Starting problem when hot

[rwmastel]

Tried again this time holding the throttle open various degrees, no luck.

Alchemist,
This is probably the source of the fuel smell, holding the throttle down while cranking & not starting.

[toneypenna]

You may search "Mercedes Hot Vapor Lock" which was and still is a notorious problem in the 1970's and for a variety of Mercedes models such as 450SL. It has to do with bubbles in the gas lines when the car is hot. Good Luck.

Thank you for your input. I'm surprised to hear of a vapor lock problem on the later Mercedes that I believe were also fuel injected. The way I or we used to correct vapor lock problems on older carbureted domestic cars was to install a three nipple fuel filter ( I think were used in Jeeps) between the mechanical pump and the carburetor and run the third nipple back to the vent line on the tank, in essence a return line.
Since fuel injected cars run at a higher pump pressure and also have a return line, I didn't think vapor lock could be a problem, but I suppose anything is possible.
Thanks,

Jim

[toneypenna]

Smelling gas is an indication of flooding. You may check the spark plug after cranking and smell it. If you find sign of flooding, then you need to adjust the knob at the back of the injection pump. Turn it counter clockwise few notches when the engine is not running.

Good thought, I will check it out. Never had this problem before, wasn't running rich when it last started, but who knows.

Thanks,

Jim

[ja17]

Vapor lock on these cars is usually due to fuel not circulating back to the fuel tank. The fuel flow is a continuous loop on these engines, which depends on the cool fuel circulating from the tank to keep all the components (IP, fuel lines and gasoline) cool. When circulation is poor, the heat from the engine warms the entire system and can cause the fuel to vaporize. Difficult hard starting can result. The most common problems of poor circulation are; low fuel pressure, low fuel volume (flow rate), a plugged fuel return line, plugged fuel filter, plugged fuel pump screen, plugged tank screen, debris in fuel tank or a stuck or improper fuel return check valve at the injection pump. Modern alcohol fuels can aggravate the problem since they have a lower boiling point than traditional gasoline. 

[toneypenna]

Vapor lock on these cars is usually due to fuel not circulating back to the fuel tank. The fuel flow is a continuous loop on these engines, which depends on the cool fuel circulating from the tank to keep all the components (IP, fuel lines and gasoline) cool. When circulation is poor, the heat from the engine warms the entire system and can cause the fuel to vaporize. Difficult hard starting can result. The most common problems of poor circulation are; low fuel pressure, low fuel volume (flow rate), a plugged fuel return line, plugged fuel filter, plugged fuel pump screen, plugged tank screen, debris in fuel tank or a stuck or improper fuel return check valve at the injection pump. Modern alcohol fuels can aggravate the problem since they have a lower boiling point than traditional gasoline.

Joe,

Thanks again for the enlightenment,
I know I have good fuel pressure and volume but before I can go any further on the hot start problem I have to get it to start when cold. Have tried almost every time I walk by it, just won't start. I'm hoping for some time tomorrow to try to get to the bottom of it. The only thing I did before the cold start problem developed was reset the timing so back to basics  first I'll try retarding it a bit and see if that helps. Still don't know if the repaired CSV would have any effect on either or both of the problems, I gueess I can always take it off and inspect it further.
Hope i'm not wearing out my welcome with you. I'll let you know what I find.

Again, Many Thanks.

Jim

[ja17]

If it has fuel, spark on time, and compression it will start. First try giving it a squirt of starter fluid and see if it kicks. If it does your problem is no or not enough
fuel.

[toneypenna]

If it has fuel, spark on time, and compression it will start. First try giving it a squirt of starter fluid and see if it kicks. If it does your problem is no or not enough
fuel.

Joe

Got a chance to spend some time on the car late today. To recap, we had power to both the CSV and pump solenoid on cranking for about 3 seconds when cold and 19 PSI on the fuel pressure taken at the return line with adequate flow.
Solved the cold start problem by retarding the spark probably 3 to 5 degrees which tells me I had the timing  to far advanced. (thought I had it at 35 at 3000 RPM.)
Let the car get to operating temp, shut it down, tested the CSV and Pump solenoid again while cranking when hot and got the same results, both lit the test light for about the same  3 or 4 seconds. Also checked fuel pressure again when warm and I'm assuming it's the same. For some reason my snap on gauge stopped working, so I used another one I had that only went to 10 PSI max , it pinned the gauge and bounced like it wanted to go further.
Tried to re start it a couple of time when hot and it would finally start on the second or third revolution only if I held the throttle open about 1/2 way. I let it run and checked the timing and it's now set at 38  so I left that alone. Let it run, shut it down numerous times and it restarted with difficulty with the throttle held open about 1/2 way.
Other than that it idles happy at about 750 / 800 rpm. I think I'm making some progress but I keep thinking that there is something simple that I'm not seeing that causes this hard hot start.
Any suggestions or corrections as to how to make it start easier when at operating temp would be greatly appreciated..

