Stalling problem on a 71 280sl

[j5aown]

Hi all, new to the forums, so far the information I've found here has been invaluable.  However, I do have one issue that I haven't been able to figure out for a few months now.  Here's the story...

The car sat for about 10 years, and after performing all the routine stuff; fluid changes, plugs, wires, filters, etc., the car fired up and seemed to run great.  However when I drive it, it begins to lose power and acts like it wants to stall after about 15-20 minutes (feels like its being starved for fuel).  Eventually the car dies, but once i let it sit for no more than a minute or so, it fires right back up and will run fine for another 15-20 minutes before stalling again.

I've checked the common areas in the fuel system; the fuel pump, changed the filters and screens, checked/cleaned the tank (which was surprisingly rust free), as well as most of the common electrical components.  Needless to say this problem has been a thorn in my side and any help would be greatly appreciated!

[Naj ✝︎]

This thread may help:

http://www.sl113.org/forums/index.php?topic=10721

naj

[j5aown]

Thanks for the reply.  Just finished checking the fuel return line and fuel seems to be flowing just fine back to the tank.  I wish i was more familiar with the systems to these cars, but it almost feels like a relay is being tripped, cutting off the fuel, and once the car is shut off it resets it.  I'm probably way off base but thats what it feels like to me...

[ja17]

Hello,

These are classic symptoms of fuel starvation from a clogged fuel tank. Inspect the inside of the fuel tank by lifting the trunk mat, removing the plastic circular cover over the fuel sender and removing the fuel sending unit.  The iinside of the tank can now be examined. Caution fuel vapors!  Use a spark free light source.  Read the "fuel tank tour" on this site so you can see where the entrance port to the "flower pot" (thanks Dan!)  is located.  You must be sure the tank is clear before you can go any further with confidence.

 If this is the porblem, completely filling the fuel tank will improves the problem until the level falls below half.

Keep us up to date. If you follow our directions we will walk you through the steps to follow.

[j5aown]

Thanks Joe,

Took a look at the tank like you said, the fuel sending unit and the fuel inside it looked pretty rusty, but the actual tank and "flower pot" looked surprisingly clean.  I also removed the screen and cleaned that out, but it too was clean and free of debris.  In any event I filled the tank to ensure fuel was getting over the walls of the pot but still got the same result when i drove it today.  Whats the easiest way to get to the flower pot assembly?

On another note:  I ran the car today in the garage for about an hour and noticed that black exhaust was rolling out and immediately the car died as i tried backing out of the driveway.  is it possible its overloading itself on fuel?


Josh

[ja17]

Hello Josh,

With a full tank the flower pot is not an issue. The main fuel filter should be fresh or at least checked if  you have not done this yet. It is not likely that a rich mixture will stop a car which is moving down the road. Is your car moving when it cuts out or is it happening at idle or low rpms?

The Warm Running Device (WRD) on the injection pump may be stuck from long storage.  If it is stuck in the cold position, the engine will run very rich after the engine warms up.  There is a small circular air filter on the injection pump.  Air rushes into the filter when the engine is cold. As the engine warms the air passage closes.  You can check this by using a section of heater hose for a stethescope. You will hear the air rushing in when the engine is cold.  At 180 deg F  you should not hear air rushing into the filter. If it still is then this most likely is the poblem.  The WRD can be removed (two screws top stage and two screws bottom stage).  It can be cleaned and freed up so that the air slide valve moves freely in its bore.

Remember, if you have air, fuel, compression and spark on time the car will run. We can assume that the car has air and compression.  the next time it stops perform two tests;  shoot a little starting fluid in the intake, if the engine fires it is a fuel issue.  If not pull the center high voltage wire from the distributor and hold it close to an engine ground. Have someone crank the engine. Watch for spark!

[ctaylor738]

There is a small filter in the inlet fitting to the fuel pump that should be checked.  Did you do this?

