250SL won't start

[Ian45]

My Pagoda has been motionless since it cut out on my driveway last November and has not run since. The engine turns, but makes no attempt to fire. I've been sending and receiving posts about the problem on the MB Club UK website but I thought I would open up the problem to a wider audience. Spring is approaching and I'm beginning to get desperate !

This is the current situation :-

We have fuel at the inlet pipe to the injection pump and also at the return pipe, but not a drop coming from the top of the pump above the rack. As a result, needless to say, the spark plugs are bone dry.

The coil, ballast resistor, points and condenser have been replaced even though we were getting a decent enough spark to the plugs. We obviously can’t set the timing properly until we can run the engine. I’ve no reason to suspect it’s out. We have carefully done a bit of advancing and retarding to no avail, making sure it set back to it’s original position. So I think we have ruled out an ignition problem.

The fuel injection pump that was fully overhauled by Tower Bridge Diesels in 2004, has recently been returned to them and checked out on their test rig. No fault found, apparently working perfectly.

Before removing the injection pump and again after re-fitting, we took the side plate off the pump to check that the pump was being turned and activated by the engine – yes it is.

At the front end of the pump, as recommended, we removed the cover plug, inserted an M5 bolt into the thread at the front end of the control rack and checked it was moving freely – yes it is. We also turned the engine with the rack pulled forward to the maximum fuel position. Under these conditions, a very tiny amount of fuel weeps from the top of the pump outlets.

Next, we checked the operation of the cold start solenoid at the back of the pump. The plunger is popping out as required, presumably to push the rack to the maximum fuel position.

We removed the cold start valve on the inlet manifold sufficiently to be able to see that it was providing the necessary spray of fuel into the manifold – yes it is.

Even though we are getting fuel to the injection pump, we had a look at the electric fuel pump at the back of the car. That did have a leak from behind the plate where the live and earth cables screw on. We tightened the screw holding the plate on and it seems to have cured the leak. We then checked the flow rate from the back. An article that I had recommended 1 litre in 30 seconds. We received half a litre in less than 10 seconds, so that looks ok.

We have even replaced fuses, even though they looked absolutely fine.

To us, everything still points to a problem in the control rack area of the fuel pump, perhaps a major air lock or contamination of some sort.

So, is there a way to prime the injection pump ? Is there any sort of fuel cut off switch that the manuals don’t mention – I can’t imagine so.

In some ways I would like to identify a failed component so that I can replace it in the knowledge that I have cured the problem and it shouldn't happen again. Even if we manage to shift the airlock, I am going to be wondering what caused it and whether it could happen again in a far less convenient place.
 
We will check the flow rate again because I've now been told that 1 litre in 15 seconds is required. Also, we previously checked the flow rate after we had stopped the leak from the electric pump by tightening the screw holding on the plate between the electrical terminals. It was quite a bad leak. Why would it leak at that point ? What's behind the plate and would you consider taking off the electric pump and having it fully overhauled ?
 
I'm also puzzled as to why fuel gets through when the injection pump is tested on Tower Bridge Diesel's equipment but not when it's back on my car.

Any suggestions greatly appreciated.  


Ian
1967 250SL
1998 SLK230
Derby,England

[merrill]

Ian,
so, I had a simlar problem when I replaced all the fuel lines and had the fuel tank out.  the fuel was not getting to the motor.  motor would turn etc but no kick,

to "bleed the system"   - follow all safety guidelines with gas

in the engine bay , find the fuel return line from the inj pump to the metal line that runs back to the fuel tank. disconnect the line and put a vacuum on it.  (I used my mighty vac) Hopefully at some point you will have fuel coming out of the line.

from there, re connect the line.  At that point you should be able to turn the motor over a few times and it should kick.

You may get replies to loosen the lines at the injectors to further help bleed the system.  I have never tried this procedure.

Hope this helps.
matt

Matt
Austin Tx
66 230 sl - "white"
78 300 D - Blue
98 C230

[al_lieffring]

Hey Ian

I just went through a fuel delivery problem that currently seems to be OK but I never found a definitive cause to why my car was stalling out on the road.

First thing I noticed in your post is that there is fuel leaking from the electrical connections. If your car has the original pump, there should be no fuel in the motor housing of the pump.

When checking the fuel flow check it at the fuel return line where it comes off the damper mounted on the left motor mount arm where it attaches to the metal line that runs back to the tank.

you may also want to test the fuel pressure, I removed the line form the CSV and attached a guage there. Is should run about 12 psi with the fuel circulating through the loop.