Jim

[ja17]

Try disconnecting the two starting device one at a time, during warm starts, to see if it helps. You could be flooding when warm.

[rwmastel]

Following along out of general interest...

Why would pressing the gas pedal 1/2 way when cranking help start a car already in a flooding or fuel rich configuration?  The open air flap on the intake is needed?

[alchemist]

Thank you for your input. I'm surprised to hear of a vapor lock problem on the later Mercedes that I believe were also fuel injected. The way I or we used to correct vapor lock problems on older carbureted domestic cars was to install a three nipple fuel filter ( I think were used in Jeeps) between the mechanical pump and the carburetor and run the third nipple back to the vent line on the tank, in essence a return line.
Since fuel injected cars run at a higher pump pressure and also have a return line, I didn't think vapor lock could be a problem, but I suppose anything is possible.
Thanks,

Jim
Jim: I am referencing fuel injected Mercedes in the 1970's and 1980's. I mentioned 450SL which is fuel injected with Bosch injection system with no carburetor. The vapor lock problem still exist in these fuel injected Mercedes.

[Pinder]

Im also following along.  for what is causing this. I would guess the warm up device on the IP.  when cold it has the right fuel mixture  but then when all warmed up its allowing too much fuel causing rich state.

[ja17]

Rodd,
The mixture equation is not proportional since the flyweights in the injection pump spin very slow during cranking. It seems to me that the more throttle you give, the leaner the air to fuel mixture becomes. Injected fuel increases with rack movement (throttle linkage position, engine rpms and engine temperature). Since rpms are low during cranking, additional fuel from the rpms is virtually non existent. With more throttle, a higher percentage of air would be introduced along with a smaller ratio of fuel. Experimenting with throttle position can help determine starting issues, (both lean and rich). Don't depend on smell. Faulty ignition or fouled plugs will release unburned fuel. Low ignition voltage, especially with the low power coils on the early ignitions, can contribute to poor starting also.

[toneypenna]

Try disconnecting the two starting device one at a time, during warm starts, to see if it helps. You could be flooding when warm.

Joe
Looks like you were right again. What I did on Saturday: Started it cold no problem, let it get to operating temperature, shut it down, tried starting, wouldn't start. Disconnected CSV at relay, still wouldn't start, then disconnected IPS at relay and it started running rough at first. I'm assuming due to  burning off excess fuel. Shut it down and restarted it 6 or 8 times, starting immediately on the first crank the way it should, let it sit about two hours, as I was leaving I tried to start it, wouldn't start while CSV and IPS were still still disconnected.

Went back on Sunday, Wouldn't start, connected the CSV it started with no problem, then connected tie IPS while running and again let it get to operating temp then shut it down.
Tried starting with the two starting devices connected, wouldn't start. This time I disconnected the IPS first and it started, but  with difficulty, shut it down and disconnected the CSV and it started  with no problem like it should.

Note I did disconnect both starting devices each time, one at a time,  but in different sequence.

As you initially suggested, it looks like I have a fuel problem when at operating temp. What would be my next step, is there a remedy for this?

As always, thank you for your time and knowledge.

Jim

[toneypenna]

Thank you for your input. I'm surprised to hear of a vapor lock problem on the later Mercedes that I believe were also fuel injected. The way I or we used to correct vapor lock problems on older carbureted domestic cars was to install a three nipple fuel filter ( I think were used in Jeeps) between the mechanical pump and the carburetor and run the third nipple back to the vent line on the tank, in essence a return line.
Since fuel injected cars run at a higher pump pressure and also have a return line, I didn't think vapor lock could be a problem, but I suppose anything is possible.
Thanks,

Jim
Jim: I am referencing fuel injected Mercedes in the 1970's and 1980's. I mentioned 450SL which is fuel injected with Bosch injection system with no carburetor. The vapor lock problem still exist in these fuel injected Mercedes.

Agreed, I was not try to contradict you, just wasn't aware a fuel injected engine could suffer from vapor lock. I stand corrected. I realize carburated and fuel injection systems are completely different ballgames. My thinking was to correct vapor lock in a carburated engine we added a return line to the tank and it usually solved the problem. Sorry if there was a misunderstanding.

Jim

[ja17]

Jim, do you have a modern gear reduction starter on your car? You'll never guess how this may be richening your starts, if you do.

[toneypenna]

Jim, do you have a modern gear reduction starter on your car? You'll never guess how this may be richening your starts, if you do.

Not as far as I know, sounds and looks like a normal starter, however I did convert to an electronic 123 distributor a while ago. At the time I searched the forum and the consensus for this was favorable upgrade.
I don't want to mess with the fuel adjustment on the injection pump unless I have some direction so I don't make matters worse. Is this a possibility or is there something else I can try?