[Iconic]

Josh,
I've been meaning to post these values, so here is my chance.
I had the EXACT symptoms you described. The stalling after 20 minutes, not the black exhaust.
I too thought I had flow going back to my tank because I sat in my trunk and watched it flow into the flower pot.
I am assuming that you have your stall problem even with the fuel level above the top of your flower pot. If not, stop reading.
It wasn't until I measured the fuel flow that I solved the issue.
Fuel Flow Measurements:
Spec: 1 liter in 15 seconds or less measured at the return side of the fuel damper !!!
Actual at fuel pump outlet: 3 liters in 15 seconds !! A gusher.
Actual at return side of fuel damper: approximately 3/4 to 1 liter in 15 sec. It is hard to get a container in to catch the flow to measure at this point. But, it seems close to spec.
Actual at return line close to the fuel tank: 1/5 liter in 15 sec !!!! It flowed, but not enough. This is the problem.
I blew out the return line with compressed air, fuel injection cleaner, carb cleaner, and penetrating oil.
After this procedure, the Actual flow at the return line close to the fuel tank was 1/2 to 3/4 liter in 15 seconds. A huge improvement over 1/5 of a liter.
Most importantly, I've been driving my car  without this issue ever since I did it (only ~3 weeks ago). And, I had never driven my car up until this point.
(When you measure flow BE CAREFUL and block the short line from the fuel pump that goes into the return "circuit".)

Guys, how did I do? Have I learned well from you?
Your car that hasn't run for 10 years, was it yours back then, or is it new to you??
GOOD LUCK.
Mark

[ja17]

Nice job Mark!

I could not have said it better myself!

[Iconic]

Thanks Joe.
That means a lot to me, especially coming from you !
Now, should I go a step further and discuss/ask why the restriction causes the car to stall?
The additional flow, additional (a bunch) beyond what the engine could use, is for cooling the system. That I am sure of (I think  ).
But, why does the heat build up kill the engine?
Does it have to do with Vapor lock? If so, what actually is vapor lock and how does it kill the engine?
Sorry, I'm very curious !

Josh, do yourself a favor and measure (or have someone else measure) the fuel flow at different points in the system. Even if it checks out OK, at least you will know a whole bunch of things are good !
Mark

[ja17]

Hello Mark,

Yes the fact that the fuel is always ciculating back to the fuel tank keeps "cool" fuel available at the engine.  The boiling point of gasoline is much lower than that of water. If fuel begins to boil in the fuel lines air bubles form in the fuel and the injection pump cannot inject proper fuel quantities causing hard starting and rough running or stalling. This is vaporlock.

[Iconic]

It all makes sense, THANK YOU.

[j5aown]

Alright finally had a chance to do some work on the car.  First checked the WRD and CSV, both checked out fine, then measured the fuel flow return rate at the T between the fuel tank and pump, measured out to about 1 liter in 15 seconds (filled half a 2 liter bottle), then took it for a drive to determine igniton or fuel problem as joe suggested.  When it first began to die, i quickly pulled over, and tried to turn the car over with no luck.  Sprayed some starting fluid in and the car fired right up and continued to run GREAT.  Usually it will start rough or may not start for up to 5 minutes, so i was trilled with this.  Spark tested out fine.  So initially im thinking fuel, right?  Well upon further investigation, the intake is absolutely CAKED with crap.  So i let it idle and cleaned out what i could with the starting fluid and managed to get a fair amount of it out.  Anyway, started it up, took it out, and it ran almost 20 miles before i had problems again, much longer thank usual before it begins to have problems.  When it died again, got the starting fluid out, sprayed it down and it ran great again for a longer period of time, almost a half hour now.  Got the car home and cleaned out the intake as best i could with some air intake cleaner, while doing this i noticed a line (not sure what it is, pictures included) that was disconnected!  Looks like a vacuum line, but not sure exactly.  Anyway, reconnected the line and buttoned the intake back up, and took it for a drive and IT RAN GREAT!  The car ran for 40 minutes without an issue whatsoever, which it has never done since ive tried working on it.  My question is, what exactly did I do?  Im beginning to think this wasn't an issue of fuel or spark, but one of AIR.  I kind of stumbled across the problem on accident but it was running beautifully after i finished.  Hopefully someone can make sense of this.

[j5aown]

Pictures...

[66andBlue]

That line is connected to the distributor.
For what it does see here: http://www.sl113.org/wiki/Electrical/Distributor
When was it checked last - points replaced??
Hope this solved your problem

[j5aown]

To be honest its the first time that noticed it.  The points haven't been replaced...yet.  Ive got the points just trying to find a dwell meter to borrow so i can change them out.

