser  ballast  resistor   coil   injection pump was check and put on the machine for an hour  all working to specs----this is frustrating to say the least----   this one has no ball bearing in the return  line----gas tank was  boiled out  4  times  ----then used POR-15  tank cleaner  and  sealer----I had a guy that was a Benz  foreman back in 69. He’s a walking book of  info. He had the car for 3 weeks, took a pressure test on the fuel line  and swore it was  a bad  fuel  pump---it  wasn't---he is stumped  now----The car  was  at  Gullwing  Motors,  the owner is the tech  advisor of a Benz  chapter---he’s worked on these cars for 40 years---he’  stumped--- can’t figure what  it  is---the car  drives on parkway  going  50--60--70-plus  for an hour  plus  no problem ---as soon as the car  hits  traffic  or is at  idle,  it  stalls  in 3-5  minutes---starts up  and  stalls in  3--4  minutes  all the time.

[WILL2614]

I don't think this has anything to do electrically ---The car just doesn't just shut down as if you turned the key off---it drops RPM'S and then shuts down as if it is starving for gas----This had to be a common problem with these cars---I  know of 2 other people with the same car with a similar problem-----Does vapor lock exist on these cars?---Could it be a heat shield between the manifold and lines? A previous poster said a heat shield took minutes and worked----Could this problem be so simple----Am I overlooking something?

[66andBlue]

Will,
no need to shout here - we hear you! ****
Please read this: http://www.sl113.org/forums/index.php?topic=9648.0 reply #4

****Please don't use all caps when typing a message

[tel76]

Have you tried any of the following --
  1 - Remove the flexi: return to tank fuel line from the FIJ to fuel damper and the one from the damper to steel return line,blow through them to see if they are blocked.
  2 - Remove the damper and remove the screws on the rear so that you can clean inside, at the same time renew the diaphram,this part is obtainable from MB dealers.
  3 - Remove the return hose from the fuel tank end and see if this hose is blocked,and blow through the pipe to see if it is blocked.
  4 - Where you have removed the rubber hose from the tank blow through this to make sure your POR15 has not blocked the return pipe in the tank.
  5 - Remove the cover inside the trunk/boot and remove the two small hoses on the fuel tank and blow through the steel ends (you have to be very carefull useing POR15 as it could block these breather pipes.
  6 - When your car stalls have you removed the fuel cap to hear if there is any vacuum,suggesting blockage in the venting system.

[WILL2614]

NO ONE IS SHOUTING----WHATS WITH THAT

Response:

On message boards, ALL CAPS is a sign of shouting. Please use upper and lower case letters.

Thank you,

Richard M, Moderator