Engine Cuts Out

[n/a]

Dear members;
I'm posting this to try to help a friend with an SL....
He is a member but wanted me to cite the problem which several mechanics can't troubleshoot properly, not even the local MB dealership...
His '71 SL engine cuts out after a 20 minute warm up...I believe problem is due to a malfunctioning warm up device. As engine warms up, coolant passing through warm-up device thermostat moves plunger, which changes fuel injector pump mixture from rich to lean. Adjustment is critical as evidenced by the shims used under the warm up unit. Possible that paraffin button responsible for expanding and contracting with temperature is either not working or not stroking correct distance. Has anyone had a similar engine cut out after 20 minute run? Are warm up devices still available new? Should the unit be re-shimmed?

I recommended to him to have the MB dealer have the car be placed on dynamometer and started cold and run at approximately 20-30 MPH while at the same monitoring tailpipe emissions, preferably on a chart recorder which tracks CO and HC output. Believe point of engine cut-out will be evidenced by sudden lean out condition, which should be corrected by replacement and adjustment of warm up device located on top of injector pump.

Instead, dealer refused to to this and insisted on changing points and condensor/capacitor...I checked these OK before but stated if they were going to do this, then, prefer secondary output be measured and tracked using oscilloscope…if breakdown in coil, condensor leakage transpires, coil HV secondary output will drop significantly. Again, they refused, changing points but doing no more. Now they have told my friend he needs a new distributor, fuel injection pump and a fuel pump to the tune of about $6K...they never measured fuel rail pressures or pump pressure and I feel they are just shotgunning...

What do you guys think? Appreciate any input.
Many thanks.
Regards,
Joe


 

[jeffc280sl]

Hi Joe,

I'll respond in the order of your inquiry.  The WRD does pretty much what you say.  Shims are a one of the last items to check and adjust.  I can't remember reading where changing the shims helped in any big way.  The WRD has a thermostatically controlled plunger that does what you say.  The thermostat assembly can be had for $25 or so and is pretty easy to replace.  Many people including myself have replaced this part and the thermo time switch and other relays and solenoids in the cold start to warm run fuel system.

Some more information would be helpful.  Does the problem occur at idle and/or higher revs?  Is the failure a sudden engine shut down or gradual?  What do the plugs look like?  That may help determine too rich or too lean.  Does the car start up again after the failure?  With more info we may be able to help determine if its a fuel or ignition issue.

Let us know.  There are many guys who have been through these kinds of problems.  Help us narrow it down.


Jeff C.
1970 280SL 4-speed

[TheEngineer]

Joe your friend is so lucky: An aquaintance brought her 230SL to a shop because it was smoking. They removed the engine, I'm told, and left the car outside in the rain for half a year. They can't make the engine run at all and now the car is soaking wet inside to boot.

[ja17]

Hello Joe,

You are probably on the right track about a fuel problem. However before tampering with the injection pump some other fuel items should be checked. Naturally the car should be in good tune as you have stated.

You could have a fuel tank problem clogging filters and screens and not allowing fuel to return to the tank for pick-up in the "flower pot".  

Remove and replace the main fuel filter and check for dirt and rust. With a fresh filter you can check supply pressure and volume produced by the electric fuel pump.

The engine accelerator linkages should be checked and set if needed.

You can move on to the warm up device next if you do not turn up anything. Its basic function can be checked by listening to the small air cleaner on the injection pump. Use a section of hose for a stethoscope. You will hear air being sucked into the warm up device when the coolant is cold. The air flow will stop as the engine approaches running temperature. The actual fuel delivery quantities is also altered during this warm-up cycle.

Adding shims will make the entire range richer, this is unusual since these pumps usually wear rich and the shims need to be removed.

Check these items out and report back. A little history would be helpful also.

Lets face it these cars were made before most of the dealers mechanics were born! They will not spend time and money to train there technicians on these old cars. If they do not understand something they just replace it!