[menesesjesse]

Yes this line is connected to the distributor.  Since the line is probably old and brittle I would change it with a new one.  The small vacuum lines are still available and should correct and future problems.  The line provides advance for engine timing and the leak would most definitely cause some driveability issues.  Good to see you found the leak and I hope this solves your problem.
Jesse

[Iconic]

j5aown,
You said: "then measured the fuel flow return rate at the T between the fuel tank and pump, measured out to about 1 liter in 15 seconds (filled half a 2 liter bottle), ".

I'm sorry, I have to ask. Did you measure the fuel flow coming back from the front of the car, at the fuel tank, while blocking the flow from the pump through the bypass to the fuel return line?
Mark

[j5aown]

Iconic,
What I did was disconnect the return line close to the fuel tank at the "T" (connecting the return line, the pump bypass and the fuel tank), connected a nipple with an extra piece of hose and ran that into the 2 liter while blocking off the port I disconnected the return line from.  The fuel measured was strictly from the return line.  I reread what i wrote and it sounded pretty confusing, hopefully this makes more sense.

Josh

[Iconic]

That makes perfect sense.
I'm sorry that advise didn't fix your issue, but at least you know your fuel pump and plumbing are in good shape.
More importantly, it sounds like you've got it taken care of.
Enjoy driving it!!!
Mark

[j5aown]

Well Mark I thought I did...went out for a ride yesterday and it reverted back to it's old ways!  This time spraying out the throttle body and manifold had no effect...perhaps the trouble free ride the other day was a fluke, or maybe I was close to something causing the problems?

Josh

[j5aown]

Side Note:  While messing around today, i disconnected the vacuum line running between the throttle body and the 2-way valve, just as it was a couple days ago.  With it disconnected, the car fired right up idled nicely, but when i reconnected the line, it killed the engine.  Could this system be the culprit?  A few of the ideas running through my head...

Distributor problems/points?
Timing?
2-way valve and/or the relay controlling the 2-way valve?

Josh

[ja17]

Hello Josh,

Just one other easy item to check. If the fuel tank vent is clogged you will have fuel delivery problems.  Loosen the gas cap the next time you have problems and see if it temporarily cure the problem.

[j5aown]

Hey Joe,

That also crossed my mind and in fact had the gas cap removed a couple days ago while driving to see if it was perhaps the problem.  The car stalled out, and that when i used the starting fluid to test for fuel problems.

Josh

[ja17]

Hello Josh,

Does your injection pump have the deceleration solenoid on the injection pump? This device actually shuts off the fuel supply to  the injectors during deceleration. The system can become faulty causing fuel delivery problems. If this is the case, just disconnect it.

[j5aown]

Joe,

This solenoid is present on my injection pump and was disconnected a couple weeks ago when I ran across some threads of cars with similar problems, but with no effect unfortunately.  Sounded so promising when I came across it, because thats exactly what it feels like; the fuel is being shut off...

Just out of curiousity, what does the idle throttle switch control?  I started going through the emission control systems and this device failed.

Josh

[Benz Dr.]

So with the vacuum line disconnected the engine runs OK? When you connect the line the engine stalls?

 This is what happened:
Before you fixed the vacuum line you havd no vacuum going to the distrbutor. The ignition timing was set at this point and all you had was mechanical advance which is something like 10 - 15 degrees max.
When you fixed the line and hooked it up now you have 15 - 20 degrees of extra movement ( retard ) and it's pulling the timing way past TDC so the engine won't even run. All you need to do is turn the distrbutor to advance it enough to get the engine to idle properly. Use a timing light to set it to specs after it's warmed up.

[Cees Klumper]

I had similar symptoms to yours (stalling after warming up, over and over again) when I first got my car, now ten years ago when I knew nothing about it. The garage that finally fixed it (Van Dijk here in Holland) told me I had the wrong kind of distributor on the car that was causing incorrect timing, probably just like Dr Benz describes. So when I read your symptoms, after "fuel delivery" I also thought "ignition". I would make sure the ignition timing, dwell, advance/retard etc etc are what they should be, and given that you seem to have all you can/need vis-a-vis fuel delivery, let's hope that puts this very annoying problem to rest.
My car kept dying on me as I was going through heavy Amsterdam down-town traffic, just a week after I got it in the summer of 1999. All eyes on you with your beautiful convertible car, as you are pushing it out of the way, is definitely not a fun memory. At least it induced me to get up to speed (pun intended) on the inner workings and actually is a little bit of the history of how this group got started way back when.
Good luck on the fix and please keep us posted!