If the fuel flow rate and pressure checks out OK, try attaching a momentary contact switch to the cold start injector valve and hold it on for about a second before cranking the starter, it shoud deliver enough fuel to make the motor start for a moment. If priming with the CSV doesn't have any effect check things like compression, check if the distributor rotor points to cylinder #1 when the cam lobes on the front cylinder are pointing up and the timing marks are on TDC. and check to see if the valve timing marks are lining up.

Keep us posted on how things are going

Al

66 230sl
113-042-10-014715
904/396 blue, Ivory Tex
condition: not-as-rusty-as-before-bucket

[waltklatt]

Ian,
You say the spark plugs are dry?  
Did you crack open the fuel lines from the pump to the injectors?
Also, what made the car cut out last Nov?
Anything out of the ordinary?  Odd noises, clunkings, rattles, engine misfiring?
In any case, replace the fuel filters-one in the bottom of tank and the other on the motormount arm.  How does the gas smell, old stale?  Replace with fresh gas.  The pump in the back is bad, no fuel should be leaking out at all, especially where the electrical current goes in.
Walter
1967 220SL-diesel-thankfully no gas or tuneups needed.

[Naj ✝︎]

Hello, Ian,
 

quote:Also, we previously checked the flow rate after we had stopped the leak from the electric pump by tightening the screw holding on the plate between the electrical terminals. It was quite a bad leak. Why would it leak at that point ? What's behind the plate and would you consider taking off the electric pump and having it fully overhauled ?

If you have a later/shorter pump (electrical terminals with red and brown plastic plates) it can leak from the treminals because it is  a 'wet' pump which is cooled by the fuel. One reason could be that there is a build up of pressure because one fuel feed line to the engine is partially blocked.
I did reply to your post on the MB site. I asked if you had checked/changed the filters.
Let us know what you find.
naj

68 280SL

[glennard]

Hi, Oil lubrication in the MFI pump?   Hook up a manual switch to the Cold Start Valve.  Run the engine on the manual manipulation(on/off) of the CSV.  Or spray a controlled spray of gasoline(or Quick Start-carefully) into the butterfly intake.  If there is spark, it will run!

[Ricardo]

Ian
I think Glenn could be on to something here with the lube oil in the injection pump. If the pump becomes overfull, this can seriously effect operation. Some of the earlier pumps (up to 18y, I think)did not have check valves from the engine oil return line, though I'm not sure if this can cause an overfil situation, but it's certainly worth checking to make sure the pump has the correct level of lube oil. It's hard to imagine the company that did the rebuild wouldn't have checked this when you sent it back though.

[J. Huber]

My intuition tells me there is debris blocking the fuel lines near fuel pump or one of the filters. No expert (as we all know!)

James
63 230SL

[George Des]

Should be pretty easy to rule some things out. If you suspect you're not getting fuel to the FI Pump, open the line where it comes out of the outlet side of the fuel filter or damper and check the flow there. If all is well there as far as flow and pressure, the problem is not your electric fuel feed pump. If you do have restricted flow there, it could be a couple of things. It could be the inlet side of you fuel feed pump has a cruded up screen--easy to clean this out, or the outlet side check valve is stuck in the closed position--this may also help explain why you have a leak at the terminals if it is causing excessive pressure in the pump body, although the lak may simply be the loose terminal plate--there are two o-rings behind this plate that also could be faulty.

George Des

[Benz Dr.]

This makes no sense. The fuel system should self bleed if everything is working right. It can take a while for fuel to work its way over to the injectors if the lines are dry but the fuel from the pump should go back to the tank in a matter of seconds after turning the ignition on.

An overlooked problem is often a pugged return line inside of the fuel tank. Checking the fuel flow at the dampner will lead you to believe that all is well ( and it is up to that point ) but in reality, it isn't.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[ja17]

Hello Ian,

Sounds like a fuel delivery problem to me also.  Do the pressure check. Check the fine screen in the intake fitting of the electric fuel pump.
Actually a very small amount of fuel is squirted from the injection pump on each stroke. It does take a while to fill an empty injector line. However, the original problem sounds like fuel starvation. You should be able to remove the easiest injection line at the pump and with full throttle and cranking, watch a small amount of fuel emerge each revolution of the engine. If you have a fuel delivery problem, or injection pump not always turning (damaged timing gear or key) you will not get enough fuel to run. Try temporarily squirting a little fuel or starting fluid in the intake to see if the engine is capable of running.

This much I will assure you, if you have fuel, spark on time, and compression, the engine will run. You will have to verify all of the three above requirements. If fuel delivery is fine we will move onto the next possibility. Keep us up to date.