Fortunately there are a few dealers left with some experienced technicians, sadly, less each year. This web site is the best place anywhere to find experienced and knowledgeable help. Diagnosis from long distance is tough however.  Be patient, ask questions and keep us up to date.

Joe Alexander
Blacklick, Ohio

[n/a]

Dear Guys;
My friend addeded the following to answer some of Jeff's questions...
Joe,
Thanks for posting the pagoda problem.
In answer to Jeff's questions: The problem occurs like this: After 20 minutes, the engine will "stumble or stutter"  (ie loose power 50%) while my foor is on the gas.  The engine misses and sounds as if it is about to stall.  If I take my foot off the gas (ie red light, or while shifting, it stalls immediately).  The engine just dies (it is not gradual). Sometimes the engine stalls while my foot is on the gas also (at higher revs).  Either way, you can almost set a clock after 20 minutes. Re-starting is impossible for at least the next 15 minutes (engine cools).

(I can't believe that other issue where they took the engine out! My God!)

Thanks.
Regards,
Joe
 

[glennard]

Joe,  Sounds like rust in the fuel tank.  Rust and crud impede the flow of make-up fuel to the 'Shroud of Fueling'(holding about a quart of gas-15 minutes or so of low load operation) in the center of the gas tank. Check the fuel flow coming from the tank to the electric fuel pump when this happens.  Carefully open line, drain gas into a bucket- probably stops to a drip!  Remember- Crud in the Shroud of Fuel'n  and there will be no Tour'n!

[jeffc280sl]

Hi Joe,

To me the problem sounds ignition related. The failure mode is complete rapid shutdown at any RPM.  I had a similar problem with the transistorized ignition system located on the underside of the battery base plate.  Ended up replacing it with an optical trigger system which also did away with the points.  Maybe a component is failing as it electron/current passes through it.  As the part cools you are then able to start the car to be followed again by the same cycle. Maybe the connector to the unit is dirty.  As I said it sits under the battery and can get pretty dirty and grimy. I don't know how to test the unit.  Will look and see what I can find and get back to you.

BTW Joe Alexander is the real expert.  Give him enough input and he will identify the root cause problem.

Jeff C.
1970 280SL 4-speed

[glennard]

Joe, More.  The quart of gas in the Shroud is consumed in the 20 minutes or so- and the engine is starved..  It takes a while(15 minutes?) for gas to slowly seep thru the crud and rust into the Shroud and fill up the lines to the fuel filter, injection pump, etc.  Then the pumps can catch suction again, and repeat the cycle.  Just one scenario that has happened to me.

[Naj ✝︎]

Joe,
Ensure that the fuel return line is clear all the way into the tank.
Mine was blocked inside the tank and caused exactly your symptoms.
naj



65 230SL
68 280SL

[n/a]

Hi everyone!
I just joined this site because my hair is falling out with the stress of trying to get my car running right. The car is a 280 sl 1971 model manual and the biggest problem I have is that I am living in Dubai and for most mechanics here they have never worked on a Pagode before. I get passed from one garage to the next generally on the back of a trailer. Anyways I find the posting regarding the engine cutting out after 20 minutes excellent cos that is what is exactly happening to mine as soon as the engine becomes hot, she starts up again straight away and I can almost here something starving the fuel. I am getting to a stage now where there really isnt anything more to replace on the car!if i drive in astraight line it will go forever however it will not tick over longer than 20 min from cold and I can set my watch by it.Also I get a judder at exactly 45 mph, smooth before and smooth after but you can shake yourself to death at 45!any ideas.
P.S the tank has been flushed filters checked,return line.
Cheers Garry

[ja17]

Hello Gary,
Just flushing the fuel tank does not cure  your fuel delivery problems in most cases.