Jim

[ja17]

Have you tried using a lot more pedal during hot starts?

[toneypenna]

Have you tried using a lot more pedal during hot starts?

Joe

Been through the more and less pedal when hot more than a few times, sometimes it does and sometimes doesn't start no matter what amount I depress the pedal. The few times it did start it was with great difficulty. Not a reliable way to restart when at operating temperature. The only way it has started as it should at operating temp is by disconnecting the CSV and IPS. as you suggested, then it starts no problem. Question is how to correct this? It's evidently an excess fuel problem, can this be adjusted in some way? I would think that leaning out the fuel mixture (which I don't have any experience with) may have an adverse effect on the overall way the engine runs. In other words, setting the fuel mixture for hot starting may be to lean for cold start and overall running of the engine. I have searched the tech manual and forum on this type of problem but have not come up with a definitive answer. Possibly I'm not looking in the right places.
My other thought was to rig up some sort of switch to disable the CSV and IPS to facilitate starting when hot. Just a thought, I don't even know if that's possible. I really wouldn't want to go that route unless it was absolutely necessary for fear of causing another problem. I would much rather have the car functioning as it should.

Many Thanks,

Jim

[ja17]

If yours is actually version 3, then the two starting aids are wired together. Reducing fuel supply to the IP solenoid would result in a reduction of fuel at the CSV. Do you know how to do the "split linkage test"?

[ctaylor738]

The only way to really test the cold start valve is to remove it, turn it around, reconnect the fuel line, and the wiring (jumpers are OK). Put the valve in a plastic bag and crank the starter.  To be effective, the valve has to spray, not pee or dribble.

To test the solenoid, remove the cap on the fitting at top front of the pump and thread a M5x40 bolt or screw into the end of the rack.  Crank the starter and see it the screw moves out.

I feel your frustration.  My 230sl is a real pain to start hot as well.  Even if it is shut off for less than a minute, it takes a lot of cranking with the accelerator on the floor to get it going.  When it starts to fire, it's one cylinder at a time.  But no stink out the exhaust.  All of the "starting aids" have been tested and are working.  It hasn't left me stranded yet, but there have been a couple of close calls.

Cheers,

CT

[toneypenna]

The only way to really test the cold start valve is to remove it, turn it around, reconnect the fuel line, and the wiring (jumpers are OK). Put the valve in a plastic bag and crank the starter.  To be effective, the valve has to spray, not pee or dribble.


CT
I believe what you’re telling me is to test if these devices are working mechanically. Testing with a test light only tests if they are working electrically.
Correct? I will try this, however I believe they are working because of the following.9
What’s confounding me is when it doesn’t start hot, if I disconnect the CSV and the IPS at their respective relays, it starts immediately as it should.
Thank you for your input.
Jim

To test the solenoid, remove the cap on the fitting at top front of the pump and thread a M5x40 bolt or screw into the end of the rack.  Crank the starter and see it the screw moves out.

I feel your frustration.  My 230sl is a real pain to start hot as well.  Even if it is shut off for less than a minute, it takes a lot of cranking with the accelerator on the floor to get it going.  When it starts to fire, it's one cylinder at a time.  But no stink out the exhaust.  All of the "starting aids" have been tested and are working.  It hasn't left me stranded yet, but there have been a couple of close calls.

Cheers,

CT

[toneypenna]

If yours is actually version 3, then the two starting aids are wired

If yours is actually version 3, then the two starting aids are wired together. Reducing fuel supply to the IP solenoid would result in a reduction of fuel at the CSV. Do you know how to do the "split linkage test"?
[/quote

No I don’t, is it in the technical manual?
I’ll search for it unless it’s a simple thing and you wouldn’t mind explaining it.

Thanks
Jim

[Lorsar]

https://www.sl113.org/wiki/Restricted/Linkage-tour

[ctaylor738]

Jim -

Yes, that's exactly what I'm saying.  Testing the electricals will not tell you that the cold start valve is spraying or that the rack is actually moving.

Earlier, I had cold start problems as well.  After verifying the electricals and testing the as described, I found I had a peeing cold start valve.  I installed an expensive new valve that sprayed perfectly.  Still no start.  A new battery got it going after long cranks.  In desperation, I disconnected the cold start valve and was astounded when the car started on the turn of the key.  I have left it that way since.

I also have a manual switch for the cold start valve, but it makes no difference on hot starts.

I call it COPS - Cranky Old Pump Syndrome.

My theory is that the Warm Running Device alone gets the engine going when cold.  Hot, the injection pump is not developing enough pressure to open the injectors.

I have a new starter that I am going to install to see if higher cranking speed will help the hot start.

Cheers,

CT

[toneypenna]

https://www.sl113.org/wiki/Restricted/Linkage-tour

Thank you, I have already done all those adjustments and installed all new socket joints to alleiate the play in the linkage.

Jim