Joe Alexander
Blacklick, Ohio

[Naj ✝︎]

Ian,
One more question:  :?:

Does the oil pressure gage come up while cranking the engine?

naj

68 280SL

[Bearcat]

I agree with the fuel theory. I had crap in my lines and crap at the bottom of the tank....replaced and repaired same...never looked back.


280SL 1970
cls
e class

[Ian45]

Wow - I'm overwhlemed with the response to my post. Thanks everyone. It will take me a while to digest all your suggestions. I will be having another go with the car soon and will feedback. Thanks again.

Ian
1967 250SL
1998 SLK230
Derby,England

[Ian45]

Still haven't got the car going. Fuel flow from the electric pump to the injection pump is 850-900ml in 15 seconds, so slightly under the recommended level, but I'm told that would be enough so that's unlikely to be the problem. My injection pump has only the one solenoid at the back. Does that mean that I don't have an electrical fuel cut off device of any sort ?



Ian
1967 250SL
1998 SLK230
Derby,England

[al_lieffring]

quote:Originally posted by Ian45

Still haven't got the car going. Fuel flow from the electric pump to the injection pump is 850-900ml in 15 seconds, so slightly under the recommended level, but I'm told that would be enough so that's unlikely to be the problem. My injection pump has only the one solenoid at the back. Does that mean that I don't have an electrical fuel cut off device of any sort ?



Ian
1967 250SL
1998 SLK230
Derby,England

Ian

Only the cars made for export to the USA 69 and later models have a fuel shut off solenoid. 69 models have both an enrichment and shut off solenoid, 70 and 71  have only a shut off.
I once encountered a 68 280 sl where the customer complained about the car not restarting when warm. I found that he had a salvage yard pump installed at another shop and it was off a 70 sedan engine. The motor was wired for an enrichment solenoid but the pump had a shutoff and was engaging when the motor was cranking preventing the motor from starting. I disconected the wire and taped it off.

I would think if this were the case on your car, the injection shop would have noticed that it was the wrong pump application. it took me about 3 seconds to diagnose the car mentioned above.

Al

66 230sl
113-042-10-014715
904/396 blue, Ivory Tex
condition: not-as-rusty-as-before-bucket

[ja17]

Hello Ian,

Remember if you have fuel, spark on time and compression, it will start. You may want ro remove the spark plugs to see how they look. While you have them out make sure you have compression.

Joe Alexander
Blacklick, Ohio

[glennard]

Squirt some 'Starting Fluid' in the open butterfly throttle.  If you have spark and compression , you should get a bang(when you crank it over).  Check the spark with a seventh plug, i.e. take the wire off no. 1 plug and put it on an extra plug grounded to the engine somewhere.  Crank engine- should have a strong spark visible on the seventh plug.

[Markus]

Did you check voltage/current to the injection pump shut off solenoid (bad connector, or wire, also bad ignition switch)? Is injection pump correctly timed to the engine?  Does this thing ever fire, even with a sniff of starting fluid?

[Mike Hughes]

quote:Originally posted by glennard

Squirt some 'Starting Fluid' in the open butterfly throttle.  If you have spark and compression , you should get a bang(when you crank it over).  Check the spark with a seventh plug, i.e. take the wire off no. 1 plug and put it on an extra plug grounded to the engine somewhere.  Crank engine- should have a strong spark visible on the seventh plug.

Be bloody careful using starting fluid!  An article in a recent issue of Sports Car Market had before and after pictures of a very rare car whose owner tried some starting fluid on it inside his garage.  He had done this before many times in the 40+ years that he owned this car with no ill effects.  This time the garage and car both were reduced to ashes and a burned out hulk.  Worse still, he was severely underinsured so there is no hope of even trying to resurrect the remains of his lifelong automotive companion.

- Mike Hughes  -ô¿ô-
  1966 230SL Auto P/S
  Havanna Brown (408)
  Light Beige (181)
  Cream M-B Tex (121)

[Mike Hughes]

I'm going to hi-jack this thread to post a similar problem:

Last weekend my wife & I took the 230SL out for a quick spin.  I try to exercise it at least onec a month in the winter IF there is no salt on the roads.  Altogether this trip was about 20-25 miles, enough to get everything including the exhaust pipes thoroughly warmed up.  The engine purred along just fine.  The last section of the drive was a 9-10 mile burst on the interstate.  Again, the engine purred along just fine.  When we pulled off the interstate onto the exit ramp to home it started missing on deceleration.  By the time we got to the end of the exit ramp the engine died completely.  Two times I started it up and it would idle roughly for maybe 10-15 seconds and quit.  After that I ran the battery down trying to get it to fire again.  