The fuel tank has a screen built in the drain plug which I assume you have cleaned in addition the fuel tank has a baffle unit built in the bottom of it which we refer to  as a "flower pot" (thanks Dan). This flower pot has a small port which is allows fuel to enter the flower pot so it will be picked up by the electric fuel pump. This port must be clear. Otherwise the car will run out of fuel every 15 or 20 minutes as the flower pot empties and is unable to refill through the port.
To counter this problem run test with a full fuel tank. This will allow fuel to flow over the flower pot wall keeping the flower pot full. Search up and read the "fuel tank tour".

The next item to inspect is the screen in the electric fuel pump. It is directly under the intake line fitting in the pump. It can be clogged.

The main fuel filter is the last line of defense. I assume this has been changed.

Lastly Check the fuel pressure and delivery quantity of the electric fuel pump. If the fuel pressure is too high the return fuel line is clogged. If the fuel pressure is too low or the fuel delivery quantity is low you have a restricted fuel supply, a problem with the return check valve on the injection pump or a defective electric fuel pump.

The fuel pump pressure should be 13.2 to 16.1 psi  (.8 to 1.1) with the engine off, at least 1/2 tank of fuel, min. of 11 volts at the electric fuel pump and the fuel return line pinched off or blocked. Hook up the test gauge at the metal fuel line on the starter valve on the engine intake.
After the pressure check check fuel delivery volume by measuring the fuel pumped from the same fuel line (now open). The system should deliver about one liter every 15 seconds.

Download Attachment: pressure check.JPG
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Hooking a fuel pressure gauge to the engine and temporarily installing it in the cockpit, then going for a test drive can be very helpful for diagnosis also.

After these checks you can be fairly certain that the fuel delivery system is operating correctly. You can now with confidence move on to other possible problem areas. Keep us up to date! Good luck.



Joe Alexander
Blacklick, Ohio

[nirmal]

Gary
I am in Dubai and have a 1969 280sl automatic. I know a mechanic who has worked on these cars and started his own workshop after retiring from Gargash (MB agent here). He is out of the country at the moment but expected to return in a week or so. Send me an e mail if you need any assistance.
Nirmal
1969 white 280 SL

[A Dalton]

<<<After the pressure check check fuel delivery volume by measuring the fuel pumped from the same fuel line (now open). The system should deliver about one liter every 15 seconds.  >>>

 ....to add to JA post , when doing the above delivery test, it is a good idea to submerge the test hose  in your measure container.
 This allows one to monitor for any air bubbles . If you do see any, you have a leak on the suction side of the fuel feed.  [ porous hose/clamps/etc.] Original braided fuel lines between the tank/pump were infamous for this.
 You will note in the picture Joe supplied that the Benz gauge has a glass eye-sight on it [ item 5 ]for this purpose. The same results can be obtained by simply submerging the end of your hose during the test and watching the delivery for any evidence of air............

[n/a]

Hi Nirmal
That sounds very good, I have the car here at my home in Mirdif Im sure you know the area,There seems to be a few Pagodes getting spotted around lately.Feel free to give me a call my Mob is 050- 6248560
Cheers Garry

quote:Originally posted by nirmal

Gary
I am in Dubai and have a 1969 280sl automatic. I know a mechanic who has worked on these cars and started his own workshop after retiring from Gargash (MB agent here). He is out of the country at the moment but expected to return in a week or so. Send me an e mail if you need any assistance.
Nirmal
1969 white 280 SL

[n/a]

Hey guys,

Problem found...my friend had his SL towed to a facility in NJ where it was discivered that after installing new points, after running the engine for 20 minutes or so, the new points were pitted and of course the dwell was way off. It turns out the last mechanic installed the wrong ignition coil, one designed for electronic ignition which slugs more current through the points than they were designed for...

thanks for all your help...

Regards,
Joe

[ja17]

Hello Joe,

Great, a fairly inexpensive fix also. No engine removal this time!
It is especially difficult to diagnose these kinds of problems when people install the incorrect new parts!



Joe Alexander
Blacklick, Ohio