A passing motorist helped me push it to a safe place and gave me a ride home so I could get my truck and trailer and haul it the last mile home.  After recharging the battery it simply won't fire.  The tank is full and I can hear the fuel pump whirring away under there.  I've opened the bleed screw on the top of the main fuel filter and I get flow.  I've pulled a plug wire and I get spark.

Any thoughts?

- Mike Hughes  -ô¿ô-
  1966 230SL Auto P/S
  Havanna Brown (408)
  Light Beige (181)
  Cream M-B Tex (121)

[waltklatt]

Hello Mike,
Sorry to hear of your misfortune.  But am glad you got the jewel back home safely.
I would crack open the injection lines to see if you get anything from the IP to the cylinders.  Might be a blockage there, or the IP has failed.
 
You are not the only one who had difficulty getting the jewel home.
I drove the 220SL to my parents to park in front as a show piece for my dad's 75th party.  Then I drove home on Sat, it was a little drizzly.  The clutch pedal sank to the floor and when I trying to put into first gear it ground with the pedal all the way to the floor.  So I had to drive home by cutting out the engine at the stoplights and putting it into first and then crank start to get moving.  Once moving I played with the gas to get the engine speed and car speed right to slip the lever to the next gear.  Got home just perfectly.  Now I need a new master clutch cylinder.  Bummer, but it was worth the drive!  

Walter
1967 220SL-curretnly clutchless.

quote:Originally posted by Mike Hughes

I'm going to hi-jack this thread to post a similar problem:


After recharging the battery it simply won't fire.  The tank is full and I can hear the fuel pump whirring away under there.  I've opened the bleed screw on the top of the main fuel filter and I get flow.  I've pulled a plug wire and I get spark.

Any thoughts?

- Mike Hughes  -ô¿ô-
  1966 230SL Auto P/S
  Havanna Brown (408)
  Light Beige (181)
  Cream M-B Tex (121)

[Bob G ✝︎]

I do not have the experience of a Dan Carconsand some of our more experienced experts. but I can tell you that when I first got my 280SL it would cut out and quick at odd times. no electrical items would work  and this frustrated me to no end. finally I pulled the ignition coil to fine it was old and useless. put a new one in and that solved my problem. Another area to check is under the car were the starter and positive battery terminal connect to a box make sure the screws are secure and tight.
Just my 2 cent and a cup of coffee.

Bob Geco
1968 280SL under restoration.

[Mike Hughes]

Update:  Over the weekend I changed the main fuel filter.  There was very little loose debris in the bottom of the filter housing.  I next disconnected the line from the tank to the pump at the pump.  There did not appear to be any debris inside the filter in the pump.  However, it took nearly two hours to drain 5 gallons of gas from the tank.  After finding a suitable 22m device (a lower control arm bolt and castellated nut, courtesy of a nearby MBCA member, with a hardened finishing nail punch in the cotter pin hole to keep the nut from turning when a wrench is applied - works like a charm!), I removed the in-tank filter/drain plug.  Lots of debris and a couple of shot glasses worth of water were mixed with the remaining 1/2 gallon of gas.  The filter was completely black and pretty clogged - one couldn't even see daylight through the mesh.  So I blew debris in the mesh out with an air chuck until it was greyish beige in color and one could see through the mesh, reinstalled it and refilled the tank with about 4 gallons of gas.

The engine fired right up and idled smoothly and normally - for about 45 seconds - then quit again and won't fire for more than a few seconds.  When it runs it sounds quite normal, no missing or anything until it just quits.  This seems more and more like a simple fuel delivery issue.  What else should I be looking at?



- Mike Hughes  -ô¿ô-
  1966 230SL Auto P/S
  Havanna Brown (408)
  Light Beige (181)
  Cream M-B Tex (121)

[ja17]

Hello Mike,

Yes, fuel delivery is most likely the problem. the screen in the tank is just the tip of the iceberg.  As Dan has mentioned, the intake hole to the flower is most likely plugged. You should also remove the screen and plug one last time and "snake" the fuel output line from the tank outlet pipe down to the plug/filter opening.  Alcohol will dissolve the varnish on the screen and tank better than most any other solvent. Some of the electric fuel pumps had a screen at the intake fitting of the electric fuel pump. This must also be checked and cleared if your car has one. The fitting must be removed.



Joe Alexander
Blacklick, Ohio